How do GIMP 2.10 unsharp mask "Standard Deviation" and "Scale" relate to radius and amount?
Asked 12/23/2015
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2 answers
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In GIMP 2.10, the GEGL-based Unsharp Mask uses Standard Deviation and Scale instead of the older Radius, Amount, and Threshold controls from earlier versions. How do these new parameters map to the classic terminology, and how can I approximate common sharpening uses such as fine-detail sharpening, edge sharpening, and large-radius local contrast enhancement? Also, is there an equivalent to the old Threshold control?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
1
The documentation of the corresponding GEGL operation can be found here. There, the meaning of the parameters is briefly explained. Standard deviation would translate to radius and scale to amount, but there may be differences in implementation of the founding operations such as the gaussian blur which may lead to different results or different parameter scaling. The functionality represented by the threshold slider seems not to be implemented in GEGL yet. This parameter causes small values in the difference “mask” of original image and blurred image, that is later added to the original image, to be neglected. If you need this functionality, you could use the G'MIC plug-in version of that filter, which is (as its description states) inspired by the original unsharp mask of gimp but with more parameters in the UI to control what happens.
Originally by user44828. Source · Licensed CC BY-SA 4.0
user44828
10y ago
0
Generated from our catalog & community — verify before relying on it.
In practice, Standard Deviation is the new control that most closely matches Radius, and Scale behaves much like Amount. The mapping is not guaranteed to be numerically identical, because the GEGL implementation may differ from the older one, but they are the closest equivalents.
The old Threshold control does not appear to be implemented in the GEGL version, so there may be no direct equivalent there. Threshold was used to suppress sharpening of small tonal differences such as noise. If you specifically need that behavior, one community suggestion was to use the G'MIC plug-in’s unsharp mask instead.
As rough starting points for your old workflows, try:
- fine-detail sharpening: 0.4 / 5.0
- edge sharpening: 3.0 / 0.5
- local contrast enhancement: 50 / 0.15
These are only starting values; the GEGL tool should be treated as a similar but not necessarily identical sharpening tool, so some experimentation is expected.
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AI10y ago
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