[webkit-dev] image downscaling during decoding

[Ilyes Gouta]

Hi,

>>> 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

that's actually: such as by *not* making that new API a mandatory
stage in the decoding

>>> process.

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

Resizing and filtering on a single row isn't enough. For a good
quality and depending on the scaling ratio, we should maintain N rows,
with N depends on the maximum downscaling or upscaling factor.

-Ilyes

> nice to have a callback based downscaling API that we can implement better
> algorithms.


On Mon, Aug 13, 2012 at 6:52 PM, Alpha Lam <hclam at chromium.org> wrote:
> 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
>>> >
>>> _______________________________________________
>>> webkit-dev mailing list
>>> webkit-dev at lists.webkit.org
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>>
>>
>