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Export of Geographics anti-aliasing problem

Sander Huisman, University of Twente

Posted 8 years ago

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I have the following code: img= [IMAGE]; out=GeoGraphics[{GeoStyling[{"GeoImage",img}],poly},ImageSize->1000,GeoRange->"World",GeoProjection->"Equirectangular"] Export["out.png",out] 'out' looks good and only has some slight problems with anti-aliasing around the lines in img. See also the notebook. The image in mathematica looks like: But the exported file looks much worse: The 'overlay' is created in mathematica, rastering a ContourPlot as "Image" with Background->None. The overlay image (img) does not show this anti-aliasing artifacts. The preview in mathematica shows a bit of anti-aliasing problems, but the export a lot. How can I remedy the (lack of) anti-aliasing? Any ideas? Attached is the notebook. Attachments:

POSTED BY: Sander Huisman

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Posted 8 years ago

I think the problem comes when the lcp image is resized (because the transparency). Doing the composition in other way lets you have the nice image we all expect: ImageResize[ ImageCompose[ GeoGraphics[{}, ImageSize -> 2000, GeoRange -> {{-89, 89}, {-180, 180}}, GeoZoomLevel -> 2, GeoProjection -> "Equirectangular"] // Image, lcp], 1000] I tried first doing the resize over the lcp, but got the same bad result, so better do the composition first, then the resizing. I know this looks like a workaround, but the `"GeoImage"` way does perform something like the resize, so has the same artifacts as `ImageResize[lcp, 1000]`.

POSTED BY: Francisco Rodríguez

Posted 8 years ago

This works better! Thanks. I still think, though, this is a bug. The resizing of something anti-aliased/opacity channel should not matter that much and should not introduce these dark grey-ish pixels.

POSTED BY: Sander Huisman

Posted 8 years ago

Does this solve the problem Export["output.png", out, ImageSize -> 3000] if you resample image back to 1000 px ? You could adjust thickness of lines accordingly.

POSTED BY: Vitaliy Kaurov

Posted 8 years ago

Vitaliy, I think it more something fundamental. Probably you can make it less by resampling very high resolution. But I keep seeing it, not really sure if it gets less. I think the transparancy channel for the rasterize does something wrong...