Optimisation: Use dummy frames for repeated images #210
Description
ImageMagick with layers optimize-plus uses a nice optimisation technique:
- For animations that have repeated images:
1-2-1-... - Frame 0, disposal=1. Frame 1, disposal=3 (restore to previous).
- Frame 3 is then a 'dummy' 1x1px image (since we restored Image 1), to maintain the delay timing. Ideally we color the pixel using the same color from the first pixel to avoid local palettes. IM strategy is to create a 1bit transparent pixel, since this might be more robust, but adds more bytes for the local palette.
- The next frame is then a full (or delta) image as normal.
This can save some bytes. Example here.
