Re: Converting colors to height values

*To*: mathgroup at smc.vnet.net*Subject*: [mg109748] Re: Converting colors to height values*From*: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>*Date*: Fri, 14 May 2010 08:28:55 -0400 (EDT)

Hi, the scale looks like they used the color-angle of the HUE-colorspace. So lets check: Taking the colorscale region of one of the image and calculating (an slightly adapted) HUE-angle gives: img = Import[ "http://lro.gsfc.nasa.gov/lola/images/weekly/20100318.jpg";] scaleimg = ImageTake[img, {-50, -30}, {5, 305}] scale = ImageData[scaleimg, "Real"]; h2[{r_, g_, b_}] := Block[{\[Alpha] = 1/2 (2 r - g - b), \[Beta] = Sqrt[3]/2 (g - b)}, If[\[Alpha] == \[Beta] == 0., \[Beta] += 10^-6.]; Mod[ArcTan[\[Alpha], \[Beta]] + 0.1, 2 Pi] ]; DistributeDefinitions[h2] ListPlot[h2 /@ (Mean /@ Transpose[scale])] Looks promising. Not really linear but since it is a low quality jpg image the negative HUE-angle should be ok as height. So lets take the part of the image with the map and using a gaussian filter to smooth the data a bit: img2 = ImageTake[GaussianFilter[img, 5], {1, -90}]; heights = ParallelMap[-h2[#] &, ImageData[img2, "Real"], {2}]; ListPlot3D[heights] Cheers Patrick On Fri, 2010-05-14 at 05:36 -0400, finkh wrote: > The Lunar Orbiter Laser Altimeter has a website http://lro.gsfc.nasa.gov/lola/science.html > where jpegs are posted of regions of the moon. I would like to > convert the color information to height values. A scale is posted > with the images that looks a lot like Rainbow, a ColorFunction. I > have Inserted the jpeg of Copernicus into a mathematica notebook. It > has 5 dimensions, which look like rows, columns, and RGB, where RGB > runs from 0 to 255. How can I convert an RGB Rainbow triple to a > single number? > >