I'm converting images with embedded ICC profiles to the sRGB color space using LittleCMS. I want to efficiently detect when this conversion is lossy due to the image containing pixels that are out-of-gamut for the sRGB (e.g. the image is using Display P3 and contains saturated colors).
Note that I don't want to merely check if the embedded profile has a wide gamut, because the image pixels may not be taking advantage of its full gamut, and still fit in sRGB.
I know there's cmsSetAlarmCodes, but this seems like it could cause false positives, because there's nothing stopping the image from actually containing the same color that I set for my alarm color. Does LCMS have some out of band signal for this?
Another approach that comes to my mind is applying conversion twice: to sRGB and then back to the original color space, and checking how lossy it was. But that more than doubles processing time. Is there a more efficient way?