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Color temperature correction in Photoshop

Luis Saavedra , Sep 02, 2004; 06:27 a.m.

Hi there! don't know much about photoshop and digital editing so this question might be pretty basic to some of you. I'd like to know how to correct the color temperature of JPGs or TIFs in PS. When I shoot RAW is very simple to do it with the built-in RAW converter of PS CS, but what if I don't shoot RAW or it comes to scanned images? The RAW converter plugin does a fantastic job in this matter but I'm not able to get the same look when editing the picture with levels. Which is the best tool for that? and how to do it? Thanks a lot in advance

Responses

Michael Darnton , Sep 02, 2004; 08:08 a.m.

The most versatile tool is curves, best used as a layer (layer/new adjustment layer/curves). With that you can adjust color, contrast, AND local contrast in various tonal ranges.

To do correction the way the raw converter does it, use the three eyedropper buttons--click on the right one, find the area in the photo you want to be pure white, and click on that. Then click on the left button, and click on an area you want to be pure black. Then, if you have a true grey somewhere in the photo (but it's got to be true) you can use the middle button and click on the grey. To cancel everything, press ALT, and the "cancel" button becomes "reset" to start over.

This is the simple way, but if you read up on it, there are many, many other things you can do with curves. For instance, to darken or lighten without messing with white or black, click on the center of the diagonal line and drag it up or down. By putting s-curves in the line, you can change even more stuff.

Curves is essentially a more complex and more versatile version of levels, which really is a crude tool, when it comes down to it, except for very simple corrections, but the eyedroppers in the levels box work the same, as does the midpoint slider compare with pushing the center of the curve around. Levels won't let you adjust local problems by putting twists in the curve, though.

Ellis Vener , Sep 02, 2004; 10:12 a.m.

In Photoshop CS use the color filter tool ( Image > Adjustment > Color Filter) and use different densities. I wouldn't worry about precise Kelvin temperature settings although if you look up the filter values you should be able to get pretty close to assigning exact color temperature adjustment levels.

Brandon Hamilton , Sep 02, 2004; 04:01 p.m.

The last response was the best answer, but the truth is, unless you shoot in raw, you cannot change the white balance after you take the picture. Hence, one of the major advantages to a RAW capture.

As described directly above, you can alter the photos color's, but I don't think you are quite as accurately changing the white balance... just trying to compensate.

Shoot RAW!

Stephen Gallimore , Sep 02, 2004; 05:12 p.m.

As you are a digital shooter the advice to shoot RAW always is a good one. However as a non digital shooter I use the White Balance plugin from the Imaging Factory (http://www.theimagingfactory.com). Its a damm sight cheaper and more flexible than a bag full of Lee filters and a colour temperature meter :-) The main advantage it has over the suggested photoshop methods is the ability to change the overall colour temperature of the scene while locking the original white point. This allows you to easily correct, for instance the casts from blue sky reflecting on leaves and water, without having your clouds turn yellow. The main disadvantage of all the plugings from The Imaging Factory is the very small preview, however IIRC you can try them free for a short time so make up your own mind.

Regards, -stephen

Michael Darnton , Sep 02, 2004; 09:29 p.m.

I can see how a filter could take out a linear error, color problems are seldom linear. I guess I'll have to try the color filter thing, but I can't believe it does a better job than curves or levels, and I's sure it's not as automatic.

Gary Megrenne , Sep 02, 2004; 10:14 p.m.

If you decide to try to use curves, here is a good tutorial on PS.

Michael Darnton , Sep 03, 2004; 07:50 a.m.

Dan Margulis' "Professional Photoshop" is a fabulous book for color correction. I had a horrible time getting through the book (very steep learning curve) and never had a bit of color problems after that.

He's a professional color guy, and digs out all the common strategic errors that people make (Gary, your link person is making one of them, in that he appears to be attacking a global problem locally), along with suggesting some extremely simple strategies. That's where, for instance, my eyedropper idea came from: though he doesn't use them, he does a lot of correction the same way. The punchline of the book comes when he tests it using a colorblind friend who's never done color correction: the friend does better on some of the test examples than Margulis.

If you want to put your color problems behind you and are a good reader, I highly recommend the book.

Pam R , Sep 03, 2004; 12:11 p.m.

I second Michael's recommendation of Dan Margulis' book. The learning curve is steep, but it will be time very well spent. He also has a Yahoo group that he frequents. Chock full of info, it's an invaluable resource:

http://groups.yahoo.com/group/colortheory/

Gary Megrenne , Sep 03, 2004; 02:34 p.m.

Thanks for the info - I'll definitely get a copy of the book.

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