341–350 of 622 posts
Earlier quoted context omitted.
That makes two image format names which I will refuse to pronounce correctly (the other being GIF [1]). [1] https://edition.cnn.com/2013/05/22/tech/web/pronounce-gif
The only logic I ever hear for using a hard G is because that's how Graphics is said. Yet I never hear people saying jay-feg.
It is just a spec on something widely implemented already. Assuming Next gen PNG will still require new decoder. They could just call it PNG2. JPEG-XL already provides everything most people asked for a lossless codec. If there are any problems it is its encoding and decoding speed and resources. Current champion of Lossless image codec is HALIC. https://news.ycombinator.com/item?id=38990568
Can anyone explain how they maintain backwards compatibility on formats like this when adding features? I assume there are byte ranges managed in the format, but with things like compression, wouldn’t compressed images be unrenderable on clients that don’t support it? I suppose it would behoove servers to serve based on what the client would support.
In this case there could be an embedded reduced colour space image next to an extended color space one
Can anyone explain how they maintain backwards compatibility on formats like this when adding features? I assume there are byte ranges managed in the format, but with things like compression, wouldn’t compressed images be unrenderable on clients that don’t support it? I suppose it would behoove servers to serve based on what the client would support.
There is also some leeway for how encoding is done as long as you end up with a valid stream of bits at the end (called the bit stream format), so encoders can improve over time. This is common in video formats. I don’t know if a lossless image format would benefit much from that.
Seems a bit too late? And also, JPEG XL supports all the features and uses already advanced compression (finite-state entropy, like ZStandard). It offers lossy and lossless compression, animated pictures, HDR, EXIF etc. There is just no need for a PNG update, just adopt JPEG XL.
Tell that to Google. They gave up on XL in Chrome[1] and essentially killed its adoption.
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That doesn't seem to apply to images that aren't multiples of 8 in size, does it?
the stored image is always a multiple of 8, with padding that is ignored (and heavily compressed).
It is just a spec on something widely implemented already. Assuming Next gen PNG will still require new decoder. They could just call it PNG2. JPEG-XL already provides everything most people asked for a lossless codec. If there are any problems it is its encoding and decoding speed and resources. Current champion of Lossless image codec is HALIC. https://news.ycombinator.com/item?id=38990568
WebP lossless is close to state of the art and widely available. It's also not widely used. The takeaway seems to be that absolute best performance for lossless compression isn't that important, or at least it won't get you widely adopted.
Can anyone explain how they maintain backwards compatibility on formats like this when adding features? I assume there are byte ranges managed in the format, but with things like compression, wouldn’t compressed images be unrenderable on clients that don’t support it? I suppose it would behoove servers to serve based on what the client would support.
PNG is a highly structured file format internally. It borrows design ideas from formats like EA's Interchange File Format in that it contains lists of chunks with fixed headers encoding chunk type amd length. Decoders are expected to parse them and ignore chunk types they do not support.
Earlier quoted context omitted.
Is there any risk that if I open a JPEG-XL in something that knows what a JPEG is but not what a JPEG-XL is and then save it, it'll get lossy compressed? Backwards compatibility is awesome, but I know that if I save/upload/share/copy a PNG, it shouldn't change without explicit edits, right?
a sw that does not know what jpeg xl is, will not be able to open jxl files. How would it? Not sure what the previous poster meant with “backward compatible” here. jxl is a different format. It can include every information a jpeg includes, which then maybe qualifies as “backward compatible” but it still is a different format.
Original JPEG -> JPEG XL -> Recreated JPEG.
Sha256(Original JPEG) == Sha256(Recreated JPEG).
That's what people meant by "backward compatible".
Can anyone explain how they maintain backwards compatibility on formats like this when adding features? I assume there are byte ranges managed in the format, but with things like compression, wouldn’t compressed images be unrenderable on clients that don’t support it? I suppose it would behoove servers to serve based on what the client would support.
The PNG format has chunks with types. So you can add an additional chunk with a new type and existing decoders will ignore it. There is also some leeway for how encoding is done as long as you end up with a valid stream of bits at the end (called the bit stream format), so encoders can improve over time. This is common in video formats. I don’t know if a lossless image format would benefit much from that.