Re: Pure white in OS X
Re: Pure white in OS X
- Subject: Re: Pure white in OS X
- From: Joseph Holmes <email@hidden>
- Date: Thu, 13 Mar 2003 10:32:41 -0800
Greg,
One way to not get all pure white pixels in a conversion to CMYK in
Photoshop is to have dithering turned on in the Color Settings
dialog. The dithering feature can be very useful for optaining
perfectly smooth printed gradients on smooth paper from gradient
files that have been processed into printer space from a working
space or other profile. This would be most important when printing
black and white images on smooth paper, but it can also help to avoid
posterization in color. I presume what you are describing is an even
effect, equally applied to all pixels, but it's good to keep the
dithering functionality in mind and to understand it. To that end,
set the eyedropper to single pixels to measure them, or make an
extreme levels adjustment on a processed patch of white to see the
dithering pattern. The conversion I just did resulted in scattered
pixels of (1, 0, 0, 0).
Usually, the so-called scum dots are the result of printer profiles
that don't interpolate accurately to white, or which don't force the
white result to all zeros, and this may involve the CMM, as Andrew
said. This is one reason that some who make profiling software
prefer odd-numbered BtoA table sizes in their printer profiles.
Joe Holmes
Message: 10
Date: Wed, 12 Mar 2003 17:47:31 -0500
Subject: Pure white in OS X
From: <email@hidden>
To: <email@hidden>
On a 867 DP G4 (running OS 10.2.4) in Photoshop 7.0.1 I can't get a cmyk
reading of 0,0,0,0 even though the rgb numbers read 255,255,255. CMYK
reads as 1,1,1,0. When I set a pure white in the color palette it will read
0,0,0,0 but when filling a selection the white in the image will read
1,1,1,0 again. I am using the same profiles, preferences & colorsync
settings as other G4's running OS 9 & do not have this problem. Has anyone
else experienced this? Very frustrating!
Greg DeBri
South Florida Photo & Imaging
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