[Lcms-user] Rgb to Lab input profile

[Christopher P. <cpo...@gl...>]

I have a scanner profile, which is embedded into a tiff, I extract the profile and apply the transform but the lab values have a larger delta e than expected. Converting a single pixel.

hInput  is the RGB input profile that was extracted from the tiff.

dwInIntent = Perceptual
dwLabColorspace = Lab Double
dwInColorspace = Rgb double
InputDouble =   0.0006, 0.6555, 0.6730

cmsHTRANSFORM hTransLab  = cmsCreateTransform(hInput, dwInColorspace, hLab,  dwLabColorspace,  dwInIntent, 0);
cmsDoTransform(hTransLab,  InputDouble,  l_lab,  1);

Output lab is 62, -36,  -13 What is expected is 60,-42,-13 (B8 on a digital sg card)

If I test the same tiff in photoshop the deltaE is much closer 1 vs 2.8 some others are as far off as 6.5.

Any ideas?