Depixelizing Pixel Art

http://research.microsoft.com/en-us/um/people/kopf/pixelart/supplementary/multi_comparison.html

by epsylon • 12 years ago

637 159 12 years ago

research.microsoft.com

rsiqueira2• 12 years ago

Amazing image zoom algorithm, t creates a hires version of a low res image. I would love to see this image zoom feature implemented the in ImageMagick.

adamnemecek2• 12 years ago

Technology almost caught up with CSI.

bradyd• 12 years ago

There is a technique that might actually be able to do this called compressed sensing[1] that I first heard about it in a Wired article from several years ago[2]. The technique allows reconstructing images, music, etc. by sampling a portion of the original and applying an algorithm that reconstructs the missing information and is apparently used in MRI image processing to get by with shorter scans. Researchers from Rice University constructed a camera with only a single pixel image sensor that, using this technique, produced legible images with as little as a 2% sampling of the final image resolution, although more complex images required 10-20% or more[3]. I don't see why this technique couldn't be used to take already good quality images and "enhance" areas of them like in CSI.

[1] https://en.wikipedia.org/wiki/Compressed_sensing [2] http://www.wired.com/magazine/2010/02/ff_algorithm/ [3] http://dsp.rice.edu/cscamera

nivla2• 12 years ago

Is there a paper or code associated with this?

adamnemecek2• 12 years ago

http://research.microsoft.com/en-us/um/people/kopf/pixelart/

nivla2• 12 years ago

Thank you.

mxfh• 12 years ago

Which also has the original HN discussions

https://news.ycombinator.com/item?id=2673271

and links to +1000 day old threads:

https://news.ycombinator.com/item?id=2601347

https://news.ycombinator.com/item?id=2578706

yet those space invaders still haunt me.

computerslol• 12 years ago

Looks great :) Makes me a bit less tense about the appearance of older programs in the 4k+ display future.

joosters2• 12 years ago

This would be awesome if it was available as a scaler for high-DPI screens and old apps. Or even bundled into televisions for upscaling.

The paper does note that it is designed for hand-edited pixel art, where every different coloured pixel is treated as significant. So I wonder how it behaves when scaling photos?

(Edit: the paper does note that it doesn't do well on anti-aliased graphics...)

panzi5• 12 years ago

Televisions have upscale algorithms. But nothing like this. But they don't need anything like this because they don't scale pixle art with sharp borders and very low resolution. They scale video footage (which one could say is "anti-aliased") with about 640x480 resolution.

mrbuttons454• 12 years ago

to me, hq4x looks better every time.

tibbon2• 12 years ago

I was thinking that too, but then came to terms with 'ours' version

Ricapar• 12 years ago

I think it depends on what your end goal is. Are you trying to scale and hide the pixel-ness of the original? The "ours" does pretty darn well, especially if you look at the Boo example as mentioned above.

However, if you're looking at in the case of an SNES emulator or something.. then hq4x seems like the best choice. It keeps true to the original pixel art, while appearing significantly better.

fuzzywalrus• 12 years ago

Linked earlier:

Video of Ours vs HQ4X. Ours seems to have a slight advantage to my eyes, admittedly it is a personal preference. Text has a distinct advantage on HQ4X but Mario and Yoshi look better even if less "accurate". https://research.microsoft.com/en-us/um/people/kopf/pixelart...

gverri• 12 years ago

Looks like a normalized version of the EPX algorithm.

th0ma5• 12 years ago

I thought this looked familiar! It is from 2011 https://research.microsoft.com/en-us/um/people/kopf/pixelart...

tibbon2• 12 years ago

Are there any emulators that support this?

cedel2k1• 12 years ago

Yay, tons of.. at least with the algo's they compare their stuff to.

jrockway3• 12 years ago

I wish they would use this in Windows 8. As far as I can tell, their scaling algorithm for 4k displays is: scale up 2x using nearest neighbor, then randomly drop pixels to get back to 125% or 150%. The result is horrifyingly bad. Not just kind of bad, but unusably bad. (Adding insult to injury, they ClearType the text before scaling.)

bluedino2• 12 years ago

I would guess it's for performance reasons.

jrockway3• 12 years ago

I have 4 i7 cores and a $500 graphics card. I feel like it's possible :)

TF2, for example, plays beautifully at 3840x2160@60Hz. Scaling up the graphics for an 800x600 visual novel that plays at 1 frame per 30 seconds is computationally possible.

