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<h1 id="_1">视觉语言模型<a class="headerlink" href="#_1" title="Permanent link">&para;</a></h1>
<p><em>视觉语言模型共同理解图像和文本,实现视觉问答、图像描述和视觉推理。本文件涵盖 VQA、图像描述、视觉定位,以及 VisualBERT、BLIP、LLaVA、Flamingo、PaLI 和 Qwen-VL 等将视觉编码器与大型语言模型融合的架构。</em></p>
<ul>
<li>
<p>想象一位博物馆导览员,他能看着一幅画并清晰描述画中的一切:有哪些物体、讲述了什么故事、传达了怎样的情感,还能回答参观者的任何问题。<strong>视觉语言模型(VLM</strong> 就是计算领域的等价物——一个能同时理解图像和文本的系统,能够描述视觉场景、回答相关问题、执行视觉指令,甚至根据自然语言查询在图像中定位特定物体。</p>
</li>
<li>
<p>VLM 位于你在第 8 章学到的视觉编码器和第 7 章的语言模型的交汇点。核心工程挑战在于桥接两个截然不同的表征世界:视觉骨干网络产生的空间化、连续的 feature map,与语言模型产生的序列化、离散的 token 嵌入。本文件中的每一种架构,本质上都是对同一个问题的不同回答:如何融合视觉和语言?</p>
</li>
</ul>
<p><img alt="VLM 高层次分类:双编码器、融合编码器和编码器-解码器家族及其输入与输出" src="../../images/vlm_taxonomy.svg" /></p>
<h2 id="_2">视觉问答<a class="headerlink" href="#_2" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>想象有人向你展示一张照片并问:"公园里有几只狗?"你毫不费力地解析图像、定位狗、数出数量并给出答案。<strong>视觉问答(VQA</strong> 将这一过程形式化:给定一张图像 <span class="arithmatex">\(I\)</span> 和一个自然语言问题 <span class="arithmatex">\(q\)</span>,预测答案 <span class="arithmatex">\(a\)</span></p>
</li>
<li>
<p>该任务可以有多种定义方式。最常见的方式将 VQA 视为<strong>开放式分类</strong>:模型从最常见的答案构成的固定词汇表中选择(例如 VQA v2 中排名前 3,129 的答案)。另一种方式是<strong>生成式回答</strong>,模型生成自由形式的文本字符串——这是现代 VLM 采用的方法。</p>
</li>
<li>
<p>形式上,你需要学习一个最大化正确答案似然的函数 <span class="arithmatex">\(f(I, q) \to a\)</span>。在分类设置中,这变为:</p>
</li>
</ul>
<div class="arithmatex">\[p(a \mid I, q) = \text{softmax}(W \cdot g(v, h))\]</div>
<ul>
<li>
<p>其中 <span class="arithmatex">\(v\)</span> 是视觉特征向量(来自 CNN 或 ViT),<span class="arithmatex">\(h\)</span> 是问题编码(来自 LSTM 或 Transformer),<span class="arithmatex">\(g\)</span> 是融合函数。<span class="arithmatex">\(g\)</span> 的设计正是真正的架构创造力所在。</p>
</li>
<li>
<p><strong>VQA v1</strong>(Antol 等人,2015)引入了该基准,包含来自 MS COCO 的 204,000 张图像上的 614,000 个问题。研究人员很快发现,模型可以通过利用<strong>语言先验</strong>达到惊人高的准确率——对"多少个"问题回答"2",对"有没有"问题回答"是",甚至不需要看图像。</p>
</li>
<li>
<p><strong>VQA v2</strong>(Goyal 等人,2017)通过为每个问题配对不同答案的两张相似图像来解决这个问题。这迫使模型真正将其推理建立在视觉内容之上。平衡配对设置使数据集规模大约翻倍,并使纯语言捷径的效果大打折扣。</p>
</li>
<li>
<p>其他重要的 VQA 数据集包括 <strong>GQA</strong>Hudson &amp; Manning,2019),包含需要多步推理的组合性问题;<strong>OK-VQA</strong>Marino 等人,2019),需要超出图像范围的外部知识;以及 <strong>TextVQA</strong>(Singh 等人,2019),答案依赖于读取图像中的文字。</p>
</li>
</ul>
<p><img alt="VQA 流水线:图像经视觉编码器编码,问题经文本编码器编码,两者表征融合后,融合向量被分类为答案" src="../../images/vqa_pipeline.svg" /></p>
<ul>
<li>
<p>早期的 VQA 模型使用简单策略:从预训练 CNN 中提取图像特征(通常是第 8 章中 ResNet 或 VGGNet 的倒数第二层),用 LSTM(第 6 章)对问题进行编码,然后将它们组合。组合函数 <span class="arithmatex">\(g\)</span> 演变迅速:从简单的逐元素乘法,到双线性池化,再到多模态 Tucker 分解。<strong>双线性注意力</strong>计算 <span class="arithmatex">\(v^T W h\)</span>,其中 <span class="arithmatex">\(W\)</span> 是可学习的交互矩阵,但完整的双线性形式有 <span class="arithmatex">\(O(d_v \times d_h)\)</span> 个参数,规模过大。<strong>MLB</strong>(多模态低秩双线性池化)将其分解为两个低秩投影,使其变得可行。</p>
</li>
<li>
<p>VQA 的突破是注意力机制。<strong>堆叠注意力网络</strong>(Yang 等人,2016)使用问题编码在空间图像区域上施加注意力,迭代式地精炼需要关注的图像部分。这个思想——让问题"关注"相关图像区域——成为了标准做法。</p>
</li>
</ul>
<h2 id="_3">图像描述<a class="headerlink" href="#_3" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>想象一位朋友看着你的度假照片并叙述他们所看到的:"一只金毛猎犬在阳光明媚的沙滩上接飞盘。"<strong>图像描述</strong>是生成图像的自然语言描述的任务。与 VQA 不同,这里没有提问——模型必须自行决定哪些内容值得描述。</p>
</li>
<li>
<p><strong>Show and Tell</strong>Vinyals 等人,2015)建立了描述任务的标准编码器-解码器架构。CNN 编码器(如 Inception 或 ResNet)生成一个单一图像特征向量 <span class="arithmatex">\(v\)</span>。该向量被用作 LSTM 解码器的初始隐藏状态,然后逐词自回归地生成描述:</p>
</li>
</ul>
<div class="arithmatex">\[p(w_t \mid w_{1:t-1}, I) = \text{LSTM}(w_{t-1}, h_{t-1})\]</div>
<ul>
<li>
<p>整个模型通过最大化真实描述的对数似然进行端到端训练。推理时使用束搜索(第 7 章)来找到高概率的描述。</p>
</li>
<li>
<p>Show and Tell 的问题在于整张图像被压缩成一个单一向量。对于复杂场景,单一向量无法捕捉所有相关细节。你会丢失空间信息——模型在生成不同词语时无法"回看"图像的特定区域。</p>
</li>
<li>
<p><strong>Show, Attend and Tell</strong>Xu 等人,2015)通过引入<strong>图像区域上的注意力</strong>解决了这个问题。模型不是将图像编码为一个向量,而是由 CNN 产生一个空间特征网格(例如来自 VGGNet 最后一个卷积层的 <span class="arithmatex">\(14 \times 14 \times 512\)</span>)。在每个解码步骤,模型计算这些空间位置上的注意力权重,生成一个突出当前词语最相关区域的上下文向量。</p>
</li>
<li>
<p>回顾第 6 章的注意力机制:解码器隐藏状态充当查询,空间特征充当键和值,注意力权重告诉模型应该看哪里。作者提出了两种变体:<strong>软注意力</strong>(可微分,所有区域的加权平均)和<strong>硬注意力</strong>(对单个区域进行随机采样,使用 REINFORCE 训练)。</p>
</li>
</ul>
<p><img alt="基于注意力的描述:在每个解码步骤,模型关注图像的不同空间区域,例如在生成&quot;狗&quot;这个词时聚焦于狗所在区域" src="../../images/attention_captioning.svg" /></p>
<ul>
<li>
<p>这些模型产生的注意力图具有显著的可解释性:生成"狗"时,注意力集中在狗的区域;生成"海滩"时,注意力转移到沙子和水面。这是注意力机制提供内置可解释性的最早令人信服的演示之一。</p>
</li>
<li>
<p><strong>CIDEr</strong>Vedantam 等人,2015)、<strong>METEOR</strong><strong>BLEU</strong><strong>SPICE</strong> 是标准描述评估指标。CIDEr 计算生成描述与参考描述之间的 TF-IDF 加权 n-gram 相似度,专门为描述评估设计。现代 VLM 通常在 MS COCO Captions 和 NoCaps 等描述基准上用 CIDEr 进行评估。</p>
</li>
<li>
<p>后来的描述模型引入了<strong>自底向上注意力</strong>Anderson 等人,2018),其中目标检测器(Faster R-CNN,第 8 章)首先提出显著的图像区域,然后描述模型在这些区域特征而非均匀网格上施加注意力。在基于 ViT 的编码器接管之前,这是主导方法。</p>
</li>
</ul>
<h2 id="_4">架构模式<a class="headerlink" href="#_4" title="Permanent link">&para;</a></h2>
<ul>
<li>每个 VLM 都必须回答一个基本设计问题:视觉和语言在哪个节点交互?答案决定了模型的架构家族。有三种主要模式,各自具有不同的权衡。</li>
</ul>
<h3 id="_5">双编码器<a class="headerlink" href="#_5" title="Permanent link">&para;</a></h3>
<ul>
<li>
<p>想象两位独立工作的译者——一位读法语文件,另一位读英语文件——他们各自用一种共享的"通用语言"生成摘要。他们在翻译过程中从不交流,但他们的摘要可以直接比较。这就是<strong>双编码器</strong>模式。</p>
</li>
<li>
<p>视觉编码器 <span class="arithmatex">\(f_v\)</span> 和文本编码器 <span class="arithmatex">\(f_t\)</span> 独立地将各自的输入映射到一个维度为 <span class="arithmatex">\(d\)</span> 的共享嵌入空间。图像嵌入为 <span class="arithmatex">\(v = f_v(I) \in \mathbb{R}^d\)</span>,文本嵌入为 <span class="arithmatex">\(t = f_t(q) \in \mathbb{R}^d\)</span>。相似度通过点积或余弦相似度计算:<span class="arithmatex">\(\text{sim}(I, q) = v^T t / (\|v\| \|t\|)\)</span></p>
</li>
<li>
<p><strong>CLIP</strong>Radford 等人,2021),在前一篇关于多模态表示的文件中已介绍,是典型的双编码器。它在从互联网抓取的 4 亿图像-文本对上使用对比目标函数(InfoNCE)进行训练。由于编码器相互独立,你可以预计算并缓存所有图像嵌入,使检索极其高效——搜索时只需对查询文本进行编码。</p>
</li>
<li>
<p>双编码器的缺点在于视觉和语言从未在特征层面进行交互。模型无法进行细粒度的跨模态推理:例如,它无法确定描述中的特定词是否对应图像中的特定区域。这限制了它在 VQA 或 grounded 描述等任务中的实用性。</p>
</li>
</ul>
<h3 id="_6">融合编码器<a class="headerlink" href="#_6" title="Permanent link">&para;</a></h3>
<ul>
<li>
<p>现在想象两位译者共处一室,积极讨论两篇文件。他们可以指向特定段落、互相提问,并建立共同的理解。这就是<strong>融合编码器</strong>模式。</p>
</li>
<li>
<p>两种模态都被编码,然后通过<strong>交叉注意力层</strong>进行融合,其中一种模态的 token 关注另一种模态的 token。图像首先由视觉编码器处理为一系列 patch 或区域 token <span class="arithmatex">\(V = [v_1, \ldots, v_N]\)</span>。文本被分词化为 <span class="arithmatex">\(T = [t_1, \ldots, t_M]\)</span>。在融合层中,文本 token 通过交叉注意力关注图像 token:</p>
</li>
</ul>
<div class="arithmatex">\[\text{CrossAttn}(T, V) = \text{softmax}\!\left(\frac{(TW_Q)(VW_K)^T}{\sqrt{d_k}}\right)(VW_V)\]</div>
<ul>
<li>这实现了细粒度的交互:每个文本 token 都可以关注其所需的特定图像区域。<strong>VisualBERT</strong><strong>VilBERT</strong><strong>UNITER</strong> 等模型使用这种模式。代价是你无法为检索预计算独立的嵌入——每个图像-文本对都需要通过融合层进行完整的前向传播。</li>
</ul>
<p><img alt="双编码器与融合编码器对比:双编码器计算独立嵌入和相似度得分,而融合编码器通过交叉注意力层合并模态" src="../../images/dual_vs_fusion_encoder.svg" /></p>
<h3 id="-">编码器-解码器<a class="headerlink" href="#-" title="Permanent link">&para;</a></h3>
<ul>
<li>
<p><strong>编码器-解码器</strong>模式将视觉编码器与自回归生成输出 token 的文本解码器相结合,类似于第 7 章中的 seq2seq 模型。视觉编码器产生上下文图像表征,文本解码器在生成输出文本时对其执行交叉注意力。</p>
</li>
<li>
<p>这种模式天然支持生成式任务:图像描述、自由形式答案的 VQA 以及视觉对话。<strong>GIT</strong>Generative Image-to-text TransformerWang 等人,2022)、<strong>CoCa</strong>Contrastive CaptionerYu 等人,2022)和 <strong>PaLI</strong> 使用这种架构。CoCa 巧妙地将双编码器和编码器-解码器模式结合起来:文本解码器的前半部分作为单模态文本编码器(用于对比学习),而后半部分对图像特征执行交叉注意力(用于生成式描述),兼得两者之优势。</p>
