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A new PNG spec

(www.programmax.net)
616 points bluedel | 1 comments | 24 Jun 25 13:01 UTC | HN request time: 0.331s | source
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LeoPanthera ◴[25 Jun 25 05:06 UTC] No.44373778[source]▶
> I know you all immediately wondered, better compression?. We're already working on that.

This worries me. Because presumably, changing the compression algorithm will break backwards compatibility, which means we'll start to see "png" files that aren't actually png files.

It'll be like USB-C but for images.

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Lerc ◴[25 Jun 25 05:35 UTC] No.44373928[source]▶
It has fields to say what compression is used. Adding another compression form should be handled by existing software as recognizing it as a valid PNG that they can't decompress.

The PNG format is specifically designed to allow software to read the parts they can understand and to leave the parts they cannot. Having an extensible format and electing never to extend it seems pointless.

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shiomiru ◴[25 Jun 25 07:23 UTC] No.44374501[source]▶
The difference between valid PNG you can't decompress and invalid PNG is fairly irrelevant when your aim is to get an image onto the screen.

And considering we already have plenty of more advanced competing lossless formats, I really don't see why "feed a BMP to deflate" needs a new, incompatible spin in 2025.

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1. Arnt ◴[25 Jun 25 08:50 UTC] No.44375023[source]▶
It's a new and compatible spin. https://svgees.us/blog/img/revoy-cICP-bt.2020.png uses the important new feature and your old software can display it.

More generally, PNG has a simple feature to specify what's needed. A file consists of a number of chunks, and one bit in the chunk specifies whether that chunk is required for display. All of the extensions I've seen in the past decades set that bit to "optional".

For example, this update includes a chunk containing EXIF data. As you'd expect, the exif chunk sets that bit to "optional".