Using LAB Adjust to remove color cast

TeetimeNC wrote on 1/11/2014, 3:52 PM
I would like to use the LAB adjust fx to remove a color cast. The best way to do this is in Photoshop is to use the color picker to select an example of the offending cast, and then reverse the signs on the resulting "a" and "b" values. But there is no color picker in the SVP Lab adjust tool. This seems like a pretty significant oversight by SCS. Has anyone come up with a clever workaround?

/jerry

Comments

PeterDuke wrote on 1/11/2014, 4:40 PM
Try the free AAV ColorLab plugin. You select a point to click on that should be white, or preferably medium grey in case a channel is saturated. After colour correction, blue sky, for instance, that is partially saturated may end up with a green or pink cast.

http://code.google.com/p/colorlab/downloads/list
Grazie wrote on 1/11/2014, 10:59 PM
Why not just use the Sony Colour Corrector and be done? What does the LAB adjustment give you, with this cast issue, over and above the SVP CC? Had you tried Colour Curves? I realise that the LAB adjust the amount and movement of Secondary Colours, but here?

Always willing to learn.

Cheers

Grazie

Grazie wrote on 1/12/2014, 1:03 AM
Here's Frédéric Baumann's "White Balance Vegas Plug" using LAB in separate channels (£57.22GBP) :-



Frédéric Baumann's White Balance plug-in for Sony Vegas

Grazie

Richard Jones wrote on 1/12/2014, 5:59 AM
And if White Balance doesn't fix it for you, try Colour Curves (If, for example, you've got a redish cast, select green, double click at the middle of the line and drag the curve upwards). Alternatively, try levels and use the colour needed to correct and then drag the sliders.

More than one way of skinning a cat in Vegas!

Richard
Dexcon wrote on 1/12/2014, 6:18 AM
Yes, Color Levels is very useful I've found. If that doesn't prove successful, there's always Color Corrector. And if you've got another similar shot with a good white/color balance, there's always Color Match - it's been very good on the few times I've used it to get rid of a color cast.

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Grazie wrote on 1/12/2014, 6:47 AM
You want to post a screengrab? I could do a "fix" and post back the VEG? Up to you.

Grazie

robwood wrote on 1/13/2014, 12:39 PM



LAB colorspace handles luma separately from the chroma.
Provides another way of breaking an image apart to get at just the color or brightness. Don't hear of LAB much in video, but there's entire books written about using it in photo work.
TeetimeNC wrote on 1/13/2014, 3:38 PM
LAB colorspace handles luma separately from the chroma.

First, I've been without Internet since Saturday afternoon's storm here in Raleigh. A tree fell on the power line, taking out power to the Uverse VRAD in our neighborhood. They are running the VRAD on generator now.

Back to LAB... I'm very familiar (and somewhat skilled) in the various Vegas tools used for color correction. I use Katrin Eismann's excellent "Photoshop Restoration & Retouching" to guide me in both photography and video editing. It is the experience with LAB in photo editing that had led me to desire comparable capability in Vegas. Specifically as robwood stated, the ability to affect the colors apart from the luminosity is what I would like. In photoshop, you can use the color picker to set the ab channel values. Then you reverse the polarity of those two channels and you have the opposite color on the color wheel which removes the color cast, much in the same way as the color corrector (CC) in Vegas does, except in LAB you are not affecting the luminance. What I ended up doing is setting the color balance with CC, then setting the luminance with LAB Adjust.

EDIT: Corrected link to ]"Photoshop Restoration & Retouching".

/jerry
Grazie wrote on 1/13/2014, 10:35 PM
Rob and TT, yes, I understand that, but to be more specific, do you have actual Real World examples I could look at?

Always willing to learn.

Grazie

robwood wrote on 1/14/2014, 12:13 PM
do you have actual Real World examples I could look at? -Grazie

here's an example using sharpen in LAB
photo.net/learn/digital-photography-workflow/advanced-photoshop-tutorials/sharpening-in-lab-color/
compare "figure #6" (RGB) and "figure #12" (LAB) to get an idea of the difference.

--

but if you wanna dig deep, this forum link is an in-depth chapter-by-chapter study of Dan Margulis's LAB Color Book, with forum members posting examples of their own stuff.
Margulis LAB Color Book - Reading group
farss wrote on 1/14/2014, 12:50 PM
Thanks for those links Rob, I found a comment in the last one that explained something that has puzzled me for decades.

I can see a scene that looks fantastic and yet when I capture a part of the scene with a camera it looks dull and boring. Thing is the camera doesn't capture the context of that part of the image, it doesn't know what my brain knew when my eyes looked at that part of the scene.

When that's happened to me in the past I blamed my lack of skills or the camera. Now I realise neither is to blame and it's valid to adjust the image in post to get it back into the context. I would guess LAB is the better colorspace for this as it is more in line with how our eyes work than RGB.

Bob.