</li>
<li>
<p>这三种模式的选择取决于目标任务。双编码器最适合大规模检索。融合编码器最适合细粒度理解任务。编码器-解码器对于生成任务最为通用。现代最先进的 VLM 越来越多地采用编码器-解码器或仅解码器范式,将每项视觉语言任务都视为文本生成。</p>
</li>
</ul>
<h2 id="flamingo">Flamingo:少样本多模态学习<a class="headerlink" href="#flamingo" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>想象一位经验丰富的专家,经过多年对艺术和文学的研究,只需要看一两个例子就能优雅地描述一种全新的绘画风格。<strong>Flamingo</strong>Alonso 等人,2022DeepMind)基于相同原理构建:它利用强大的预训练语言模型和预训练视觉编码器,通过轻量级架构组件将其连接,实现多模态任务上的少样本学习。</p>
</li>
<li>
<p>Flamingo 的设计理念保守而有效:保持预训练的视觉编码器(NFNet)和语言模型(Chinchilla)冻结,仅学习连接它们的"胶水"。这种胶水由两个组件组成:<strong>Perceiver 重采样器</strong><strong>门控交叉注意力层</strong></p>
</li>
<li>
<p><strong>Perceiver 重采样器</strong>将视觉编码器的变长输出(取决于图像分辨率)压缩为一组固定数量的 <span class="arithmatex">\(N\)</span> 个视觉 token(通常 <span class="arithmatex">\(N = 64\)</span>)。它的工作原理是初始化一组 <span class="arithmatex">\(N\)</span> 个可学习的查询向量,并使用交叉注意力让这些查询关注完整的视觉编码器输出。这本质上是 Perceiver 架构(Jaegle 等人,2021)作为瓶颈的应用——无论输入图像大小如何,它都能生成紧凑的、固定大小的视觉表示。</p>
</li>
</ul>
<div class="arithmatex">\[z = \text{CrossAttn}(Q_{\text{learned}}, V_{\text{image}}) \in \mathbb{R}^{N \times d}\]</div>
<ul>
<li><strong>门控交叉注意力层</strong>交错插入在冻结的语言模型层之间。在每个这样的层中,语言模型的文本 token 对 Perceiver 重采样器产生的视觉 token 执行交叉注意力。关键之处在于,每个门控交叉注意力层包含一个可学习的标量门控 <span class="arithmatex">\(\alpha\)</span>,初始化为零,将交叉注意力输出乘以 <span class="arithmatex">\(\alpha\)</span> 后再加到残差流中:</li>
</ul>
<div class="arithmatex">\[\hat{x} = x + \alpha \cdot \text{CrossAttn}(x, z)\]</div>
<ul>
<li>初始化 <span class="arithmatex">\(\alpha = 0\)</span> 意味着训练开始时交叉注意力不贡献任何信息,模型行为与原始的冻结语言模型完全相同。门控在训练过程中逐渐打开,平滑地整合视觉信息,同时不破坏语言模型的预训练表示。</li>
</ul>
<p><img alt="Flamingo 架构:冻结的视觉编码器输入 Perceiver 重采样器,生成固定长度的视觉 token,通过交错在 LM 块之间的门控交叉注意力层注入冻结的 LM" src="../../images/flamingo_architecture.svg" /></p>
<ul>
<li>
<p>Flamingo 原生支持<strong>交错图像-文本序列</strong>。你可以向它输入包含多张图像穿插文本的提示,例如:"[图像 1] 这是一只猫。[图像 2] 这是一只狗。[图像 3] 这是一个 ___。"模型将每张图像通过视觉编码器和 Perceiver 重采样器处理,得到的视觉 token 插入到文本序列中的对应位置。语言模型的因果注意力掩码确保每个文本 token 只能关注当前及之前图像的视觉 token。</p>
</li>
<li>
<p>这种交错机制实现了强大的<strong>少样本多模态学习</strong>。通过在上下文中提供少量图像-文本示例,Flamingo 可以在没有任何梯度更新的情况下执行新任务。在 VQAv2、OK-VQA 和描述等基准上,具有 800 亿参数的 Flamingo 实现了最先进的少样本性能,仅需 4 到 32 个示例即可匹配甚至超越经过微调的专家模型。</p>
</li>
</ul>
<h2 id="llava">LLaVA 与视觉指令微调<a class="headerlink" href="#llava" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>想象你有一位出色的语言专家(一个 LLM)和一位出色的艺术评论家(一个视觉编码器)。如果你能教会艺术评论家"说语言专家的语言",他们就可以无缝协作。<strong>LLaVA</strong>Large Language and Vision AssistantLiu 等人,2023)正是这样做的:它使用一个简单的线性层将视觉特征投影到 LLM 的 token 嵌入空间,然后在指令遵循数据上微调整个系统。</p>
</li>
<li>
<p>LLaVA 的架构出奇地简单。图像由一个预训练的 CLIP ViT-L/14 视觉编码器编码为一个 patch 特征网格 <span class="arithmatex">\(V \in \mathbb{R}^{N \times d_v}\)</span>,其中 <span class="arithmatex">\(N = 256\)</span> 个 patch(对于 336px 图像和 14px patch)。一个<strong>投影层</strong> <span class="arithmatex">\(W\)</span> 将这些视觉特征映射到 LLM 的嵌入维度:</p>
</li>
</ul>
<div class="arithmatex">\[H_v = VW, \quad W \in \mathbb{R}^{d_v \times d_{\text{LLM}}}\]</div>
<ul>
<li>投影后的视觉 token <span class="arithmatex">\(H_v\)</span> 直接与文本 token 嵌入拼接,作为一个单一序列输入到 LLM(Vicuna,一个微调后的 LLaMA)。LLM 使用其标准因果自注意力处理它们——没有特殊的交叉注意力层,没有 perceiver,只有拼接。视觉 token 被当作恰好编码了视觉信息的文本 token 来处理。</li>
</ul>
<p><img alt="LLaVA 架构:CLIP ViT 将图像编码为 patch 特征,线性投影将其映射到 LLM 嵌入空间,投影后的视觉 token 拼接在文本 token 之前并输入到 LLM" src="../../images/llava_architecture.svg" /></p>
<ul>
<li>
<p><strong>视觉指令微调</strong>是 LLaVA 的关键训练创新。作者使用 GPT-4 从 COCO 图像生成了 158,000 个多模态指令遵循示例。每个示例包含一张图像和一个对话式指令(例如"详细描述这张图像"、"这张图像有什么不寻常之处?"、"如果我是一名游客参观这个地方,我应该知道什么?")。模型接受训练,根据图像和指令生成 GPT-4 撰写的回答。</p>
</li>
<li>
<p>训练分为两个阶段。<strong>阶段 1(预训练)</strong>:仅训练投影层 <span class="arithmatex">\(W\)</span>,使用图像-描述对(来自 CC3M 的 595K 数据),视觉编码器和 LLM 都保持冻结。这教会 <span class="arithmatex">\(W\)</span> 将视觉特征与 LLM 的嵌入空间对齐。<strong>阶段 2(微调)</strong>:投影层和 LLM 在指令遵循数据上联合微调,视觉编码器保持冻结。这教会模型遵循复杂的视觉指令。</p>
</li>
<li>
<p><strong>LLaVA-1.5</strong> 通过三项关键更改改进了原始版本:将单层线性投影替换为两层 MLP(更具表现力的映射),使用更高分辨率的图像(336px 而非 224px,产生更多 patch token),以及在训练混合数据中加入学术 VQA 数据集。这些看似细微的修改带来了基准性能的大幅提升。</p>
</li>
<li>
<p>LLaVA 的方法证明,你不需要像 Flamingo 的 Perceiver 重采样器或门控交叉注意力那样复杂的架构创新。一个简单的线性投影,结合高质量的指令微调数据,就足以有效地将视觉编码器连接到 LLM。这种简洁性使得 LLaVA 极具影响力——后续大多数开源 VLM 都遵循类似的方案。</p>
</li>
</ul>
<h2 id="_7">扩展视觉语言模型<a class="headerlink" href="#_7" title="Permanent link">&para;</a></h2>
<ul>
<li>该领域从概念验证型 VLM 迅速发展为在数十亿图像-文本对上训练的工业级系统。三个模型家族展示了不同的扩展方法。</li>
</ul>
<h3 id="pali">PaLI<a class="headerlink" href="#pali" title="Permanent link">&para;</a></h3>
<ul>
<li>
<p><strong>PaLI</strong>Pathways Language and Image modelChen 等人,2022Google)同时扩展视觉编码器和语言模型。PaLI 使用 ViT-e(40 亿参数)作为视觉编码器,mT5(130 亿参数)作为语言模型,总计 170 亿参数。图像被编码为一系列 patch token,拼接在文本 token 之前,输入到编码器-解码器架构的 mT5。</p>
</li>
<li>
<p>PaLI 的关键洞见是<strong>扩展视觉编码器与扩展语言模型同样重要</strong>。先前的工作通常使用固定的、中等规模的视觉骨干网络(如 ViT-B 或 ViT-L),将参数预算全部投入 LLM。PaLI 表明,一个 40 亿参数的 ViT-e,在 JFT-4B(40 亿张标注图像)上预训练后,能够显著提升 OCR 和空间推理等细粒度视觉任务的性能。</p>
</li>
<li>
<p>PaLI 在 WebLI(一个包含 109 种语言、100 亿图像-文本对的数据集)上训练,因此天然具备多语言能力。模型通过混合任务进行预训练:图像描述、VQA 和图像-文本匹配,全部作为文本到文本生成任务(遵循第 7 章的 T5 范式)。<strong>PaLI-X</strong>550 亿参数)和 <strong>PaLI-3</strong>(50 亿,使用 SigLIP 作为视觉编码器)是后续迭代版本。</p>
</li>
</ul>
<h3 id="qwen-vl">Qwen-VL<a class="headerlink" href="#qwen-vl" title="Permanent link">&para;</a></h3>
<ul>
<li>
<p><strong>Qwen-VL</strong>(Bai 等人,2023,阿里巴巴)在 Qwen LLM 基础上增加了一个 ViT 视觉编码器和一个单层交叉注意力模块(类似于 Flamingo 的 Perceiver 重采样器),将视觉编码器的输出压缩为一组固定的 256 个视觉 token。视觉 token 与文本 token 拼接后由 Qwen LLM 处理。</p>
</li>
<li>
<p>Qwen-VL 的训练采用三阶段方案。阶段 1:在 14 亿个弱监督图像-文本对上预训练,仅解冻视觉编码器。阶段 2:在更高质量的数据上进行多任务预训练,包括 VQA、描述、定位和 OCR 数据集,整个模型解冻。阶段 3:在指令遵循和对话数据上进行监督微调。这种从噪声网络数据到精选指令数据的渐进式精炼,是大多数现代 VLM 共享的模式。</p>
</li>
<li>
<p><strong>Qwen2-VL</strong>2024)引入了<strong>动态分辨率</strong>支持:模型不是将所有图像缩放到固定大小,而是通过动态调整视觉 token 数量以原始分辨率处理图像。更高分辨率的图像产生更多 token,更低分辨率的图像产生更少 token。这在不浪费低分辨率输入计算量的前提下,提升了文档理解和细粒度识别等对细节敏感的任务的性能。</p>
</li>
</ul>
<h3 id="internvl">InternVL<a class="headerlink" href="#internvl" title="Permanent link">&para;</a></h3>
<ul>
<li>
<p><strong>InternVL</strong>(Chen 等人,2024,上海人工智能实验室)激进地扩展了视觉编码器,使用 InternViT-6B——一个 60 亿参数的视觉 Transformer——与语言模型配对。关键的架构贡献是<strong>动态高分辨率处理</strong>:图像被分割为 448x448 像素的图块,每个图块由视觉编码器独立处理,得到的图块特征与完整图像的缩略图特征拼接。这使得模型能够处理任意宽高比和分辨率的图像。</p>
</li>
<li>
<p>InternVL-2 进一步引入了<strong>渐进对齐训练</strong>:首先用对比目标(如 CLIP)对齐视觉编码器,然后通过轻量级 MLP 连接器将其连接到 LLM,最后在指令数据上进行端到端微调。这种渐进策略防止了视觉编码器预训练表示的灾难性遗忘。</p>
</li>
</ul>
<p><img alt="扩展 VLMPaLI、Qwen-VL 和 InternVL 的比较,展示了连接视觉编码器和语言模型的不同方法,包括其训练阶段" src="../../images/scaling_vlms_comparison.svg" /></p>
<ul>
<li>所有三个模型家族的一个共同主题是<strong>训练数据精选</strong>的重要性。从网络抓取的原始图像-文本对是噪声大且常常不对齐的。后续的训练阶段逐步过滤和精炼数据,从数十亿噪声对过渡到数百万高质量指令示例。最终微调数据的质量往往比模型的原始参数数量更为重要。</li>
</ul>
<h2 id="_8">定位与指代<a class="headerlink" href="#_8" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>想象你在人群中指着一个人说"戴红帽子的女士"。你在用语言指代一个特定的空间区域。<strong>视觉定位</strong>是相反的过程:给定一张图像和一个自然语言表述,模型必须识别(定位)所指的对象。<strong>指代表达理解</strong>产生边界框;<strong>指代表达分割</strong>产生像素掩码。</p>
</li>
<li>
<p>形式上,给定一张图像 <span class="arithmatex">\(I\)</span> 和一个指代表达 <span class="arithmatex">\(r\)</span>(例如"左边那只大型棕色狗"),模型预测一个边界框 <span class="arithmatex">\(b = (x, y, w, h)\)</span> 或一组定位所引用对象的坐标。数据集包括 <strong>RefCOCO</strong><strong>RefCOCO+</strong><strong>RefCOCOg</strong>,每个数据集包含具有多个对象的图像以及每个对象的明确指代表达。</p>
