Lab Color Question

[Larry Rutledge]

So, I have an image I'm working on and I switched to Lab Color mode to see what kind of a grayscale image that would give me. However I accidentally turned on the 'Lightness' and 'b' channel together and when I did it turned the image to an interesting green color. I really like how it looks and want to keep the image like that, but when I switch back to RGB color mode it goes back to the original color.

I tried the Apply Image option, but that only allows me to apply one Lab Color channel, not two.

Any ideas how I might achieve this?

[Tom Marshall]

In LAB mode, go into your channel editor and delete the layer you don't want. Then convert back to RGB. That *should* do what you want it to.

[Matt Grunau]

you can also try when you have the layer the way you want it to look, ctrl+C to copy, go back to RGB and paste. That will do it.

[Tom Marshall]

Ok, I tried both my suggestion and Matt's suggestion. Neither one works.

Here's what you do:

Since you're disabling the A channel by only selecting L and B channels, go into your A channel. Then select a mid-gray color. It needs to be 128, 128, 128. Fill the entire A channel with that color and then convert it to RGB mode.

[Larry Rutledge]

Yes! That's it!! Thanks Tom! :thumbsup:

Here's the original image:
http://www.day7studios.com/personal/not_green.jpg

And here's what it does when I remove the 'a' lab channel

http://www.day7studios.com/personal/green.jpg

I think that's worth figuring this out :)

Thanks again!!

[Tom Marshall]

Ooh, very very cool, Larry! :)

[CherryTime]

Looks fantastic.
Tom, you're pretty good at PS arent ya ;o)

[Tom Marshall]

I've been using Photoshop for a while now and have read a bunch of books.

I also have to use it at work so the more I know, the easier my job will be... :)

[Matt Grunau]

Larry, I misunderstood completely what you were wanting. I thought you wanted to grab the grayscale value of a particular channel and use that.


Like this which is just the Lab Lightness channel:

http://www.dvxuser6.com/uploaded/6995/1216492331.jpg




Or this, which is the Black channel information only from CMYK.


http://www.dvxuser6.com/uploaded/6995/1216492271.jpg






Sorry about the bum directions.

Tommy, nice solution. Major kudos.

[Larry Rutledge]

No worries ... it all worked out in the end :)

I did mention in the original question that I was looking at the LAB mode for grayscale. It was while in there that I stumbled on the green version and liked it a lot and was trying to figure out how to make that the final result of LAB mode, but when I went back to RGB it turned all the LAB channels back on.

I don't understand LAB mode at all so I don't even know why Tommy's suggestion works ... but it does the trick

[Tom Marshall]

Tommy, nice solution. Major kudos.

Thanks, Matt. :)


Basically, with an RGB image (or CMYK), each channel holds a specific color. If you go into the channels of an RGB image, for example, and get rid of all the information for the RED channel by setting all pixels off (black), then you effectively get rid of the RED channel. The same for BLUE and GREEN.

The thing about LAB mode, is there's one channel for Luminance (L channel) and the other 2 are for Magenta/Green (A channel) and Yellow/Blue (B channel). Since the A and B channels share colors, by setting each pixel to a center value (128 gray), you're effectively voiding a Magenta or Green hue (or Blue or Yellow).

I hope that helps a little. :)

[Matt Grunau]

I know about the channels, more than I want to. Here's a little trick you may not know which can help out depending one the situation:

If you are going to be working on a picture and you plan on doing major color work, color replacement, oversaturation, sweeping sweeping the color temp around, if you switch to LAB mode first, you wont get any of the pixle anomolies you do in RGB mode. And mean none. Then you switch back to rgb for you fine tuning and contrast.

What I didn't think of was to turn a channel into 50% gray, to negate its effects.
I use 128,128,128 all the time when making diplacement maps for AE, for compund blurs and for Lens Blur.

I never would have thought to use it the way you did. Again, Kudos.