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What would be the easiest way to make a bump map of the dimples on a citrus fruit such as an orange or lemon in gimp/photoshop without using pictures of it? e.g:

enter image description here

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I'm not sure if I should've asked this on the graphics design site. –  Dan the Man Dec 8 '11 at 20:03
    
I figure most of the folks around here are programmers, but perhaps some graphics programmer with experience in creating his own maps might have a clue. –  David Gouveia Dec 8 '11 at 20:32
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+1 How to create (programmer needed) particular textures is an important (and often forgotten) subject. I'd love to check out how people have coded (and artistically created) materials like (worm) skin, metal, mud, and so forth. GPU gems is a start but not really a extensive guide. –  Valmond Dec 8 '11 at 20:43
    
So you want to make normal maps without a texture? Why can't you use a texture? Normally I would just say take a source image and throw it in crazybump. –  Tetrad Dec 8 '11 at 22:21

2 Answers 2

up vote 5 down vote accepted

The skin is fairly smooth with some big dimples. A first approximation would be (in the GIMP):

  1. Take a black image (in greyscale mode)
  2. Filters | Noise | Hurl to get some dimple locations
  3. Colors | Threshold to reduce it to black and white
  4. Filters | Gaussian blur at a small radius (maybe 2px)
  5. Colors | Curves to restore the necessary contrast and normalise the background to 127 or 128 (whatever the "no bump" value is).

I suspect you'll find that that gives too much clumping, so the second approximation would be to replace step 2 with random nudging from a hex grid. Either do this in code or create a hex grid in the GIMP and use Filters | Noise | Spread.

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Create a flat plane of orange skin in high definition 3D (ie. a Lot of polygons + an orange colour texture).

Bake it.

Use it :-)

This link Might help you get the general idea of baking.

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