How do you make THEMIS "true color" VIS images?

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The five color filters of the THEMIS VIS camera do not span the full range of colors available to the human eye, so extensive processing, and an artistic touch, is applied to convert a raw image into an approximately "true color" image. Several of the THEMIS Team members are experts in VIS spectroscopy and have used their experience with the Hubble Space Telescope (HST) observations of Mars to generate a limited number of VIS color images. Their multi-step process:

  1. Use a standard VIS-RDR calibrated radiance image.
  2. Convolve the Sun spectrum over the VIS available bands and remove the solar effects from the radiance image.
  3. Scale to 8-bit and display the Red, Green, and Blue bands (654, 540, and 425 nm) in an image display program.
  4. Adjust the saturation and intensity of the image to approximate true color images available from HST and other instruments. Depending on the amount of contrast enhancement at this step, color variation of the scene may become slightly exaggerated.
  5. Note: that the long edges of THEMIS VIS images commonly contain color artifacts that do not represent surface variation.