Digital BW, The Print

In a message dated 11/10/06 6:41:02 PM, rcooke@... writes:


> On the QTR site there is a page that lists "Ideal
> Densities for Various dMax" which shows a 0.682D for the 50% for a
> gamma of 2.20.  So I'm confused on which ones to use for my curves.
> 
> My question to all of the experts out there is:  Is there some web
> site or reference work that explains all of this?  I'l like to be able
> to print the same image onto different papers and have them look similar.
> 

QTR is a great program at a modest price; with limited documentation, and 
scattered tutorials. The enthusiasts who use it seem to enjoy the challenge, but 
it certainly limits popular usage. Gamma refers to a single number curve that 
adjusts the measurable linearity of a ramp, in this case a gray ramp. The 
human eye's response curve, compared to the linear values measures by a spectro, 
are at gamma 2.2. AdobeRGB, sRGB, and Gray Gamma 2.2 (obviously, in this last 
case) are all gamma 2.2 spaces. Monitors are typically calibrated to gamma 2.2 
as well. So with all the stuff you'll need to learn, you can simplify your 
life by just starting out assuming gamma 2.2 for now. To see a gamma curve in 
action, open a grayscale file in Photoshop, go to the "curves" command, place a 
point in the center of the linear (straight diagonal) curve, type in 128 as the 
starting value, and then other values in the lower box. The results will be 
differing gamma curves. At gamma 2.2 (which you'll get in any of the spaces 
noted above), 128 is not 50% gray, but it shows the concept of how a single value 
can define a gamma shaped curve.

C. David Tobie
Product Technology Manager
ColorVision Business Division
DataColor Inc.
CDTobie@...
www.colorvision.com


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