RGB or LAB

[Rocco Bellantoni]

My lab offers drum and Imacon scans only in RGB and LAB on speical request. I have 4x5 BW negs to scan and I'm wondering which of these two colour modes is best for preserving the tonality of the negs.

thanks in advance

[David R Munson]

Unless you need your scans for some sort of specialized application, just stick with RGB. The only time I've used LAB colorspace is when doing a study at Case Western on the fading of color dyes and had to cross-reference color values against other data.

[mark blackman]

Ask them to scan in rgb mode, and embed the scanner's ICC profile in the tiff file.

[Leigh Perry]

If you’re scanning black and white, the colour space probably doesn’t matter too much. Of the LAB data, only the ‘L’ (luminance) will be significant; ‘a’ and ‘b’ carry isoluminant colour information. If you’ll convert to greyscale the result is probably the same.

If scanning colour though, LAB is far too big a colour space for the gamut of your film. In 8 bit, this leads to coarse quantisation and posterisation effects. The Lab colour space is spread too thin over not enough bits. In 16 bit, there is plenty of resolution for the colour space, so it doesn’t matter whether you use RGB or Lab. Lab has the advantage that you can make contrast adjustments (on the L channel) without skewing the colour. But lots of people like the colour skewing – it generally leads to a saturation increase, which is always popular :)

I think the most important choice is to get 16 bits scans (if available). You do need the embedded profile as Mark pointed out.