In this next quick demo, I'll show you how to make a texture for a moon or planet. And make it so there are no visible seams.
First of all, here is a part of the dark side of the moon (please: no Pink Floyd quips!). I deliberately chose an area that has similar texture around the edges... No "craters on one side, seas on the other", because we want this to blend.
First step: we offset that texture.
A good amount to offset is half the width of the texture.
I believe planets have textures of 1024 or 512 squared Planets have larger textures... I'm just using a set area for illustrative purposes of around 400 pixels in length / height, so I offset at 200 pixels. Don't forget to wrap around the texture.
...and if you look in the middle of the image, you can see the lines where one part suddenly ends and the next part suddenly starts.
I'll get rid of that with the Clone Stamp.
I choose a crater-filled area away from the seam as my area to use, then sweep away at the seam. Be careful not to go right up to the edge and beyond or you'll be creating a whole new seam! Pretty soon, there's no join to be seen.
Just to be sure there IS no additional seam, I offset the texture again (this time by 100 pixels) and clean up any last lines.
You can leave the texture just as-is. I prefer to make it look Mars red, so I use the Variation tool to add red and yellow. That gives the planet that rusty look.
Save your texture as a PNG. You're done!
Just to make sure it looks good, you can copy and paste the tiles together, just to make sure they're seamless. Here's a 2x2 example of my moon texture, colored Mars red, showing no joins. You can see the repeating patterns in the rocks, and no seam in the texture means it's a success.
