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How can I add a dark border around the edge of an image in the gimp?

I am trying to create a parchment paper as a background for game pages. I would like to add a darkened border that simulates burnt edges. The border should start in the edges and fade gradually to the normal background color. The inside edge of the dark border should have a random look and not be straight lines.

Ideally it would not require any painting as I would like to include the step(s) in a script-fu that I wrote.

I would like something similar to this:

Burnt edges

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Using just Gimp:

  • Make a border selection slightly inside your sheet
  • Use `Select/Distort' to randomize the edges
  • Fill with black to transparent to darken the edges
  • Make a selection again slightly inside the sheet
  • Randomize it
  • Use it to cut an irregular border

All the art is finding adequate parameters in Select>distort. You can also obtain something a bit more realistic by using a more complex gradient.

Proof-of-concept, starting with:

original image

  • Enlarge canvas
  • Layer>Transparency>Alpha to selection
  • Select>Shrink (20px)
  • Select>Border (40px)
  • Select>Distort (150/15/4/2, smooth H+V)
  • Blend tool:
    • Gradient: FG to transparent (with FG: Black)
    • Shape: shaped (spherical)
  • Layer>Transparency>Alpha to selection
  • Select>Shrink (20px)
  • Select>Distort (55/15/4/2, smooth H+V)
  • Select>Invert
  • Edit>Clear

burned image

  • I like this answer. I'm going to try it in my script. Thanks. – Ralph Jun 15 '17 at 20:09
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You can take a piece of ordinary copy paper. Burn its edges. Put the paper between a thick magazine to prevent the total burning. Take a photo against a light, Remove the background. The black edge allows easy selection:

enter image description here

This unfortunately is still ordinary paper. Select a smaller not burned area of it, copy to another layer and stretch the piece to full size. Now the texture is big enough.

Make a selection with the original burned edge and delete the exessive area of the stretched layer. Give to the stretched layer blending mode hard light and by the curves tool fit it's tone range to good effect (=increase contrast):

enter image description here

I have also a little sharpened the stretched layer to make the texture stronger. The brown color is an accident because the white balance wasn't perfect. The same is easy to achieve by colorizing.

If you want an illusion of thickness, emboss(see NOTE1) the texture. The opacity had to be reduced to keep the effect plausible:

enter image description here

NOTE1: Embossing in GIMP is difficult due the poor feedback during the adjustment. This is easiest to do in the old way. Duplicate the layer, invert the duplicate, give to it 50% opacity and shift the layer few pixels for good effect.Do not merge the layers until you are sure.

Embossing unfortunately removed the good color. I compensated by adding a blurred copy of the non-embossed texture. This also is hard light. Blurring is essential to make the embossing and color both well visible:

enter image description here

To add more, you can increase the saturation of the color layer and add a layer mask to keep the saturation lower in the middle:

enter image description here

The next step is to add some shading and edge warping to simulate non-planar form, ie. bending. But that must be done to the writings an images, too. Here the shading is made by adding a new hard light layer with low opacity and a multistop BW gradient fill.

enter image description here

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