Re: Converting from CMYK to Grayscale in Photoshop
Re: Converting from CMYK to Grayscale in Photoshop
- Subject: Re: Converting from CMYK to Grayscale in Photoshop
- From: Marco Ugolini <email@hidden>
- Date: Thu, 15 Nov 2007 18:56:08 -0500 (EST)
Bob Gardner wrote:
>I have recently noticed that when I convert from CMYK in Photoshop CS3, my
>100K areas are converting to 87K. I don't recall ever seeing this in the
>past. I have tried alternate gray color space options and get different
>results. The results that I seek are that 100K stays 100K when converting to
>grayscale.
A C0, M0, Y0, K100 patch in CMYK -- say using U.S. Sheetfed Coated v2 -- is *not* the darkest black you can get within that color space. That is why, upon conversion to Grayscale, it does not translate to K100: because there exist possibly darker tonalities than that in the CMYK space.
Try this exercise:
1) Open a new CMYK file, using the U.S. Sheetfed Coated v2 profile: make its size 2" x 2" at 300ppi;
2) Hit the "D" key on your keyboard: this will make the foreground color *rich black* (which with U.S. Sheetfed Coated v2 equals C95, M85, Y85, K85, for a 350% TAC);
3) Fill your document with that 4-color foreground black;
4) Now, use the marquee tool to select a square in the center of the image; click on the foreground color patch in the Tools panel, and make that color C0, M0, Y0, K100;
5) Fill the selected area with the new foreground color, then deselect (Command-D on a Mac): you will notice that the area in the center looks lighter than the surrounding;
6) Go to Edit > Convert to Profile: select Gray Gamma 2.2 as your destination profile; also, select the Relative Colorimetric intent and check the "Use Black Point Compensation" check box; click "OK";
7) Now, with the eyedropper, sample the two areas of black in the file: you will see that the areas of rich black read K100, whereas the lighter area in the center reads 87%.
NOTE: A bug of some kind in Photoshop CS3 returns a value of K99 in Grayscale using this procedure. CS2, on the other hand, returns K100.
Marco Ugolini
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