</li>
<li>
<p>早期的定位模型使用两阶段方法:首先生成区域提议(使用 Faster R-CNN 或类似方法),然后使用融合模型对每个提议与语言查询进行评分。评分最高的区域即为预测结果。这种方法计算代价高昂,且受限于提议的质量。</p>
</li>
<li>
<p>现代 VLM 将定位直接整合到生成式框架中。关键思想是将边界框坐标表示为<strong>文本 token</strong>。你将连续的坐标空间离散化为槽位(例如 <span class="arithmatex">\(x, y, w, h\)</span> 各 1000 个槽位),并向词汇表中添加特殊的位置 token,如 <code>&lt;loc_342&gt;</code>。然后模型通过输出一系列位置 token 来生成边界框:</p>
</li>
</ul>
<div class="arithmatex">\[\text{输出: } \texttt{&lt;loc\_102&gt;&lt;loc\_215&gt;&lt;loc\_487&gt;&lt;loc\_398&gt;}\]</div>
<ul>
<li>
<p>这种 token 化技巧使得任何自回归语言模型无需架构更改即可执行定位——它只需学会"说坐标"。<strong>Pix2Seq</strong>(Chen 等人,2022)率先将这种方法用于目标检测,而 Qwen-VL、Ferret 和 Kosmos-2 等模型将其扩展到指代表达理解和短语定位。</p>
</li>
<li>
<p><strong>Kosmos-2</strong>Peng 等人,2023Microsoft)通过将空间位置表示为嵌入在生成文本中的特殊 token,为多模态 LLM 增加了定位能力。例如,它可以生成:"一只 <code>&lt;phrase&gt;</code> 金毛猎犬 <code>&lt;/phrase&gt;</code> <code>&lt;box&gt;</code> <code>&lt;loc_102&gt;</code> <code>&lt;loc_215&gt;</code> <code>&lt;loc_487&gt;</code> <code>&lt;loc_398&gt;</code> <code>&lt;/box&gt;</code> 正在接飞盘。"这种文本和空间 token 的交错融合实现了同步描述和定位。</p>
</li>
</ul>
<p><img alt="通过坐标 token 化实现定位:模型生成文本 token 与离散化的边界框坐标 token 交错在一起,定位描述中提到的物体" src="../../images/grounding_coordinate_tokens.svg" /></p>
<ul>
<li><strong>定点指向</strong>将定位更进一步:模型不再输出边界框,而是预测一个单一的点(通常是指代物体的中心)。这对于交互式应用非常有用,例如用户问"最近的出口在哪里?",模型返回一个叠加在图像上的坐标。<strong>Shikra</strong><strong>Ferret</strong> 等模型支持基于点的指代以及基于框的定位。</li>
</ul>
<h2 id="ocr">免 OCR 文档理解<a class="headerlink" href="#ocr" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>传统的文档理解流水线很复杂:首先运行 OCR 引擎提取文本和布局,然后将提取的文本输入语言模型。这种多阶段方法很脆弱——OCR 错误向下游传播,空间布局信息常常丢失或表征不良。如果模型能像人类一样直接从像素中读取信息呢?</p>
</li>
<li>
<p><strong>Donut</strong>Document Understanding TransformerKim 等人,2022)完全消除了 OCR。它使用 Swin Transformer(第 8 章)作为视觉编码器处理文档图像,并使用 BART 风格的 Transformer 解码器直接从视觉特征生成结构化文本输出。解码器可以根据任务生成 JSON、键值对或纯文本。</p>
</li>
<li>
<p>Donut 的训练分为两个阶段。<strong>预训练</strong>:模型通过执行合成 OCR 来学习阅读——给定一张文档图像,生成完整的文本内容。这在从文本语料库渲染的数百万张合成文档图像上进行训练,教会视觉编码器识别字符、字体和布局。<strong>微调</strong>:模型通过训练生成特定于任务的结构化输出,适应特定的下游任务,如收据解析、表格理解或文档分类。</p>
</li>
<li>
<p>Donut 解码器使用特殊的提示方案:任务由提示 token 指定(例如分类用 <code>&lt;doc_class&gt;</code>,收据解析用 <code>&lt;parse_receipt&gt;</code>),模型根据此提示生成输出。这种统一接口使得单个模型可以处理多种文档理解任务。</p>
</li>
<li>
<p><strong>Pix2Struct</strong>Lee 等人,2023Google)将免 OCR 思想应用于网页理解和图表/图形理解。关键的预训练目标是<strong>截图解析</strong>:给定一个网页的带掩码截图,模型生成产生可见区域的底层 HTML。这教会模型理解视觉呈现与结构化标记之间的关系。</p>
</li>
<li>
<p>Pix2Struct 引入了<strong>可变分辨率输入处理</strong>:它并不是将所有图像缩放到固定大小(这会扭曲宽高比并破坏精细文字),而是在保持原始宽高比的同时将图像打包为固定数量的 patch。一个高而窄的文档产生一个高而窄的 patch 网格。这对于文档理解至关重要,因为宽高比携带着语义信息(收据窄而高;表格宽而短)。</p>
</li>
</ul>
<p><img alt="免 OCR 文档理解:Donut 和 Pix2Struct 通过视觉编码器直接处理文档图像,无需任何 OCR 预处理即可生成结构化文本输出" src="../../images/ocr_free_document_understanding.svg" /></p>
<ul>
<li>
<p><strong>Nougat</strong>Blecher 等人,2023Meta)将 Donut 架构专门应用于学术论文,直接从 PDF 页面图像生成完整的 LaTeX 标记。它可以处理复杂的数学方程、表格和图形——这些任务正是传统 OCR 流水线难以应付的。该模型在 PDF 页面图像及其对应的 LaTeX 源代码对上进行训练。</p>
</li>
<li>
<p>免 OCR 模型的成功展示了深度学习中的一个更广泛原则:直接从原始输入(像素)学习的端到端模型通常优于复杂的多阶段流水线,因为它们可以联合优化所有组件,并学习专门针对最终任务定制的表示。中间的 OCR 步骤是一个瓶颈,限制了模型能够学习的内容。</p>
</li>
</ul>
<h2 id="token">视觉 Token 流水线<a class="headerlink" href="#token" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>无论架构家族如何,每个 VLM 都必须将图像转换为语言模型可以处理的一系列 token。理解这一流水线至关重要。不同模型的处理过程有所差异,但总体流程如下:</p>
</li>
<li>
<p><strong>第 1 步:Patch 提取。</strong> 图像(高度 <span class="arithmatex">\(H\)</span>,宽度 <span class="arithmatex">\(W\)</span>)被划分为不重叠的、大小为 <span class="arithmatex">\(P \times P\)</span> 的 patch,产生 <span class="arithmatex">\(N = HW / P^2\)</span> 个 patch。对于 336x336 图像和 14x14 patch<span class="arithmatex">\(N = 576\)</span></p>
</li>
<li>
<p><strong>第 2 步:视觉编码。</strong> 每个 patch 经过线性投影并通过视觉编码器(通常是 ViT)。输出是一系列上下文 patch 嵌入 <span class="arithmatex">\(V = [v_1, \ldots, v_N] \in \mathbb{R}^{N \times d_v}\)</span>。这些嵌入既携带局部外观信息,也携带全局上下文(来自自注意力)。</p>
</li>
<li>
<p><strong>第 3 步:Token 压缩(可选)。</strong> 一些模型将 <span class="arithmatex">\(N\)</span> 个视觉 token 压缩为更少的 <span class="arithmatex">\(M \ll N\)</span> 个 token,以减少语言模型的计算负担。Flamingo 使用 Perceiver 重采样器(<span class="arithmatex">\(M = 64\)</span>);Qwen-VL 使用交叉注意力(<span class="arithmatex">\(M = 256\)</span>);<strong>Q-Former</strong>(在 BLIP-2 中使用,Li 等人,2023)使用一组 <span class="arithmatex">\(M = 32\)</span> 个可学习查询 token,对视觉编码器的输出执行交叉注意力。</p>
</li>
<li>
<p><strong>第 4 步:投影。</strong> 视觉 token(全部或压缩后的集合)通过线性层或 MLP 投影到语言模型的嵌入空间。投影后,视觉 token 与文本 token 嵌入具有相同维度,可以与它们拼接。</p>
</li>
<li>
<p><strong>第 5 步:注入 LLM。</strong> 投影后的视觉 token 在特殊 <code>&lt;image&gt;</code> 占位符 token 的位置插入到 token 序列中,组合后的序列由语言模型处理。LLM 的自注意力使文本 token 能够关注视觉 token,反之亦然。</p>
</li>
</ul>
<p><img alt="视觉 token 流水线:图像 patch 被提取,由 ViT 编码,可选地由 Perceiver 或 Q-Former 压缩,投影到 LLM 维度,并与文本 token 拼接" src="../../images/visual_token_pipeline.svg" /></p>
<ul>
<li>
<p>视觉 token 的数量直接影响计算成本。每个视觉 token 参与 LLM 的自注意力,其复杂度与序列长度的平方成正比。具有多个 patch 的高分辨率图像可能产生数百或数千个视觉 token,占据 LLM 上下文窗口的主导地位。这就是 token 压缩的重要性所在:将 576 个视觉 token 减少到 64 个,可将视觉部分在注意力中的贡献减少约 9 倍。</p>
</li>
<li>
<p><strong>BLIP-2</strong>(Li 等人,2023)以其高效的桥接策略而闻名。它引入了一个轻量级的 <strong>Q-Former</strong>(一个带有可学习查询的小型 Transformer),位于冻结的视觉编码器和冻结的 LLM 之间。Q-Former 是唯一可训练的组件——视觉编码器和 LLM 都保持冻结。它的预训练分为两个阶段:首先是图像-文本对比学习、匹配和描述目标(连接视觉编码器),然后是语言生成目标(连接 LLM)。这种模块化设计使得 BLIP-2 可以将任何视觉编码器插入到任何 LLM 中。</p>
</li>
</ul>
<h2 id="_9">训练目标<a class="headerlink" href="#_9" title="Permanent link">&para;</a></h2>
<ul>
<li>
<p>VLM 使用多种目标的组合进行训练,具体取决于架构模式:</p>
</li>
<li>
<p><strong>图像-文本对比损失(ITC):</strong> 在共享嵌入空间中对齐图像和文本表示,如 CLIP 中所示。这是双编码器的主要目标,也常被用作融合模型的预训练目标。该损失就是上一篇文件中的 InfoNCE 损失。</p>
</li>
<li>
<p><strong>图像-文本匹配(ITM):</strong> 一个二分类目标——给定图像和文本,预测它们是否匹配。困难负样本(与不同图像配对的相似文本)使这项任务具有挑战性,迫使模型学习细粒度的对齐。</p>
</li>
<li>
<p><strong>语言建模(LM):</strong> 标准的自回归语言建模目标——给定之前的所有 token 预测下一个 token。对于 VLM"之前的 token" 包括视觉 token,因此模型学习在视觉输入条件下生成文本。这是编码器-解码器和仅解码器 VLM 的主要目标。</p>
</li>
</ul>
<div class="arithmatex">\[\mathcal{L}_{\text{LM}} = -\sum_{t=1}^{T} \log p(w_t \mid w_{&lt;t}, V)\]</div>
<ul>
<li>
<p><strong>前缀语言建模:</strong> 一种变体,其中图像和文本前缀作为上下文提供(不进行训练),模型仅训练生成后续部分。这用于 PaLI 和 SimVLM 等模型。</p>
</li>
<li>
<p>大多数现代 VLM 在预训练期间结合多个目标(例如 BLIP 中的 ITC + ITM + LMCoCa 中的 ITC + LM),然后在指令数据上使用纯 LM 目标进行微调。</p>
</li>
</ul>
<h2 id="colab-notebook">编程练习(使用 CoLab 或 notebook<a class="headerlink" href="#colab-notebook" title="Permanent link">&para;</a></h2>
<ol>
<li>
<p>实现一个简单的基于注意力的图像描述解码器。使用随机的"图像特征"作为编码器输出,训练解码器生成固定的描述,观察注意力权重在每个解码步骤如何跨空间位置移动。
<div class="highlight"><pre><span></span><code><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a><span class="kn">import</span><span class="w"> </span><span class="nn">jax</span>
<a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a><span class="kn">import</span><span class="w"> </span><span class="nn">jax.numpy</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">jnp</span>
<a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a><span class="kn">import</span><span class="w"> </span><span class="nn">matplotlib.pyplot</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">plt</span>
<a id="__codelineno-0-4" name="__codelineno-0-4" href="#__codelineno-0-4"></a>
<a id="__codelineno-0-5" name="__codelineno-0-5" href="#__codelineno-0-5"></a><span class="c1"># 模拟 4x4 空间网格的图像特征(16 个区域,dim=32)</span>
