Colormaps RGBPoints clarification

Web
1

I am familiar with colorTransfer function and what the next two lines would do

const ctfun = vtkColorTransferFunction.newInstance();
ctfun.addRGBPoint(200.0, 1.0, 1.0, 1.0);

However, there are a number of colormaps here in colorMaps.json that I would like to get more information about.

  • What is the mapping between RGBPoints in to the colors?
  • Is there a min and max for RGBPoints array? Why there is a -1 (I thought it should be between [0,1]?
  • What is "NanColor" in some of the colormaps

Thanks!

Here is the jet colormap as an example

{
  "ColorSpace" : "RGB",
  "Name" : "jet",
  "RGBPoints" : [
      -1,
      0,
      0,
      0.5625,
      -0.777778,
      0,
      0,
      1,
      -0.269841,
      0,
      1,
      1,
      -0.015873,
      0.5,
      1,
      0.5,
      0.238095,
      1,
      1,
      0,
      0.746032,
      1,
      0,
      0,
      1,
      0.5,
      0,
      0
  ]
},
2

The RGBPoints array is a contiguous array of 4-tuples that match the signature of the addRGBPoint function: [value1, red1, green1, blue1, value2, red2, green2, blue2, ...].

The negative values should make sense once you understand the array structure. So [-1, 0, 0, 0.5625] means map the value -1 to the rgb color [0, 0, 0.5625].

NanColor tells the color transfer function to map NaN values to a particular color.

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3

Thanks, and does every other value get linearly interpolated between the min and max of the “values” portion of the array?

4

Thanks, and does every other value get linearly interpolated between the min and max of the “values” portion of the array?

Yes, values are linearly interpolated.

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