[webkit-dev] image downscaling during decoding

Anton Obzhirov a.obzhirov at samsung.com
Mon Aug 13 07:46:49 PDT 2012

Libjpeg has some internal support for downscaling already (2x, 4x). Not sure

Libpng and other libraries.  In general probably it can be implemented  by
downscaling decoded row of the pixels on the fly using callback API


From: tomhudson at google.com [mailto:tomhudson at google.com] On Behalf Of Tom
Sent: 13 August 2012 15:00
To: webkit-dev at lists.webkit.org; Anton Obzhirov
Subject: Fwd: [webkit-dev] image downscaling during decoding


On Mon, Aug 13, 2012 at 9:39 AM, Anton Obzhirov <a.obzhirov at samsung.com>


We are looking for ways to improve page loading speed and reduce memory
usage for WebKit in general and for GTK port of WebKit in particular.

One of the ideas is to implement downscaling of the images during decoding
for image elements with rectangle less then original image size.

At the moment such images are full decoded to a full size buffer and get
downscaled during rendering. 

It can be quite beneficial in term of memory usage and should speed up
rendering of the pages like image galleries for example.

So what are your thoughts about it?


Interesting idea! I know Chrome sees memory pressure from the downsampling
two-step on some pages, so I'd think this is could be useful for us, too.


Isn't it going to require fairly large and intrusive changes to several
different third-party libraries, though?

Also, different ports use different image downscaling algorithms; I can
think of ways to try to enable incremental downscaling callbacks so you
don't have to implement N downscales in each of M decoders, but none that
are both general and performant.


I'd love to see a proposal on this.



(from the right account this time) 

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