Llava简述

2024-09-02

介绍

Llava是一个多模态大模型，本文以如下代码大致介绍下。

import os
os.environ['HF_ENDPOINT'] = 'https://hf-mirror.com'  # noqa

import requests
from PIL import Image
from transformers import AutoProcessor, LlavaForConditionalGeneration, LlavaConfig


config = LlavaConfig.from_pretrained("llava-hf/llava-1.5-7b-hf")


model = LlavaForConditionalGeneration(config=config)

processor = AutoProcessor.from_pretrained("llava-hf/llava-1.5-7b-hf")
prompt = "USER: <image>\nWhat's the content of the image? ASSISTANT:"
url = "https://www.ilankelman.org/stopsigns/australia.jpg"
image = Image.open(requests.get(url, stream=True).raw)
inputs = processor(text=prompt, images=image, return_tensors="pt")

generate_ids = model.generate(**inputs, max_new_tokens=15)
processor.batch_decode(generate_ids, skip_special_tokens=True,
                       clean_up_tokenization_spaces=False)[0]

print()

模型结构


LlavaForConditionalGeneration(
  (vision_tower): CLIPVisionModel(
    (vision_model): CLIPVisionTransformer(
      (embeddings): CLIPVisionEmbeddings(
        (patch_embedding): Conv2d(3, 1024, kernel_size=(14, 14), stride=(14, 14), bias=False)
        (position_embedding): Embedding(577, 1024)
      )
      (pre_layrnorm): LayerNorm((1024,), eps=1e-05, elementwise_affine=True)
      (encoder): CLIPEncoder(
        (layers): ModuleList(
          (0-23): 24 x CLIPEncoderLayer(
            (self_attn): CLIPAttention(
              (k_proj): Linear(in_features=1024, out_features=1024, bias=True)
              (v_proj): Linear(in_features=1024, out_features=1024, bias=True)
              (q_proj): Linear(in_features=1024, out_features=1024, bias=True)
              (out_proj): Linear(in_features=1024, out_features=1024, bias=True)
            )
            (layer_norm1): LayerNorm((1024,), eps=1e-05, elementwise_affine=True)
            (mlp): CLIPMLP(
              (activation_fn): QuickGELUActivation()
              (fc1): Linear(in_features=1024, out_features=4096, bias=True)
              (fc2): Linear(in_features=4096, out_features=1024, bias=True)
            )
            (layer_norm2): LayerNorm((1024,), eps=1e-05, elementwise_affine=True)
          )
        )
      )
      (post_layernorm): LayerNorm((1024,), eps=1e-05, elementwise_affine=True)
    )
  )
  (multi_modal_projector): LlavaMultiModalProjector(
    (linear_1): Linear(in_features=1024, out_features=4096, bias=True)
    (act): GELUActivation()
    (linear_2): Linear(in_features=4096, out_features=4096, bias=True)
  )
  (language_model): LlamaForCausalLM(
    (model): LlamaModel(
      (embed_tokens): Embedding(32064, 4096)
      (layers): ModuleList(
        (0-31): 32 x LlamaDecoderLayer(
          (self_attn): LlamaSdpaAttention(
            (q_proj): Linear(in_features=4096, out_features=4096, bias=False)
            (k_proj): Linear(in_features=4096, out_features=4096, bias=False)
            (v_proj): Linear(in_features=4096, out_features=4096, bias=False)
            (o_proj): Linear(in_features=4096, out_features=4096, bias=False)
            (rotary_emb): LlamaRotaryEmbedding()
          )
          (mlp): LlamaMLP(
            (gate_proj): Linear(in_features=4096, out_features=11008, bias=False)
            (up_proj): Linear(in_features=4096, out_features=11008, bias=False)
            (down_proj): Linear(in_features=11008, out_features=4096, bias=False)
            (act_fn): SiLU()
          )
          (input_layernorm): LlamaRMSNorm()
          (post_attention_layernorm): LlamaRMSNorm()
        )
      )
      (norm): LlamaRMSNorm()
    )
    (lm_head): Linear(in_features=4096, out_features=32064, bias=False)
  )
)

一共三部分：

CLIPVision负责处理图像部分
Llama负责文本部分
multi_modal_projector负责将图像hidden_size投影到Llama一样维度。

数据处理

图像部分走的是CLIP处理流程，resize到336*336,所以pixel_values shape为(3, 336, 336)，其他没啥特殊。文字部分走的是Llama,这个就很熟悉了。

visual和text对齐

image走ViT,kernel_size为14，所以计算过程和结果如下：

1
2
3

(336-14)/14+1 = 24
24 * 24 = 596
# 如果考虑CLIP CLS的话就是597。

由于CLIP输出是1024,经过multi_modal_projector后维度为(1,576,4096)，这个也是下面image_features的维度。
至此同一个维度4096。

image插入位置

原prompt如下：

1	prompt = "USER: <image>\nWhat's the content of the image? ASSISTANT:"

<image>是插在指定位置的，那么这里图文对齐和之前的对齐就增添了另外一个含义：不仅要能图文对齐，还要考虑图像插入位置。

参考上图中_merge_input_ids_with_image_features函数以及结合上图中的信息，那么不难得出如下结论：

1 2	(final_embedding[:, 5:576+5, :] == image_features[:, :, :]).all() # > tensor(True)

由于后续target task为VQA、Image Caption之类的，先到此为止。