Real world analysis of google's webp format versus jpg
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Real world analysis of google's webp format versus jpg
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Re: Real world analysis of google's webp format versus jpg
#2Unfortunately, webp claims to have same image quality with smaller file size, but the 'real world analysis' compares images quality at the same file size.
Further, image quality is measured in terms of mean RGB or value difference, which is very technical and does not matter to the human eye (a lot). For example, in the portrait, the last picture, the JPEG artifacts in the person's face really hurt more than the blurring of webp, yet both have about the same statistical mean values.
Last, without the original lossless image (at hand), it is hard to tell which lossy encoder is better. Again with the portrait picture as an example, you have to download the provided lossless image to see that webp blurred the face too much.
Still, better than other quick-and-dirty 'analysis' I've seen so far.
Re: Real world analysis of google's webp format versus jpg
#3Strange artifacts in the first JPG image, looks more like a GIF with reduced colors.
Re: Real world analysis of google's webp format versus jpg
#4Unfortunately, webp claims to have same image quality with smaller file size, but the 'real world analysis' compares images quality at the same file size. Further, image quality is measured in terms of mean RGB or value difference, which is very technical and does not matter to the human eye (a lot). For example, in the portrait, the last picture, the JPEG artifacts in the person's face really hurt more than the blur…
1. How else would you construct an objective test? Creating images of the same quality and then comparing their file sizes seems prohibitively difficult if not impossible. This test, otoh, implies the same information (minus the exact difference in file size), but is pretty easy to set up.
2. Those were the reported numbers, but it's not like that was the only data point discussed in the article. Every single photo had deeper analysis and included subjective evaluation. He even directly made the point that you did about the last photo.
3. Loading megabytes of photo data into folks browsers by default doesn't seem worth the benefit (the page is already sluggish). If you're interested, the originals are available for download.
Re: Real world analysis of google's webp format versus jpg
#5Unfortunately, webp claims to have same image quality with smaller file size, but the 'real world analysis' compares images quality at the same file size. Further, image quality is measured in terms of mean RGB or value difference, which is very technical and does not matter to the human eye (a lot). For example, in the portrait, the last picture, the JPEG artifacts in the person's face really hurt more than the blur…
1. How else would you construct an objective test? Creating images of the same quality and then comparing their file sizes seems prohibitively difficult if not impossible. This test, otoh, implies the same information (minus the exact difference in file size), but is pretty easy to set up. 2. Those were the reported numbers, but it's not like that was the only data point discussed in the article. Every single photo h…
About 1: This test looks at the dual claim, and that's more or less justified. (Look up duality in linear optimization for the definition. It's useful.)
Re: Real world analysis of google's webp format versus jpg
#6Unfortunately, webp claims to have same image quality with smaller file size, but the 'real world analysis' compares images quality at the same file size. Further, image quality is measured in terms of mean RGB or value difference, which is very technical and does not matter to the human eye (a lot). For example, in the portrait, the last picture, the JPEG artifacts in the person's face really hurt more than the blur…
1. How else would you construct an objective test? Creating images of the same quality and then comparing their file sizes seems prohibitively difficult if not impossible. This test, otoh, implies the same information (minus the exact difference in file size), but is pretty easy to set up. 2. Those were the reported numbers, but it's not like that was the only data point discussed in the article. Every single photo h…
There's more than one "objective" test for image quality, and some of them are closer to human perception than PSNR. The trouble with comparisons like this is that the JPG encoder might be tuned to minimize PSNR, but if the WebP encoder is tuned to optimize for something else, of course it won't perform as well when you compare the PSNR!
More info on the issues with this type of benchmark from Jason Garrett-Glaser (a.k.a. Dark Shikari), an x264 developer: http://x264dev.multimedia.cx/?p=458
Re: Real world analysis of google's webp format versus jpg
#7Earlier quoted context omitted.
1. How else would you construct an objective test? Creating images of the same quality and then comparing their file sizes seems prohibitively difficult if not impossible. This test, otoh, implies the same information (minus the exact difference in file size), but is pretty easy to set up. 2. Those were the reported numbers, but it's not like that was the only data point discussed in the article. Every single photo h…
There's more than one "objective" test for image quality, and some of them are closer to human perception than PSNR. The trouble with comparisons like this is that the JPG encoder might be tuned to minimize PSNR, but if the WebP encoder is tuned to optimize for something else, of course it won't perform as well when you compare the PSNR! More info on the issues with this type of benchmark from Jason Garrett-Glaser (a…
That's fine, I agree. My point was not "His metric is the most awesome, shut up", it was "Despite only giving one kind of number, the author still included other analysis and subjective opinion in the writeup for each photo, so it's not as bad as you're trying to imply".
Re: Real world analysis of google's webp format versus jpg
#8Earlier quoted context omitted.
There's more than one "objective" test for image quality, and some of them are closer to human perception than PSNR. The trouble with comparisons like this is that the JPG encoder might be tuned to minimize PSNR, but if the WebP encoder is tuned to optimize for something else, of course it won't perform as well when you compare the PSNR! More info on the issues with this type of benchmark from Jason Garrett-Glaser (a…
That's fine, I agree. My point was not "His metric is the most awesome, shut up", it was "Despite only giving one kind of number, the author still included other analysis and subjective opinion in the writeup for each photo, so it's not as bad as you're trying to imply".
You asked How else would you construct an objective test? And my answer is, just make sure you're being fair in measuring the same thing the encoders are optimising for.
Re: Real world analysis of google's webp format versus jpg
#9Page not coming up for me, but over at http://lwn.net/Articles/407884/#Comments there was a link to another less-than-thrilled appreciation: http://x264dev.multimedia.cx/?p=541
(by Jason Garrett-Glaser, aka Dark Shikari, x264 Developer)
Re: Real world analysis of google's webp format versus jpg
#10Earlier quoted context omitted.
That's fine, I agree. My point was not "His metric is the most awesome, shut up", it was "Despite only giving one kind of number, the author still included other analysis and subjective opinion in the writeup for each photo, so it's not as bad as you're trying to imply".
You asked How else would you construct an objective test? And my answer is, just make sure you're being fair in measuring the same thing the encoders are optimising for.
That was in response to the complaint that the post looked at images of the same size and compared their quality, rather than looking at images of the same quality and comparing their size. If you know of a practical way to objectively do the latter, please share.