René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"PGF Backend: Support interpolation='none'?","articleBody":"I'm currently trying to figure out the best way to unify the figures for my thesis, and intend to use the PGF backend to directly `\\include` figures in my LaTeX document.\n\nWhen creating PGF figures that include raster graphics (e.g., via `imshow`), the graphic gets stored as a PNG file and imported via `\\pgfimage`, which is great. Unfortunately, it doesn't support `interpolation='none'` as the PDF backend does:\n\n``` python\nimport numpy as np\nimport matplotlib as mpl\nimport matplotlib.pyplot as plt\n\nnp.random.seed(42)\ndata = np.random.randn(5,6)\nplt.imshow(data, cmap='hot', interpolation='none')\n\nplt.savefig('test.pdf')\n\nmpl.rcParams['pgf.texsystem'] = 'pdflatex'\nplt.savefig('test.pgf')\n```\n\nChecking the created PDF file in Evince, it indeed includes a PNG graphic of 5x6 pixels. The graphic for the PGF file is blown up, though:\n\n```\n$ file test-img0.png \ntest-img0.png: PNG image data, 577 x 481, 8-bit/color RGBA, non-interlaced\n```\n\nI can manually fix this by replacing it with a 5x6 PNG file and tweaking the PGF output as follows:\n\n``` diff\n59c59\n\u003c \\pgftext[at=\\pgfqpoint{1.220000in}{0.600000in},left,bottom]{\\pgfimage[interpolate=true,width=5.770000in,height=4.810000in]{test-img0.png}}%\n\n---\n\u003e \\pgftext[at=\\pgfqpoint{1.220000in}{0.600000in},left,bottom]{\\pgfimage[interpolate=false,width=5.770000in,height=4.810000in]{test-img0.png}}%\n```\n\nCan we modify the PGF backend such that it emits the unscaled raster graphic and uses `interpolate=false`?\n\n---\n\nI'm willing to work on this myself, but would appreciate some guidance. Looking through the code, the image is written in https://github.com/matplotlib/matplotlib/blob/f1bab50/lib/matplotlib/backends/backend_pgf.py#L612.\nThe corresponding code in the PDF backend starts at https://github.com/matplotlib/matplotlib/blob/f1bab50/lib/matplotlib/backends/backend_pdf.py#L1600.\nIt overrides the `option_scale_image()` function to return `True`, and it takes an additional `transform` parameter in `draw_image()`. I guess this is where the magic happens -- if there's a transformation to apply, it will get the unmodified image and construct the PDF so the image is scaled appropriately.\nThe documentation on that parameter is scarce (https://github.com/matplotlib/matplotlib/blob/f1bab50/lib/matplotlib/backend_bases.py#L511), but it seems you can convert it into six values giving an affine transformation.\n\nIf I want the PGF backend to handle scaling, will the backend have to handle the full range of possible affine transformations (scaling would suffice for me)? Is the `transform` guaranteed to only be used for `interpolation='none'`, so I can set `interpolate=false` in this case? Is there any better documentation on the `transform`?\n","author":{"url":"https://github.com/f0k","@type":"Person","name":"f0k"},"datePublished":"2016-07-14T19:11:36.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/6740/matplotlib/issues/6740"}