W3C home > Mailing lists > Public > public-respimg@w3.org > April 2015

Fuzzy logic

From: Eric Portis <lists@ericportis.com>
Date: Mon, 13 Apr 2015 11:19:03 -0600
To: public-respimg@w3.org
Message-ID: <D3EE4F40-AB57-4999-A49C-D3FE282C6529@ericportis.com>
## Fuzzy logic

Blink’s `srcset` selection logic [just 
changed](https://codereview.chromium.org/1045353002/), “due to 
complaints of quality issues related to the geometric-mean based 
resource selection.”

Uh, [come again?](http://bukk.it/hamm-wat.gif)

Let me explain – say you’re a browser. Due to the flexibility 
afforded by the spec, you approach every `srcset` like a tiny 
choose-your-own-adventure: you’re presented with a set of options, and 
while none of them are ever going to be wrong, per-se, some of them are 
definitely 
[worse](http://youchosewrong.tumblr.com/post/94449663144/from-choose-your-own-adventure-17-the-race).

So, let’s say that you, the browser, have been tasked with picking a 
resource to paint across a 900-`px`-wide piece of the layout on a 1x 
screen. Here are your options:

```
srcset="tiny.jpg 400w, medium.jpg 800w, enormous.jpg 1600w"
```

Which JPEG do you choose? You can either save a bunch of bytes and 
upscale `medium.jpg` by ~10%, or load an enormous amount of extra data 
only to downscale `enormous.jpg` by ~40%.

Blink’s original implementation followed an old rule-of-thumb: never 
upscale, because it looks [awful](http://ericportis.com/etc/updog.html).

But it’s easy to come up with examples where upscaling is the right 
thing to do. What if the too-small resource is only a pixel short, and 
the too-big resource weighs a megabyte more? There’s a line, 
somewhere.

Blink’s first attempt at drawing that line used something called a 
“[geometric mean](http://en.wikipedia.org/wiki/Geometric_mean).” In 
short, Blink began picking whichever resource was *closer* to the 
optimal size, rather than picking the *smallest resource that was 
bigger*.

Which meant a lot of upscaling, a lot of the time. Front-end developers 
have begun to notice this upscaling and have reacted with suprise and 
dismay. Some are [coding 
around](https://twitter.com/PerryGStudio/status/578908993608921089) it; 
some are [filing 
bugs](https://code.google.com/p/chromium/issues/detail?id=471337). Jason 
Grigsby made a strong case against the new geometric-mean-based logic 
[in the RICG 
IRC](http://ircbot.responsiveimages.org/bot/log/respimg/2015-03-30#T121658):

> I believe browsers should err on the side of never scaling up unless 
> they can demonstrably prove they can do so without it looking 
> terrible.
>
> This is the first time that I know of that authors have intentionally 
> given the browser options. That’s a trust issue. Break that trust 
> and it will be hard to get back.

A compromise was enacted: Blink will now never upscale on 1x screens, 
where the resulting blur is especially noticeable. But it’ll upscale 
freely (using the aforementioned geometric mean) on HiDPI displays. To 
my eyes, a 1.5x image on a 2x screen looks fine, but a 0.75x image on a 
1x screen looks bad, so this seems reasonable.

Picking something that “seems reasonable” is fine for now, but 
browsers have an opportunity to do better. What we need is *science*. 
Dave Newton has [proposed a 
survey](https://github.com/nwtn/browser-scaling-test/blob/master/README.md) 
meant to determine what level of upscaling subjects find A) noticeable 
and B) acceptable, and Yoav Weiss has [started thinking 
about](http://ircbot.responsiveimages.org/bot/log/respimg/2015-03-30#T121700) 
how to use computable metrics like 
[DSSIM](http://en.wikipedia.org/wiki/Structural_similarity) in this 
quest. Me myself, I’m still trying to understand all of the variables 
that play into the problem of picking an image that’s “sharp 
enough,” which led me to whip up a little [visual angle 
calculator](http://ericportis.com/etc/visual-angle-calculator/).

If any of this sounds exciting (or, better yet, frustratingly amateur) 
and you’d like to point us to (or conduct!) some applicable research, 
please hop on the [WC3 IRC](https://www.w3.org/wiki/IRC) (channel: 
“respimg”), fire an email off to the RICG [mailing 
list](https://lists.w3.org/Archives/Public/public-respimg/), or simply 
hit up the [RICG Twitter](https://twitter.com/respimg).

Hm, that went a bit long, didn’t it? Let’s cram everything else into 
the grab bag!

## Grab bag

- Microsoft’s new Spartan browser – just released in the [Windows 10 
Technical 
Preview](http://windows.microsoft.com/en-us/windows/preview-iso) – 
[implements 
`srcset`](http://blogs.msdn.com/b/ie/archive/2015/03/30/quot-project-spartan-quot-in-the-windows-technical-preview-build-10049.aspx)! 
It’s `x`-descriptors only at the moment, but you can always fill out 
the rest of the respimg functionality with Picturefill. The Picturefill 
team is getting [way out ahead of this 
one](https://github.com/scottjehl/picturefill/issues/478), and have 
pushed out v2.3.1 for the sake of Spartan support.

- Jason Grigsby’s excellent <cite>Responsive Images 101</cite> series 
has a new installment: 
[`picture`](http://blog.cloudfour.com/responsive-images-101-part-6-picture-element/).

- Dave Newton is porting his amazing, byte-saving 
[grunt-respimg](https://www.npmjs.com/package/grunt-respimg) 
optimal-image-resizing tool to 
[PHP](https://github.com/nwtn/php-respimg/).

- Yoav’s [asynchronous image loading 
patch](https://bugs.webkit.org/show_bug.cgi?id=134488) (the last brick 
in the lower-level foundation he needs before he can start implementing 
the new bits of markup in earnest) landed in WebKit ... only to be 
reverted a few hours later because the patch caused a few tests to go 
wonky.

- Yoav landed [a Blink 
patch](https://codereview.chromium.org/1078633003/) that’ll send [RW 
hints](http://igrigorik.github.io/http-client-hints/#the-rw-client-hint) 
to the server based on an image’s `sizes` attribute, if present. This 
is a vast improvement over the initial implementation, which just used 
the width of the viewport.

- Mark Crawford wrote up a [nice 
recap](http://www.iterate.ie/blog/getting-ready-responsive-images) of 
Yoav’s SmashingConf Oxford presentation.

- Mozilla’s respimg implementation is 
[shaping](https://bugzilla.mozilla.org/show_bug.cgi?id=1139560) 
[up](https://bugzilla.mozilla.org/show_bug.cgi?id=1064083) nicely, just 
in time for its version 38 debut.

See you in a couple of weeks!

—eric
Received on Monday, 13 April 2015 17:19:38 UTC

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