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## matplotlib-users

 [Matplotlib-users] Contour plots and colors From: Dominique Orban - 2005-01-18 19:17:02 ```Hello, I am a big consumer of contour plots and it is great that matplotlib now features them. I didn't find the 'colors' argument to contour() intuitive to use though, and I wonder whether contour() should accept a colormap instance, much as imshow, so we can also display a colorbar. Browsing through colors.py and cm.py it didn't appear clearly to me how all of that works. There is some info in the mailing list archives but I still didn't feel comfortable enough with such aspects of matplotlib to go ahead and modify contour(). Instead I wrote this simple class which returns a range of colors around the spectrum. There are as many colors as specified, and i use the same number as the number of levels in my contour plot. Perhaps this could be the default colors in contour()? I don't mean to be reinventing the wheel; if there is a simpler way to do this with colormap instances, i'd love to know how. =============== class mycolors: def __init__( self, nlevels ): jet6 = ( (0,0,1), (0,1,1), (0,1,0), (1,1,0), (1,0,0), (1,0,1) ) self._jet6 = jet6 if nlevels <= 6: jet = jet6[:nlevels] else: spectrum = linspace( 0, nlevels-1, 6 ) for i in range( 6 ): spectrum[i] = round( spectrum[i] ) # Initialize colors to black jet = [] for i in range( nlevels ): jet.append( (0,0,0) ) # Insert basic colors for i in range( 6 ): jet[ int( spectrum[i] ) ] = jet6[i] # Insert spectrum in each bin for i in range( 5 ): inthisbin = int( spectrum[i+1] - spectrum[i] - 1 ) eps = 1.0/(inthisbin + 1) tones = linspace( eps, 1 - eps, inthisbin ) thistone = [ jet6[i+1][0] - jet6[i][0], jet6[i+1][1] - jet6[i][1], jet6[i+1][2] - jet6[i][2] ] for j in range( inthisbin ): thiscolor = [ jet6[i][0] + thistone[0] * tones[j], jet6[i][1] + thistone[1] * tones[j], jet6[i][2] + thistone[2] * tones[j] ] jet[ int( spectrum[i] ) + j + 1 ] = tuple( thiscolor ) self.jet = jet self.nlevels = nlevels def get_colors( self ): return self.jet def get_levels( self ): return self.nlevels ================= Here is an example script where i use the same number of colors as levels: from pylab import * def rosenbrock(x,y): return 10*(y-x**2)**2 + (x-1)**2 x = y = arange( -2, 2, 0.1 ) X, Y = meshgrid( x, y ) Z = rosenbrock( X, Y ) nlevels = 30 cols = mycolors( nlevels ) contour( Z, x = X, y = Y, levels = nlevels, colors = cols.get_colors(), origin = 'lower' ) show() If this is useful to anyone, feel free to use it. Dominique ```