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feat(ColorMaps): Add grayscale sigmoid colormap based on DICOM standard #3365

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feat(ColorMaps): Add grayscale sigmoid colormap based on DICOM standard #3365

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72 changes: 72 additions & 0 deletions Sources/Rendering/Core/ColorTransferFunction/ColorMaps.json
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Original file line number Diff line number Diff line change
Expand Up @@ -529,6 +529,78 @@
"NanColor" : [ 1, 0, 0 ],
"RGBPoints" : [ 0, 0, 0, 0, 1, 1, 1, 1 ]
},
{
"ColorSpace" : "RGB",
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@finetjul finetjul Nov 19, 2025

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why not rely on midpoint+sharpness ?
https://github.com/Kitware/vtk-js/blob/master/Sources/Rendering/Core/ColorTransferFunction/index.js#L721-L725

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@finetjul finetjul Nov 19, 2025 •
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Maybe add support for a "Nodes" key/value in addition to "RGBPoints".
See applyColorMap in ColorTransferFunction/index.js

"Name" : "Grayscale-DICOM-sigmoid",
"Notes": "This is a 16 point sample of a sigmoid grayscale colormap described in the DICOM standard. See equation C.11-1 in section C.11.2",
"NanColor" : [ 1, 0, 0 ],
"RGBPoints" : [
-1,
0.01798620996209156,
0.01798620996209156,
0.01798620996209156,
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@finetjul finetjul Nov 19, 2025

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why not 0 ?

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@jadh4v jadh4v Nov 20, 2025

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Good point. I am using the equation specified by the DICOM standard:
1 / (1 + e^(4x))
The multiplying factor of 4 could be increased to make the ends closer to 0 and 1 but they are asymptotic, so they only converge to those values. I think the purpose of the sigmoid is to increase the gradient at the center of the scalar range (window). And it is probably ok to sacrifice some color range at the ends.

-0.8666666666666667,
0.030275691986950463,
0.030275691986950463,
0.030275691986950463,
-0.7333333333333334,
0.05053016223541345,
0.05053016223541345,
0.05053016223541345,
-0.6,
0.08317269649392238,
0.08317269649392238,
0.08317269649392238,
-0.4666666666666667,
0.13392788832407365,
0.13392788832407365,
0.13392788832407365,
-0.33333333333333337,
0.2086085273260449,
0.2086085273260449,
0.2086085273260449,
-0.19999999999999996,
0.31002551887238755,
0.31002551887238755,
0.31002551887238755,
-0.06666666666666665,
0.4337256058045608,
0.4337256058045608,
0.4337256058045608,
0.06666666666666665,
0.5662743941954392,
0.5662743941954392,
0.5662743941954392,
0.19999999999999996,
0.6899744811276125,
0.6899744811276125,
0.6899744811276125,
0.33333333333333326,
0.791391472673955,
0.791391472673955,
0.791391472673955,
0.46666666666666656,
0.8660721116759263,
0.8660721116759263,
0.8660721116759263,
0.6000000000000001,
0.9168273035060777,
0.9168273035060777,
0.9168273035060777,
0.7333333333333334,
0.9494698377645865,
0.9494698377645865,
0.9494698377645865,
0.8666666666666667,
0.9697243080130495,
0.9697243080130495,
0.9697243080130495,
1,
0.9820137900379085,
0.9820137900379085,
0.9820137900379085
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@finetjul finetjul Nov 19, 2025

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why not 1 ?

]
},
{
"ColorSpace" : "RGB",
"Name" : "BkRd",
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