[FFmpeg-user] Why is format=rgb24 required after maskedmerge?

[Michael Koch]

Please add this to the documentation (for example in chapter 20.9 image2)

FFmpeg supports the following image formats: BMP, DNG, GIF, JPG, PAM, 
PGM (binary P5 files are read/write, ascii P2 files are read-only), 
PGMYUV, PNG, PPM, TGA, TIFF.

Michael