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Re: Proposal: background-image-opacity or background-opacity

From: David Woolley <forums@david-woolley.me.uk>
Date: Thu, 04 Jun 2009 08:27:19 +0100
Message-ID: <4A277757.10802@david-woolley.me.uk>
To: www-style@w3.org
Brad Kemper wrote:

> I don't think that is necessarily so, especially if the alpha is all one 
> value, because PNGs compress better. They also look better than JPEGs 
> that have been compressed down to the file size of a PNG of the same 
> content/dimensions.
> 

That depends on the content type.  For the sort of image for which JPEG 
was intended, it is much smaller than PNG.  The problem is that there is 
a one size fits all mentality which makes people use JPEG for all bitmap 
images, possibly because they have heard it is the most compact or 
possibly because it is the only one they know.  (Windows paintbrush 
doesn't help, as its GIF support is very poor and not so many people 
have heard of PNG).

What really irritates me is when people use JPEG for screen shots, 
especially when using standard controls.  That does produce worse 
compression than PNG and lots of artifacts.  However, even that is not 
clear cut, because quite a lot of straightforward user interfaces are 
now decorated with the sort of imagery that is best handled by JPEG. 
There is no really good way of compressing bitmaps of that sort of 
screen; one really needs a graphics metafile.

Incidentally, isn't TIFF capable of representing DCT images with alpha 
channels, possibly even with deflate'd alpha channels?

-- 
David Woolley
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Received on Thursday, 4 June 2009 07:27:56 GMT

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