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Zopfli Optimization: Literally Free Bandwidth (codinghorror.com)
188 points by temp on Jan 2, 2016 | hide | past | web | favorite | 66 comments

Somewhat OT; As a swiss, the omitted ö is really beginning to bug me.

It's Zöpfli. Gopferteckel.

(The second word is a somewhat soft cuss word - But don't try to use it as a non-native).

Also, you can't "zopfli" something - it's a noun! You "zöpf" - or, since we're in the alemannic german space; "zöpfle".

/rant /vent

How do you feel when someone badly appropriates a word like this and it gets really big, like Uber? :)

I understand why the umlaut gets dropped, but it super bugs me too - especially as it's as easy as dropping an 'e' next to the letter if you don't have an easy way to add an umlaut.

Keeping things slightly off-topic for a moment - I love Swiss German. I lived in Bavaria and speak reasonably fluent German, so I can understand bits of it, but it's mostly incomprehensible to me, but in a delightful way. Its 'sing-song' nature and fun pronunciation are the best.

I also found in Switzerland people were far more willing to tolerate and respond to my German than in Germany (where people tend to switch to English), which I very much appreciated when I was still learning the language.

Given that zopfli was created in the Google office in Zürich by non-Swiss people, blame it on your fellow Swiss citizens for lack of intervention.

Same thing with Löve 2D, or is it Love 2D?

The problem here is that the naming isn't consistent. Sometimes it's Love and sometime Löve. I never know what to call it, but I think the whole idea of naming a software package with diacritics is just asking for trouble. If they would have transcribed it to Loeve it would at least be obvious what's going on.

This is perhaps exacerbated by my native tongue treating ö not as an o with umlaut, but as a completely different character distinct from o and at another place in the alphabet. To me it's like naming a package Blam but half the time referring to it as Blym instead.

Löve is not a German or Swiss German word, so the umlaut is simply gratuitious.

(Other languages such as Dutch or French use diacritics to mark a vowel as not-dipthongised, but that doesn't apply here either.)

If it's not German it's gratuitious?

I'll try not to take that as an insult to speakers of Swedish, Finnish, Icelandic, Estonian, Hungarian, Turkish, and any of the other dozen languages which make use of the character.

The name originates from this bread;


That's German, but the swiss variant is a Zöpfli so using the ö would be correct since Zöpfli/Zopfli was created in Zürich

Genau so mit Brötli.

Doesn't this happen in every language that borrows words? Accent/diacritic marks appear and disappear to suit the speakers/writers of the "guest" language.

Also regarding our US-centric naming conventions wouldn't it be very unconventional to include a non-ASCII character in the name of an imported library or called function?

Yesterday I tried creating a Rails project with the name containing the Lithuanian character ė. In some parts the letter was reproduced correctly, in others it was incorrectly capitalised (it should be Ė - so not complicated - but was still the lowercase version), and in others was silently dropped :D

> Also, you can't "zopfli" something - it's a noun!

They should have googled it.

Ja das git mier o so.

You Swiss and your fancy ö's

Regarding the avatar images:

Why not a <div> with a border-radius & background color? Seems you could achieve the same thing without another HTTP request (1 for each unique avatar), no need to zopfli 45,000 unique files.

That's what I was thinking too, but they really want it to be pixel perfect in every browser, email, etc. They have a good in-depth discussion about all the options and pros/cons of each approach here:


These are default (placeholder) avatars. Users can upload their own avatar image as well. They're serving PNGs so they don't have to deal with the case where users using default avatars get HTML output whereas users who have uploaded an avatar get an image inserted.

Also font and alignment issues cross browser can be brutal. There is a lot to be said for a tiny image that works everywhere, on any device.

What about an svg?

That wont work in email... I'm generating a usage graph (svg) that is emailed and the graph will not display in the client.. Must be opened in a browser

Seems like you could use an SVG avatar for clients that can handle it and fallback to PNG for email.

See the comments: lots of tweaking and unreliability and not guaranteed to work in emails, apparently.

I was confused by this as well, you could also support more colors this way. Since it's just a circle with a letter, I don't think there would be concerns with crispness of the icon.

> It's a smaller file to send over the wire, and the smaller the file, the faster the decompression.

Can someone elaborate on this? Why do smaller files decompress faster?

> However, remember that decompression is still the same speed, and totally safe

Wait, what? Didn't we just establish that it's faster to decompress?

The first faster refers to total time spent decompressing being lower. The second time speed is mentioned he's saying the rate is the same.

With constant rate, smaller loads are completed faster. And the rate is constant but the load is smaller.

Decompression speed is normally measured in bytes per second of output, not input. Since the output is the same, two algorithms that decompress at the same rate take the same time, regardless of compression ratio.

Googling finds a benchmark [1] which shows Zopfli decompression rate as intermediate between deflate 1 and deflate 9. On two our of three tests, Zopfli produces smaller files but is slower to decompress than deflate 9. So "the smaller the file, the faster the decompression" isn't correct.

