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Re: Some comments on <image>

From: Anthony Grasso <anthony.grasso@cisra.canon.com.au>
Date: Mon, 20 Sep 2010 09:10:24 +1000
Message-ID: <4C969860.5040109@cisra.canon.com.au>
To: David Woolley <forums@david-woolley.me.uk>
CC: ddailey <ddailey@zoominternet.net>, www-svg@w3.org


On 20/09/2010 4:22 AM, David Woolley wrote:
> ddailey wrote:
>
>> 1. The spec says "Conforming SVG viewers need to support at least PNG, JPEG
>> and SVG format files." Why not GIF? I recall a profound nervousness
>
> I think the basic reason is that PNG can exactly represent any image that GIF
> can represent, except for animations, and usually does so more compactly for
> equal quality, but also has the option of better quality.
>

In saying that, there is nothing stopping an SVG viewer/editor (to my knowledge) 
from supporting GIF in addition to JPEG and PNG. :)

>> that spread like squid ink through the open source community [1] 10 or 12
>> years ago as the holders of the GIF patent threatened to go after those who
>> used it without license. I believe, however, that the patent has since
>> expired. [2] A search of gif in Google images shows about a billion files with
>> close to half that number for PNG. In many cases GIF
>
> Image formats are often chosen without any real understanding. There are an
> awful lot JPEG images (or PDF images using DCT) that are totally unsuitable for
> JPEG, either because people believe it produces the best compression for
> everything (and only make one dimensional decisions), or because they don't know
> PNG and paintbrush produces very poor GIFs.
>
>> files are smaller than PNG files, I think, and lots of the older public
>
> Although it is possible, and may be more common for very small images, the
> compression scheme used in PNG is generally better than that used in GIF (the
> LZW used in GIF, and the actual subject of the patent, is designed as a
> compromise between compression speed and and compression ratio - it was really
> intended for real time compression of streamed data. That in PNG is designed to
> give good compression, at the expense of slow compression speeds.
>
> Apart from the possibility that PNG may have a higher overhead, the other reason
> that you may observe this is that PNG has more possible formats, and, for
> example, paintbrush uses 24 bit unpalletised for PNG and uses a non-optimised
> palette for GIF.
>
>> domain imagery sites on the web used gif because, well, PNG wasn't available
>> then. All the browsers I know of go ahead and support GIF anyhow, but it is
>> one thing we can be certain of that no longer has patent entanglements. PNG??
>> Who can ever be completely sure until the 20 years pass?
>>
> It's very likely that any such patent would also affect GIF.
>
Received on Sunday, 19 September 2010 23:10:59 GMT

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