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Guetzli: A New Open-Source JPEG Encoder

research.googleblog.com

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Re: Guetzli: A New Open-Source JPEG Encoder

#11

Post by iainmerrick »

corybrown wrote: post #5

Very cool. I'm not an expert, but does JPEG generally have a ton of flexibility in compression? Why so much difference in sizes?

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.

Re: Guetzli: A New Open-Source JPEG Encoder

#12

Post by vladdanilov »

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 modification of PSNR-HVS-M, and there's still a lot of room for improvement.

Re: Guetzli: A New Open-Source JPEG Encoder

#13

Post by Scaevolus »

ktta wrote: post #10

I wonder how Dropbox's Lepton[1] compresses JPEGs encoded using Guetzli. Since they already pack more info/byte would there be noticeable compression? Someone out there must have tried this. [1]: https://blogs.dropbox.com/tech/2016/07/lepton-image-compress...

I'd expect it to still save >20%. Lepton uses arithmetic encoding instead of Huffman (-10%), and predicts each 8x8 block based on its neighbors (-20%). Guetzli shouldn't interfere with either of these.

Re: Guetzli: A New Open-Source JPEG Encoder

#15

Post by SloopJon »

The Github README says, "Guetzli generates only sequential (nonprogressive) JPEGs due to faster decompression speeds they offer." What's the current thinking on progressive JPEGs? Although I haven't noticed them recently, I don't know whether they're still widely used.

Re: Guetzli: A New Open-Source JPEG Encoder

#18

Post by theandrewbailey »

SloopJon wrote: post #15

The Github README says, "Guetzli generates only sequential (nonprogressive) JPEGs due to faster decompression speeds they offer." What's the current thinking on progressive JPEGs? Although I haven't noticed them recently, I don't know whether they're still widely used.

I use progressive JPEGs if they have a smaller filesize, which is true most of the time.
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