Please try this patch. It slightly improves details in averaged areas and tone accuracy in darker areas.
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<x2.new.webp><x2.old.webp><x2.png>
It doesn't modify WebP. (I wanted to attach a ZIP now, but I half expect Google Groups to unpack and repack it.)
PS. The patch in the first post has a minor patch format error.
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The constants are from Rec.709, but I got them from some w3.org page initially.
I'm posting samples at quality 75 and 50 for comparison, with adjusted quality for equal file size.I should add that I really focus on the lost detail caused by subsampling. Those additionally bytes may now have to be compromised elsewhere at low quality. (I consider below default, 75, low.)
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Thanks for splitting those up. I'll try them with more samples. I didn't use the Rec.709 function, because the w3.org page recommended sRGB gamma with Rec.709 luminance. (I'll try and find it.) And since the goal is to match sRGB, I don't know if it's good. Both are close*, but different. Whereas both Rec.709 and sRGB have the same chromaticity.
I'll try the combinations and report back.
On the topic of banding: what does SFIX do exactly?
I noticed that increasing SFIX to 6 helps banding in some cases, because it increases the size of the gamma table, but it doesn't appear to be a simple correlation. In particular code like luma >> SFIX confuses me, because it should have a very adverse effect.
I've tried the 6 combinations now, but before I get to that, I'm wondering: why did my patch yield many of the same improvements as the recent fixes? It's like a side-effect, that for some reason quite consistently pushed the code past the criterion? Strange.
skal/
Hi,On Thu, Sep 15, 2016 at 10:17 PM, Pascal Massimino <pascal.m...@gmail.com> wrote:Hi,On Thu, Sep 15, 2016 at 8:23 AM, pdknsk <pdk...@gmail.com> wrote:I've tried the 6 combinations now, but before I get to that, I'm wondering: why did my patch yield many of the same improvements as the recent fixes? It's like a side-effect, that for some reason quite consistently pushed the code past the criterion? Strange.Not sure exactly, maybe helping compensating for the sub-optimal initial state. That could be an explanation.FYI, i've uploaded the following patch: https://chromium-review.googlesource.com/386557It does the simple trick of sharpening the U/V plane after conversion.
Differences are subtle.
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Hi,On Sat, Sep 17, 2016 at 4:08 AM, pdknsk <pdk...@gmail.com> wrote:Differences are subtle.nice, very useful page!After some experimentation, it seems that the combination of both patches (so: srgb+r709) is useful for:a) accelerating the convergence (with srgb+r709, most images finish in just 1 pass. There's not even iterations)b) helping with dark green areas.Here's an example picture link for b). Note how the green area on the right is too light without the srgb+r709 combo.This is because the initial state is not close enough, and iterations can't recover the initial gap.With srgb+r709, the initial guess is much better and convergence is overall better.
Just a short note on the patch, or rather the patch description: the autoritative source for the values is in sections 1.1 and 3.1 of the PDF. (Only the reverse value of 0.018 is mentioned, but 0.081 is obviously 0.018 * 4.5.)
I notice you merged it already. Another step towards quality.
(When you compare default WebP with the new pre4, it's impressive.) Just in time for Firefox adding (preliminary) WebP support.
A good opportunity to make either pre4 or pre8 default with a renamed switch, I think. I'd argue to go for pre4 (with pre8 being the fast* variant), but pre8 is good too.* IMO WebP encoding is fast already, with any switch.
Another idea would be activating pre4/pre8 depending on the image hints (PICTURE/PHOTO/DRAWING/...).
Another idea would be activating pre4/pre8 depending on the image hints (PICTURE/PHOTO/DRAWING/...).(Do people actually use the hints?)
Hi,On Tue, Sep 20, 2016 at 12:27 PM, pdknsk <pdk...@gmail.com> wrote:I notice you merged it already. Another step towards quality.yes, the only point remaining was whether to go srgb+709 or 709+709, but it was a close tie-break. With small preference for the latter, so let's merge and iterate.I expect work on speed next, so it can reasonably be made default without penalizing speed too much.Maybe one idea would be the activate it automatically for method 4 and up.Another idea would be activating pre4/pre8 depending on the image hints (PICTURE/PHOTO/DRAWING/...).Not sure yet, but speeding things up can't be bad.An SSE2 version of pre8 is right around the corner already [1](When you compare default WebP with the new pre4, it's impressive.) Just in time for Firefox adding (preliminary) WebP support.indeed, good timing!A good opportunity to make either pre4 or pre8 default with a renamed switch, I think. I'd argue to go for pre4 (with pre8 being the fast* variant), but pre8 is good too.* IMO WebP encoding is fast already, with any switch.thanks!here's where we stand right now, using [1]:cwebp bryce_big.jpg -vTime to encode picture: 3.146scwebp bryce_big.jpg -v -pre 8Time to encode picture: 3.247scwebp bryce_big.jpg -v -pre 4Time to encode picture: 4.475s
cwebp bryce_big.jpg -v -sharp_yuv
Time to encode picture: 3.852s
37% is not totally dramatic when encoding one-off for storage, but still a bit problematic for on-the-fly serving. 20% or less would be ideal.