<a id="__codelineno-0-6" name="__codelineno-0-6" href="#__codelineno-0-6"></a><span class="n">key</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">PRNGKey</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
<a id="__codelineno-0-7" name="__codelineno-0-7" href="#__codelineno-0-7"></a><span class="n">k1</span><span class="p">,</span> <span class="n">k2</span><span class="p">,</span> <span class="n">k3</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<a id="__codelineno-0-8" name="__codelineno-0-8" href="#__codelineno-0-8"></a><span class="n">img_features</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k1</span><span class="p">,</span> <span class="p">(</span><span class="mi">16</span><span class="p">,</span> <span class="mi">32</span><span class="p">))</span> <span class="c1"># 16 个空间区域,32 维</span>
<a id="__codelineno-0-9" name="__codelineno-0-9" href="#__codelineno-0-9"></a>
<a id="__codelineno-0-10" name="__codelineno-0-10" href="#__codelineno-0-10"></a><span class="c1"># 词汇表:0=&lt;start&gt;, 1=&quot;a&quot;, 2=&quot;red&quot;, 3=&quot;car&quot;, 4=&lt;end&gt;</span>
<a id="__codelineno-0-11" name="__codelineno-0-11" href="#__codelineno-0-11"></a><span class="n">vocab_size</span><span class="p">,</span> <span class="n">embed_dim</span><span class="p">,</span> <span class="n">hidden_dim</span> <span class="o">=</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">32</span>
<a id="__codelineno-0-12" name="__codelineno-0-12" href="#__codelineno-0-12"></a><span class="n">W_embed</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k2</span><span class="p">,</span> <span class="p">(</span><span class="n">vocab_size</span><span class="p">,</span> <span class="n">embed_dim</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span>
<a id="__codelineno-0-13" name="__codelineno-0-13" href="#__codelineno-0-13"></a><span class="n">W_attn_q</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k3</span><span class="p">,</span> <span class="p">(</span><span class="n">hidden_dim</span><span class="p">,</span> <span class="mi">32</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span> <span class="c1"># 查询投影</span>
<a id="__codelineno-0-14" name="__codelineno-0-14" href="#__codelineno-0-14"></a>
<a id="__codelineno-0-15" name="__codelineno-0-15" href="#__codelineno-0-15"></a><span class="k">def</span><span class="w"> </span><span class="nf">attend</span><span class="p">(</span><span class="n">h</span><span class="p">,</span> <span class="n">img_feats</span><span class="p">,</span> <span class="n">W_q</span><span class="p">):</span>
<a id="__codelineno-0-16" name="__codelineno-0-16" href="#__codelineno-0-16"></a><span class="w"> </span><span class="sd">&quot;&quot;&quot;在给定解码器状态 h 的情况下计算图像特征上的软注意力。&quot;&quot;&quot;</span>
<a id="__codelineno-0-17" name="__codelineno-0-17" href="#__codelineno-0-17"></a> <span class="n">query</span> <span class="o">=</span> <span class="n">h</span> <span class="o">@</span> <span class="n">W_q</span> <span class="c1"># (32,)</span>
<a id="__codelineno-0-18" name="__codelineno-0-18" href="#__codelineno-0-18"></a> <span class="n">scores</span> <span class="o">=</span> <span class="n">img_feats</span> <span class="o">@</span> <span class="n">query</span> <span class="c1"># (16,)</span>
<a id="__codelineno-0-19" name="__codelineno-0-19" href="#__codelineno-0-19"></a> <span class="n">weights</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">softmax</span><span class="p">(</span><span class="n">scores</span><span class="p">)</span> <span class="c1"># (16,)</span>
<a id="__codelineno-0-20" name="__codelineno-0-20" href="#__codelineno-0-20"></a> <span class="n">context</span> <span class="o">=</span> <span class="n">weights</span> <span class="o">@</span> <span class="n">img_feats</span> <span class="c1"># (32,)</span>
<a id="__codelineno-0-21" name="__codelineno-0-21" href="#__codelineno-0-21"></a> <span class="k">return</span> <span class="n">context</span><span class="p">,</span> <span class="n">weights</span>
<a id="__codelineno-0-22" name="__codelineno-0-22" href="#__codelineno-0-22"></a>
<a id="__codelineno-0-23" name="__codelineno-0-23" href="#__codelineno-0-23"></a><span class="c1"># 简单的 GRU 风格步骤(为说明目的,仅用线性 + tanh)</span>
<a id="__codelineno-0-24" name="__codelineno-0-24" href="#__codelineno-0-24"></a><span class="n">W_h</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">PRNGKey</span><span class="p">(</span><span class="mi">0</span><span class="p">),</span> <span class="p">(</span><span class="n">embed_dim</span> <span class="o">+</span> <span class="mi">32</span><span class="p">,</span> <span class="n">hidden_dim</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span>
<a id="__codelineno-0-25" name="__codelineno-0-25" href="#__codelineno-0-25"></a>
<a id="__codelineno-0-26" name="__codelineno-0-26" href="#__codelineno-0-26"></a><span class="k">def</span><span class="w"> </span><span class="nf">decode_step</span><span class="p">(</span><span class="n">h</span><span class="p">,</span> <span class="n">word_idx</span><span class="p">,</span> <span class="n">img_feats</span><span class="p">):</span>
<a id="__codelineno-0-27" name="__codelineno-0-27" href="#__codelineno-0-27"></a> <span class="n">context</span><span class="p">,</span> <span class="n">attn_weights</span> <span class="o">=</span> <span class="n">attend</span><span class="p">(</span><span class="n">h</span><span class="p">,</span> <span class="n">img_feats</span><span class="p">,</span> <span class="n">W_attn_q</span><span class="p">)</span>
<a id="__codelineno-0-28" name="__codelineno-0-28" href="#__codelineno-0-28"></a> <span class="n">word_emb</span> <span class="o">=</span> <span class="n">W_embed</span><span class="p">[</span><span class="n">word_idx</span><span class="p">]</span> <span class="c1"># (16,)</span>
<a id="__codelineno-0-29" name="__codelineno-0-29" href="#__codelineno-0-29"></a> <span class="n">inp</span> <span class="o">=</span> <span class="n">jnp</span><span class="o">.</span><span class="n">concatenate</span><span class="p">([</span><span class="n">word_emb</span><span class="p">,</span> <span class="n">context</span><span class="p">])</span> <span class="c1"># (48,)</span>
<a id="__codelineno-0-30" name="__codelineno-0-30" href="#__codelineno-0-30"></a> <span class="n">h_new</span> <span class="o">=</span> <span class="n">jnp</span><span class="o">.</span><span class="n">tanh</span><span class="p">(</span><span class="n">inp</span> <span class="o">@</span> <span class="n">W_h</span><span class="p">)</span> <span class="c1"># (32,)</span>
<a id="__codelineno-0-31" name="__codelineno-0-31" href="#__codelineno-0-31"></a> <span class="k">return</span> <span class="n">h_new</span><span class="p">,</span> <span class="n">attn_weights</span>
<a id="__codelineno-0-32" name="__codelineno-0-32" href="#__codelineno-0-32"></a>
<a id="__codelineno-0-33" name="__codelineno-0-33" href="#__codelineno-0-33"></a><span class="c1"># 运行解码序列:&lt;start&gt; -&gt; &quot;a&quot; -&gt; &quot;red&quot; -&gt; &quot;car&quot; -&gt; &lt;end&gt;</span>
<a id="__codelineno-0-34" name="__codelineno-0-34" href="#__codelineno-0-34"></a><span class="n">target_seq</span> <span class="o">=</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
