One technique prepress uses to check press runs is to include a set of color patches which can then be measured post run but this is not so easy when printing photographs.
Photographers typically send out images either in a standard colorspace (sRGB ugh) or wider RGB spaces and, for high end printers, with an image converted and tagged with the printer profile.
While patches can be added and measured or colors can just be checked in an area that has consistent color and is large enough for a spectrophotometer, aperture color measurements will still be different from the Lab values seen inspecting them in Photoshop because printing in anything other than Absolute colorimetric will not produce the color Lab values of the original image and Abs. Col. is not appropriate in most cases of photographic reproduction.
So here's the process to determine, in Photoshop, what the printed colors should be when measured with a spectrophotometer.
- Starting from an image in your standard working RGB space, convert it to the printer profile using the desired Rendering Intent.
- Then change the color settings under Edit->Color Settings->Conversion Options->Intent to Absolute Colorimetric. Remember to reset it to the original values after finishing.
- Make sure your info tab has the color display selected for Lab and either 8 bit or 32 bit (high precision Lab)
Now, when you mouse over the image colors in Photoshop the Lab values should correspond to the colors measured on the physical prints. On a good, color managed workflow these colors should be within an average of 1 or 2 Delta E.
This works equally well for "proof only" profiles that print houses sometimes provide such as WHCC which requires images be sent to them with a standard RGB tag such as sRGB or Adobe RGB.
