17 days ago
- JPEG files can be saved with low frequency components first, allowing partially downloaded images to display at low resolution instead of being cut off.
- This is achieved through multiple scans in the file, each with a header; the first scan includes the lowest DC Fourier bin for all three color channels.
- Scans define spectral ranges and precision, enabling construction of JPEGs where future scans overwrite already rendered data.
- Concatenating multiple images with the same resolution can create a file that switches between images over a slow network, but decoders often limit scans to avoid issues.