W3C home > Mailing lists > Public > public-respimg@w3.org > November 2014

Re: Informing the browser of the expected size of the image

From: Frédéric Kayser <f.kayser@free.fr>
Date: Thu, 6 Nov 2014 20:24:38 +0100
Cc: Simon Miles-Taylor <smilestaylor@gmail.com>, Ilya Grigorik <igrigorik@google.com>
Message-Id: <97C45B55-D971-430F-85D9-A18C104A7EB0@free.fr>
To: "public-respimg@w3.org" <public-respimg@w3.org>
Hello,
I sought a bit about this before going to bed and wake up with this idea, HTTP/2 servers could send progressive JPEG images sliced exactly at scan borders (each progressive "refinement pass" is called a scan and starts after a xFFDA Start Of Scan marker), the effect could be especially neat if servers send the first image scan of each image first, this could be relatively fast. To get an idea of the data size needed to send just this part you can apply JSK (JPEG Scan Killer) to a progressive JPEG and check the size of the first file it produces. Parsing a JPEG file to find the scan borders is quite easy and fast since no real decompression of the image has to be performed, it could be done in realtime or cached if needed.

Frédéric Kayser

Le 5 nov. 2014 à 01:48, Ilya Grigorik <igrigorik@google.com> a écrit :

> Simon, I'm not sure I follow.. I think what you're describing is orthogonal to what Kornel and I are saying.
> 
> With HTTP/2 the server can send the first KB (or whatever amount) of the image to allow the browser to decode the image header and get the geometry of the image much earlier.. which minimizes reflows during initial page load (which is awesome).
> 
> ig
> 
> On Wed, Nov 5, 2014 at 9:01 AM, Simon Miles-Taylor <smilestaylor@gmail.com> wrote:
> IIya,
> 
> The trick with images is to put them in a Div and the text underneath that way the browser can place the text underneath and deposit the image into a "container" above.
> 
> If you put a Null image preceding the real image with Height of 100% and Width of 0 and use vertical align on both images you will get vertical alignment.
> 
> I cheat I have VB code that collects and stores the image attributes. 
> 
> Simon  
> 
> On 4 November 2014 22:14, Ilya Grigorik <igrigorik@google.com> wrote:
> 
> On Fri, Oct 31, 2014 at 10:38 AM, Kornel <pornel@pornel.net> wrote:
> > On 27 Oct 2014, at 17:03, steve@steveclaflin.com wrote:
> >
> > Now, in particular, when we could have images with different aspect ratios, it seems like the browser wouldn't know until it downloads one what the aspect ratio is.  And we might end up with a very jumpy page.
> 
> For this I'm rooting for "smart" HTTP/2 servers that can push all image file headers (that contain image dimensions) to the client very early, and resume sending of the rest of the image data only after other assets have been sent. In theory HTTP/2 allows servers to do this automatically with very little overhead and it would "just work" without need for any extra markup.
> 
> Of course, we're not there yet. I feel your pain, interaction between image height and max-width is really annoying.
> 
> s/we're not there yet/we'll be there in few weeks time/
> 
> Chrome 39 is shipping http/2 in stable, so is FF 35. Meaning, in a few weeks time we'll have a significant fraction of users running HTTP/2 capable browsers... and we can start experimenting with above server implementations.
> 
> ig
> 
> 


Received on Thursday, 6 November 2014 19:25:20 UTC

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