Re: Getting Dot Gain From Profile
Re: Getting Dot Gain From Profile
- Subject: Re: Getting Dot Gain From Profile
- From: Don Hutcheson <email@hidden>
- Date: Tue, 13 Apr 2004 12:03:10 -0400
On 04/13/04 01:00 From: Kevin Muldoon <email@hidden> wrote:
>
Could someone please post a method for determining the Dot Gain of a
>
profile?
If you have Excel and Photoshop it's pretty straight forward, at least for
black ink. CMY inks are harder to calculate because you have to extract
status T densities from Lab, for which I don't have a method, at the moment.
For black ink:
1. In Photoshop, create three patches of 0%, 50% and 100% black.
2. Assign your CMYK profile to the patches.
3. Convert the image to Lab Color, Intent Absolute Colorimetric.
4. Transfer the Lab values of each patch to an Excel sheet.
5. In Excel, calculate the Y value of each patch from its L* value. (For
black ink you can effectively ignore the a* and b* values, but for CMY they
would of course be critical.) I use the following formula, which you can cut
and paste into Excel;
Y = 100*IF(L*>8,((L*+16)/116)^3,L*/(116*7.787))
6. Dot gain = 100*[Y(0%)-Y(50%)]/[Y(0%)-Y(100%)]-50
Example:
Using U.S. Web Coated (SWOP) v2
0% K = L* 89 = Y 74.16
50% K = L* 55 = Y 22.93
100% K = L* 19 = Y 2.75
Dot gain = 100 * (74.16 - 22.93) / (74.16 - 2.75) - 50
Dot gain = 21.74%
If anyone has a good method for calculating status T CMY densities (or any
status, for that matter) from Lab, please let me know. Due to the absence of
original spectral data, any method will be flawed, but there has to be a way
of obtaining a reasonable approximation.
Regards,
Don
******************************
Don Hutcheson
Hutcheson Consulting
(Color Management Solutions)
Phone: (908) 689 7403
Mobile: (908) 500 0341
Fax: (908) 689 5305
E-mail: email@hidden
******************************
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