On 2014/05/16 4:41 PM, Michael Goerz wrote: > Hi, > > While playing around for an afternoon with colors in matplotlib, I came > across some inconsistencies. I was trying to define colors in sRGB (my > understanding is that sRGB as a standardized color space is > device-independent). Giving RGB values to matplotlib, I checked the > output with a color picker -- Color Maker from the Mac App Store, set > to the sRGB mode, but the built-in DigitalColor Meter gives the same > result. It turns out that the colors I see in the output are not what I > specified. This makes playing around with colors, a bit difficult: > http://nbviewer.ipython.org/gist/goerz/9aab94f5322d5a457625 > As far as I can tell, Matplotlib does not specify in > which color model in interprets RGB values (this should ideally be > stated in the documentation). Also, the output in different backends > (IPython notebook, and interactive GUI) gave different results. As a > minimal example, consider the following:
Matplotlib doesn't interpret RGB values; that is left to the display device. Matplotlib simply writes the RGB values in a file, unmodified, or sends them via a GUI backend to a display, also unmodified *by mpl*. What you put in, is what it puts out. Thanks for pointing out the DigitalColor Meter--I hadn't noticed it. What I see with your example is that the MacOSX backend *display* is interpreting RGB as sRGB, and the qt4agg backend *display* is interpreting RGB as native values (based on matching with DigitalColor Meter). I haven't tried this with inline plots in the notebook, but mpl is merely feeding RGB values to the browser, just as would occur when displaying a png, and it is up to the browser to decide how to convert them into pixel intensity. I don't see that there is a bug here. Eric > > import pylab > import numpy as np > import matplotlib > #%matplotlib inline > # draw line with sRGB color 228, 26, 28 > pylab.plot(np.linspace(0,10, 10), np.linspace(0,20,10), linewidth=10, > color=(0.894, 0.102, 0.110)) > pylab.show() > # Colorpicker shows 210, 46, 13 in GUI view > # Colorpicker shows 229, 39, 27 in iPython Notebook > > In the IPython notebook, direct PIL graphics do seem to give the right > colors cf. In [5] in the linked IPython notebook (even though PIL also > does not explicitly specify its color model). Just matplotlib seems > off. Of course, I'm doing some slightly crazy stuff in the Notebook, > displaying every matplotlib output through PIL, but I cecked that > `%matplotlib inline` actually produces the same colors. > > Should I file this on github as a bug report? > > Best, > Michael > > P.S.: please CC for direct replies > > ------------------------------------------------------------------------------ > "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE > Instantly run your Selenium tests across 300+ browser/OS combos. > Get unparalleled scalability from the best Selenium testing platform available > Simple to use. Nothing to install. Get started now for free." > http://p.sf.net/sfu/SauceLabs > _______________________________________________ > Matplotlib-users mailing list > Matplotlib-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/matplotlib-users > ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
