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A new PNG spec

(www.programmax.net)
672 points bluedel | 6 comments | 24 Jun 25 13:01 UTC | HN request time: 1.393s | source | bottom
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albert_e ◴[25 Jun 25 05:09 UTC] No.44373786[source]▶
So animated GIFs can be replaced by Animated PNGs with alpha blending with transparent backgrounds and lossless compression! Some nostalgia from 2000s websites can be revived and relived :)

Curious if Animated SVGs are also a thing. I remember seeing some Javascript based SVG animations (it was a animated chatbot avatar) - but not sure if there is any standard framework.

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riffraff ◴[25 Jun 25 05:22 UTC] No.44373868[source]▶
I was under the impression many gifs these days are actually served as soundless videos, as those basically compress better.

Can animated PNG beat av1 or whatever?

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layer8 ◴[25 Jun 25 06:42 UTC] No.44374256[source]▶
APNG would be for lossless compression, and probably especially for animations without a constant frame rate. Similar to the original GIF format, with APNG you explicitly specify the duration of each individual frame, and you can also explicitly specify looping. This isn’t for video, it’s more for Flash-style animations, animated logos/icons [0], or UI screen recordings.

[0] like for example these old Windows animations: https://www.randomnoun.com/wp/2013/10/27/windows-shell32-ani...

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fc417fc802 ◴[25 Jun 25 07:58 UTC] No.44374716[source]▶
All valid points, however AV1 also supports lossless compression and is almost certainly going to win the file size competition against APNG every time.

https://trac.ffmpeg.org/wiki/Encode/AV1#Losslessencoding

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1. meindnoch ◴[25 Jun 25 08:50 UTC] No.44375025[source]▶
False, or misleading.

The AV1 spec [1] does not allow RGB color spaces, therefore AV1 cannot preserve RGB animations in a bit-identical fashion.

[1] https://aomediacodec.github.io/av1-spec/av1-spec.pdf

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2. pornel ◴[25 Jun 25 15:04 UTC] No.44378181[source]▶
AV1 supports YCoCg, which encodes RGB losslessly.

It is a bit-reversible rotation of the RGB cube. It makes the channels look more like luma and chroma that the codec expects.

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3. meindnoch ◴[25 Jun 25 17:42 UTC] No.44379922[source]▶
False.

8-bit YCoCg (even when using the reversible YCoCg-R [1] scheme) cannot represent 8-bit RGB losslessly. The chroma channels would need 9 bits of precision to losslessly recover the original 8-bit RGB values.

[1] https://www.microsoft.com/en-us/research/wp-content/uploads/...

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4. pornel ◴[27 Jun 25 02:17 UTC] No.44393200{3}[source]▶
AVIF supports 10 and 12 bit encoding, which losslessly fits the 9-bit rotation of 8-bit data.

It's also possible to directly encode RGB (channels ordered as GBR) when you set identity matrix coefficients, it's just less efficient.

I've implemented this in my AVIF encoder, so I know what I'm saying.

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5. meindnoch ◴[27 Jun 25 15:39 UTC] No.44397658{4}[source]▶
Show me any of the popular image conversion tools (avifenc, imagemagick, photoshop, ffmpeg, whatever...) that does the identity matrix hack when asking for lossless AVIF. None of them do it. Many people have been burned by "lossless" AVIF, where they converted their images in the mistaken belief that the result will be bit-identical to the original, only to find out that this wasn't the case, after they've deleted the original files.
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6. fc417fc802 ◴[27 Jun 25 20:54 UTC] No.44400131{5}[source]▶
That's shifting the goalposts from what the standard supports to the current state of the ecosystem. It's certainly an interesting point though. If common implementations all have bugs regarding lossless encoding that's a pretty bad situation.