wrote:

In comp.publish.prepress Lee Blevins wrote:

: There's one gotcha here.

: When converting to CMYK from the RGB image you want to use heavy GCR. : This will make your black printer the fullest and save you the grief of : gray balance shifts on press.

: This is much more important than you might think. I'd suggest exploring : how you can get MAX GCR....

Thanks. This is just the sort of information I needed -- and it makes plenty of sense! The gotcha you describe is just the sort of problem I feared.
Burrowing down into the Photoshop options for conversion, I notice there is a "heavy GCR and a "Max GCR" conversion; the latter appears to leave no CMY gray component at all (at least by the curves in the "custom CMYK" window). "Heavy" starts to replace with K at about 25% and crosses over at about 50%, while the default "Medium" has the breakpoints at about 45% and 85%. You mentioned both "heavy" and "MAX" above
So which one is more appropriate (given you haven't seen the images)? My intuition would say "heavy", but I'm not the prepress expert. Actually performing the conversions on the pre-desaturated image shows the "MAX" setting leaving nothing but the faintest whispers in the CMY channels (probably all of the color artifacts I complained about ;-)
I also left the dot gain curves alone, and assume I should do so unless otherwise advised. Dot gain is set to 20%, with the curves showing C pushed to 50% >> 74%, versus 50% >> 70% for the others.
Bob

I only have CS2 on this laptop at the moment so I can only give you information relative to that.

But the key is in the "Color Settings" which are in the "Edit" menu this version.

Here's a recipe to make a "heavy" GCR image from a "neutral" rgb image.

Open the "Color Settings" dialog (Edit -> Color Settings):

In the "Working Spaces area:

1. Set the RGB working space to Adobe RGB (1998)
2. Set the CMYK to "Custom CMYK"

This will open a "Custom CMYK" dialog.

What you set the "Ink Options" to is the stuff religions are made of but the "Separation Options" will control how this image separates.

3. Set the "Seaparation Type" to "GCR"
4. Set the "Black Generation" to "Heavy"
5. Set the "Black Ink Limit" to 98.
6. Set the "Total Ink Limit" to 300.
7. Don't forget to name this setting before saving the dialog.

Now this setting will appear as a CMYK working space.

Use this setting when converting the RGB back to the final CMYK to arrive at a heavy GCR setting.

The arguments here are about art. To each person who would do this there are a myriad of approaches and reasons for a particular setting that they choose for to achieve a particular effect.

I gave numbers here for reference only but I'm reasonably sure that would produce a nice image that would be easy to print.

leeb

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