Here is one very interesting thing i figure during Photoline testing. There is a not too widely known problem with data loss due convert to LAB from wide gamut RGB color spaces. It is common to all existing graphic editing apps. In short - for some reason imaginary colors that exists in Wide color spaces are usually hard clipped when converted to LAB. This is easy to inspect with synthetic gradient created in 16bit wide color space that represents all possible colors. The original gradient created in 16bit ProPhoto RGB looks like this:
When we convert it to LAB we can see some clipping due some amount of imaginary colors in ProPhoto RGB color space. Those colors are lost forever now:
And here is the fix for this problem that i found by accident during Photoline testing:
1. Up-convert mage to 32 bit.
2. Convert to LAB.
Perfect transform of all colors including imaginary colors. No any colors loss!
P.S. I am not to technical and can not explain the nature of this bit depth phenomenon, but hope someone from developers team may explain it.