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While using Adobe Illustrator CC 2017.1 release on a Macbook, I get these strange lines as outlines/connecting around my shapes and they appear even in my png and pdf exports. See image below.

In the image, the white rectangle cutout in the brown part had no stroke and I think I used Shape builder to remove the extra part. As for the black circular shape, I think I used a pen with white fill, no stroke and drew inside the circular shape. And I've seen this error in both RGB and CMYK file mode. And i've even tried unchecking Anti Alias settings in Preferences to no avail.

Is this a bug or some setting mistake ? Very problematic as I need to use Illustrator for work. Please help!

enter image description here

And this is the outline mode below.

enter image description here

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  • Looks like conflation. Do you have a white shape on top of the objects? show the outline mode...
    – joojaa
    Oct 19, 2019 at 7:32
  • hi @joojaa i've edited the question to add the outline mode
    – Asim
    Oct 19, 2019 at 8:15
  • Try giving all your white filled objects a thin white stroke.
    – Billy Kerr
    Oct 19, 2019 at 14:48
  • @BillyKerr thanks for the suggestion. That is an OK workaround that I can use at times but might not be suitable in all situations. But thanks again!
    – Asim
    Oct 19, 2019 at 15:34
  • No probs. There are other methods too, such as using a very slight outset for the overlying shapes. The basic idea is to get an overlap of some kind which removes the conflation problem where shapes butt up against each other.
    – Billy Kerr
    Oct 19, 2019 at 15:57

2 Answers 2

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This is called a conflation artifact. See, the programmers have made an assumption when designing the rendering engine, they have assumed that transparency and coverage are the same thing (in other words they have conflated the two). They are not. Its a bug, although by now its a accepted way of working.

You should not attempt to draw a object that is exactly on top another. You can get rid of this effect if you turn off the hinting based antialiasing. In other words save with the old save for web and turn the art optimized option on in image size tab. enter image description here

This isn't really adobes fault as such, almost all other vector engines have the same issue when anti aliasing is involved. I would say its the general failing of how computer science is taught in universities. That and incremental design. See CS classes worldwide start by introducing the graphics rendering form a line that they then perfectly antialias a line. Being mathematically oriented they take this as a proof and draw the conclusions (unknown to them is that while this is true to a line its not true to 2 lines).

It would be easy for us to eradicate this issue if we would scrap all our vector drawing code and start over. And thereby decide that nobody is to do any vector drawings for a period of 2-10 years.

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    PS: this same problem also happens in each an every raster image ever.
    – joojaa
    Oct 19, 2019 at 10:22
  • Wow. Thanks @joojaa for the detailed response. I tried what you suggested with the anti-aliasing unchecked in Preferences but the line did not go away (will it still be there?) but after exporting via the Save for Web and turning off the art optimized option, I get a clean png export without that wretched line. But it still appears in the pdf export (which I need to do via the 'Export for Screens' route)...is there anyway I can prevent it in the pdf export too ?
    – Asim
    Oct 19, 2019 at 11:59
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Yes, this is a bug in Illustrator. For reasons unknown, that they'll never admit to (many have challenged them about this, for decades) they refuse to attempt to make a good rendering system that's accurate, truly representative of results and performant. In fact, I don't think they care about any of these criteria. On a Mac, Illustrator should be avoided.

Further, and what's even more annoying, alternative software has "copied" this bug, seemingly thinking that since Adobe can get away with this crap, they can, too.

Affinity Designer has this issue around art-boards, overlaying objects, nested objects and even symbols. As does Illustrator.

This can be somewhat mitigated by operating at a zoom where you don't see it, but the only thing that will teach you when this is the bug you're seeing, versus some extraneous shape colour outside where you want it, is time with a printer and output graphics.

And this is far from being the only bug that's been around forever in Adobe products.

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  • Thanks for your suggestion! @Confused I've now understood this bug thing affecting Illustrator but I wonder how they can't get something so essential as a shape builder tool fixed for white space. Thanks again!
    – Asim
    Oct 19, 2019 at 15:36

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