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Researchers Show Improved Algorithm For Smoothing Upscaled Pixel Art
Researchers Show Improved Algorithm For Smoothing Upscaled Pixel Art
May 25, 2011 | By Kyle Orland

A paper from researchers at Microsoft Research and Hebrew University details a new, spline-based algorithm for transforming pixel art, such as that from early sprite-based games, into scalable vector images.

Johannes Kopf and Dani Lischinski's "Depixelizing Pixel Art" [PDF] describes an upscaling technique that differs from popular methods used by companies like Adobe in ways that are particularly suited for the low-resolution sprites of classic games.

For example, the algorithm assumes that pixels in the initial image were placed deliberately by artists, and that lone pixels don't appear simply as artifacts of a digital imaging process.

The algorithm also evaluates pixel connections across the entire image, rather than focusing on a series of local areas, to determine whether pixels form a part of a long line that should be smoothed out or a corner that should be given a sharper edge.

The researchers have also implemented a series of heuristics to determine whether ambiguous pixel patterns, like a zig-zagging checkerboard, should be grouped together or separated into distinct lines.

Results for a variety of sample images presented in the paper improve drastically on existing algorithms, though the researchers admit their method fails for anti-aliased sprites like those found in Doom, and for situations where a more angular look is actually desired.

Scaling pixel art images to look natural on high-definition displays has been a problem for many modern updates to classic games, with most companies simply hiring artists to redraw those sprites in much greater detail, often at great cost.

The researchers hope future work will optimize their algorithm to the point where it can be used in real time on emulators, and even potentially form the basis for a method that generates additional frames to keep upscaled sprites from appearing jumpy.

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Harris Javed
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This is pretty cool. I guess it could cut cost a lot for companies wanting to release classic 2D games in HD.

Jeffrey Crenshaw
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Very impressive :]

Arnaud Clermonté
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That pdf link seems to be broken...?

Anatoly Ropotov
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Wow, this is so much more advanced than anything out there, like

Scott Southurst
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The difference being that hq4x is "simply" upscaling the images (supposedly) which means that if you want to increase to full HD you have to keep upscaling it until you get the desired resolution. This technique convertis the images to vector graphics, allowing them to be upscaled to any resolution without further processing.

Maurício Gomes
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hq4x internally DOES convert to vectors.

It is just a matter of using them.

J Benjamin Hollman
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Good news all around! It'll make it easier to expose classic games to younger audiences who are turned off by highly pixellated images on high-def screens.

Even better, it could free up true, talented pixel artists from having to make a living through rehashing art assets that were conceived before they were, every time a publisher decides they want to release an updated retro-classics pack. Thus potentially pushing demand for original skilled pixel art into a new, more creative environment, as recently exemplified by Sword & Sworcery EP.

One small step toward an 8-bit renaissance! Intriguing, indeed! Hoo hoo!

more coffee now

John Polson
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If this or something similar were a part of Nintendo's new hardware or R&D, I'd feel that an "HD" Virtual Console could be viable. Renaissance, indeed!

Jamie Mann
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Sadly (?), the site was slashdotted earlier and hasn't recovered. However, there's several mirrors of the PDF listed in the SD thread:

Ed Alexander
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Submitting this to ZSNES! (And hoping it's still an active project...)

Chris Melby
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That fish looks fine, but the other examples they provide are mix of passable and horrible. More so the ladder.

I'm not a fan of blurry vectory art, which is what this generates. It looses all the charm of the original.

Anyways, I'v never had a problem with SD content on my HD set, because I bought a plasma.

Tyler Martin
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"I'm not a fan of blurry vectory art, which is what this generates. It looses all the charm of the original."

Have to agree, especially when seeing this in motion with the Mario World video posted. I'd imagine it could work with some games or art styles, but with the Mario world examples (as well as many of the others), things started to look kind of blurry like they were made with blobs of colour. Just looking at the example on the last page, Mario's eyes don't look like anything more than two black dots. Ironically, there's a certain sharpness and clarity to the pixel art that's getting lost by trying to convert it to a higher resolution image with this technique and the original just ends up reading better visually if you ask me.

David Campbell
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I would LOVE to see the reverse of this.

Jorge Hebrard
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I agree with you. Pixel art is popular for a reason. I would love to draw some vectors and pixelate them (pixelate filters on Photoshop doesn't work the way I want).

Brent Orford
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Cooincidently, that's much easier to program. :)

Ujn Hunter
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Sign me up too! Not a fan of these HD "Upgrades"

Hakim Boukellif
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This doesn't really work well. While it solves some of the problems of previous attempts at such algorithms, such as Super Eagle and hqnx (which had a tendency of turning circles into polygons), it still doesn't manage to make the end result look as good as the original pixel art.

Look at the algorithm being used in the context of a game:

It managed to make Super Mario World, what in my eyes is still a very appealing looking game, look like a cheap flash game.

I don't think it's actually possible to make an algorithm that does this well, at least not without involving computer vision AI in some way. The problem is is that making pixel art isn't a matter of simply scaling down high-resolution art. If that were true, computers could do it, which is still not the case. As such, creating high-resolution art out of pixel art isn't a matter of simply scaling it up and applying a few filters.

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Why is it moving so slow?

Jeffrey Crenshaw
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I don't know, the SMW demo looked good to me aside from the framerate. Perhaps artists could go over an upscaled version, add more pixel art, upscale some more, etc a few times for an ideal result. At that point, it might be easier to start from scratch though *shrug*.

Arnaud Clermonté
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"It looks like a cheap flash game"...

That's like saying that high-framerate movies look like cheap TV soap operas...

It's undeniably an improvement, but people don't like it just because it reminds of something they don't like that just happened to have a better tech because it was invented later..

I think that SMW demo looks great, despite losing all the pixelated retro charm.

Arnaud Clermonté
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and yet we have graphics chips that display a blurry mess whenever they try to scale a bitmap...

Why focus on emulators and old 2d games,

this tech needs to make its way into 3d texture rendering for future games.