GIMP
Using enhanced layer features with G’MIC
Karsten Günther takes a look beyond GIMP’s standard layer functions. Besides special GIMP operations, tasks provided by G’MIC loom into view.
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Karsten Günther has written entire books about using GIMP, so four pages is just a morning’s work to him.
Both GIMP and the plugin G’MIC have a number of layer functions that – in contrast to those in the article from LXF298 – are neither simple nor obvious. We’ll examine them in more detail here. With G’MIC, it usually looks like this: a number of functions available with GIMP can be found with extended possibilities and usually there are a range of additional functions that offer something similar. Some of these functions are rather theoretical, but many are quite practical. The layer-specific functions are mainly found in the Layers, Sequences or Colour sections ,and scattered in the Testing section.
Separate colours
GIMP supports the idea of separating colours in layers with the Decompose functions described in the tutorial in LXF298. G’MIC extends these possibilities with the Tone values in difficult exposures can be specifically influenced with Tones To Layers. Due to the division into layers, far-reaching possibilities – including layer modes – are available.
Channels To Layer filter, which enables you to separate channels in layers instead of RGB, CMY and (limited) HSV. However, these functions work somewhat differently from GIMP’s own. For example, the RGB layers have to be combined with the Lighten or Screen mode to get a colour-correct image again. For CMY layers, the Difference mode is preset. With HSV splitting, G’MIC creates only two layers: one greyscale layer with the lightenings and one with the colours.
>> G’MIC ON THE COMMAND LINE
G’MIC is currently being developed in two variants in parallel: as a plugin for GIMP ( gimp-plugin-gmic ) and as a command-line program ( gmic and gmic_qt ). Both variants differ only in details, adapted to the way they are used. For example, the command-line program has a demo mode that would make no sense with the plugin; gmic demos starts this special mode.
Without specifying an option or function, gmic works as a universal display program; gmic tst.png displays the image. Normally, however, the command is called with both an input file and a function. The option -h outputs extensive help. To write the output to a file, the option output TST.jpg is available.
On the command line, G’MIC can convert the RGB data of images into very different colour models. For example, gmic IMAGE.jpg rgb2cmyk split c calculates the CMYK conversion and displays the result. If -output /tmp/ tst.png is added to the line, G’MIC writes LAB, LCH, HSL, HSV and a number of other, less well-known colour models. Note that GIMP and G’MIC use different formulas for the conversions in detail.
Interactive and special G’MIC functions are provided by G’MIC demos. As the name suggests, they are mainly used to demonstrate G’MIC capabilities.