algorithm - make seamless height-map texture for sphere (planet)

Question

I'm trying to generate height-map for spherical planet with perlin noise. How can I make it with seamless left/right borders? I smoothed heightmap in poles, but cannot understand how can I loop left and right sides.

This is how my textures look liked for now:

Answer 1

1. Mirroring (by y-axis)

   This is great for making seamless background textures. But as you mentioned the texture must not contain distinct patterns otherwise it would be obvious. This can be used as a start point for texture generator

   

2. Morphing

   There are vector and raster morphs out there depend on the content of image. You can try to use simple raster morph done by Linear interpolation (if resolution is the same which is your case) but this can make the texture blurry which can be disturbing on some images. For starters you can try to morph texture and its mirror together:

   This is cosine weight distribution (50%:50% on sides and 100%:0% in the middle):

   

   This is constant weight distribution (50%:50%):

   

3. adjusted texture generators

   You can adjust your current texture generator to render seamlessly

   1. create/use seamless texture background (created by #1,#2 or even #3)

   2. add random number of random features with looped x axis

      • so if x is going out from the left it will go in from the right ...
      • x' = x%xs where xs is texture x-resolution