CLIPScore

The CLIPScore is a model-based image captioning metric that correlates well with human judgments.

The benefit of CLIPScore is that it does not require reference captions for evaluation.

Here’s a hypothetical Python example demonstrating the usage of the CLIPScore metric to evaluate image captions:

import matplotlib.animation as animation
import matplotlib.pyplot as plt
import numpy as np
import torch
from matplotlib.table import Table
from skimage.data import astronaut, cat, coffee

from torchmetrics.multimodal import CLIPScore

Get sample images

images = {
    "astronaut": astronaut(),
    "cat": cat(),
    "coffee": coffee(),
}

Define a hypothetical captions for the images

captions = [
    "A photo of an astronaut.",
    "A photo of a cat.",
    "A photo of a cup of coffee.",
]

Define the models for CLIPScore

models = [
    "openai/clip-vit-base-patch16",
    # "openai/clip-vit-base-patch32",
    # "openai/clip-vit-large-patch14-336",
    "openai/clip-vit-large-patch14",
]

Collect scores for each image-caption pair

score_results = []
for model in models:
    clip_score = CLIPScore(model_name_or_path=model)
    for key, img in images.items():
        img_tensor = torch.tensor(np.array(img))
        caption_scores = {caption: clip_score(img_tensor, caption) for caption in captions}
        score_results.append({"scores": caption_scores, "image": key, "model": model})

Create an animation to display the scores

fig, (ax_img, ax_table) = plt.subplots(1, 2, figsize=(10, 5))


def update(num: int) -> tuple:
    """Update the image and table with the scores for the given model."""
    results = score_results[num]
    scores, image, model = results["scores"], results["image"], results["model"]

    fig.suptitle(f"Model: {model.split('/')[-1]}", fontsize=16, fontweight="bold")

    # Update image
    ax_img.imshow(images[image])
    ax_img.axis("off")

    # Update table
    table = Table(ax_table, bbox=[0, 0, 1, 1])
    header1 = table.add_cell(0, 0, text="Caption", width=3, height=1)
    header2 = table.add_cell(0, 1, text="Score", width=1, height=1)
    header1.get_text().set_weight("bold")
    header2.get_text().set_weight("bold")
    for i, (caption, score) in enumerate(scores.items()):
        table.add_cell(i + 1, 0, text=caption, width=3, height=1)
        table.add_cell(i + 1, 1, text=f"{score:.2f}", width=1, height=1)
    ax_table.add_table(table)
    ax_table.axis("off")
    return ax_img, ax_table


ani = animation.FuncAnimation(fig, update, frames=len(score_results), interval=3000)

Once Loop Reflect