On Sep 3, 2009, at 6:07 PM, Bob and Carol Schoner wrote:
Print the line using your profile and then measure one or more of the squares using the spectro. It will tell you the “color” in Lab units which you can use to adjust the sliders and make a new profile. If you’re like me you may want to find an on line Lab to RGB converter (I can’t think in Lab).
Thinking in Lab is very useful for this type of work; RGB is not a good set of units for it. First the L* value is luminance, from dead black (L*=0) to perfect white (L*=100). This is much more effective than Density units, or RGB units for measuring the brightness component of a color. Next, a* is a scale of red to green. Red is positive, green in negative. But this scale is especially good for grays, with neutrals having near zero values. Similarly, b* is a scale from yellow (positive) to blue (negative), with neutrals being near zero. Yellow is rather hidden in RGB, and its not a obvious when you have a whitened paper in RGB (in Lab it shows a negative b* value). So I suggest leaving your Lab measurements in Lab when using them to analyze the smoothness of steps in a gray ramp, or the neutrality of grays, blacks, and whites, as its a very good color space for those functions. This doesn't mean that I can, off the top of my head, tell you the Lab values that would create slate blue, or pie pumpkin orange, but for work near the gray axis, its ideal.
Just for kicks, measure the “white” of the paper you are using, you may be surprised to find some blue.
Clearly visible in Lab space, as a negative b* value... which indicates either artificial whiteners, or paper with an actual blue tint; but thats far less often the case, except in pastel stationary...
C. David Tobie
Datacolor
www.datacolor.com/Spyder3
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