[webkit-dev] WebKit runtime image compression
hyatt at apple.com
Mon Dec 15 13:28:22 PST 2008
On Dec 14, 2008, at 1:12 AM, Paul Pedriana wrote:
> For a lot of web pages, images are the primary source of memory
> usage. These images seem to be typically stored as RGB or ARGB data
> in the BitmapImage class.
This isn't always true though. For example, the ports that use CG
have CGImageRefs and not raw ARGB data.
> It seems to me that applications that wish or need to save runtime
> memory could benefit from runtime image compression whereby images
> are stored in some compressed form instead of RGB or ARGB formats. I
> am currently looking into this possibility and I'm wondering if
> anybody has previously looked into it.
> My current idea is to support two kinds of compressed images: RLE
> and YCoCg-DXT5. The former could be for any images that are simple
> enough, and the latter could be for general images and give a fixed
> 4:1 compression ratio. RGB transforms to YCoCg with better
> decorrelation (breakdown of RGB to YCC) than YCbCr and many images
> can get PSNR values over 40 (i.e. hard to tell from original). If
> the computer has decent vector processing or a programmable GPU, the
> performance could be decent, otherwise it depends on the CPU. (A)RGB
> could of course remain as a fallback.
> I'm wondering if anybody has looked into runtime image compression
> with WebKit and considered options such as this.
This could in theory be done as a separate library that is then just
used by the specific ports of WebKit that might need it. I'm not
convinced it would need to be part of WebKit itself.
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