red-blue heightmap convert to greyscale?

[Dune]

Yeah, I requested GIS data now. Working with an .img file works nicely.

[PabloMack]

Judging by the height legend, anything between red and dark green could probably be extracted from the Hue channel, if you can convert the image to HSL or HSV. Below dark green, where it stays greenish but becomes lighter, I would try using the luminance channel, but it'll take some experimentation.

Matt

Matt is right. You need to take the hue channel and scale it to become the brightness channel. Since Red is highest in your map but lowest in the EM sprectrum then you will probably need to invert then monochrome map after you obtain it.