(The good news is that someone has written an emulator for one VN that I'm working through, so I should be able to play with scaling in that way. If I can get it to compile.)

rkuykendall-com4• 12 years ago

Do you know if MS is working on Mac-Style resolution independence for W9? I'm currently running a Retina MBP, at 2x res I think, and it works _perfectly_. The first few months some apps didn't work well, but the community adapted very quickly.

bri3d4• 12 years ago

Windows has had support for resolution independence where DPI is configurable across a continuum (rather than only available as 1x or 2x scale like on the Mac) for quite some time - the issue is that with a huge legacy application base, a giant morass of drawing technologies, and no shipped "HiDPI" or "Retina" Windows hardware until recently, there's been no real incentive for app developers to support it.

In Windows 7 and 8, WPF apps are already supposed to be resolution independent (vector-based).

Old-style GDI+ apps which aren't marked as "resolution aware" (i.e. almost everything) are poorly scaled by the window manager and hideously ugly.

bluedino2• 12 years ago

It works perfect on the Mac but I wonder if that would be the case if you could still run old 'classic' apps.

You'd think Microsoft of all companies would work in compatibilty fixes for at least the major apps. Like how they worked in so many fixes to make them compatible from 98-XP and such.

cmelbye• 12 years ago

Even when there were a few apps that didn't work well, in my experience at least, it was no one near as bad as W8's HiDPI features continue to be today. Apple did a really good job with that.

jjcm• 12 years ago

While something similar would probably be better, this is heavily optimized for pixel artwork. Lots of curves, shading, and most importantly - limited colors. UI is generally much straighter, less shaded, with far more colors.

Here's an example of UI that's scaled with potrace (a similar algorithm): http://i.imgur.com/jDq4M7e.png (left side is the converted side, right side is nearest-neighbor. Top is 3x, bottom is 2x)

That's with the highest amount of colors/depth that potrace allows. On an i7 processor, it takes a LONG time to compute all of that. Each icon is no longer just a couple hundred pixels, it's a couple hundred vector paths. Even rendering it takes a number of seconds to refresh the screen in inkscape.

krakensden• 12 years ago

That's with the highest amount of colors/depth that potrace allows. On an i7 processor, it takes a LONG time to compute all of that.

OTOH, for icons, you just need to compute that once and then cache the png.

dublinben• 12 years ago

1. That looks awful.

2. We just need vector-based icons already.

mistercow4• 12 years ago

To be fair, that would look a little better with ClearType off.

balls187• 12 years ago

Unfortunately I think this is just the price of being an early adopter.

rkuykendall-com4• 12 years ago

Does anyone know where I can find an implementation of this? I can't even figure out what to call it. They just refer to it as "our method."

jonathanj2• 12 years ago

Here's a pure Python implementation: https://github.com/jerith/depixel

jonathanj2• 12 years ago

A work in progress implementation, anyway.

rkuykendall-com4• 12 years ago

Thanks!

See? Even he doesn't know what to call it!

sp332• 12 years ago

I wonder why they all fall down on Peach and Peach 2? None of them look nearly as good (to me) as bicubic.

Lerc• 12 years ago

I think it comes down to your point of focus. With peach and peach 2, The eyes change shape quite a bit. Humans notice that much more than other aspects.

In general, I think the "ours" method could benefit by moving the boundaries between colours in and out until they get an average brightness match with the similar area in the nearest neighbour version. A lot of the "ours" images have a higher proportion of black.

mistercow4• 12 years ago

Super2xSaI looks better to me at 4x than bicubic, and EPX does an OK job but the others look pretty terrible.

I think the problem is that those sprites use multiple strategies for handling diagonal outlines. Those look fine when the image is blurred together, but when you try to detect the outlines and upscale them, the differences between techniques are exaggerated.

frik• 12 years ago

hq4x looks better (IMHO), sadly the website is offline (default blank wordpress site): http://hiend3d.com/hq4x.html

backup on archive.org: https://web.archive.org/web/20120630044334/http://www.hiend3...

http://en.wikipedia.org/wiki/Hqx

Source: https://code.google.com/p/hqx/source/browse/trunk/src/hq4x.c

lloeki6• 12 years ago

Only if you look at the first ones. All of Boo, Dolphin, all of SoM, Invaders, Golden Axe, Windows assets and Lost Vikings look great and have vastly reduced artifacts compared to hqx. Also, according to the paper abstract[0], it outputs vector, not scaled up bitmap.

[0] http://research.microsoft.com/en-us/um/people/kopf/pixelart/

panzi5• 12 years ago

As you say: It depends. E.g. the sword looks better with hq4x, because the result isn't rounded.

Camillo2• 12 years ago

No, hq4x is still better on almost all of them. Microsoft's makes everything too round and blobby. It pretty much only works really well when everything is round, like in Boo. But look at what it does to the Golden Axe characters' faces.

scott_karana2• 12 years ago

I agreed with you, but then I realized they're representing hqx deceptively.

