Do not assume that the RP has as many channels as the image.
Do not assume that the RP has as many channels as the image.

In particular, noise will cause 3 additional channels to be present in
the RP.

libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl