This shows a histogram created with ippiHistogram_16u_C4R from the 16u RGB image at http://adriaan.biz/preview/DSCA_002205-preview.tif
The histogram of the same 16u RGB image after a call to ippiRGBToHSV_16u_AC4R and ippiHSVToRGB_16u_AC4R.
The histogram of the same 16u RGB image after a call to ippiRGBToHLS_16u_AC4R and ippiHLSToRGB_16u_AC4R.
The histogram of the same 16u RGB image after a call to ippiRGBToXYZ_16u_AC4R and ippiXYZToRGB_16u_AC4R.
The histogram of the same 16u RGB image after a call to ippiRGBToLUV_16u_AC4R and ippiLUVToRGB_16u_AC4R.
The histograms show that the RGB to HSV and HLS conversions (and back to RGB) are good. The RGB to XYZ conversion (and back) isn't precise in the high tones. The RGB to LUV conversion (and back) looses information in the high tones. I think 16u is precise enough that the XYZ and LUV round-trip conversions should be better. So, I am reporting this as a bug.
Regards,
Adriaan van Os