Lazy loaded image11.4 EVA

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Objective: Select a Masked Image Modeling (MIM) visual pre-training task with excellent transfer performance to downstream tasks.
Candidate Methods:
  • Recover masked semantic visual token features: Based on CLIP visual features, recover the masked semantic features.
  • Feature Distillation: Perform feature distillation from strong pre-training representations.
Experimental Results:
  • Additional tokenization (i.e., BEiT) on CLIP features is not necessary for performance improvement in downstream tasks.
  • Longer feature distillation time during pre-training does not provide consistent performance improvement.
  • Optimal choice: Directly reconstructing the masked CLIP visual features based on visible patches.
Note that this MIM task is not proposed for the first time, it has been studied in MVP and MILAN. EVA demonstrated that this task can be extended to billions-scale parameters and millions-scale images, and does not require:
  • Semantic quantization/tokenization;
  • Explicit use of image-text pairs as pre-training data.

Model Architecture

  • Model Framework: EVA is a common ViT with 10 billion parameters.
  • Features:
    • Complies with ViT giant and BEIT-3 visual encoders.
    • Relative position embedding and layer-scale are not used during pre-training.

Pre-training Objective

  • Task: Reconstruct masked CLIP visual features based on visible image patches.
  • Masking Strategy:
    • Use [MASK] tokens to corrupt input patches.
    • Employ block-wise masking, with a masking ratio of 40%.
  • Target Features: From OpenAI CLIP-L/14 vision tower (originally trained on 224x224 images).
  • Output Processing:
    • First, normalize EVA's output features.
    • Then, project them to the same dimension as CLIP features via a linear layer.
  • Loss Function: Negative cosine similarity.

Data

  • Datasets:
    • CC12M and CC3M: Image data only, no captions.
    • COCO and ADE20K: Training set data only.
    • ImageNet-21K and Object365: Image data used.
  • Total: 29.6 million images.
  • CLIP Features: Trained on 400 million pairs in a self-supervised behavior. EVA implicitly utilizes the image-text pairs from this dataset.

Hyperparameters

  • Optimizer: Adam, weight decay 0.05.
  • Learning Rate: Peak value 1e-3, decayed according to a cosine learning rate schedule.
  • Data Augmentation: RandResizeCrop (0.2, 1).
  • Color Jitter: Not used.
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