<a id="__codelineno-0-35" name="__codelineno-0-35" href="#__codelineno-0-35"></a><span class="n">h</span> <span class="o">=</span> <span class="n">jnp</span><span class="o">.</span><span class="n">zeros</span><span class="p">(</span><span class="n">hidden_dim</span><span class="p">)</span>
<a id="__codelineno-0-36" name="__codelineno-0-36" href="#__codelineno-0-36"></a><span class="n">all_attn</span> <span class="o">=</span> <span class="p">[]</span>
<a id="__codelineno-0-37" name="__codelineno-0-37" href="#__codelineno-0-37"></a><span class="k">for</span> <span class="n">word_idx</span> <span class="ow">in</span> <span class="n">target_seq</span><span class="p">[:</span><span class="o">-</span><span class="mi">1</span><span class="p">]:</span>
<a id="__codelineno-0-38" name="__codelineno-0-38" href="#__codelineno-0-38"></a> <span class="n">h</span><span class="p">,</span> <span class="n">attn_w</span> <span class="o">=</span> <span class="n">decode_step</span><span class="p">(</span><span class="n">h</span><span class="p">,</span> <span class="n">word_idx</span><span class="p">,</span> <span class="n">img_features</span><span class="p">)</span>
<a id="__codelineno-0-39" name="__codelineno-0-39" href="#__codelineno-0-39"></a> <span class="n">all_attn</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">attn_w</span><span class="p">)</span>
<a id="__codelineno-0-40" name="__codelineno-0-40" href="#__codelineno-0-40"></a>
<a id="__codelineno-0-41" name="__codelineno-0-41" href="#__codelineno-0-41"></a><span class="c1"># 可视化每一步的注意力图(重塑为 4x4 网格)</span>
<a id="__codelineno-0-42" name="__codelineno-0-42" href="#__codelineno-0-42"></a><span class="n">words</span> <span class="o">=</span> <span class="p">[</span><span class="s2">&quot;&lt;start&gt;&quot;</span><span class="p">,</span> <span class="s2">&quot;a&quot;</span><span class="p">,</span> <span class="s2">&quot;red&quot;</span><span class="p">,</span> <span class="s2">&quot;car&quot;</span><span class="p">]</span>
<a id="__codelineno-0-43" name="__codelineno-0-43" href="#__codelineno-0-43"></a><span class="n">fig</span><span class="p">,</span> <span class="n">axes</span> <span class="o">=</span> <span class="n">plt</span><span class="o">.</span><span class="n">subplots</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="n">figsize</span><span class="o">=</span><span class="p">(</span><span class="mi">14</span><span class="p">,</span> <span class="mi">3</span><span class="p">))</span>
<a id="__codelineno-0-44" name="__codelineno-0-44" href="#__codelineno-0-44"></a><span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="p">(</span><span class="n">ax</span><span class="p">,</span> <span class="n">w</span><span class="p">)</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="nb">zip</span><span class="p">(</span><span class="n">axes</span><span class="p">,</span> <span class="n">words</span><span class="p">)):</span>
<a id="__codelineno-0-45" name="__codelineno-0-45" href="#__codelineno-0-45"></a> <span class="n">ax</span><span class="o">.</span><span class="n">imshow</span><span class="p">(</span><span class="n">all_attn</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="o">.</span><span class="n">reshape</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="n">cmap</span><span class="o">=</span><span class="s1">&#39;viridis&#39;</span><span class="p">)</span>
<a id="__codelineno-0-46" name="__codelineno-0-46" href="#__codelineno-0-46"></a> <span class="n">ax</span><span class="o">.</span><span class="n">set_title</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;生成&quot;</span><span class="si">{</span><span class="n">w</span><span class="si">}</span><span class="s1">&quot;</span><span class="se">\n</span><span class="s1">关注的区域&#39;</span><span class="p">)</span>
<a id="__codelineno-0-47" name="__codelineno-0-47" href="#__codelineno-0-47"></a> <span class="n">ax</span><span class="o">.</span><span class="n">axis</span><span class="p">(</span><span class="s1">&#39;off&#39;</span><span class="p">)</span>
<a id="__codelineno-0-48" name="__codelineno-0-48" href="#__codelineno-0-48"></a><span class="n">plt</span><span class="o">.</span><span class="n">suptitle</span><span class="p">(</span><span class="s1">&#39;每个解码步骤的图像区域注意力&#39;</span><span class="p">)</span>
<a id="__codelineno-0-49" name="__codelineno-0-49" href="#__codelineno-0-49"></a><span class="n">plt</span><span class="o">.</span><span class="n">tight_layout</span><span class="p">();</span> <span class="n">plt</span><span class="o">.</span><span class="n">show</span><span class="p">()</span>
<a id="__codelineno-0-50" name="__codelineno-0-50" href="#__codelineno-0-50"></a><span class="c1"># 尝试修改 img_features,观察注意力模式如何变化!</span>
</code></pre></div></p>
</li>
<li>
<p>模拟视觉 token 流水线:将图像划分为 patch,将 patch 投影到嵌入空间,与文本 token 嵌入拼接,并在组合序列上运行单层自注意力。
<div class="highlight"><pre><span></span><code><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="kn">import</span><span class="w"> </span><span class="nn">jax</span>
<a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a><span class="kn">import</span><span class="w"> </span><span class="nn">jax.numpy</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">jnp</span>
<a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="kn">import</span><span class="w"> </span><span class="nn">matplotlib.pyplot</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">plt</span>
<a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a>
<a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="n">key</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">PRNGKey</span><span class="p">(</span><span class="mi">7</span><span class="p">)</span>
<a id="__codelineno-1-6" name="__codelineno-1-6" href="#__codelineno-1-6"></a>
<a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="c1"># 创建一个合成的 8x8 &quot;图像&quot;3 个通道</span>
<a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="n">k1</span><span class="p">,</span> <span class="n">k2</span><span class="p">,</span> <span class="n">k3</span><span class="p">,</span> <span class="n">k4</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="n">key</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span>
<a id="__codelineno-1-9" name="__codelineno-1-9" href="#__codelineno-1-9"></a><span class="n">image</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">uniform</span><span class="p">(</span><span class="n">k1</span><span class="p">,</span> <span class="p">(</span><span class="mi">8</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">3</span><span class="p">))</span>
<a id="__codelineno-1-10" name="__codelineno-1-10" href="#__codelineno-1-10"></a>
<a id="__codelineno-1-11" name="__codelineno-1-11" href="#__codelineno-1-11"></a><span class="c1"># 第 1 步:划分为 4x4 patch -&gt; 4 个 patch</span>
<a id="__codelineno-1-12" name="__codelineno-1-12" href="#__codelineno-1-12"></a><span class="n">patch_size</span> <span class="o">=</span> <span class="mi">4</span>
