Consider disabling antialiasing in ImageMagick

[vlakoff]

There are many advantages to disabling ImageMagick's antialiasing when generating QR codes:

• Sharp instead of blurry images (main advantage)
• Smaller PNG files — several times smaller in size
• Simpler SVG representation
• Rescalable without quality loss — sharpness preserved when using nearest-neighbor scaling

Caveat:

• Round shapes may show a "stair-step" effect

Overall, I think that the advantages clearly outweigh the caveats. While it might be possible to enable antialiasing selectively (e.g., only for round shapes), such step-specific configuration would probably be complex to implement.

Additionally, explicitly setting antialiasing on/off is more consistent than relying on the default behavior of ImageMagick.

[DASPRiD]

Well, this would not only affect any non-rectangular shapes, but it would also have negative effect on QR codes with a small resolution. So I'm kinda hesitant to do that change. On top of that, it'd definitely be considered a breaking change in a current major version.

Even in a new major version I'd prefer to only use this with a switch. So my recommendation would be to add a third option to the ImagickImageBackEnd, like bool $antialias = true, so not to change the default.

[vlakoff]

Making it a configurable setting definitely sounds like a good idea.

That being said, I still don’t understand why the current file snapshots (refs #204) are non‑antialiased. ImageMagick has antialiasing enabled by default, and as far as I know the only way to change that default is by manually running magick with a command‑line option. To locally produce non‑antialiased snapshots I had to hack in a couple of ->setAntialias(false) calls in the PHP code.

[DASPRiD]

I just looked at the (now current) snapshots, and they are antialiased.

[vlakoff]

I think I got my local files mixed up — the committed snapshots are indeed antialiased, even previously (they were not modified during #206).