[webkit-dev] image downscaling during decoding

[Alpha Lam]

I agree we should have a separate row-based downscaling phase.

JPEGImageDecoder.cpp already supports downscaling with a given width and
height, but it's using point sampling which has poor quality. It would be
nice to have a callback based downscaling API that we can implement better
algorithms.

Alpha

2012/8/13 Alpha (Hin-Chung) Lam <hclam at google.com>

> I agree we should have a separate row-based downscaling phase.
>
> JPEGImageDecoder.cpp already supports downscaling with a given width and
> height, but it's using point sampling which has poor quality. It would be
> nice to have a callback based downscaling API that we can implement better
> algorithms.
>
> Alpha
>
>
> 2012/8/13 Ilyes Gouta <ilyes.gouta at gmail.com>
>
>> Hi,
>>
>> On Mon, Aug 13, 2012 at 3:46 PM, Anton Obzhirov <a.obzhirov at samsung.com>
>> wrote:
>> > Libjpeg has some internal support for downscaling already (2x, 4x). Not
>> sure
>> > about
>> >
>> > Libpng and other libraries.  In general probably it can be implemented
>>  by
>> > downscaling decoded row of the pixels on the fly using callback API
>> > provided.
>>
>> If such a callback API for row-based resizing comes to fruition, then
>> let's (also) not rule out whole-picture h/w accelerated resizing -
>> such as by making that new API a mandatory stage in the decoding
>> process.
>>
>> -Ilyes
>>
>> >
>> > From: tomhudson at google.com [mailto:tomhudson at google.com] On Behalf Of
>> Tom
>> > Hudson
>> > 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
>> >
>> > wrote:
>> >
>> >
>> >
>> > 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.
>> >
>> >
>> >
>> > Tom
>> >
>> > (from the right account this time)
>> >
>> >
>> > _______________________________________________
>> > webkit-dev mailing list
>> > webkit-dev at lists.webkit.org
>> > http://lists.webkit.org/mailman/listinfo/webkit-dev
>> >
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>
>
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