<a id="__codelineno-1-13" name="__codelineno-1-13" href="#__codelineno-1-13"></a><span class="n">patches</span> <span class="o">=</span> <span class="n">image</span><span class="o">.</span><span class="n">reshape</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="n">patch_size</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="n">patch_size</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<a id="__codelineno-1-14" name="__codelineno-1-14" href="#__codelineno-1-14"></a><span class="n">patches</span> <span class="o">=</span> <span class="n">patches</span><span class="o">.</span><span class="n">transpose</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span><span class="o">.</span><span class="n">reshape</span><span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="n">patch_size</span> <span class="o">*</span> <span class="n">patch_size</span> <span class="o">*</span> <span class="mi">3</span><span class="p">)</span> <span class="c1"># (4, 48)</span>
<a id="__codelineno-1-15" name="__codelineno-1-15" href="#__codelineno-1-15"></a><span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;Patch 数量: </span><span class="si">{</span><span class="n">patches</span><span class="o">.</span><span class="n">shape</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="si">}</span><span class="s2">, Patch 维度: </span><span class="si">{</span><span class="n">patches</span><span class="o">.</span><span class="n">shape</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>
<a id="__codelineno-1-16" name="__codelineno-1-16" href="#__codelineno-1-16"></a>
<a id="__codelineno-1-17" name="__codelineno-1-17" href="#__codelineno-1-17"></a><span class="c1"># 第 2 步:将 patch 投影到嵌入维度 (d=16)</span>
<a id="__codelineno-1-18" name="__codelineno-1-18" href="#__codelineno-1-18"></a><span class="n">d_model</span> <span class="o">=</span> <span class="mi">16</span>
<a id="__codelineno-1-19" name="__codelineno-1-19" href="#__codelineno-1-19"></a><span class="n">W_patch</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k2</span><span class="p">,</span> <span class="p">(</span><span class="n">patches</span><span class="o">.</span><span class="n">shape</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="n">d_model</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span>
<a id="__codelineno-1-20" name="__codelineno-1-20" href="#__codelineno-1-20"></a><span class="n">visual_tokens</span> <span class="o">=</span> <span class="n">patches</span> <span class="o">@</span> <span class="n">W_patch</span> <span class="c1"># (4, 16)</span>
<a id="__codelineno-1-21" name="__codelineno-1-21" href="#__codelineno-1-21"></a>
<a id="__codelineno-1-22" name="__codelineno-1-22" href="#__codelineno-1-22"></a><span class="c1"># 第 3 步:创建文本 token 嵌入(模拟 3 个文本 token)</span>
<a id="__codelineno-1-23" name="__codelineno-1-23" href="#__codelineno-1-23"></a><span class="n">text_tokens</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k3</span><span class="p">,</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="n">d_model</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span>
<a id="__codelineno-1-24" name="__codelineno-1-24" href="#__codelineno-1-24"></a>
<a id="__codelineno-1-25" name="__codelineno-1-25" href="#__codelineno-1-25"></a><span class="c1"># 第 4 步:拼接视觉 + 文本 token</span>
<a id="__codelineno-1-26" name="__codelineno-1-26" href="#__codelineno-1-26"></a><span class="n">combined</span> <span class="o">=</span> <span class="n">jnp</span><span class="o">.</span><span class="n">concatenate</span><span class="p">([</span><span class="n">visual_tokens</span><span class="p">,</span> <span class="n">text_tokens</span><span class="p">],</span> <span class="n">axis</span><span class="o">=</span><span class="mi">0</span><span class="p">)</span> <span class="c1"># (7, 16)</span>
<a id="__codelineno-1-27" name="__codelineno-1-27" href="#__codelineno-1-27"></a><span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;组合序列长度: </span><span class="si">{</span><span class="n">combined</span><span class="o">.</span><span class="n">shape</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="si">}</span><span class="s2"> (4 个视觉 + 3 个文本)&quot;</span><span class="p">)</span>
<a id="__codelineno-1-28" name="__codelineno-1-28" href="#__codelineno-1-28"></a>
<a id="__codelineno-1-29" name="__codelineno-1-29" href="#__codelineno-1-29"></a><span class="c1"># 第 5 步:在组合序列上运行单头自注意力</span>
<a id="__codelineno-1-30" name="__codelineno-1-30" href="#__codelineno-1-30"></a><span class="n">W_Q</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k4</span><span class="p">,</span> <span class="p">(</span><span class="n">d_model</span><span class="p">,</span> <span class="n">d_model</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span>
<a id="__codelineno-1-31" name="__codelineno-1-31" href="#__codelineno-1-31"></a><span class="n">k5</span><span class="p">,</span> <span class="n">k6</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="n">k4</span><span class="p">)</span>
<a id="__codelineno-1-32" name="__codelineno-1-32" href="#__codelineno-1-32"></a><span class="n">W_K</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k5</span><span class="p">,</span> <span class="p">(</span><span class="n">d_model</span><span class="p">,</span> <span class="n">d_model</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span>
<a id="__codelineno-1-33" name="__codelineno-1-33" href="#__codelineno-1-33"></a><span class="n">W_V</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">random</span><span class="o">.</span><span class="n">normal</span><span class="p">(</span><span class="n">k6</span><span class="p">,</span> <span class="p">(</span><span class="n">d_model</span><span class="p">,</span> <span class="n">d_model</span><span class="p">))</span> <span class="o">*</span> <span class="mf">0.1</span>
<a id="__codelineno-1-34" name="__codelineno-1-34" href="#__codelineno-1-34"></a>
<a id="__codelineno-1-35" name="__codelineno-1-35" href="#__codelineno-1-35"></a><span class="n">Q</span> <span class="o">=</span> <span class="n">combined</span> <span class="o">@</span> <span class="n">W_Q</span>
<a id="__codelineno-1-36" name="__codelineno-1-36" href="#__codelineno-1-36"></a><span class="n">K</span> <span class="o">=</span> <span class="n">combined</span> <span class="o">@</span> <span class="n">W_K</span>
<a id="__codelineno-1-37" name="__codelineno-1-37" href="#__codelineno-1-37"></a><span class="n">V</span> <span class="o">=</span> <span class="n">combined</span> <span class="o">@</span> <span class="n">W_V</span>
<a id="__codelineno-1-38" name="__codelineno-1-38" href="#__codelineno-1-38"></a><span class="n">attn_scores</span> <span class="o">=</span> <span class="p">(</span><span class="n">Q</span> <span class="o">@</span> <span class="n">K</span><span class="o">.</span><span class="n">T</span><span class="p">)</span> <span class="o">/</span> <span class="n">jnp</span><span class="o">.</span><span class="n">sqrt</span><span class="p">(</span><span class="n">d_model</span><span class="p">)</span>
