SSIM

Evaluation of general video inpainting usually directly computes whole-frame reconstruction error (PSNR, SSIM, or LPIPS), but this protocol is not suitable for video subtitle removal, because subtitles occupy only a small region of the frame and whole-frame metrics are diluted by the large amount of unmodified background pixels.

SSIM (structural similarity index) measures the similarity between a reconstructed image and a reference image from three dimensions: luminance, contrast and structure, with values ranging from 0 to 1, where closer to 1 indicates better structure preservation.

When validating the quality of a density field, the PSNR or SSIM of the RGB rendering cannot be used as the sole criterion; additional density-sensitive measurement means need to be introduced, or appropriate regularization constraints imposed on the appearance capacity.

CLIP score measures semantic consistency rather than visual quality and cannot capture perceptual issues such as image blurriness, artifacts, or color distortion; in practice it is typically used in combination with SSIM or FID.

Viewport quality is a specific concept in VR video quality assessment, distinct from traditional video's full-frame PSNR or SSIM metrics, and requires simulating the user's actual viewing region during evaluation.

By rendering the generated LaTeX as an image and comparing it with the original scanned region using structural similarity (SSIM) or a formula recognition model, semantic-level errors missed by pure syntax checking (such as η being recognized as n) can be captured.

LPIPS (Learned Perceptual Image Patch Similarity) has a far higher correlation with human subjective evaluation than traditional PSNR and SSIM metrics.

Evaluation frameworks typically contain three layers of mechanisms: rule-based checks, semantic checks, and visual regression checks.

Benchmark evaluation methods combine automated metrics (CLIP-Score, LPIPS, SSIM) with human evaluation.