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I have the following image that I rendered using Blender:

Image

What I want is to remove those black lines (wireframe) but keep the image as smooth as possible. I tried removing them using the Color to Alpha removing the black color and then use a gray layer behind it but that didn't work.

Is there a way to remove those lines in Gimp?

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    Why did you render it that way? AFAIK, Blender will happily render your model without them, if you set the right parameters.
    – Rudy Velthuis
    Mar 25, 2018 at 2:38
  • @RudyVelthuis Yeah I know. Too late for that I'm affraid. I have a bunch of those and I don't want to rerender them all. I hope there is a way to do it in gimp so that I'll just pack them in one big image, apply the change then unpack them.
    – ibrahim mahrir
    Mar 25, 2018 at 4:54
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    @ibrahimmahrir still. Rendering probably is a hands off task so you can leave it overnight and be done with it. While the removal of lines is a manual task.
    – joojaa
    Mar 25, 2018 at 11:07
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    Adding to what @joojaa wrote, as you can see in the answers, if you try this with Gimp, the results are probably not very satisfying, while if you do it with Blender, the results will can be exactly what you want. Just take some time to set Blender up to let these things render overnight. In the end, it might save you a lot of time and frustration.
    – Rudy Velthuis
    Mar 25, 2018 at 15:24

2 Answers 2

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Hard to do given the grainy surface:

A first shot is to use a heavy Gaussian (with alpha-lock):

enter image description here

And maybe restore the grainy surface by multiplying with a noise-filled layer:

enter image description here

To be a bit more technical, take the blurred image, set it in Difference mode over the initial image, Layer>New from visible and threshold to get the lines:

enter image description here

You can then use this as a selection (possibly after a Select>Grow), and if you have the Resynthesizer plugin, use Filters>Enhance>Heal Selection:

enter image description here

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  • Thanks. Very close to what I want. I'll try it out and see how it looks. If it works I'll use it, if not I'll just re-render the whole thing.
    – ibrahim mahrir
    Mar 25, 2018 at 18:12
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You can apply "Selective Gaussian Blur" with big enough radius and treshold=255. You will get something like this:

enter image description here

Making the radius bigger wipes off more details.

Unfortunately GIMP has no idea, do you want some black lines to be saved. You must redraw them or make a selection which covers only the areas to be blurred or blur it in pieces.

Here the middle blade was selected and blurred (selective gaussian blur) separately. The selection was inverted to blur the rest. Blur radius was 20 for the blade and 40 for the rest.

enter image description here

Doing it well takes a lot of work. Blurring wipes off all fine surface texture. The result will be "non glossy plastic" at best, if you do not add anything as a substitute. As well you can go back to Blender, as already suggested or even more preferably make a 3D model which isn't a polygon mesh, but a smooth NURBS surface, like this:

enter image description here

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  • Thank you for your suggestion, but unfortunately this is not quite what I want. I'll probably just re-render them.
    – ibrahim mahrir
    Mar 25, 2018 at 18:12

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