<a id="__codelineno-1-39" name="__codelineno-1-39" href="#__codelineno-1-39"></a><span class="n">attn_weights</span> <span class="o">=</span> <span class="n">jax</span><span class="o">.</span><span class="n">nn</span><span class="o">.</span><span class="n">softmax</span><span class="p">(</span><span class="n">attn_scores</span><span class="p">,</span> <span class="n">axis</span><span class="o">=-</span><span class="mi">1</span><span class="p">)</span> <span class="c1"># (7, 7)</span>
<a id="__codelineno-1-40" name="__codelineno-1-40" href="#__codelineno-1-40"></a>
<a id="__codelineno-1-41" name="__codelineno-1-41" href="#__codelineno-1-41"></a><span class="n">output</span> <span class="o">=</span> <span class="n">attn_weights</span> <span class="o">@</span> <span class="n">V</span> <span class="c1"># (7, 16)</span>
<a id="__codelineno-1-42" name="__codelineno-1-42" href="#__codelineno-1-42"></a>
<a id="__codelineno-1-43" name="__codelineno-1-43" href="#__codelineno-1-43"></a><span class="c1"># 可视化跨模态注意力模式</span>
<a id="__codelineno-1-44" name="__codelineno-1-44" href="#__codelineno-1-44"></a><span class="n">labels</span> <span class="o">=</span> <span class="p">[</span><span class="s1">&#39;V1&#39;</span><span class="p">,</span> <span class="s1">&#39;V2&#39;</span><span class="p">,</span> <span class="s1">&#39;V3&#39;</span><span class="p">,</span> <span class="s1">&#39;V4&#39;</span><span class="p">,</span> <span class="s1">&#39;T1&#39;</span><span class="p">,</span> <span class="s1">&#39;T2&#39;</span><span class="p">,</span> <span class="s1">&#39;T3&#39;</span><span class="p">]</span>
<a id="__codelineno-1-45" name="__codelineno-1-45" href="#__codelineno-1-45"></a><span class="n">fig</span><span class="p">,</span> <span class="n">ax</span> <span class="o">=</span> <span class="n">plt</span><span class="o">.</span><span class="n">subplots</span><span class="p">(</span><span class="n">figsize</span><span class="o">=</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span> <span class="mi">5</span><span class="p">))</span>
<a id="__codelineno-1-46" name="__codelineno-1-46" href="#__codelineno-1-46"></a><span class="n">im</span> <span class="o">=</span> <span class="n">ax</span><span class="o">.</span><span class="n">imshow</span><span class="p">(</span><span class="n">attn_weights</span><span class="p">,</span> <span class="n">cmap</span><span class="o">=</span><span class="s1">&#39;Blues&#39;</span><span class="p">)</span>
<a id="__codelineno-1-47" name="__codelineno-1-47" href="#__codelineno-1-47"></a><span class="n">ax</span><span class="o">.</span><span class="n">set_xticks</span><span class="p">(</span><span class="nb">range</span><span class="p">(</span><span class="mi">7</span><span class="p">));</span> <span class="n">ax</span><span class="o">.</span><span class="n">set_xticklabels</span><span class="p">(</span><span class="n">labels</span><span class="p">)</span>
<a id="__codelineno-1-48" name="__codelineno-1-48" href="#__codelineno-1-48"></a><span class="n">ax</span><span class="o">.</span><span class="n">set_yticks</span><span class="p">(</span><span class="nb">range</span><span class="p">(</span><span class="mi">7</span><span class="p">));</span> <span class="n">ax</span><span class="o">.</span><span class="n">set_yticklabels</span><span class="p">(</span><span class="n">labels</span><span class="p">)</span>
<a id="__codelineno-1-49" name="__codelineno-1-49" href="#__codelineno-1-49"></a><span class="n">ax</span><span class="o">.</span><span class="n">set_xlabel</span><span class="p">(</span><span class="s1">&#39;&#39;</span><span class="p">);</span> <span class="n">ax</span><span class="o">.</span><span class="n">set_ylabel</span><span class="p">(</span><span class="s1">&#39;查询&#39;</span><span class="p">)</span>
<a id="__codelineno-1-50" name="__codelineno-1-50" href="#__codelineno-1-50"></a><span class="n">ax</span><span class="o">.</span><span class="n">set_title</span><span class="p">(</span><span class="s1">&#39;自注意力:视觉(V)和文本(T)Token&#39;</span><span class="p">)</span>
<a id="__codelineno-1-51" name="__codelineno-1-51" href="#__codelineno-1-51"></a><span class="n">plt</span><span class="o">.</span><span class="n">colorbar</span><span class="p">(</span><span class="n">im</span><span class="p">,</span> <span class="n">ax</span><span class="o">=</span><span class="n">ax</span><span class="p">);</span> <span class="n">plt</span><span class="o">.</span><span class="n">tight_layout</span><span class="p">();</span> <span class="n">plt</span><span class="o">.</span><span class="n">show</span><span class="p">()</span>
<a id="__codelineno-1-52" name="__codelineno-1-52" href="#__codelineno-1-52"></a><span class="c1"># 观察:文本 token 关注视觉 token(跨模态注意力)!</span>
</code></pre></div></p>
</li>
<li>
<p>实现用于视觉定位的坐标 token 化。给定一个边界框,将其转换为离散 token;给定离散 token,重构边界框。在不同槽位分辨率下可视化量化误差。
<div class="highlight"><pre><span></span><code><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="kn">import</span><span class="w"> </span><span class="nn">jax.numpy</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">jnp</span>
<a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="kn">import</span><span class="w"> </span><span class="nn">matplotlib.pyplot</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">plt</span>
<a id="__codelineno-2-3" name="__codelineno-2-3" href="#__codelineno-2-3"></a>
<a id="__codelineno-2-4" name="__codelineno-2-4" href="#__codelineno-2-4"></a><span class="k">def</span><span class="w"> </span><span class="nf">encode_bbox</span><span class="p">(</span><span class="n">bbox</span><span class="p">,</span> <span class="n">num_bins</span><span class="o">=</span><span class="mi">1000</span><span class="p">):</span>
<a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a><span class="w"> </span><span class="sd">&quot;&quot;&quot;将连续的边界框 (x, y, w, h)(在 [0,1] 范围内)转换为离散 token。&quot;&quot;&quot;</span>
<a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></a> <span class="n">tokens</span> <span class="o">=</span> <span class="n">jnp</span><span class="o">.</span><span class="n">round</span><span class="p">(</span><span class="n">jnp</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="n">bbox</span><span class="p">)</span> <span class="o">*</span> <span class="p">(</span><span class="n">num_bins</span> <span class="o">-</span> <span class="mi">1</span><span class="p">))</span><span class="o">.</span><span class="n">astype</span><span class="p">(</span><span class="n">jnp</span><span class="o">.</span><span class="n">int32</span><span class="p">)</span>
<a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></a> <span class="k">return</span> <span class="n">tokens</span>
<a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a>
<a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a><span class="k">def</span><span class="w"> </span><span class="nf">decode_bbox</span><span class="p">(</span><span class="n">tokens</span><span class="p">,</span> <span class="n">num_bins</span><span class="o">=</span><span class="mi">1000</span><span class="p">):</span>
<a id="__codelineno-2-10" name="__codelineno-2-10" href="#__codelineno-2-10"></a><span class="w"> </span><span class="sd">&quot;&quot;&quot;将离散 token 转换回连续的边界框。&quot;&quot;&quot;</span>