There was a video posted here, with them rendered at the same resolution side by side.

https://news.ycombinator.com/item?id=7307975

It's really a matter of taste in this video.

GhotiFish2• 12 years ago

even so. I suspect a live rendering of the vector process would be fairly attractive. I'd love to see this technique used on the textures for n64 games. The rendering times wouldn't be such an issue in that case.

whywhywhy52• 12 years ago

hq4x definitely looks the best and most accurate. If it only further smoothed the jaggies, it would look phenomenal.

mberning• 12 years ago

Boo is the best example of 'ours'. Looks amazing.

zem• 12 years ago

yeah, it seems to handle patches of complex colouring badly (especially where two tones of the same colour were used to good effect in the icon, but scaled up as messy blobs), but boo and the invaders were very impressive.

Trufa• 12 years ago

I think bower looks badass! http://research.microsoft.com/en-us/um/people/kopf/pixelart/...

smackfu• 12 years ago

From when this first came out:

https://news.ycombinator.com/item?id=2601347

https://news.ycombinator.com/item?id=2578706

josh-wrale4• 12 years ago

I chose to embrace the Pixels, myself: http://vulariter.wordpress.com/tag/jewel-punk/

rsiqueira2• 12 years ago

The authors of this paper also have other amazing image processing/optimization algorithms. Eg: Deblurring, Optimizing Color Consistency, Content-aware Automatic Photo Enhancement, Object Discovery and Segmentation in Internet Images and more:

Dani Lischinski's page: http://www.cs.huji.ac.il/~danix/

Johannes Kopf page: http://johanneskopf.de/

vanderZwan• 12 years ago

Wow, the content-aware downscaling seems very useful!

http://research.microsoft.com/en-us/um/people/kopf/downscali...

This paper introduces a novel content-adaptive image downscaling method. The key idea is to optimize the shape and locations of the downsampling kernels to better align with local image features. [...] Besides natural images, our algorithm is also effective for creating pixel art images from vector graphics inputs, due to its ability to keep linear features sharp and connected.

IIRC, this is one of the major reasons that vector graphics based icons have not taken off.

JasonFruit• 12 years ago

Sometimes the Vector Magic results are truly magical; striking poses become even more striking when the figure is reduced to a collection of simpler shapes.

vsviridov• 12 years ago

I like a lot of VectorMagic results... Very abstract art!

zimpenfish• 12 years ago

Yeah, I really like the VM ones - particularly how the space invader turns into a StarTrek badge and the Bombermans(men?).

Orangeair• 12 years ago

It reminds me of old Microsoft Word clipart.

zeidrich• 12 years ago

This is a pretty old paper, but I hadn't seen the live demo. That's pretty cool.

A problem with this algorithm is that it's pretty slow. It would be hard to use it for real time scaling.

I think that it's pretty cool though for any precalculated conversion to vector format. It would also be pretty cool if there were software that allowed you to create a pixel art image with a live preview in this format and the ability to export into a vector format.

One of the benefits of pixel art IMO is that it's got a pretty distinct style and its simplicity and restrictions means it's easy to be aware of composition where if you are given an unrestricted canvas that freedom can make it hard to know where to start. If you are given a 8x8 pixel grid to indicate "happy" there's only so many ways to do it, a symbolic heart, a little smiley face, etc. Given a whole sheet of paper you'll have more difficulty.

With the high res displays, there's more to consider than just the upscaling of old programs, the fact is people (especially indie game devs) still want to work with pixel art, and the number of titles with the term "8-bit" in their name that have come out recently. Part of that's because it's in vogue now, but a big part of it is simply that a poor artist can make a passable 24x24 sprite.

But it's still a shame that on high res displays they end up looking like a blocky mess. If you had a program that let you author your sprites under the same conditions, but let you preview an upscaled version and left you with a vector image (or high res texture with mip maps) you can make use of the fidelity while maintaining the simplicity. I think that would be cool.

ahassan3• 12 years ago

Well SuperEagle seems even slower for me, and I know for a fact that I can emulate with SuperEagle scaling on and it works fine (>30 FPS). So I don't think their algorithm is out of the question.

lloeki6• 12 years ago

If you had a program that let you author your sprites under the same conditions, but let you preview an upscaled version

Combine Atwood's law with a proposed law of mentioning ideas on HN being implemented shortly thereafter and there may be a HTML5+JS implementation popping up as a "Show HN" soon.

glhaynes• 12 years ago

A problem with this algorithm is that it's pretty slow. It would be hard to use it for real time scaling.

