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Combined spectral parameter map

Download graph: combined.pcot

This is used when we want to show an RGB image where each channel comes from a different spectral parameter. For example,

RGB = 610/530, 670/440, BD610

i.e.

  • red channel = ratio of 610nm/530nm
  • green channel = ratio of 670nm/440nm
  • blue channel = band depth at 610nm

where the band depth is calculated according to Clark and Roush (1984) as given in Viviano and Seelos et al. (2014).

In this graph,

  • A rect adds a rectangular region of interest - the part of the image we are interested in.
  • A croproi cuts out this part of the image, producing a new image the same size as the ROI.
  • This image is then fed into three different nodes, each of which performs a different operation:
    • An expr node performs a$610/a$532 - extracting two bands and creating a new image with their ratio
    • Similarly, another expr node performs a$671/a$482.
    • A banddepth node finds the band depth at 610nm (double-click the node to view and change parameters)
  • These three 1-band images are merged together into a single 3-band image by another expr node, which also normalises the result. The optional second argument to the norm function is non-zero, which means we should normalise each channel separately.
  • Another expr then raises all the pixels to the power 0.7, performing a simple gamma correction.
  • Finally, the inset node takes the 3-channel image we have just made, and insets it into an RGB representation of the original image as defined by the RGB mappings in the canvas of the input node, using the rectangular ROI we originally used.

Output of index node, and graph.
Figure: Output of index node, and graph.. Click on image to expand.

If you want to see both images side by side, you can double-click on a tab's header to pop it out into a separate window. It can be particularly useful to have the rect node and the inset node open at the same time because you can change the rectangle in the rect node and see the changes reflected immediately in the inset.

References

  • Viviano, Christina E., et al. "Revised CRISM spectral parameters and summary products based on the currently detected mineral diversity on Mars." Journal of Geophysical Research: Planets 119.6 (2014): 1403-1431.
  • Clark, Roger N., and Ted L. Roush. "Reflectance spectroscopy: Quantitative analysis techniques for remote sensing applications." Journal of Geophysical Research: Solid Earth 89.B7 (1984): 6329-6340.