# Topic: Lab Sat - ChOps like this (Page 1 of 1)

warjournal

From:
Insane since: Aug 2000

posted 03-14-2006 20:12

Lab is a sphere, but Photoshop insists on using a cube. This means that saturation can't exactly be rho for whatever reasons and things. So, the sphere has to be cubed. Eh? What was that? No, we won't be using a straight-edge and a compass. Rather, let's take a trip with Mr. Peabody and visit with Kai the Krause of ChOps.

Using the range -128 to 127, sat in lab as PS uses it:
Sat = Max ( abs(a), abs(b) )

(Don't ask because I don't even want to begin to explain how I know that. Maybe later if you whisper nicely in my ear.)

Since will be using ChOps in the Channels palette, the range in 0 to 255. This means offsetting by -128. We now have
Sat = Max ( abs(a-128), abs(b-128) )

You know your ChOPs, right? Just by looking at that you know the ChOps needed, right? Right? Right?

- grab some photograph and go into Lab mode
- copy it to a new layer

Now, because of the 128 thing, we will need a channel with 128 to work with in a few of the steps. Since we want the colour information and Lab seperates colour and Lightness, might as well use L* channel.

- channels palette > Lightness channel
- Edit > Fill
-- Use: 50% grey
-- Mode: Normal

Now, going to use that L @ 50% for the abs() part.

- channels > a channel
- Image > Apply Image
-- Channel: Lightness
-- Blending: Difference

Cool beans.

Now to abs() the b channel.

- channels > b channel
- Image > Apply Image
-- Channel: Lightness
-- Blending: Difference

Cool beans x2.

Now, how do we get the Max of those those two? Lighten!

- channels > a channel
- Image > Apply Image
-- Channel: b
-- Blending: Lighten

Uber cool beans.

Now all we have to do is clean it up so that it's all in one channel for easy tweaking.

- channels > b channel
- Edit > Fill
-- Use: 50% Grey
-- Mode: Normal

Uber cool beans x2.

Go back to Layers and set to Saturation. Turn it on/off and be amazed at the differences that you don't see. Oh... Ah...

To tweak, of course, you tweak the a channel. And, because of the 128 thing, you only tweak half. Yeah, kind of sucks that sat in Lab is limited to such a small range, but still a good technique for global saturation. Even if you think it sucks as a technique, it is still fun and a good exercise.

Still shaking pillars.

play.fiddle.learn

(Edited by warjournal on 03-14-2006 20:14)

Maruman
Paranoid (IV) Inmate

Insane since: Oct 2000

posted 03-21-2006 07:38

It scares me that i dont understand

*sits in the corner feeling stupid*
*makes some excuse about not having enough time to do more PS*

warjournal

From:
Insane since: Aug 2000

posted 04-20-2006 20:13

Don't worry too much about it, Maruman. Tuck it away and maybe someday it will tickle your brain.

Shortcut ahoy.

- Colourzie turned on
- Hue = 0
- blending mode = Hue

On top of that, new layer and fill with 50% Grey.
For this grey layer:
-- Turn off a channel

Now use your favorite method to copy merge and paste.

Zenigata
Obsessive-Compulsive (I) Inmate

From:
Insane since: Oct 2006

posted 10-25-2006 23:09

It can be used also for removing unwanted color casts...

"Go back to Layers and set to Saturation. Turn it on/off and be amazed at the differences that you don't see. Oh... Ah..."

- duplicate the layer, and toggle visibility to the first one;
- leave the opacity slider at 100%;
- copy/merge;
- invert;
- set Color as blending mode;
- reduce the opacity as taste.

Retouching limited only by ones imagination[GLENN HONIBALL]

(Edited by Zenigata on 10-25-2006 23:17)

(Edited by Zenigata on 10-25-2006 23:19)

docilebob

From: buttcrack of the midwest
Insane since: Oct 2000

posted 10-26-2006 07:32

~Tucks it away~

Goes to Stupid corner w/popcorn

kimson
Paranoid (IV) Inmate

From: Royal Horsing Ground
Insane since: Jan 2005

posted 10-26-2006 11:53
quote:

docilebob said:

~Tucks it away~

Goes to Stupid corner w/popcorn

Does so too, with a tin of tuna instead

NoJive
Maniac (V) Inmate

From: The Land of one Headlight on.
Insane since: May 2001

posted 10-26-2006 17:17

And here's an interesting interview with GLENN HONIBALL.
http://bermangraphics.com/press/retouch.htm

As for being in the 'stupid corner' ... that's where I get my food delivered.

___________________________________________________________________________
The goal in Life's Journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting "holy moly what a ride!"

docilebob

From: buttcrack of the midwest
Insane since: Oct 2000

posted 10-27-2006 06:59

That boy is good NoJive.
Nice link. It`s not always the technology that matters.
That was one of the most important things I learned here from Mr Garden, Weadz and DL in the early days.