Even if it's too slow for realtime on today's hardware, I'd love to see some prerendered sample videos.

josh-wrale4• 12 years ago

Here's a video: https://research.microsoft.com/en-us/um/people/kopf/pixelart...

yzh2• 12 years ago

I did a GPU version in 2012. Unfinished though. http://yzhwang.github.io/depixelization/

tumes• 12 years ago

I must be a luddite, I prefer my pixilation like my soup: chunky :)

10098• 12 years ago

But the blocky versions actually look better than vectorized ones. Most of the vectorized sprites look hideous with the exception of Boo and dolphin.

GhotiFish2• 12 years ago

they have a certain style to them that is lost at higher resolutions.

userbinator• 12 years ago

Count me as another one who likes the pixel aesthetic. The title made me ask myself "why would you want to do this?"

(I also loathe most forms of antialiasing, including ClearType, so that might have something to do with it... I like sharp, clearly contrasted edges, including pixel edges.)

Kiro• 12 years ago

No, I think the vectorized versions are much better but yeah, Boo is the best one.

sz4kerto• 12 years ago

I can't believe noone linked this so far. https://www.youtube.com/watch?v=3uoM5kfZIQ0&hd=1

panzi5• 12 years ago

https://www.youtube.com/watch?v=JMIHNiR3CP8 ;)

pesenti2• 12 years ago

I can't believe you are linking to CSI instead of Blade Runner, the grand daddy of all enhance scenes http://www.youtube.com/watch?v=qHepKd38pr0 makes me feel old...

neals• 12 years ago

Funny how I don't remember those vikings to be so low-detail and tiny.

sitkack• 12 years ago

Todo: Blend hq4x and the kopf techniques in a post processing step.

Lambdanaut• 12 years ago

The Space Invaders "ours" were very impressive. The text was always really good too. The algorithm works well on more regular shapes.

josephschmoe• 12 years ago

Doesn't work well with geometric objects. Look at the swords, shields, the letter 'A'.

kaeso• 12 years ago

A C++ LGPL implementation of this has been as been developed as part of last year Inkscape GSoC and is available as a standalone library: https://launchpad.net/libdepixelize

It will be released in the next Inkscape major version, expected soon :)

SimHacker• 12 years ago

Perfect! Thanks for the link. I want to run this over the classic SimCity tile set (and the additional ones in the add-on graphics sets like the moon base, etc), to generate high resolution pixel and vector tiles for the JavaScript browser based version of Micropolis (GPL SimCity).

panzi5• 12 years ago

Is there no 8x or 16x version of hq4x? I thought you can use it to get full HD resolution from 320x240 (in realtime using GLSL shader).

dlsym• 12 years ago

Well I guess it's retro week again on HN... Better check my bookmarks from 3 years ago...

anon4• 12 years ago

The issue with depixelizing pixel art is that you need an AI that can identify semantically what the features in the sprite are. When you look at Mario you know you're looking at a stout little man with a hat, you can identify his eyes, ears, nose, hair, hat, moustache, shirt, gloves, overalls and shoes. Given that knowledge, if I were to depixelize Mario's sprite, I'll know the rough shape of his shoes and where the shading should go and what shape it should have, i.e. I can reason what the 3D shape is and how the 2D shape was derived from that. I'll also be able to identify which lines were put there to make sure separate elements can be legible and not make those thicker than needed. Or that his eyes blend with his hat simply because there aren't enough pixels to make them separate.

For simple shapes, like the background, their algorithm works really well, but for complex objects it fails, because it distorts details that were put in with very careful thought and completely depend on the resolution. Such small sprites rely a lot on being looked at by someone who can identify semantically what they're looking at, and any really successful depixelization solution will need to be able to understand what basic shapes the sprite is made of based on what it's supposed to represent.

Houshalter2• 12 years ago

I've been thinking about doing something like this. Compress images down to half resolution, then train a neural network to blow it back up and guess the pixels as accurately as possible.

mistercow4• 12 years ago

I did something very much like this years ago (upscaling used to be an obsession of mine). The results were pretty disappointing.

But there's a lot of space to explore there in terms of choosing and designing the neural net, choosing the right training set, and figuring out an initial transform for data that is input to the neural net.

Ziron• 12 years ago

There has been a neural network scaler called NNEDI3 available as a plugin for avisynth for a few years. It was trained in exactly the way you are talking about and does an amazing job at both deinterlacing and upscaling video.

