SELECT video_id, frame_num FROM hashes_table WHERE hamming_distance(image_hash, frame_hash) < N;
FLIF is a novel lossless image format which outperforms PNG, lossless WebP, lossless BPG, lossless JPEG2000, and lossless JPEG XR in terms of compression ratio.
WebP lossless images are 26% smaller in size compared to PNGs.
cpaldjvu - DjVuDocument encoder for low-color images.
cpaldjvu [options] inputppmfile outputdjvufile
Program cpaldjvu is a DjVuDocument encoder for images containing few colors. It performs best on images containing large solid color areas such as screen dumps. Compression ratios on such
images can be much higher than those achieved by GIF or PNG compression.
This program works by first reducing the number of distinct colors to a small specified value using a simple color quantization algorithm. The dominant color is encoded into the background
layer. The other colors are encoded into the foreground layer.
delta = abs(R-G) + abs(G-B) + abs(B-R)