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Question:What is the algorithm used in generating the fastie colormap from NDVI in Infragram?

Jtaw is asking a question about general: Subscribe to answer questions on this topic

Jtaw asked on March 14, 2017 12:41
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###What I want to do or know

I want to know how the NDVI values were converted into its equivalent fastie color. I know that the NDVI values were adjusted in a way that it will be represented into a grey image. from that grey image how does infragram convert it to an image with a fastie colormap.

###Background story

I am currrently doing a project that is using a raspberry pi to generate an NDVI image, what I am planning to do is every time I am able to obtain the necessary images I'll be able to instantly produce the NDVI image in fastie colormap without using the Infragram and other software. I just want it to be a part of my code. If ever my project will become succesful, I'll surely give an acknowledgement/credit to you guys and to the creator of fastie colorspace.



colormap fastie

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3 Answers

I think the algorithm to convert a blue- or red-filtered NIR photo to color NDVI is something like this:

  1. Start with a color photo in which one channel has captured NIR light and another has captured visible light.
  2. Compute NDVI for each pixel.
  3. Scale NDVI in each pixel (which ranges from -1.0 to +1.0) so instead it ranges from 0 to 255.
  4. You now have a grayscale image (one color channel only) with brightness related to NDVI.
  5. Produce a new image in which the NDVI value in each pixel is converted to a three channel color using a look up table.
  6. You now have a color image in which color encodes values for NDVI.

The look up table used for the Fastie colormap is here. This might not be the exact table used at infragram.org but it is the one used by that Fastie fellow.

NDVI_VGYRM_lutA.jpg

Chris


Jtaw 7 months ago

The lookup table will do for me. I'll try to generate an equation from this one. thanks a lot!

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update : I used the lookup table above and did not give me a good result. I hope it is not the colormap used by infragram and there is something else.


cfastie 7 months ago

The text file attached above gives the correct RGB values for the NDVI_VGYRM lookup table. I put an image of the NDVI_VGYRM color gradient in my answer above.

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