: Vectors: How do you deal with background 'spill' on overlapping edges? When covering one vector shape with another; if the edges overlap, the background shape's color is used as a (distasteful

@BetL875

I did a few tests duplicating your scenario in AI CS5.1, and the fringing effect was (barely) visible on my big honking Cinema display when zoomed out, but not visible when zoomed in. My secondary display has a coarser pitch than the Big Guy, and it was more visible there. This tends to confirm what I suspected was the problem, and is more or less what e100 pointed out: this is an artifact of antialiasing by the application at the relatively coarse resolution of your monitor. It's a bit like the fine hairlines that sometimes show up in PDFs and cause clients to make frantic phone calls to the designer.

For obvious reasons, the effect is visible primarily on curved and diagonal edges, doesn't exist on vertical and horizontal ones that fall on pixel boundaries and is somewhat there when an edge falls between pixels, forcing anti-aliasing.

You can mitigate the problem by checking "Align New Objects to Pixel Grid" in the "Advanced" section of the New File dialog, but I found the effect disappeared completely when I turned off "Anti-Alias Artwork" in the Preferences > General section. You end up with "jaggies," but no false color artifacts.

It doesn't show in SfW because it's not really there. It's also not there in PDF if you zoom in. PDF "knows" there's a shape behind, and tries to anti-alias it at the resolution of the screen, so it shows up at small image sizes and disappears as you zoom. It also won't show on Export to jpeg if you change "Text Optimized (Hinting)" in the export dialog to "Art Optimized."

SVG is at the mercy of the browser's rendering engine. None of them (IE9, Chrome, FF, Opera and Safari) are up to the task, based on my tests. EPS, similarly, renders according to the application but will print or export to raster formats without problem.

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@Sims5801359

This isn't really an Illustrator issue, but a general problem when vector art is rasterized. Displaying vector art on a pixel-based screen involves rasterizing just as exporting vector art to a pixel-based image format does.

Why is "Save for Web" better at this? Difficult to say, but it might require relatively slow, complex calculations to give the best result, which would be unacceptably slow if applied in real-time while you're editing.

I would imagine there are academic papers on this if you want to look into it further.

When supplying vector logos, it would definitely be best practice to eliminate the possibility of the issue occurring.

In your examples, you could either nudge the foreground object up and to the left, or subtract a copy of the foreground object from the background object and ensure that no traces of the background object remain at upper left.

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@Michele215

I would suggest trying a couple of things:


Nudge the top object over just enough to cover that extra line
Add a border to the top object the same color as the fill.


Using Illustrator is as much about creating the illusion of shape as it is creating the shape itself, and that requires a bit of strategy to get to work right.

Asking why Illustrator does this is unanswerable.

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