# Colormaps RGBPoints clarification

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

``````const ctfun = vtkColorTransferFunction.newInstance();
``````

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
]
},
``````

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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Thanks, and does every other value get linearly interpolated between the min and max of the â€śvaluesâ€ť portion of the array?

Thanks, and does every other value get linearly interpolated between the min and max of the â€śvaluesâ€ť portion of the array?

Yes, values are linearly interpolated.

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