[Tinalles]

Well, here's a question for all the photoshop devotees on the forum.

As a web designer, I frequently have to take photographs and turn them into seamlessly tiling background textures. For example, today I took this stone image (CC attribution license, courtesy of "James Snape") and produced a seamless tiling stone texture from it.

The problem I often run into is uneven colors. Take a look at the stone texture when it's tiled. The top half of the image is a light brown, but the bottom half has rather more red in it. The result is that when you tile the image, it forms noticeable stripes -- light brown, red brown, light brown, red brown. Which is unattractive and noticeable.

So my question is -- does anyone know how to take an image and ensure that the colors are even and consistent throughout? Suppose I have an image of a brick wall like this. It's got uneven colors, thus. How do I fix that? Correcting the mis-aligned edges of the bricks is a simple matter of using the clone stamp. But for a smooth textured use, it has to have even colors, and it doesn't.

In the stone texture above I tried to compensate by creating a second layer with the blending mode set to "Darken", and then used a layer mask to selectively color over the brighter areas of the image underneath. You can look at the stone texture PSD file if you like. But it didn't work very well.
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[Asa]

You could try using the copy-paint tool (I'm forgetting what it's called, but it's the one that acts like a transcriber with the alt key?) to copy the 'perfect' section, and paint it over the other areas. Maybe on half translucency or something.

I'm sure there's a better way. I'm merely an enthusiast, not an expert.

Or, check out deviantart and google for tutorials.
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[sunshine]

I would think the easiest way to work around an issue of color variation would be to take more direct control over the stock image being used in the first place, ie. shoot them yourself in a situation where you can directly control things like lighting and tonal continuity. However it's not very easy to bring a brick wall into a studio, so that's not much of an all-around solution.

My other suggestion would be to try desaturating the image first, then going in and altering contrast and brightness levels on the whole piece, as well as in spots with the ever accursed burn & dodge tools, then create a second layer for your color and fiddle with the layer options until you find a look that works. A bit of alchemy, unfortunately, but it ought to work for most cases.
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[Tinalles]

I've continued doing some research. One technique I found -- the Teton Technique -- seemed promising, but turned out to be for correcting lighting between two separate images, not normalizing the lighting and coloration between two sections of the same image.

Ah, well, I'll keep looking ...
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[Maeniel]

A variation of Sunny's idea, you could probably make a duplicate layer of the tile. Set the top one to "color" mode, then desaturate the bottom layer. You can go through and use a soft white or black brush set on 5% flow and basically paint the brightness you want on top of that.

Alternately, you could try Filter > Render > Lighting Effects and choose one that bathes the entire image in a uniform light. It may make it too bright, so you may have to adjust using brightness/contrast later...but at least it'll be uniform.
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[thespaceinvader]

How's your pixel art? It wouldn't take too much to make a single brick image that you could tile up...
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[Tinalles]

Mane: Interesting techniques. I've tried both of them -- I think the lighting effects filter did a better job.

Space: I don't actually care about the brick texture, there are a bazillion better ones available free anyway. The whole thing is just an exercise. I'm planning on teaching a lesson about making tiling textures, and I want to make sure I know what I'm talking about first.

For the lesson, I'll supply the students with pre-chosen raw images to start from. I think I'm just going to be careful to select ones with even, regular lighting.
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[Squeeself]

Welcome to the fine art of color correction Tin...There's no easy answer. Your best bet is likely the Levels tools in photoshop, combined with some clever soft selections. In other words, make a channel mask of the areas that need to change value, load that mask as a selection, then use the levels and color correction tools on only those areas. By using gradients in the mask, you'll ensure smooth transitions. It'll probably take more than a little work...

If you want someplace to start, you might try making a copy that's greyscale, inverting the values, then pulling the levels apart to see what the contrasts in values are......Might be a helpful starting point, though Squee doubts it'll work as the actual mask.

Generally, Squee's working with tiled textures in an environment where more advanced things can be used (ala 3D) and things such as overlay textures can remove the visible tiling effect, but it's not something you can do on the web.

[Tinalles]

The easiest answer seems to be to pick a base image which already has even, consistent lighting so you don't need to worry about it. ^_^
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