Topic awaiting preservation: Lab variation for colour cast (Page 1 of 1)

Who needs sleep?

Some time ago there was that technique for getting rid of colour cast. It was originally done for getting rid of orange in film, but folks quickly adopted it for other things. It involved sampling a colour, filling, inverting, and using Colour blending mode. I'm sure you vets remember this little ditty.

I was going through making some graphics for using Lab to get rid of colour cast. One of my tutorials for Lab. After some hardcore Photoshopping, decided to take a nap. As I was about to fall asleep, the older technique came to mind and I put the pieces together for a Lab variation.

- photograph with some colour cast
- copy and Average, Gauss the snot out it, or sample and fill
- invert
- Linear Light @ 50%
- Advanced Blending > turn off L channel

The advantage is that it's like Colour Balance, but along a definable line. I did put it through some paces, but not too thoroughly just yet. I was rather pleased with what I have tried so far. And, of course, mix it up as you see fit.

play.fiddle.learn

Go to sleep! =)

Going to sleep today is going to be extra hard. My brain has been working over-time on a little ditty. Indulge me for a bit?

One of the cool things about Lab is that there really isn't a problem when Sat=0. In HSL et al, you have to add the Hue value in order to add Sat when Sat=0. Seems like I'm always talking about this.

Lab is Cartesian, which means it's trivial to move away from Sat=0. All you have to do is shift or translate away from a=0 and/or b=0. Depending on how you shift, you automatically add Hue. This is not the case in HSL and it can seriously suck.

However, Sat in Lab can pose a problem. This problem is the fact that Lab is a sphere but Photoshop uses a Lab cube.

The main part of the problem is that a and b have to limited based on Lightness. Imagine a cube. Now imagine a sphere inside that cube. Any point inside the cube but not in the sphere is illegal. Photoshop doesn't seem to care about this. The problem isn't when Sat=0, but when Sat is too high for a given value of Lightness. That damn cube needs to be spherized.

Might sound crazy, but this is the exact same problem in Dots and Distance.

Again, might sound crazy, but the way to fix this is to move Cartesian over to polar. I just did some test with this and I am *very* pleased with the results. I do not find this without irony, though. Use Cartesian to fix one problem, only to have to use polar because the problem is now at the opposite end.

Dude, I am so behind on my tutorials. So much junk to write about. For once, being a genius sucks.

Too busy thinking and playing and not enough writing and talking. Decided to bundle up all of my Lab filters and offer them up. Some are on the wiki and some are not.

labbundle.rar ~770k

Filters > Tech Slop Lab

Changed the category for Lab filters because my TS filter directory was getting rather large. I've got some filters in there that have not been released and my directory is bigger than yours. So, a new one for the Lab stuff.

All various stages of development. That is, some have more polish than others.

The saturation one that I was babbling about above is called Legal ab Sat and it is extreme beta. It works dandy, but the UI and other little things are not very pretty. Compare how this one adds saturation to stock methods in Photoshop and you should see a marked difference.

I'm gonna go play some more. I should be building graphics and writing, but I want to play, damn it.

edit:
blah!

(Edited by warjournal on 11-02-2005 13:17)

Damn it. I don't have time to write. But I love you guys and gals.

Equating HSL and Lab (previously posted in that other thread)

Lightness Limits Saturation

In the second one, the sunset photograph, I used Legal ab Sat.

edit:

Man, it feels good. I'm all school girl giggly all over again. Feeling the power of knowledge is phenomenal. Can you feel it? I can feel it. Wanna feel mine?

Rawr!
Shaking the pillars of Heaven.

(Edited by warjournal on 11-02-2005 16:18)

Here's another fun one.

I adore being able to shift, offset, or translate ab in Lab. The commons tools for this seem to be Levels and Curves. Same thing possible with other tools, but I have yet to hear anybody talk about them.

But the thing that sucks about Levels/Curves is the drop-down. I know it's a minor thing, but it really gets on my nerves. I would much rather have the controls right there in one shot. Believe it or not, but Hue/Sat can be hacked to adjust ab colour balance with a bit of savy, and you will have the controls right there instead of having to switch channel controls.

- photograph that needs some general balancing
- Image > Mode > Lab
- New Layer and fill with L=50%, a=30, and b=30 (your colour palette is in Lab mode, right?)
- set Blending mode to Linear Light
- Advanced Blending
-- turn off L channel

Right about now you should be looking at a mess. Now for the fun part.

