U of S | Mailing List Archive | alt-photo-process-l | Re: Gum Calibration 2 (How to read color samples?)

Re: Gum Calibration 2 (How to read color samples?)


Take a look at this link. It really is quite interesting.


Hope it helps


David H

On Oct 26 2008, Loris Medici wrote:

26 Ekim 2008, Pazar, 4:01 am tarihinde, Katharine Thayer yazmýþ:
> I was hoping someone else would answer this; I was curious what the
> answer would be.
> I'm not entirely sure what you're asking, overall, but as far as what
> happens when you desaturate, thought I'd offer the discovery I made
> a couple of years ago that if you set your monochrome working space
> to grey gamma 2.2, there's no discernable difference between
> desaturating and simply changing to greyscale mode, except that if
> you change to greyscale you lose two channels, which can be useful if
> you're working with big files. But as far as the pixel values
> themselves, they are identical (I checked this myself, moving back
> and forth between the modes). That may not hold if you're working in
> some unusual color space, but it works for Adobe RGB and sRGB.

I'm not sure about the MATH PS does in converting RGB value to Grayscale.
Plus, luminosity seems more natural in the context of paints.

> As for changing to Lab mode and splitting out a channel, I'm not sure
> why you'd do that. My understanding is that Lab Luminosity and HSB
> Brightness are the same, at any rate for either one of them you can
> read off the values in the info box.

Yes, but I need the RGB values to enter into the calibration sheet,
therefore I have to split channels and convert the grayscale Luminosity
image to RGB, to get RGB value of corresponding Luminosity.