Re: on ColorFunction and combined images?

*To*: mathgroup at smc.vnet.net*Subject*: [mg47972] Re: on ColorFunction and combined images?*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Tue, 4 May 2004 01:08:52 -0400 (EDT)*Organization*: Universitaet Leipzig*References*: <c6up48$b6n$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de*Sender*: owner-wri-mathgroup at wolfram.com

Hi, when you combine the plots, the ColorFunctionScaling option is removed and the colors computed incorrect and this cause your error. You should do something like mycf[x_] := RGBColor[0, 0, Mod[(x - 350)/20, 1]] pic1 = DensityPlot[350 + 20*x^2, {x, 0, 1}, {y, 0, 1}, ColorFunction -> mycf, Mesh -> False] pic2 = Plot[x^2, {x, 0, 1}]; Show[pic1, pic2]; Regards Jens Sampo Smolander wrote: > > Intro: > > If I want to combine, say, a density field plot and an overlaid > curve on it, it is rather easy: > > pic1 = DensityPlot[x^2, {x, 0, 1}, {y, 0, 1}, Mesh -> False] > pic2 = Plot[x^2, {x, 0, 1}] > Show[pic1, pic2] > > My Case: > > But say that I am plotting a densify field that that describes, just for > an example, some carbon dioxide concentrations for which a natural scale > (in the air outdoors) is something like 350...370 rather than 0...1. > > I can tell DensityPlot to feed the raw concentration values > to the ColorFunction, and I can provide it my own ColorFunction: > > mycf[x_] := RGBColor[0, 0, (x - 350)/20] > pic1 = DensityPlot[350 + 20*x^2, {x, 0, 1}, {y, 0, 1}, > ColorFunctionScaling -> False, ColorFunction -> mycf, Mesh -> False] > pic2 = Plot[x^2, {x, 0, 1}] > Show[pic1, pic2] > > The Problem: > > There is no problem in drawing the pic1, but then when I try to > combine pic1 and pic2 with that Show, I get an error message: > "Argument in RGBColor[0, 0, -17.5] is not a real number between 0 and 1." > > It apparently happens so that with Show, the pic1 is redrawn and (some > of?) the options that I gave in the original DensityPlot command are not > used anymore. > > Is there a way around this problem? > How can I overlay other graphs with densityplots for which I have used my > own colorfunctions? > > I think of the following: I could manually scale every function, that I > attempt to plot, to give out values only in the range 0...1. Then > I guess everything should work okay. But an easier way? > > -- > Sampo Smolander ............... http://www.cs.helsinki.fi/u/ssmoland/ > Division of Atmospheric Sciences ............. University of Helsinki