- Adjustment Layer > Hue/Sat and clip it to the Linear Light layer
- Open up the Hue/Sat dialog and get crazy with the Cheez Whiz

What you are basically doing is offsetting a and b in a particular direction. You use the Hue slider to set the direction, and use the Sat slider to set the amount. Seems to do decent enough with a little practice.

Should get you thinking about different ways of manipulating ab. Again, not without irony of some sort. Using a polar system to offset a Cartesian system. Man, that cracks me up.

edit:
sig be gone

(Edited by warjournal on 11-03-2005 07:05)

You never cease to amaze, WJ.
Thanks for all your time and effort. Knowing all these things is a great help, and I would never have considered them on my own. Moch less taken the time and effort to figure them out.

I'm a genius, and I'm passing the savings on to you.

This whole illegal saturation thing is cracking me up.

Let's say you want to work with saturation in Lab, but you want to keep things legal. That is, you don't want your super lows turning blue or your super highs turning yellow. Piece of cake.

- in Channels palette, copy Lightness channel to a new alpha
- Curves it using:
-- 0,0
-- 50, 100
-- 100, 0

The curve should look like a mountain. When done, what you basically just did was turn black into black, grey into white, and white into black. This will leave you with a damn fine mask for keeping colours in check.

Not a perfect mask, but Gauss bell is close enough to proper trig. With the extreme tests I did against Legal ab Sat, the differences were negligable. This means should be hardly noticable with less than extreme manipulations.

:snicker:

Too bad, though, for certain things.
:sigh:

Then again, nothing Blend If can't fix, even if it is linear.

(Edited by warjournal on 11-03-2005 12:20)

Offsetting ab

Damn it.

- Lightness is given more weight than the colour components. When it comes to compression, the colour components get crunched.

- Adding saturation with Legal ab Sat is often 'cleaner' then Hue/Sat > Sat +100. This is because Lightness is the limiting factor (in a circular fashion). Since Lightness has more 'resolution', the saturation 'gains some resolution from Lightness'.

I think I have a way to smoothify junky colour components using Lightness and rho. Kind of like using Lightness as a mask.

Back to calc. I ain't got time for this. Grrr.

edit:
Works, but I don't like it. :sigh:

(Edited by warjournal on 11-07-2005 15:04)

(Edited by warjournal on 11-07-2005 17:08)

Would you please take care of "your girls" amd get back to this as soon as you can. I want to understand and I think I might, almost.

RobertCollins
Seattle

Great stuff warJ, I plan to take some photos and deliberatly create colour cast in them so I can put this baby through the gears.
I have to admit I don't use this form of correction a lot, but that is either because I take such perfect photos or I'm lazy, I'll let you decide
Tech slop is looking mighty good I have not visited in ages. It looks so,,, beautiful, well done.

::tao:::: ::cell::

Tao, lots of here to play with: http://gal.mvc.ru/.
They are not all bad, but there is a wide variety of wrongness to mess with if look hard enough. Some have colour balance issues to varying degrees, and other have Lum or contrast problems.

Next one up and it's a mess:
Basic Lab Curves

Who's your daddy?

TS_majorabbalance.rar ~97k

I got the bug earlier today and knocked it out in a few. Ran into a really annoying logic bomb.
Logic Bomb Suck Factor: 6.8/10.0

Major ab Balance is a mix between ab Balance and Minor ab Manip. Some features of both.

Quick run-down:
- definable Lightness ranges
- option to Legalize Sat
- took out second round of offset, even though technical differences it seemed negligable
- option to see the blending mask (linear)

To Do:
- error check the Lightness sliders
- finishing hacking the Show Mask option

Not sure when I'll get to To Do because I'm ADD like that.

edit:
Almost forgot.
The logic bomb is still there, but in a limited capacity. You will have to get pretty crazy for it to manifest. I don't know if I'll be able to completely wax it out.

edit2:
Damn it. UI bomb ahoy!
I was hoping this wasn't going to be a problem, but apparently it is.
I'll fix tomorrow or so.

(Edited by warjournal on 11-13-2005 08:28)

(Edited by warjournal on 11-13-2005 08:42)

Pretty sure I got it all squished. Colour me happy.

Major ab Balance

Now that I got that out of my system, I'll get back to writing tutorials.

Scaling ab

Taking yet another detour.

Vector Flow Fields Up and Down

I'm going to keep writing about various things, but I'm going to stay under my rock for the next while.

Displacement Sharpening

I promised myself I wouldn't do any more Displace. Kind of sucks because I still have a few more notes to drop. Somebody kick my ass.

And with that, back under my rock for a bit.