The problem is highlighted; http://www.imperialviolet.org/2009/09/02/anti-aliased-clipping.html -------------------------------------------------- One solution is built into CANVAS; -------------------------------------------------- You should see two black boxes next to eachother; * The 1st one should have a sub-pixel antialiasing line. - using ctx.globalCompositeOperation = "source-over" * The 2nd one should be joined into a perfect square - using ctx.globalCompositeOperation = "lighter" -------------------------------------------------- Lighter mode is used to join the pixels, the sub-pixels of the antialiasing should always add up to 1, if the shapes really fit together perfectly! -------------------------------------------------- Both "lighter" and "darker" mode works, but only Safari supports "darker". Both modes seem to add the pixels together, when the combined alpha of the overlaying pixels is == 1. -------------------------------------------------- Mr. Doob points out it does not work in Chrome for Windows or Linux. -------------------------------------------------- It currently works in: OSX: Firefox, Chrome, Safari, Opera Windows: Opera, IE9, Safari Linux: Firefox