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webgrafisklyd og bildeCFDhjemmeserverkomprimering
theorawebp
BildekomprimeringTheora er allerede nevnt som et format egnet for å komprimere og distribuere film. Tilsvarende er også webm et slikt filmformat. Men nylig har dette formatet også fått sin egen avgreining innenfor stillbilder — kalt webp. Alle kjenner til formater som gif og jpeg, forskjellen er at webp tar sikte på å gi enda bedre valuta for bitsene. Ja, det påstås at man kan få opptil 40% mindre filer, sammenlignet med tilsvarende kvalitet for jpeg. Her er en liten sammenligning.

Alle konverteringene er gjort med utgangspunkt i samme råfil. Webp-filene er gjort med verktøyet webpconv 0.0.5. For å vise resultatet av webp-konverteringene, har disse igjen blitt gjort om til png. Størrelsene som er angitt i kB, gjenspeiler for webp-filene ikke det som faktisk vises på skjermen.

Merk: Eksemplene aktiveres ved å flytte pekeren over linkene, ikke ved klikking.

Original
367kB PNG
JPEG
19kB
webp 50%
19 kB
webp 0.1.3
19 kB


Original
275kB PNG
JPEG
11,3kB
webp 50%
11,2kB


Original
544kB PNG
JPEG
52,1kB
webp 50%
51,2kB
JPEG
30,4kB
webp 30%
30,2kB
webp 0.1.3
30,2kB


Original
446kB PNG
JPEG
24,7kB
webp 50%
24,1kB
webp 0.1.3
24,1kB


Original
361kB PNG
JPEG
13,8kB
webp 50%
13,8kB
webp 50%
13,6kB v0.1


Original
446kB PNG
JPEG
18,4kB
webp 50%
18,1kB
webp 0.1.3
18,0kB


OppsummeringDet er spennende å se at et nytt format som webp gir vesentlig bedre ytelse ved relativt "lav" filstørrelse. Det som likevel er litt uroligende, er at for bilder som er ment å være av god kvalitet — her har jeg brukt quality=90, så er forskjellen mot ordinær JPG svært liten. Og sånn alt i alt, så er det jo bilder av god kvalitet vi som regel ønsker oss, og ikke "best mulig" dårlige bilder.

Det viser seg faktisk at det er sterke meninger rundt nettopp bruken av webp, at det er feil å gå i bresjen for et format som dette, når det ikke på noen måte er bedre, og i tillegg har et dårligere utgangspunkt.

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wwwSean · Sunday 17. Apr 2011 - 10:52
gravatarFirst slide have a wrong extension, not PNG, but it is .PNG maybe other too.
But it is not a problem. But why OPERA have given JPEG files the name WEBP, when a file was JPG, it is a problem
Leif Halvard Silli · Wednesday 25. May 2011 - 20:02
gravatarI cannot subscribe to the conclusion make, ‘that WebP gives substantially better performance when using relatively “low” file size’. [my translation]

For example, for the top most photo, the 50% percent WebP image shows less detail than the JPEG of file size — there cannot be any doubt about that. You may consider that the 50% WebP is prettier — I can’t dispute your taste, but there is absolutely more detail in the same size JPEG.

Even for the 90% WepP image of that photo, I find more detail in the same size JPEG than in the WebP. For instance, the shades of the shadows have more detail in the JPEG version than the WebP has. WepP, in contrast, literally blurs the picture.

I'd say that only for the last — the red — photo might it be that the WebP performs better than the JPEG.

But otherwise, many thanks for this interesting demo. Btw, Google claims to have improved the format, again: http://blog.chromium.org/2011/05/webp-in-chrome-picasa-gmail-with-slew.html Time for an updated test?
Kjetil · Thursday 26. May 2011 - 00:58
gravatarWell, I don't agree that compression artifacts equals level of detail. Jpeg suffers from compression artifacts and blocking, and webp from some smoothing - but I disagree that the total difference between them can be addressed that Jpeg has a "better level of detail".

I have performed certain "re-tests" as development has progressed, but the difference has hardly been visible. Whenever an update is necessary, I will post one. Also, I believe the mentioned Chrome blog entry about webp has been in the making for quite a while, as I was given a heads up about this as far back as November 2010.
Leif Halvard Silli · Thursday 26. May 2011 - 01:23
gravatarDefine “artefact”, please. According to Wikipedia:

QUOTE: “A compression artifact (or artefact) is a noticeable distortion of media – an image, audio, or video – due to the application of an overly aggressive or inappropriate lossy data compression algorithm.”
http://en.wikipedia.org/wiki/Compression_artifact

Clearly, both WebP images and JPEG images get distorted when they are heavily compressed. And they both show artefacts.

The smoothing perhaps makes it less *obvious* to the viewer that - hey - there are some noise in this picture. But it nevertheless is an artefact.

Of course, you could counter that what I describe as “more detail” should rather be described as “perceived more detail”, since it, after all, is distorted. I would be OK with that …
Kjetil · Thursday 26. May 2011 - 08:27
gravatarFamous last words, Leif. This adds to your trolling account. Webp shows far less artifacts and blocking for 90% compression.
Leif Halvard Silli · Thursday 26. May 2011 - 11:20
gravatarThanks for reminding me that I - after all - live under the law of Jante! Else, blocking is specific kind of artefact. As is the socalled smoothing. I prefer the JPEG degradation over the WebP degradation. But I accept if you have other preferences. Thanks again for a nice page.
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