Working with LAB color space

[dots]

..or L*A*B whatever the proper name is.

What's the benefits? How do you work effectively in it?

I tried doing some curves adjustments in it but the results looked weird. Working in curves in RGB seems to result in unwanted changes to saturation which then have to be resolved, Is this a benefit of working in LAB instead? But how is it best done? What tools should be employed in LAB for better results?

 

[Snyder]

It basically makes the colors space 3 dimensional and larger portraying the human perception of color. LAB is diffacult to use, I only use it if I have to sharpen a jpeg.

http://www.aces.edu/dept/fisheries/...e/documents/ExplanationoftheLABColorSpace.pdf

 

[KmH]

Everything you ever wanted to know about the L* a* b* color space - Lab color space - Wikipedia, the free encyclopedia

 

[gsgary]

I use it for B+w's

 

[mjhoward]

Have you tried working in the HSL (Hue, Saturation, Luminance) color space? You should be able to adjust curves without effecting the Saturation component.

 

[dots]

@KMH yes i looked at that..thanks for the reply though. @Gary, I'll give that a go. @MJ maybe a bit around (Photivo and PWP), but not seriously..I'll take another look at using HSL.

 

[clanthar]

I use Lab constantly. It's rare that I process a photo and not convert it to Lab. I try to get the tone and color of my photo correct in a RAW file processor first, but if I need to fine-tune tone and color once the image is RGB, I switch straight to Lab to do it and I use Levels. If I need to make local tone adjustments to a photo I use a Levels adjustment layer with mask and again do that with the image in Lab. It's much easier to control changes using Lab.

If you make a Levels or Curves change to the RGB master in order to alter the tone response you get a color saturation change as well. You're trying to do one thing and two things happen -- losing control. If you make a Levels or Curves change to the Lightness channel in Lab mode in order to alter the tone response you get a tone response change; one thing happens -- keeping control.

Color is much easier to change in Lab mode. Simply access Levels and adjust the midpoint slider in either or both the "a" and "b" channels.

Lab is ideal if you want to raise or lower saturation in just one color. Try that using Hue/Saturation with an RGB image and you get noise buildup. Do it using Lab mode and no noise.

Joe

 

[dots]

Thanks Joe..that's very helpful. Which editor do you use for those LAB adjustments? Photoshop?

 

[clanthar]

Thanks Joe..that's very helpful. Which editor do you use for those LAB adjustments? Photoshop?

Yep -- Photoshop.

 

[dots]

Thankyou

 

[clanthar]

So I'm stuck here in the school lab watching over my students as they work on an assignment -- got time to make an example.

This won't work on any image, but it's surprising how often it will work. If you get some color shift in areas you don't want you can always history brush it out.

I switched the photo to Lab and then used Curves to raise blue saturation. Look at the statue -- left original and right adjusted. I inset the curve that did it. You could use Hue/Saturation with an RGB image to do the same, but you'll get a noisier result especially at color borders. This is really the ticket when you want to pump up saturation in a sunset for example but using H/S you build noise along the orange/blue border.

Joe

 

[dots]

Interesting. I want to begin extending what i can do, e.g via LAB. Thanks for organizing the screenshots.

 

[dots]

Clanthar...I'm trying out using curves tool within LAB. When i modified the curve with just one input, the image brightened which is good. Then i added a second 'node' (is that the right term?) to the curve and dragged it down to see its effect..and the image has changed to become sortof softer like this...

What's occuring to make look softer ? This is what i mean by weird in my original post Are only simple curves adjustments the way to go, using curves in LAB space? ..where the curve is modified by just a single input?

This is good anyhow..i'm trying and learning new things!


EDIT: Actually this 'curve' is a shadows/highlights tool. I thought it looked similar to S/H tool in FastStone Image Viewer (and i always wondered how that tool did what it does..mustt be within LAB space d'oh!)

 

[dots]

Wow this is a powerful toolset! i'm getting into this!!

 

[clanthar]

Not familiar with Photivo I'm afraid so I'm not sure what's happening there.

One big advantage of Lab is that it separates tone from color. This then allows you to alter the tone response of the photo without changing the color and vise versa -- you can't do that with RGB photos. Your editor has to give you individual Lab channel access.

Joe