Handsum: A lossy thumbnail image format
11 hours ago
- #LQIP
- #DCT
- #Image Compression
- LQIPs are small images that load quickly, providing immediate visual feedback while full-resolution images load.
- Handsum is a new LQIP file format based on Discrete Cosine Transform (DCT) like Blurhash, Thumbhash, and JPEG.
- Handsum files have fixed sizes: 48 bytes at lowest quality and 147 bytes at highest, enabling fixed-size database columns.
- The format uses YCbCr color space with 4:2:0 chroma subsampling to reduce file size by prioritizing luma over chroma.
- Encoding involves stages like resizing to 16x16, DCT on 2x2 blocks, quantization, and dropping high-frequency coefficients.
- Handsum compares favorably to other formats in quality vs. size, offering predictable byte budgets unlike variable WebP.
- A loop filter is applied during decoding to smooth block boundaries, similar to WebP's VP8 Loop Filter.
- Reference implementations are available in Go and C, including a Wasm demo for web use.
- Handsum is designed for thumbnails in embedded apps where fixed byte budgets are crucial, such as art catalogs.