It does a great job of scaling pixel art too. I'm kinda surprised it hasn't been implemented in any emulator. With the newer opencl implantation it is finally able to run in real-time.

http://screenshotcomparison.com/comparison.php?id=46792

NicoJuicy• 12 years ago

They forgot natural neighbour interpolation... Should show better results then their research ;)

TepidSolarsoul• 12 years ago

I have a hard time believing the use of Nintendo IP in this case (big corporation-backed research lab) falls under Fair Use.

galactus• 12 years ago

I wrote an implementation of this in common lisp when they published it:

http://dev.crazyrobot.net/2011/07/12/pixelart-to-vector/

fisherprice• 12 years ago

The 'ours' filter (I guess it's the one from MS) is mind-blowing.

rangibaby• 12 years ago

HQ4X and Ours are the clear winners if you must resample like this; the downsides are that HQ4X occasionally has jaggies and Ours makes makes a lot of fine details look "blobby".

The Vector Magic results reminded me a lot of this: http://www.cowboybooks.com.au/html/acidtrip1.html

jatin085• 12 years ago

Regarding HQ4X, they used the algorithm to create 4X image but used Nearest neighbor to create 8X and 16X images. I think doing HQ4X two times would have resulted into a better 16X images without jags.

omegote• 12 years ago

I'm amazed to find that no one has mentioned that ScummVM has implemented some of these algorithms for years and they work pretty nice with the classical games.

baumgarn• 12 years ago

and snes emulators ...10 years ago?

granttimmerman• 12 years ago

Here's the home page: http://research.microsoft.com/en-us/um/people/kopf/pixelart/

bart3r• 12 years ago

Are there any ruby libraries that would depixel an image in a similar fashion?

neona• 12 years ago

It would be interesting to see a pixelart/emulator scaler that was temporally aware - that is, able to use context from near or all relevant sprite frames to get additional detail/context. This would require a compositing emulator, as some others have discussed, but I could see it producing notably superior results, given it would have much more source data to work with.

digitalpacman• 12 years ago

This is pretty amazing of a demo.

bovermyer• 12 years ago

The Secret of Mana ones made my eyes leak, not gonna lie. Awesome graphics technology update not withstanding, that game was an integral part of my teenage years.

mjmahone17• 12 years ago

Kind of ironic that MSR is using an unregistered version of PhotoZoom.

asd• 12 years ago

Ctr+f "Invader 1" and choose the Vector Magic version. Star Trek!

Legend• 12 years ago

This seems pretty awesome. Can someone please tell me where this could be useful?

mistercow4• 12 years ago

I think the most interesting aspect of this is the internal shading. I haven't seen any other algorithm that manages that while maintaining sharp edges overall.

I imagine it would end up with pretty weird results though when a sprite was on top of a background that with similar enough colors to trigger the shading detection at its edges.

rocky5• 12 years ago

amazing.

kumarrahul• 12 years ago

Proper Video here :- https://research.microsoft.com/en-us/um/people/kopf/pixelart...

Udo• 12 years ago

At first I thought this was a live JS-based demo. That would have been amazing.

NKCSS• 12 years ago

Just awesome.

yzh2• 12 years ago

I did a GPU version in 2012 for my course project. For small size sprite, it runs roughly the same or even slower than the original paper. Anyone interested in finishing this and maybe try this on realtime emulator? http://yzhwang.github.io/depixelization/

pesenti2• 12 years ago

Enhance! http://www.youtube.com/watch?v=qHepKd38pr0

virtualritz• 12 years ago

It actually looks like as if you took the polylines from EPX and used the points as the CVs for a biquadratic or bicubic interpolating spline (e.g. Catmull-Rom), you'd be very close to their result already.

actionsketch• 12 years ago

I just learned that my favorite depixelizer is hq4x

klh_dk• 12 years ago

actually running the hqx algo on the art and then throwing it through ANY vectorisation engine with a slight roundness comes on top of any of these.

And Microsoft is not really being fair to Vector Magic here, there's a ton of settings there to improve that rendering depending on what you want...

aaronetz• 12 years ago

Something related that I stumbled upon some time ago (submitted to HN, got one upvote): http://gpuhacks.wordpress.com/2013/07/08/signed-distance-fie...

whywhywhy52• 12 years ago

I think hq4x is the best. Microsoft's curves too much - and while it can look good/stylized for some pieces, it's ultimately inaccurate and warps many of the pieces from their original form.

dangayle• 12 years ago

Am I the only one who prefers the Vector Magic versions? They're like mini Picassos.

kstenerud• 12 years ago

I needed some depixelation software for some graphics awhile back, so I threw together a quick program that depixelates using various technologies.

https://github.com/kstenerud/depixelate

So far it supports HQX, XBRZ, and Scale2x.

Depixelizing Pixel Art

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