Until using GIMP for a while, many new users including myself don’t know that GIMP 2.6 does not offer anti-aliasing on the fly, like Photoshop does. While experimenting in my last tutorial, Creating a Chrome Effect in GIMP 2.6, I figured out a way to fake anti-aliasing on rounded edges after drawing with Selection tools that looks convincing. The problem usually shows up after using the Fuzzy Select tool and creating a bump map. For objects without these features, no anti-aliasing may need to be done. So, we will replicate this here. This is not the most elegant way to anti-alias, but it is somewhat easy.

This tutorial requires knowledge of how to create a bump map in GIMP 2.6 or a prerequisite of my previous tutorial, Creating a Chrome Effect in GIMP 2.6.

For this follow up tutorial I have created a drawing of a crescent moon with a clouds filter and bump map to demonstrate how this affects aliasing.

  • Below is our drawing of a crescent moon. There are three layers: a Background layer, New Layer#1 (bump map layer) and New Layer (drawing layer). The bump map here was set to 10 pixels. If we look at the edges, we can see that they are jagged; this is because after using the fuzzy select tool to select and filling with a color or texture, GIMP does not anti-alias the jagged lines. I assumed there was nothing that can be done
  • screen15_layers
  • screen14_cr_before
  • In this case, we select the area around the moon shape on the drawing layer (New Layer) and Invert (Crtl+I) the selection. Then we Select the Border (Select > Border) by 2 pixels
  • screen16_borderselect
  • We then apply a Gaussian Blur of 4 pixels horizontal and vertical. Select None (Shift+Ctrl+A)
  • It is looking good, but we’re not done. Reselect the area outside the drawing. This time we’ll Grow (Select > Grow) the selection by 1 pixel
  • While the area is still selected, we change the selection to a path (Select > To Path). Hit the delete key. The before and after is shown below
  • screen14_cr_before
  • screen17_cr_after

In conclusion, the above is a quick fix for GIMP anti-aliasing nightmares. In this simple example, the differences may be subtle, but in drawings with many more selection based fills, filter effects and instances of using the Fuzzy Select tool, these methods may be what you need to give your drawing a polished look.