[1] PDF: https://cran.r-project.org/web/packages/brotli/vignettes/bro...

You can think of a compressed file as a program (a set of instructions) executed by an interpreter (the decompressor) that builds the original file.

A smaller compressed file is usually going to contain fewer instructions for the decompressor to execute, so there's less work to do to reconstruct the original file.

> Why do smaller files decompress faster?

The same reason why "no code" is faster than optimized code. ;)

The trivial identity "compressor" is fastest to decompress, since it requires no work. Likewise PNG has literal blocks, which are longer but faster to decompress. So is it actually true that Zopfli-compressed files decompress faster?

The original PNG of that PBF comic is 671,012 bytes. ZopfliPNG crunches it down to 585,117 bytes.

Not bad, but if you use newer image formats, you can do better.

Lossless WebP brings it down to 429,696 bytes (using -lossless -m 6 -q 100)

FLIF with default options (which means interlaced for progressive decoding) takes it down to 322,858 bytes. Non-interlaced FLIF reduces it further to 302,551 bytes.

If anyone is interested in PNG optimization in general, a wrote an article about it a while back. The deflate step is only one part of it!


You could probably have a worker system that eventually produces a Zopfli compressed file.

User uploads a provided PNG, you perform the quickest compression compression but then queue up a Zopfli compression. Up front you're only returning the less compressed file but after time you begin serving up the lesser bandwidth file.

If the uploaded file or associated post is deleted then you can wipe it from the queue.

Or maybe don't even Zopfli it until it gets 100 some hits. Cost some amount of cents of CPU time to do the compress... unless maybe you made the uploaded so it.

Yeah the smart thing to do is schedule "important" user submitted images for heavier recompression, but even then you might get in trouble for very large PNGs, and need to gate based on dimensions. For huge PNGs I am not sure the 80x - 160x time penalty is tenable, you might be talking 30 minutes in some cases.

Are the reported Zopfli numbers for PNGs achieved by recompressing the original, or by recompressing the output of PNGout? The wikipedia page for PNGout says

> PNGOUT also performs automatic bit depth, color, and palette reduction where appropriate.

Assuming the Zopfli numbers were created by recompressing the original, I wonder if there's any further savings to be had by recompressing the output of PNGout?

Alternatively, PNGcrush can also do the same sort of lossless bit depth and palette reduction, so I'd be curious about the combination of PNGcrush + Zopfli as well.

That doesn't matter - both systems decompress the losses PNGs before recompressing them.

It does kind of matter, because compression isn't the only form of optimization that can be done. Consider a 32 bit png that is actually bilevel with no transparency. If zopfli just recompresses, PNGOut will still make smaller output because it does bit depth reductions.

The zopfliPNG program does do bit depth reduction if that's possible. It even tests to see if a given small image that would be possible to bit depth reduce would actually be smaller by it keeping 32 bit, since the added pallet overhead may cost more than the gain of a smaller pixel storage cost.

Zopfli is a general purpose compressor. It's not unpacking the png data before compressing it.

It does decompress the source PNG and build a new file from the pixels. You can see the source here.


That's why I explicitly mentioned the bit depth, color, and palette reduction. That's stuff that's not related to the specific DEFLATE-compatible encoder used.

ZopfliPNG is not just changing the encoding algorithm - it's using the full suite of ping compression tricks and it is indeed starting from the decompressed pixels. Check the source or try using both programs in a row and compare the size to ZopfliPNG alone.

(Why the down vote?)

And you could save even more bandwidth if you changed the PNG standard to also allow Brotli compression. Even more probably if you created a better file format.

That's not free anymore, but it's technologically easily possible to drastically reduce the amount of resources we use. What holds us back is that it's hard to get other people to do stuff like supporting new file formats or even have a better output in their image manipulation program.

If you change the PNG standard, it's no longer PNG. If existing PNG decoders can't decode it, then all you've done is invented a new format that looks very similar to PNG.

Something similar was made with WOFF. Version 1 used deflate, version 2 uses brotli. You could now argue semantics wether WOFF2 still is WOFF, but that doesn't matter at all. The point I wanted to get across here is that it's a relatively easy change

> You could now argue semantics wether WOFF2 still is WOFF

No arguing needed. It's a different format. It uses a different extension ("woff2" instead of "woff"), a different magic number, a different Universal Type Identifier string, and a different @font-face format.

> it's a relatively easy change

But it's not. Even WOFF2 isn't supported everywhere (according to http://caniuse.com/#feat=woff2). And that's a format that's fairly recent (the W3C Recommendation doc for WOFF 1.0 is dated December 2012) and only has a handful of implementations to begin with.

PNG is a format that's a lot older and is decodable by practically everyone. Even if there's only a handful of distinct implementations (and I don't actually know how many implementations there are), and even if every single implementation updated immediately, it would still take an incredibly long time for it to get deployed widely-enough to actually use as a general-purpose format.

