Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Guetzli: A New Open-Source JPEG Encoder

research.googleblog.com

Post reply on HN
Print view View original

31–40 of 135 posts

Re: Guetzli: A New Open-Source JPEG Encoder

#31

Post by JyrkiAlakuijala »

mattpavelle wrote: post #21
jacobolus wrote: post #9

Earlier quoted context omitted.

In general if you want to avoid any color changes in blobs a few pixels in size, you’ll want to take it easy on the compression, and take the hit of a larger file size in trade. I suspect that if you give this algorithm twice the file size as a budget, that green color will come back.

I agree, giving more file size may get us our colors back. And after some experimentation I'd like to be able to confirm something a bit abstract like, "Guetzli is good for reducing artifacts by sacrificing color" or some such snippet. It would definitely have its uses as such. Or maybe it's great all around and I just found one bad example?

Guetzli sacrifices some chromaticity information, but tries to keep that in balance with the intensity loss. Guetzli sacrifices colors much less than the commonly used YUV420 mode -- the common default mode in JPEG encoding.

Re: Guetzli: A New Open-Source JPEG Encoder

#32

Post by MikusR »

ktta wrote: post #26
mtgx wrote: post #23

Earlier quoted context omitted.

If anything, they would spend the time to make it AV1-based, which apparently was expected to come out this month: http://www.streamingmedia.com/Articles/Editorial/-110383.asp... http://aomedia.org/about-us/

Nope, they pushed the expected release date to end of this year[1]. I was really hoping it would come out this month too, then I realized we won't see much adoption till 2019. 2018 will be spent with a couple releases of software decoders, and some adoption, and 2019 is when the hardware decoders will released. Which is when we can expect everyone to more to AV1. But I'm still skeptical because HEVC might be more wid…

The problem with HEVC is HEVC Advance. A second patent pool that appeared 2 years ago.

Re: Guetzli: A New Open-Source JPEG Encoder

#33

Post by JyrkiAlakuijala »

TD-Linux wrote: post #30
iainmerrick wrote: post #11

Earlier quoted context omitted.

Yes, JPEG encoding has a ton of flexibility. You rearrange each block of pixels using the discrete cosine transform, which tends to pack more significant values towards one corner, and then you have lots of freedom over how to quantize those values. See https://en.wikipedia.org/wiki/JPEG#Quantization On top of that, you could tweak the quantized values themselves to make them more compressible.

There's less flexibility than you might think - you get only one choice of quantizer and quantization matrix for the entire frame. So pretty much your only option is to twiddle the values themselves. This is usually done with trellis quantization, such as in mozjpeg. Guetzli seems to implement something simpler that just sets increasing numbers of coefficients to zero (based on my cursory reading of the source code).

I'm afraid Guetzli is quite a lot more complex. It does a global search on this, i.e., quantization decisions in neighboring blocks may impact the quantization decisions on this block. Also, quantization decisions have cross-channel impact between YUV channels.

Re: Guetzli: A New Open-Source JPEG Encoder

#34

Post by TD-Linux »

JyrkiAlakuijala wrote: post #33
TD-Linux wrote: post #30

Earlier quoted context omitted.

There's less flexibility than you might think - you get only one choice of quantizer and quantization matrix for the entire frame. So pretty much your only option is to twiddle the values themselves. This is usually done with trellis quantization, such as in mozjpeg. Guetzli seems to implement something simpler that just sets increasing numbers of coefficients to zero (based on my cursory reading of the source code).

I'm afraid Guetzli is quite a lot more complex. It does a global search on this, i.e., quantization decisions in neighboring blocks may impact the quantization decisions on this block. Also, quantization decisions have cross-channel impact between YUV channels.

There is no block to block prediction other than DC prediction, so is this effect due to your distortion function spanning multiple blocks? Same for cross YUV channels, because your metric is in RGB space?

edit: second read-through I found the paper [1] which explains it. The answer is basically "yes", where the large scale distortion function is basically activity masking. Normally this would be implemented with delta-QPs, but because JPEG doesn't have that, Guetzli uses runs of zeroes instead.

[1] https://arxiv.org/pdf/1703.04421

Re: Guetzli: A New Open-Source JPEG Encoder

#35

Post by onion2k »

Sort of related, but what's the story with fractal image compression? When I was at university (~20 years ago) there was a lot of research going in to it, with great promises heralded for web-based image transfer. There was a Netscape plugin that handled them. They seemed to just disappear in the early 2000s.

Re: Guetzli: A New Open-Source JPEG Encoder

#36

Post by 21 »

vladdanilov wrote: post #12

I'm working on a similar thing ( http://getoptimage.com ). While Guetzli is still visually better and a bit smaller in file size, it's terribly slow and requires a lot of memory. But it's a great experiment. So much knowledge has been put into it. I believe using a full blown FFT and complex IQA metrics is too much. I have great results with custom quantization matrices, Mozjpeg trellis quantization, and a modificati…

Would it be possible to accelerate Guetzli on a GPU?

Re: Guetzli: A New Open-Source JPEG Encoder

#37

Post by Veratyr »

MikusR wrote: post #32
ktta wrote: post #26

Earlier quoted context omitted.

Nope, they pushed the expected release date to end of this year[1]. I was really hoping it would come out this month too, then I realized we won't see much adoption till 2019. 2018 will be spent with a couple releases of software decoders, and some adoption, and 2019 is when the hardware decoders will released. Which is when we can expect everyone to more to AV1. But I'm still skeptical because HEVC might be more wid…

The problem with HEVC is HEVC Advance. A second patent pool that appeared 2 years ago.

Not just HEVC Advance. There are also some patent holders who aren't members of any pool, like Technicolour.

Re: Guetzli: A New Open-Source JPEG Encoder

#38

Post by TD-Linux »

onion2k wrote: post #35

Sort of related, but what's the story with fractal image compression? When I was at university (~20 years ago) there was a lot of research going in to it, with great promises heralded for web-based image transfer. There was a Netscape plugin that handled them. They seemed to just disappear in the early 2000s.

I think this paper was part of it, which showed that the advantages of fractal image compression could equivalently be achieved with smooth wavelets and efficient representation of zerotrees, except with a lot more speed and flexibility (sorry no PDF): https://www.researchgate.net/publication/5585498_A_wavelet-b...

Re: Guetzli: A New Open-Source JPEG Encoder

#39

Post by mutagen »

onion2k wrote: post #35

Sort of related, but what's the story with fractal image compression? When I was at university (~20 years ago) there was a lot of research going in to it, with great promises heralded for web-based image transfer. There was a Netscape plugin that handled them. They seemed to just disappear in the early 2000s.

My impression was that a fractured landscape of patents and some encoding performance issues doomed fractal image compression. Add rapidly expanding bandwidth and the need for better image compression dried up. DCT and related techniques were good enough to make it a tough market to enter and compete with. I could be way off base though.

Re: Guetzli: A New Open-Source JPEG Encoder

#40

Post by dbbolton »

onion2k wrote: post #35

Sort of related, but what's the story with fractal image compression? When I was at university (~20 years ago) there was a lot of research going in to it, with great promises heralded for web-based image transfer. There was a Netscape plugin that handled them. They seemed to just disappear in the early 2000s.

Seems to have been patent-encumbered and largely abandoned in the commercial world, but there is a FOSS library called fiasco (.wfa files) that is included with netpbm, available on most *NIX systems.

http://manpages.ubuntu.com/manpages/xenial/man1/netpbm.1.htm...

https://github.com/l-tamas/Fiasco

Post reply on HN