Well, I've figured out half of it: the RGB data appears to be in <cmap>._segmentdata, an RGB-keyed dictionary of tuples of triples, but, looking at this for the jet cmap, e.g., I'm confused, 'cause the red and and blue tuples have five such triples, but the green tuple has six triples, so how exactly are these remapped to an RGB array? Thanks!
DG --- On Tue, 9/9/08, David Goldsmith <[EMAIL PROTECTED]> wrote: > From: David Goldsmith <[EMAIL PROTECTED]> > Subject: Re: [Matplotlib-users] Next problem: pixel-to-pixel alpha variation > To: matplotlib-users@lists.sourceforge.net > Date: Tuesday, September 9, 2008, 9:15 AM > Thanks, John and Michael. > > Yeah, Michael, that's what I'm doing now, but > eventually (like, now) I'd like to do what John implies > is possible, i.e., "invert" a cm back to its RGB > table - John (or anyone) can you short-cut the learning > process for me w/ a code example of how to do this? :-) > Thanks! > > DG > --- On Tue, 9/9/08, Michael Droettboom > <[EMAIL PROTECTED]> wrote: > > > From: Michael Droettboom <[EMAIL PROTECTED]> > > Subject: Re: [Matplotlib-users] Next problem: > pixel-to-pixel alpha variation > > To: [EMAIL PROTECTED] > > Cc: matplotlib-users@lists.sourceforge.net > > Date: Tuesday, September 9, 2008, 7:22 AM > > David Goldsmith wrote: > > > Hi, folks. OK, I'm trying to set the alpha > > channel, pixel by pixel, using figimage w/ the data > being of > > the "luminance" type (i.e., an MxN array). > The > > Users Guide indicates that figimage takes an alpha= > keyword > > argument, and it doesn't crash when I pass an > array for > > this value, but subsequently when I try to draw it > using > > fig.draw(canvas.get_renderer()), I get: > > > > > > > > >>>> fig.draw(canvas.get_renderer()) > > >>>> > > > Traceback (most recent call last): > > > File "<stdin>", line 1, in > > <module> > > > File > > > "C:\python25\lib\site-packages\matplotlib\figure.py", > > line 607, in draw > > > im.draw(renderer) > > > File > > > "C:\python25\lib\site-packages\matplotlib\image.py", > > line 597, in draw > > > im = self.make_image() > > > File > > > "C:\python25\lib\site-packages\matplotlib\image.py", > > line 583, in make_im > > > age > > > x = self.to_rgba(self._A, self._alpha) > > > File > > > "C:\python25\lib\site-packages\matplotlib\cm.py", > > line 76, in to_rgba > > > x = self.cmap(x, alpha=alpha, bytes=bytes) > > > File > > > "C:\python25\lib\site-packages\matplotlib\colors.py", > > line 423, in __call > > > __ > > > alpha = min(alpha, 1.0) # alpha must be > between 0 > > and 1 > > > ValueError: The truth value of an array with more > than > > one element is ambiguous. > > > Use a.any() or a.all() > > > > > > which to me "smells" as if the > array-valued > > alpha is the problem. > > > > > > Clearly (?) I can do what I'm after if I use > MxNx4 > > data, but is that the only way to have a varying > alpha? > > > > > The alpha parameter always takes only a single > (global) > > value, and the > > only way to do pixel-by-pixel alpha is an MxNx4 array. > It > > should be > > fairly straightforward to create this array by > > concatenating together > > three copies of the luminance and one copy of your > alpha, > > though. > > > > Something like: > > > > # lum is MxN, alpha is MxN > > lum = lum.reshape((M, N, 1)) > > alpha = alpha.reshape((M, N, 1)) > > rgba = numpy.concatenate((lum, lum, lum, alpha)) > > > > (There might be an even more straightforward way --- > > I'm not much of a > > numpy expert...) > > > > Cheers > > Mike > > > > -- > > Michael Droettboom > > Science Software Branch > > Operations and Engineering Division > > Space Telescope Science Institute > > Operated by AURA for NASA > > > > > ------------------------------------------------------------------------- > This SF.Net email is sponsored by the Moblin Your Move > Developer's challenge > Build the coolest Linux based applications with Moblin SDK > & win great prizes > Grand prize is a trip for two to an Open Source event > anywhere in the world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > Matplotlib-users mailing list > Matplotlib-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/matplotlib-users ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
