|Fixing Lighting Irregulaties
in Self-Tiling Maps
Tutorial by Jeremy Birn
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Adapted & Shortened from
Most 3D artists know how to process a photograph into a self-tiling map in Photoshop, using Filter > Other > Offset (set to "wrap around") to bring the seams to the center, so you can clone over them. But, in problem situations such as the photograph below, the Offset filter reveals that there are color and lighting shifts running across the original picture. This tutorial shows how to get rid of overall color and brightness shifts before making a tiling map.
Here's a quick and efficient way to nuetralize overall color and brightness shifts in a picture, before you do the Offset:
1. In the Layers window, drag the Background layer
2. With the new layer active, press Ctrl-i
3. Choose Filter > Blur > Guassian Blur from the
4. In the Layers window, slide the Opacity down
5. In Layers, choose Flatten Image.
6. Choose Image > Adjust > Levels, do one channel at a
time with ctrl 1, ctrl 2, ctrl 3 and pin the levels to the existing
dark and light points of each channel, before you ctrl ~ switch
back to all at once.
Doing this right will rebuild the color balance as well as the contrast.
7. Now, finally, you can do the Filter > Other > Offset
again, and this time it will work well:
8. Clone over the seams to hide them, using the Rubber Stamp (cloning) tool. (Before Offsetting, you might also want to copy an area a few hundred pixels wide from the right side of the image, shift-ctrl-i, and crop the remaining area. After offsetting horizontally, you can paste the right edge next to the seam, and offset both layers vertically. This way you can selectively erase parts of the overlap area to start blending the seam before you begin to clone.)
One more thing to try: Press Ctrl-Alt-Z a few times to move back in history to step 4. This time, leave the opacity of the top layer at 100%, but change it's blending mode from Normal over to Soft Light. Soft Light will not be as complete and uniform an equalization, but it will help your image's consistency without lowering the contrast. Make another copy of your Soft Light layer if that result isn't strong enough at 100%.
source: The book Digital Lighting & Rendering explains this and many other texture mapping techniques in more detail.
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