Pixel art interpolation algorithms

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MetinSeven
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Pixel art interpolation algorithms

Post by MetinSeven » Wed Feb 22, 2017 11:53 am

Hi Thorsten,

Many thanks for your great, impressively versatile graphics tool. I was delighted to discover that it can even convert the Amiga IFF Anim format to PNG images or animated GIF.

I would like to request the addition of pixel art interpolation algorithms for high-quality enlargement of low-resolution pixel art.

The most desired algorithms are, in order of importance:

1: xBRZ
xBRZ is an improved variation of the xBR pixel art interpolation method, offering great enlargement results from low-res pixel graphics. Ideally, the implementation should include an option for the enlargement factor. The latest xBRZ version at the time I write this (February 2017) is 6xBRZ, supporting a maximum factor of 6 x upscaling. There are also other parameters that can be changed: luminanceWeight, equalColorTolerance, dominantDirectionThreshold and steepDirectionThreshold. It would be nice to have those included as options too.

2: Libdepixelize
An Inkscape implementation of the Kopf-Lischinski pixel art interpolation algorithm. The results are very good for enlarging pixel art, comparable with xBRZ. The Inkscape implementation can't properly handle pixel resolutions that are a bit larger than really small though. That needs improvement.

3: Waifu2x
An intelligent interpolation algorithm that is a bit of an exception in this list, because it's meant for anti-aliased graphics, but it's a great, very useful algorithm, comparable to the enlargement methods of advanced image upscalers like BenVista's Photozoom Pro or Alien Skin's Blow Up (bitmap enlargement tools that are especially popular among photographers). It would be great if the Waifu2x enlargement factor could be higher than 2 x, but I would already be very happy with the 2 x enlargement, the option to choose between artwork or photo, and the available noise reduction options. Here's a webpage that provides a simple UI for the Waifu2x algorithm.

4: HQX
An older pixel art enlargement algorithm, which is inferior to xBRZ, but nonetheless yields nice results. There are a number of variations, reflecting the enlargement factors: HQ2X, HQ3X and HQ4X.

Finally, here's some general info about different pixel interpolation algorithms.

I would be very happy if one or more of these bitmap enlargement methods would be added to GraphicConverter. I'm sure many pixel art creators who take part in the pixel graphics revival for (mobile) games would appreciate this too.

I'd be delighted to alpha-test / beta-test the implementations. I've got many suitable pixel art images that are waiting to be enlarged. :)

Many thanks in advance!

— Metin
Last edited by MetinSeven on Sat Feb 25, 2017 12:32 pm, edited 7 times in total.
Metin Seven | metinseven.com — designer • illustrator • pixel artist • visualizer • 3D (print) modeler

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Re: Pixel art interpolation algorithms

Post by forum_adm » Fri Feb 24, 2017 7:56 am

Hi Metin,

many thanks for your suggestions.

I add that onto the ToDo list.

Waifu2x will not be possible - because it requires CUDA (NVIDIA GPU processing).

Thorsten

MetinSeven
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Re: Pixel art interpolation algorithms

Post by MetinSeven » Sat Feb 25, 2017 12:17 pm

Many thanks, Thorsten, much appreciated!

Just let me know if you'd like me to test anything.
Metin Seven | metinseven.com — designer • illustrator • pixel artist • visualizer • 3D (print) modeler

MetinSeven
Posts: 4
Joined: Tue Feb 21, 2017 2:06 pm
Location: Netherlands
Contact:

Re: Pixel art interpolation algorithms

Post by MetinSeven » Sat Feb 25, 2017 12:24 pm

I've added this to my xBRZ info above:

There are also other parameters that can be changed: luminanceWeight, equalColorTolerance, dominantDirectionThreshold and steepDirectionThreshold. It would be nice to have those included as options too.

Thanks again!
Metin Seven | metinseven.com — designer • illustrator • pixel artist • visualizer • 3D (print) modeler

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