Simply Quick Woodgrain

We start with a square canvas, I chose 300x300 in RGB mode for this tutorial. With some extra tweaking, this process can be scaled up easily, though under-600px gives the best detail. You can always scale up the final artwork to suit.

Pick two wood'ish colours (I selected a tan and a medium-brown). Do a quick Filter >> Render >> Clouds. Keep hitting Ctrl-F to repeat the filter until you find a nice pattern that suits you. You should go for an fairly even spread of colour, without big blobs of one or the other.

Now give it a touch of the Filter >> Noise >> Add noise filter. I suggest you use the following settings:

Amount: 11.20
Distribution: Uniform
Monochromatic: Ticked

Now to start producing the grain. fire up the Filter >> Blur >> Motion blur filter, and use settings that you like. These settings work well for medium-grain woods… but feel free to experiment for your desired effect.

Angle: 0
Distance: 30

Now the tricky bit. Bring up the Filter >> Liquify filter and use the Bloat Tool with a medium brush (Size 64, pressure 50 works well) and click-ndrag in Short Bursts to create the knots and distortions in the woodgrain. This would have to be the most important step, because if you don't get it right, the wood will look just plain weird.

Fire up the Filter >> Sharpen >> Unsharp Mask filter and use it to bring out the texture of your new wood. I used these settings:

Amount: 243%
Radius: 2.0 pixels
Threshold: 0

All done! With some use of the Hue/Saturation Adjustment option you can easily make any wood-type you like, from Pine to Redwood.