Here is the reason and solution. Thanks to Marti Maria - the author of littlecms - to sort this out ... This program does not work because you missed the part on https://littlecms.com/blog/2020/12/09/using-lcms2-on-qt/ that says: Alpha channels are supported as long as the image is not using premultiplied alpha. To get alpha channel make sure to include cmsFLAGS_COPY_ALPHA in the flags field. This is explained in LittleCMS documentation. So, try: toDisplay = colorManage(sourceImage, profiles, INTENT_PERCEPTUAL, cmsFLAGS_COPY_ALPHA);* This fixed the issue for me.