Using black channel inversion for RGB sharpening mask

canoflan

If I wanted to sharpen the equivalent of the CMYK black channel in RGB, can I simply duplicate my RGB image, convert the duplicate to CMYK, copy the black channel into the RGB image as a new channel, invert it, then create a mask from it on a "merged visible" layer? That way, I can sharpen only the white areas (that were black in CMYK) for that layer?

Anyone tried it? I really don't like moving back and forth to CMYK on my final image, therefore, I find using a duplicate more appealing.

edgework

canoflan wrote:

If I wanted to sharpen the equivalent of the CMYK black channel in RGB, can I simply duplicate my RGB image, convert the duplicate to CMYK, copy the black channel into the RGB image as a new channel, invert it, then create a mask from it on a "merged visible" layer? That way, I can sharpen only the white areas (that were black in CMYK) for that layer?

Anyone tried it? I really don't like moving back and forth to CMYK on my final image, therefore, I find using a duplicate more appealing.

Yes.

It's a valuable tool for a whole host of shadow issues. You won't get the bang for the buck that a genuine black plate gives you in CMYK, when trying to maximize shadow detail, but it's a great way to focus curves, Shadow/Highlight moves, and sharpening when you want to isolate blacks in RGB or LAB that don't have blacks.

I did a summary of Chapter 5 for the Dan Margulis reading group, which is all about the black plate, and I showed some ways that a fake black can be useful, even when CMYK is the intended destination. Check out http://www.dgrin.com/showthread.php?t=52033

arodney

canoflan wrote:

If I wanted to sharpen the equivalent of the CMYK black channel in RGB, can I simply duplicate my RGB image, convert the duplicate to CMYK, copy the black channel into the RGB image as a new channel, invert it, then create a mask from it on a "merged visible" layer? That way, I can sharpen only the white areas (that were black in CMYK) for that layer?

Anyone tried it? I really don't like moving back and forth to CMYK on my final image, therefore, I find using a duplicate more appealing.

Read this before you pull your hair out doing lots of conversions into and out of CMYK:

http://www.creativepro.com/story/feature/20357.html

canoflan

I actually use a script for this type of sharpening...

arodney wrote:

Read this before you pull your hair out doing lots of conversions into and out of CMYK:

http://www.creativepro.com/story/feature/20357.html

I got the script from the Lights Right Studio website from http://www.thelightsrightstudio.com/home.html.

It is an incredible tool and does a great job of protecting edges. It is free as well.

When I want fast sharpening, however, I use High Pass on Hard Light Mode with about a 4 pixel radius. I like the shape it gives the pics and doesn't mess with smooth transitions or single color areas.

Haileigh

Wide Gamut CMYK

First post here on Dgrin (lurked a lot, though). Pardon my English, I'm not a native speaker.

You can also use a Wide Gamut CMYK profile. (Simply google 'Wide Gamut CMYK'.) This way you won't have the drawbacks of moving and out of a regular CMYK.

I have used a different method. I like to sharpen in LAB (the L channel, that is). For faces however, I like to have the benefits of a K sharpening. In that case I make a copy, convert it to a medium or light GCR, 100%max black (not 85%). I then sharpen the K channel, convert back to LAB. I then apply the L channel of the sharpened copy to the L channel of the original working file.

The reason I use a 100% max black is that the final result is sometimes a little faint, otherwise.

arodney

Haileigh wrote:

You can also use a Wide Gamut CMYK profile. (Simply google 'Wide Gamut CMYK'.) This way you won't have the drawbacks of moving and out of a regular CMYK.

Wide gamut or not, you're still throwing away a lot of bits and useable data moving between color spaces in 8-bit. And for Lab, you can get the same benefits with no such data loss, faster processing and more control using the Fade Luminosity option after applying the sharpening. Depending on the original color space, moving into and out of Lab can toss a good number of bits from the file for little reason.