<a id="__codelineno-2-11" name="__codelineno-2-11" href="#__codelineno-2-11"></a> <span class="k">return</span> <span class="n">tokens</span><span class="o">.</span><span class="n">astype</span><span class="p">(</span><span class="n">jnp</span><span class="o">.</span><span class="n">float32</span><span class="p">)</span> <span class="o">/</span> <span class="p">(</span><span class="n">num_bins</span> <span class="o">-</span> <span class="mi">1</span><span class="p">)</span>
<a id="__codelineno-2-12" name="__codelineno-2-12" href="#__codelineno-2-12"></a>
<a id="__codelineno-2-13" name="__codelineno-2-13" href="#__codelineno-2-13"></a><span class="c1"># 真实边界框(归一化到 [0, 1])</span>
<a id="__codelineno-2-14" name="__codelineno-2-14" href="#__codelineno-2-14"></a><span class="n">gt_bbox</span> <span class="o">=</span> <span class="n">jnp</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mf">0.123</span><span class="p">,</span> <span class="mf">0.456</span><span class="p">,</span> <span class="mf">0.333</span><span class="p">,</span> <span class="mf">0.222</span><span class="p">])</span>
<a id="__codelineno-2-15" name="__codelineno-2-15" href="#__codelineno-2-15"></a>
<a id="__codelineno-2-16" name="__codelineno-2-16" href="#__codelineno-2-16"></a><span class="c1"># 测试不同槽位分辨率下的量化</span>
<a id="__codelineno-2-17" name="__codelineno-2-17" href="#__codelineno-2-17"></a><span class="n">bin_sizes</span> <span class="o">=</span> <span class="p">[</span><span class="mi">10</span><span class="p">,</span> <span class="mi">50</span><span class="p">,</span> <span class="mi">100</span><span class="p">,</span> <span class="mi">500</span><span class="p">,</span> <span class="mi">1000</span><span class="p">]</span>
<a id="__codelineno-2-18" name="__codelineno-2-18" href="#__codelineno-2-18"></a><span class="n">errors</span> <span class="o">=</span> <span class="p">[]</span>
<a id="__codelineno-2-19" name="__codelineno-2-19" href="#__codelineno-2-19"></a><span class="k">for</span> <span class="n">n_bins</span> <span class="ow">in</span> <span class="n">bin_sizes</span><span class="p">:</span>
<a id="__codelineno-2-20" name="__codelineno-2-20" href="#__codelineno-2-20"></a> <span class="n">tokens</span> <span class="o">=</span> <span class="n">encode_bbox</span><span class="p">(</span><span class="n">gt_bbox</span><span class="p">,</span> <span class="n">n_bins</span><span class="p">)</span>
<a id="__codelineno-2-21" name="__codelineno-2-21" href="#__codelineno-2-21"></a> <span class="n">reconstructed</span> <span class="o">=</span> <span class="n">decode_bbox</span><span class="p">(</span><span class="n">tokens</span><span class="p">,</span> <span class="n">n_bins</span><span class="p">)</span>
<a id="__codelineno-2-22" name="__codelineno-2-22" href="#__codelineno-2-22"></a> <span class="n">error</span> <span class="o">=</span> <span class="n">jnp</span><span class="o">.</span><span class="n">max</span><span class="p">(</span><span class="n">jnp</span><span class="o">.</span><span class="n">abs</span><span class="p">(</span><span class="n">gt_bbox</span> <span class="o">-</span> <span class="n">reconstructed</span><span class="p">))</span>
<a id="__codelineno-2-23" name="__codelineno-2-23" href="#__codelineno-2-23"></a> <span class="n">errors</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="nb">float</span><span class="p">(</span><span class="n">error</span><span class="p">))</span>
<a id="__codelineno-2-24" name="__codelineno-2-24" href="#__codelineno-2-24"></a> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;槽位数=</span><span class="si">{</span><span class="n">n_bins</span><span class="si">:</span><span class="s2">&gt;5d</span><span class="si">}</span><span class="s2"> | Token=</span><span class="si">{</span><span class="n">tokens</span><span class="si">}</span><span class="s2"> | &quot;</span>
<a id="__codelineno-2-25" name="__codelineno-2-25" href="#__codelineno-2-25"></a> <span class="sa">f</span><span class="s2">&quot;重构=</span><span class="si">{</span><span class="n">reconstructed</span><span class="si">}</span><span class="s2"> | 最大误差=</span><span class="si">{</span><span class="n">error</span><span class="si">:</span><span class="s2">.6f</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>
<a id="__codelineno-2-26" name="__codelineno-2-26" href="#__codelineno-2-26"></a>
<a id="__codelineno-2-27" name="__codelineno-2-27" href="#__codelineno-2-27"></a><span class="n">fig</span><span class="p">,</span> <span class="n">ax</span> <span class="o">=</span> <span class="n">plt</span><span class="o">.</span><span class="n">subplots</span><span class="p">(</span><span class="n">figsize</span><span class="o">=</span><span class="p">(</span><span class="mi">8</span><span class="p">,</span> <span class="mi">4</span><span class="p">))</span>
<a id="__codelineno-2-28" name="__codelineno-2-28" href="#__codelineno-2-28"></a><span class="n">ax</span><span class="o">.</span><span class="n">plot</span><span class="p">(</span><span class="n">bin_sizes</span><span class="p">,</span> <span class="n">errors</span><span class="p">,</span> <span class="s1">&#39;o-&#39;</span><span class="p">,</span> <span class="n">color</span><span class="o">=</span><span class="s1">&#39;#e74c3c&#39;</span><span class="p">,</span> <span class="n">linewidth</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">markersize</span><span class="o">=</span><span class="mi">8</span><span class="p">)</span>
<a id="__codelineno-2-29" name="__codelineno-2-29" href="#__codelineno-2-29"></a><span class="n">ax</span><span class="o">.</span><span class="n">set_xlabel</span><span class="p">(</span><span class="s1">&#39;槽位数&#39;</span><span class="p">);</span> <span class="n">ax</span><span class="o">.</span><span class="n">set_ylabel</span><span class="p">(</span><span class="s1">&#39;最大量化误差&#39;</span><span class="p">)</span>
<a id="__codelineno-2-30" name="__codelineno-2-30" href="#__codelineno-2-30"></a><span class="n">ax</span><span class="o">.</span><span class="n">set_title</span><span class="p">(</span><span class="s1">&#39;边界框量化误差 vs 槽位分辨率&#39;</span><span class="p">)</span>
<a id="__codelineno-2-31" name="__codelineno-2-31" href="#__codelineno-2-31"></a><span class="n">ax</span><span class="o">.</span><span class="n">set_xscale</span><span class="p">(</span><span class="s1">&#39;log&#39;</span><span class="p">);</span> <span class="n">ax</span><span class="o">.</span><span class="n">set_yscale</span><span class="p">(</span><span class="s1">&#39;log&#39;</span><span class="p">)</span>
<a id="__codelineno-2-32" name="__codelineno-2-32" href="#__codelineno-2-32"></a><span class="n">ax</span><span class="o">.</span><span class="n">grid</span><span class="p">(</span><span class="kc">True</span><span class="p">,</span> <span class="n">alpha</span><span class="o">=</span><span class="mf">0.3</span><span class="p">);</span> <span class="n">plt</span><span class="o">.</span><span class="n">tight_layout</span><span class="p">();</span> <span class="n">plt</span><span class="o">.</span><span class="n">show</span><span class="p">()</span>
<a id="__codelineno-2-33" name="__codelineno-2-33" href="#__codelineno-2-33"></a><span class="c1"># 尝试:槽位非常少时(如 5)会发生什么?误差在何时是可接受的?</span>
</code></pre></div></p>
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