"Ken" wrote in message
In Photoshop, the terms 'highlights', 'midtones' and 'shadows' are used for the dodge and burn tools and for the eyedroppers in Levels and Curves.
The terms have wider meaning than just the tools in photoshop that mention them. One convention is that highlight and shadow usually designate the darkest and brightest areas, respectively, that contain important detail and, in RGB and CMYK mode, no color information.
What range does each term cover? Is it evenly divided 1/3, 1/3, 1/3 so that shadows would be RGB 0-85, midtones, 86-170 and highlights 171-255.
The ranges are approximate. Shadow and highlight are usually used to designate the extremes of the image, rather than ranges of tone. In printing, it's common to use three quartertone, midtone, and quartertone for 75, 50, and 25 percent ink.
I got thinking about this when someone suggested to me that he likes to 'boost the cyan in the blacks' to get better printed blacks. I didn't question it at the time, but having now had the chance to give it some thought, I don't understand how one can 'boost the cyan in the blacks' without affecting the rest of the image?
One common way to do this is to use Photoshop's Selective Color function to boost cyan in black, or mask for the shadows and use curves to bump cyan.
Has anyone else used this technique to improve the quality of printed blacks?
It's a standard CMYK technique, called "rich black". It will not work in RGB because pure black is RGB(0,0,0), with no ability to pile on additonal ink. If you use this to darken type or line art, be sure to trap the colors.
If one sets the RGB values for the shadow eyedropper to, say, 5,5,5 to what level of RGB value will the parts of the image be affected?
There are better techniques than using the eyedroppers, such as setting an info point and adjusting the curve endpoints to get the desired shadow value. If you do use it, it will potentially cause a slight change in RGB values throughout.
The only book that covers this sort of thing is Margulis's Professional Photoshop.
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Mike Russell - www.curvemeister.com