GIMP

G’MIC is a treasure chest with virtually inexhaustible content. But how do you use it? Karsten Günther helps open the box and explore the contents.

Credit: http://gimp.org

Most photographers are familiar with this problem: an otherwise great picture is spoilt M by a detail that almost cancels out the effect. For example, a car or a sign in a landscape photo, a spot on the lens… Usually, it helps to correct the corresponding areas with the Clone or Heal tool, or with Resynthesizer (LXF301) via the Heal Selection filter. Both methods have their limitations: manual repair quickly reaches its limits with smooth surfaces, strict structures and large areas, but Resynthesizer also often has problems. Manual methods lack options for rotating, distorting or scaling transferred material before it’s reintroduced into the image. Resynthesizer uses such small patches that this is often not noticeable, but not always. The result is new artefacts that only improve the image to a limited extent.

G’MIC tries to help with these problems with its Inpaint filters. These are various methods of painting over areas of the picture so they become invisible. However, colouring black and white images is also sometimes called inpainting (https://en.wikipedia.org/ wiki/Inpainting). In G’MIC, the Inpaint functions use material from the environment, which then comes in several scales and from different distances. Scaling often leads to significant improvements of the results. The Inpaint [Multi-Scale] filter is based on this.

In the current version 3.2, G’MIC provides six different Inpaint filters for overpainting image areas. In page 16! different ways, the filters replace an area that has either been marked in colour beforehand or a transparent area. The G’MIC variants all have a preview, which offers a big advantage over Resynthesizer. However, the processes are so computationally timeintensive that the preview only rudimentarily shows what the current parameters are doing. On the other hand, these filters have a lot of parameters and can therefore be controlled much more precisely than is the case with Resynthesizer. This makes them suitable for images where other methods fail.

Inpaint [Patch-Based] is currently probably the best controllable Inpaint filter from G’MIC. Various parameters control a large number of aspects, which doesn’t make it easy to use. In fact, three parameters are particularly important and should definitely be considered and tested with several settings: