CIE XYZ image

[feisty2]

did some color grading for a image sequence in Photoshop under float point precision Lab colorspace, now I got a float point Lab TIFF sequence as the result and it's too large to be stored on the HDD prepared for it, I wanna reduce the file size to the half of the original sequence by rounding the bitdepth to 16bit integer, 16bit precision is way too low for colorspace like Lab, and I wanna keep many valid colors as possible so no srgb, no adobe rgb, no rgb stuff, I wanna go 16bit CIE XYZ which got a smaller gamut than Lab but covers every single valid color to human vision, so no precision wasted on imaginary colors and hopefully 16bit would be enough

any uncompressed or losslessly compressed image or video format got support for CIE XYZ colorspace? and how to convert Lab to XYZ exactly (I know how to do it mathematically, I want a specific program to do it for me)?