Dan Margulis Applied Color Theory

LAB: Darken and Lighten Modes

Darken and Lighten modes in Lab
Posted by: "Ric Cohn"
Wed Jan 24, 2007 7:16 am (PST)

Sometimes when I'm working in Lab I'd like to do something that I would normally use Darken or Lighten mode for in RGB or CMYK. Is there a technical reason that Darken and Lighten layer modes are not available for Lab? Can anyone suggest a work around (other than waiting until I return to another color space).

Two examples: 1. Cloning or painting in Darken or Lighten mode. 2. Separating the light and dark sharpening.

Thanks.

Ric Cohn
___________________________________________________________________________

Re: Darken and Lighten modes in Lab
Posted by: "Duffy Pratt"
Wed Jan 24, 2007 2:36 pm (PST)

I don't know what the technical reason is for this, but you should be able to get around the limitation. Lot's of times, I make changes in a separate RGB layer and then convert to LAB without flattening and then use the Blend if... sliders to limit the move on the layer in the A or B channel. I haven't tried it, but my bet is that the same process works in reverse. Do your sharpening or cloning on separate layers in LAB. Then when you are done with LAB convert to the color space you are going to without flattening and change the Blend mode in the new color space to lighten or darken.

I hope this helps.

Duffy Pratt
___________________________________________________________________________

Re: Darken and Lighten modes in Lab
Posted by: "Jerry P'Simer"
Wed Jan 24, 2007 2:37 pm (PST)

Ric

There is not a way to do what you ask directly. You can use the darken or lighten modes with either the Apply Image command or the Calculations command. If you want to brush on a specific LAB channel you can duplicate the new channel to a new doc and convert it to grayscale and then brush in Darken or Lighten, then just copy and paste it back into the original channel. The same would be true for sharpening in the L channel. That is the only way that I have been able to figure it out so far. Maybe someone else has a better solution...

Jerry
___________________________________________________________________________

Re: Darken and Lighten modes in Lab
Posted by: "Louis Dina"
Wed Jan 24, 2007 2:40 pm (PST)

Ric,

For painting to accentuate lightness and darkness, you can add a new layer using Overlay mode (in any color mode), fill it with neutral gray (having no effect on the underlying layer), then paint with a low opacity black brush to darken and a low opacity white brush to lighten. Works well for me. Plus you can adjust layer opacity to reduce the effect as deisred.

The only way I currently know how to separate light and dark sharpening from Lab is to a sharpening layer, sharpen the L channel only, duplicate that layer so you have two sharpening layers, then convert back to RGB without flattening. In RGB mode, change the two layers to lighten and darken and adjust layer opacity as desired. There may be a better way, but I don't know what it is.

Lou Dina
___________________________________________________________________________

Re: Darken and Lighten modes in Lab
Posted by: Dan Margulis
Wed Jan 24, 2007 4:54 pm (PST)

Ric writes,

Sometimes when I'm working in Lab I'd like to do something that I
would normally use Darken or Lighten mode for in RGB or CMYK. Is
there a technical reason that Darken and Lighten layer modes are not
available for Lab?

Sloppy interface, but OTOH there are some ambiguities (it is not likely you would want to have Darken or Multiply layer modes literally affect the A and B channels as they would if they were RGB channels)

Can anyone suggest a work around (other than
waiting until I return to another color space).

Two examples: 1. Cloning or painting in Darken or Lighten mode. 2.
Separating the light and dark sharpening.

Lighten/Darken always is available channel-by-channel.

1) Duplicate layer

2) Sharpen the top layer

3) Activate the L, top layer

4) Apply Image, source background layer, channel L, target top layer, channel L, 50% Darken.

5) Adjust opacity of top layer to taste and flatten image.

This is the way I customarily sharpen in LAB now. Aslo, I use it for control of color. If I want to goose greens and blues more than warm colors I can increase everything on the top layer, and then apply the A and the B separately from the bottom layer in Darken mode, allowing a little more flexibility than doing it with Blend If.

Dan Margulis
___________________________________________________________________________

Re: Darken and Lighten modes in Lab
Posted by: "Ric Cohn"  
Thu Jan 25, 2007 8:48 am (PST)

Thanks to all for the great techniques.

On Jan 24, 2007, at 5:36 PM, dmargulisnj wrote:

Lighten/Darken always is available channel-by-channel.

1) Duplicate layer

2) Sharpen the top layer

3) Activate the L, top layer

4) Apply Image, source background layer, channel L, target top
layer, channel L, 50% Darken.

5) Adjust opacity of top layer to taste and flatten image.

Wow. I'm most of the way through PP5. Is this covered there or in the Lab book?

I just used this technique to get rid of about a million 1 pixel black dots on an old image from an over sharpened scan. First I blurred the a and b and then moved the dupe layer 1 pixel and applied the lower L to the top L in lighten mode. Add a little Blend-If and amazingly effective! Out of curiosity, I went back and tried it in RGB. From what I could see it wasn't quite as good, and I was in Lab at the time anyway.

Ric Cohn