It's also worth pointing out that web fonts have built-in fallback behavior (e.g. if a browser can't handle a WOFF2 font, you can provide a WOFF font as a backup), and they're also things that are typically set up once (so generating multiple font formats is reasonable). Images don't really have fallback behavior. On the web, the WHATWG HTML Living Standard defines a <picture> element that provides fallback but it's not supported everywhere. Outside of the web there's typically no way to do fallback either (if your browser can render an image but nothing else can, saving that image to disk isn't very useful, and sending it to someone else isn't very useful either). Also, while font files are created very rarely, images are created very frequently, and most people aren't going to want to create "PNG2" images if they also have to create PNGs and deal with fallback (just look at WebP, which was released 5 years ago and still AFAIK is not used by very many people outside of Google).

Technologically it's relatively easy: just link the brotli library and call its decoding functions instead of zlibs when you encounter a file with brotli compression. It's getting everyone to implement that which is hard. This is already what I wrote in my first post.

The "getting everyone to implement that" part is the part which actually makes it a format.

We can't even use jpg2000 everywhere yet. Maybe in another 15 years we can upgrade png...

jpg2000 is unfortunately encumbered by patents. I was going to use it for a certain project a long time ago, but had to abandon the idea due to that. It's a shame, because many of the ideas in jpg2000 are very valuable for the world.

Some of these compression patents are expiring now. I don't know if they were ever enforced to begin with. The wikipedia page is confusing, but suggests that the JPEG committee got the relevant patent holders to agree to let the patents be used freely.

From what I recall, Brotli is tuned pretty heavily for compressing English text and HTML. It's got a huge built-in dictionary of common English phrases and HTML fragments. I don't think it'd perform well on image data.

It's not even just about bandwidth. You're reducing page load time, and therefore increasing revenue. http://www.fastcompany.com/1825005/how-one-second-could-cost...

If you're a designer/developer on Mac I would strongly recommend ImageOptim (https://imageoptim.com/). It supports Zopfli and has a simple drag-n-drop user interface.

On Linux there is Trimage:


Batch files which go though all the tools and find the smallest sizes for various images and .gz files


Personally I've found this tool is faster and does a better job than most others and it's free:


I don't think tools like pngquant should be so easily dismissed. With the pixel density of todays monitors, the lossy changes they introduce can be very hard to see (which may be surprising for those of us who remember the pixelated horrors of Floyd-Steinberg from a couple of decades ago).

For some image types, lossy png has the huge advantage over jpg at the same file size that they have no jpg artifacts.

    671.012 original
    584.677 zopflipng -m
    580.180 zopflipng -m --lossy_transparent
    576.637 pngwolf --max-stagnate-time=0 --max-time=300 --normalize-alpha --strip-optional
    190.598 pngquant --speed 1
    179.638 pngquant + pngwolf

His example use case seems a little contrived. We have a similar default avatar at Quay.io, but we handle it all client-side with CSS. There's some more free bandwidth!

a little, but images are important if you want to ensure consistency across different platforms.

> ~250 color schemes

Theoretically one could use one of the indexed PNG formats and only change the palette. I don't think that those avatar images use too much number of colors (even with anti-aliasing) so 8 bit indexed PNG should be more than enough.

This is interesting - but really don't we have better things like FLIF that should be gaining developer momentum first?

That would solve basically everything wrong with today's decades old formats.

Just checked; on my MacBook it installs with a quick

$ brew install zopfli

That's assuming you have Homebrew installed, if not: http://brew.sh

the lions share of image creation these days happens on the mobile. and I cant seem to find a Zopfli library for android. I wonder why - is it too heavy duty for a mobile CPU ?

Photos maybe, but who makes images that would suit PNG on mobile?

Sounds like there should be a system to JIT images with this.

> it's about as close as it gets to literally free bandwidth in our line of work.

Listen, I'm all about inventive ways to lighten the yoke of static media on the web today.

But, in two important ways, this is not "literally free bandwidth":

1) The weaker: Despite the tone of obviousness in this article, it acknowledges that the choice of which technology to use is not made for you: there are edge cases where other methodologies are indeed superior. So, far from being free, these sorts of solution do have a time cost.

2) The stronger: We live in a world where, on a great day, the user's realized downstream bandwidth is 20% their LAN connection; their upstream 5% or less.

Connecting to a next-door neighbor via a conventional web application served through a typical corporate ISP probably means pushing packets a thousand miles or more, only for them to come back into our community.

Complicating this issue: our name service and certificate distribution are implemented in a way that is reasonably called "incorrect."

Our ISPs have a "speak when spoken to mentality" about connectivity, and competition is rare.

A solution bragging "literally free bandwidth" needs to service this concern - let me transfer a piece of media to a next door neighbor utilizing the other 95% of my network interface upstream capacity. That I'll call free bandwidth.

Both scenarios are free bandwidth.

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