Tutorial: Removing a Color Cast w/ Curves (Texture Prep.)

[requiem2d]

Texture Preparation: Removing a Color Cast using Curves

When taking your own pictures / photos for textures you always have to watch out for color casts. Indoor areas might generate warmer casts (orange, red) whilst outdoors cooler ones (blue, green). If these color casts make it into your final texture, they will most likely look out of place in-game and will be hard to pass off as real.

In this tutorial you will find out how to eliminate the cast so that you end up with a neutral image. The picture above, taken by myself last summer, shows how the sky emits a strong blue color cast on all objects in the scene. Recognizing a color cast is simple; are real life "white" items also white on the picture? Obviously they aren't. To stay flexible we will proceed with a non-destructive solution, the curves adjustment layer.

Video here, explanation below (give it 2 minutes to load):

[media="500,400,no"] http://www.game-artist.net/spotlight/curvestut/GA_Curves.mov[/media]
If you are using Internet Explorer, it will not load on this page. Firefox only!

1. Add the Curves Adjustment Layer
2. Identify an item which is suppose to be white in real-life, in this case we will take the cyclists t-shirt.
3. Find the "white" spot which is in the middle of the curve (i.e. midtones), this is so that we can produce the most balanced end-result.
4. When you have identified the sweet spot, note down the RGB values which you can see on the info box to the left. In this case R: 101, G: 131 and B: 174 .
5. Select the individual color channels in Curves, select the midpoint (as that's where you want to have the curve) and enter the values in the before field. Make sure the after field is set to 128. What the adjustment layer will do here is automatically correct or bring down the strength of any given color depending on your values.
6. Done

If this were a texture, you'd want to tile it and apply specular & normal maps, a full process of which can be found here: Tutorial: Create Tileable Texutres

It's a simple process & technique, but very effective if you have to convince your audience with realistic environments, feel free to post any before and afters below

[micster]

I never even knew I should be on the look-out for this. Thank you very much for bringing it up, sounds easy enough to fix too.

[Talon]

Definitely a great help. I hadn't really noticed I should be on the lookout for it, either. Thanks

[Psyk0]

Great one, i'll be using that trick for sure.

[retardedmonkey]

Thanks! Very helpful....just got a new camera and been taking a bunch of pics with it, so I will definitly use this! Nice picture there by the way

[CopticMike]

Thank you! Never realized why I always had that feeling that, a certain texture I created was out of place, now I know why.

[FraGGer]

Unfriendly -.-'

FF users only and I currently do not have FF installed :P, Will view when I get home

[tygereye107]

Wow... that is entirely helpful.

[Mr.Senator]

Great one Req! Definitely a good find!

[TychoCelchuuu]

Edit: Nevermind, figured it out