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4 Color Gray Image Reproduction
Here's a tough topic that I hope might spark some conversation.
Often we are called upon as prepress operators to make grayscale images produce with more of a snap in a 4 color publication. Many times the black-only halftones just look washed-out. So to achieve more impact we print them in 4 color process.
Operators are required to print grayscale images in 4/c process making sure that the image has an entirely neutral value. To give an example of this; take a RGB image/scan; convert this to grayscale ;and finally convert to CMYK. This gives you a neutral gray in all tonal areas of the image. Of course this is only an example and there are much, much better ways to produce the 4/c gray image which we can talk about in a separate discussion, but the objective here is still the same.
Upon further examination the profile GCR and gray ramp will show similar to the figure
(attached here) where the ramp up of black takes over around the 50% range. While this type of curve may be useful for reducing black ink consumption, it's unlikely to produce a controllable 4/c grayscale image. The range from 0-30% can shift dramatically with only the slightest shift in ink density. A more appropriate curve for a 4/c gray image would make use of black ink early in the curve to help keep the possibility of color shift to a minimum.
When I think back 8-10 years ago we didn't really experience much of this problem, so I went back to photoshop v4 and compared the conversions. Resent changes in color settings and profiling have made significant impact in the ability to control color management but made the conversion of 4 color grayscale images more problematic in printing.
I would be delighted to know if anyone has been successful in created any custom profiles to handle these conversions. I can certainly create my own profile with the correct color space and GCR to do this, but thought I'd post it here to see if anyone has any feedback first.
Often we are called upon as prepress operators to make grayscale images produce with more of a snap in a 4 color publication. Many times the black-only halftones just look washed-out. So to achieve more impact we print them in 4 color process.
Operators are required to print grayscale images in 4/c process making sure that the image has an entirely neutral value. To give an example of this; take a RGB image/scan; convert this to grayscale ;and finally convert to CMYK. This gives you a neutral gray in all tonal areas of the image. Of course this is only an example and there are much, much better ways to produce the 4/c gray image which we can talk about in a separate discussion, but the objective here is still the same.
Upon further examination the profile GCR and gray ramp will show similar to the figure
(attached here) where the ramp up of black takes over around the 50% range. While this type of curve may be useful for reducing black ink consumption, it's unlikely to produce a controllable 4/c grayscale image. The range from 0-30% can shift dramatically with only the slightest shift in ink density. A more appropriate curve for a 4/c gray image would make use of black ink early in the curve to help keep the possibility of color shift to a minimum.
When I think back 8-10 years ago we didn't really experience much of this problem, so I went back to photoshop v4 and compared the conversions. Resent changes in color settings and profiling have made significant impact in the ability to control color management but made the conversion of 4 color grayscale images more problematic in printing.
I would be delighted to know if anyone has been successful in created any custom profiles to handle these conversions. I can certainly create my own profile with the correct color space and GCR to do this, but thought I'd post it here to see if anyone has any feedback first.
Tags: cmyk, color, conversion, gcr, grayscale, image, photo, photoshop, prepress, print
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GCR.tiff, 27 KB
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Replies to This Discussion
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Permalink Reply by David Cardillo on -
Personally, I feel the first, and biggest step, is proper grayscale conversion. There are books written about this (at least several articles in Photoshop User magazine). This takes time and finesse. Some amount of channel mixing and/or calculations are needed
Most people will tell you a straight "convert to gray" is good enough. We then spend a lot of time putting shape and weight into some regions, while opening up others for detail, while at the same time trying to keep a neutral cast (per your question). In my opinion, if you can get the shape and tonal range you're looking for in your gray image, you're almost done.
Then, with a full-range, straight line black, add the 3-color in. Just like you don't want to convert down, you shouldn't just convert backup, for the reasons you mention. Assuming you want neutral, no tints, you should pull out the 3-color at least around 30%, probably sooner. This would depend on your dot pattern, screen, how consistently tight your register is, etc.
You could develop a baseline profile, but that only works if your photography is consistent. Variations in lighting and contrast could, and should, affect where the 3-color comes in and out.
As I'm writing this, even I'm saying, "yeah, yeah, I know that." We've had two prepress vendors work on our 4C b/w. One of them has been working on another of our titles - they've had fairly consistent photography with a consistent look, and they have a curve they drop on and are 90% done. That curve does not work so well on our art. Not only does the art for our title differ from that, it's not consistent. Both of our vendors have stock profiles they apply, but the results vary. Some have a real sepia cast, while some are more neutral.
Then there's your press. I've had warm gray images go heavy red. I couldn't take enough red out and couldn't put enough yellow back in - it was flooding the shadows, but nowhere to be found in the midrange and up. But then matching output profiles is yet another discussion.
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Permalink Reply by Kevin Convertito on -
I created a custom profile for just this very situation after months of hating the way our B&W photos were printing when I first started here at Thrasher back in 2001. The way PS converts gray to CMYK really sucks IMHO because the lightest tones are created by CMY and not K -- exactly where you see the most color shift on a web press. When running 2-page spreads, the 1/4- and mid-tones will almost always look different between the two pages even tho the press is running "within spec"...basically my custom conversion allows mid-tones and lighter to be comprised of just K, and the CMY start to come in at 50%, leading to nice, rich 3/4-tones and 4-color blacks...50% might be a little drastic for you but it's worked well for my content. You just have to be careful to load back in the SWOP standard for any RGB or LAB color conversions!!! Hit me up and I can email you the preset to load in if you don't feel comfortable saving your own...
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