Eric Firing wrote: > Tobias Wood wrote: >> Hi everyone, >> After getting fed severely fed up with Matlab in recent months I >> downloaded Python, Numpy and Matplotlib to try out as an alternative. So >> far I'm pleasantly impressed, even if building from source on Mac OS X >> is an experience ;) However, I have discovered a couple of problems with >> Matplotlib's imread() function and, shall we say, 'esoteric' PNG files. >> My research group uses a 12-bit CCD controlled through Labview to >> capture high dynamic range image stacks. Often there are ~30 images in a >> single data set. These get read into Matlab in one go for processing as >> a stack. I tried converting my code over to Python but, after digging >> through the _png.cpp source file found the following that are problems >> from my point of view: >> >> 1) All .png files in imread() are converted to 4-plane RGBA files >> regardless of original format. I would prefer greyscale images to return >> a single plane. >> 2) 16-bit PNGs are stripped to 8 bit, losing any extra precision. >> 3) The significant bits option in the PNG header was not being checked. >> Our camera software will automatically save the PNGs at the maximum >> bit-depth required to cover the dynamic range in the image, and can sum >> images before saving, so pixels can be anywhere from 6- to 16-bits (at >> least those are the values I have observed whilst using the camera). >> >> I have attached the results of an svn diff after I made an attempt at >> correcting these issues. This is the first time I have contributed to an >> open source project, so am not sure of the etiquette here. Also, I have >> only had Python and Matplotlib for a fortnight so am still unfamiliar >> with them and haven't programmed with libpng before so I apologise in >> advance if there any stupid mistakes in my code. I am aware that >> imread() is a pretty important function in Matplotlib and hence any >> changes I suggest would need comprehensive testing. In brief, I made the >> following changes: > > Tobias, > > Thank you very much for the patch and the careful explanation. I'm not > the right person to review it, but I expect someone familiar with libpng > use in mpl will do so soon. Mike D. would be a candidate, but I think > he will be unavailable for several days. If you have not gotten any > feedback within a week, *please* ping us with a reminder. If it comes > to that, you could do it by forwarding your original message to > matplotlib-devel.
Tobias, I would like to apply your patch, but the test in examples/tests/pngsuite fails. If you can submit a new patch where this test passes, and, even better, if a small example 12-bit PNG of yours is added to the test, I will apply it. Apart from that, I would echo Eric's thanks for the patch and explanation. -Andrew ------------------------------------------------------------------------------ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
