Here's a fairly simple procedure for making a nice tileable grass texture:
Create new document, make it square with dimentions that are a power of two (I usually do 256x256, but yours can be smaller or larger). Set the background to Transparent.
Choose a forground and background color (e.g. two shades of green) and run a Render/Clouds filter. Select All and run a Brush Stroke/Spatter filter. I usually then fade the spatter a little and maybe run a Blur filter.
Now you have a bunch of random colors, but it doesn't look like much yet. To add some realistic texture to the grass, you need to find a digital photo of some natural surface such as tree bark, dirt, asphalt, or whatver. Any image pulled off of the internet will work -- there are many sites full of archives of these types of images. This will effectively become your bumpmap.
Once you've chosen an image, open it in PhotoShop and re-size it so the dimensions match your grass document. It doesn't matter if the re-sized image become distorted or pixelated. Next you need to remove all the color from this image, either by selecting all and chosing Desaturate, or by changing the image mode to Grayscale. Once the color is out, copy this image to a new layer in your grass document.
From here on, you'll be working only with you grass document, which now should have two layers. Make sure the grayscale image layer is on top of the color layer and choose either Overlay or Multiply, whichever gives the best look. You can make a lot of adjustments to the overall appearance by adjusting contrast of the Grayscale image and by adjusting its opacity.
Once you have a look you're happy with, merge the two layers. The only thing left to do is to make the grass tileable. This is easily done by selecting all and choosing the Other/Offset filter. Make the Offset values half of the total image size (i.e. 64x64 if your image is 128x128). You should see a horizontal and vertical seam intersecting the middle of your image. Use the rubber stamp tool with a soft, feathered brush to smooth out these seams. Change the Offset back to zero.
Viola. You have a tileable grass texture. Similar techinques can be used to create water, rock, snow, and sand textures. The key is choosing the right colors and an appropriate image for you grayscale bumpmap. (I should mention that I think I'm technically misusing the term bumpmap here, but I don't know what else to call the thing ;-))
Other filters that work well for these sorts of textures include: Sponge, Oceanic Waves, and Craquelure.
Enjoy.
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Mauglir
(This message has been edited by Mauglir (edited 11-19-2001).)