image_processing.py

# Copyright (c) 2024, NVIDIA CORPORATION.  All rights reserved. Except portions as noted which are Copyright (c) 2023 OpenGVLab and licensed under the MIT license found in LICENSE.
from torchvision import transforms as T
from torchvision.transforms import Compose
from torchvision.transforms.functional import InterpolationMode


IMAGENET_PIXEL_MEAN = [0.485, 0.456, 0.406]
IMAGENET_PIXEL_STD = [0.229, 0.224, 0.225]
SIGLIP_PIXEL_MEAN = [0.5, 0.5, 0.5]
SIGLIP_PIXEL_STD = [0.5, 0.5, 0.5]
CLIP_PIXEL_MEAN = [0.48145466, 0.4578275, 0.40821073]
CLIP_PIXEL_STD = [0.26862954, 0.26130258, 0.27577711]


pixel_statistics = {
    "clip": (CLIP_PIXEL_MEAN, CLIP_PIXEL_STD),
    "siglip": (SIGLIP_PIXEL_MEAN, SIGLIP_PIXEL_STD),
    "internvit": (IMAGENET_PIXEL_MEAN, IMAGENET_PIXEL_STD),
    "radio": (CLIP_PIXEL_MEAN, CLIP_PIXEL_STD),
    "huggingface": (SIGLIP_PIXEL_MEAN, SIGLIP_PIXEL_STD),
}


# From https://github.com/OpenGVLab/InternVL/blob/c62fa4f7c850165d7386bdc48ac6bc5a6fab0864/internvl_chat/internvl/train/dataset.py#L685
# Copyright (c) 2023 OpenGVLab.
def find_closest_aspect_ratio(aspect_ratio, target_ratios, width, height, image_size):
    best_ratio_diff = float('inf')
    best_ratio = (1, 1)
    area = width * height
    for ratio in target_ratios:
        target_aspect_ratio = ratio[0] / ratio[1]
        ratio_diff = abs(aspect_ratio - target_aspect_ratio)
        if ratio_diff < best_ratio_diff:
            best_ratio_diff = ratio_diff
            best_ratio = ratio
        elif ratio_diff == best_ratio_diff:
            if area > 0.5 * image_size * image_size * ratio[0] * ratio[1]:
                best_ratio = ratio
    return best_ratio


def find_closest_area_weighted_aspect_ratio(aspect_ratio, target_ratios, width, height, image_size):
    """
    Find the best number of tiles based on the aspect ratio and the area covered by the tiles.
    """
    best_factor = float('-inf')
    best_ratio = (1, 1)
    area = width * height
    for ratio in target_ratios:
        target_aspect_ratio = ratio[0] / ratio[1]
        factor_based_on_area_n_ratio = (
            min((ratio[0]*ratio[1]*image_size*image_size)/ area, 0.6) *
            min(target_aspect_ratio/aspect_ratio, aspect_ratio/target_aspect_ratio))
        if factor_based_on_area_n_ratio > best_factor:
            best_factor = factor_based_on_area_n_ratio
            best_ratio = ratio
    return best_ratio


def get_visual_transform(
    img, img_h, img_w, use_tiling=False, max_num_tiles=1, use_thumbnail=False, augment=False,
    vision_model_type="clip", find_closest_aspect_ratio_fn=find_closest_aspect_ratio):
    pixel_mean, pixel_std = pixel_statistics[vision_model_type]

    assert not augment, "Image augmentation not implemented."
    transform = build_transform(img_h, pixel_mean, pixel_std, vision_model_type)

    if use_tiling:
        assert img_h == img_w, "dynamic tiling expects equal tile height and width"
        imgs = dynamic_preprocess(
            img, min_num=1, max_num=max_num_tiles, image_size=img_h, use_thumbnail=use_thumbnail,
            find_closest_aspect_ratio_fn=find_closest_aspect_ratio_fn)
        imgs = [transform(img) for img in imgs]
    else:
        imgs = [transform(img)]

    return imgs


# From https://github.com/OpenGVLab/InternVL/blob/c62fa4f7c850165d7386bdc48ac6bc5a6fab0864/internvl_chat/internvl/train/dataset.py#L702
# Copyright (c) 2023 OpenGVLab.
def dynamic_preprocess(
    image, min_num=1, max_num=6, image_size=448, use_thumbnail=False,
    find_closest_aspect_ratio_fn=find_closest_aspect_ratio):
    orig_width, orig_height = image.size
    aspect_ratio = orig_width / orig_height

    # calculate the existing image aspect ratio
    target_ratios = set(
        (i, j) for n in range(min_num, max_num + 1) for i in range(1, n + 1) for j in range(1, n + 1) if
        i * j <= max_num and i * j >= min_num)
    target_ratios = sorted(target_ratios, key=lambda x: x[0] * x[1])

    # find the closest aspect ratio to the target
    target_aspect_ratio = find_closest_aspect_ratio_fn(
        aspect_ratio, target_ratios, orig_width, orig_height, image_size)

    # calculate the target width and height
    target_width = image_size * target_aspect_ratio[0]
    target_height = image_size * target_aspect_ratio[1]
    blocks = target_aspect_ratio[0] * target_aspect_ratio[1]

    # resize the image
    resized_img = image.resize((target_width, target_height))
    processed_images = []
    for i in range(blocks):
        box = (
            (i % (target_width // image_size)) * image_size,
            (i // (target_width // image_size)) * image_size,
            ((i % (target_width // image_size)) + 1) * image_size,
            ((i // (target_width // image_size)) + 1) * image_size
        )
        # split the image
        split_img = resized_img.crop(box)
        processed_images.append(split_img)
    assert len(processed_images) == blocks
    if use_thumbnail and len(processed_images) != 1:
        thumbnail_img = image.resize((image_size, image_size))
        processed_images.append(thumbnail_img)
    return processed_images


# Based on https://github.com/openai/CLIP/blob/dcba3cb2e2827b402d2701e7e1c7d9fed8a20ef1/clip/clip.py#L79
# and https://github.com/OpenGVLab/InternVL/blob/aa521e6eb1df4cf153aa4118fcf13e673c055d46/internvl_chat/internvl/train/dataset.py#L276
def build_transform(input_size, pixel_mean, pixel_std, vision_model_type):
    if vision_model_type in ("siglip", "internvit", "radio", "huggingface"):
        transform = T.Compose([
            T.Lambda(lambda img: img.convert('RGB') if img.mode != 'RGB' else img),
            T.Resize((input_size, input_size), interpolation=InterpolationMode.BICUBIC),
            T.ToTensor(),
            T.Normalize(mean=pixel_mean, std=pixel_std)
        ])
    elif vision_model_type == "clip":
        transform = Compose([
            T.Resize((input_size, input_size), interpolation=InterpolationMode.BICUBIC),
            T.Lambda(lambda img: img.convert('RGB') if img.mode != 'RGB' else img),
            T.ToTensor(),
            T.Normalize(mean=pixel_mean, std=pixel_std),
        ])
    else:
        raise NotImplementedError(f"image processing not defined for vision model {vision_model_type}")

    return transform