@BertrandCaron From my (pretty limited) understanding, YCCK is derived from the CMYK color model, similarly to how YCbCr is derived from the RGB model. See also: https://en.wikipedia.org/wiki/YCbCr Under JPEG conversion section: "JPEG also defines a "YCCK" format from Adobe for CMYK input. (...) As a result, a similar set of subsampling techniques can be used"