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Re: proposal: background-image-alpha

From: David Woolley <david@djwhome.demon.co.uk>
Date: Tue, 9 May 2006 07:25:22 +0100 (BST)
Message-Id: <200605090625.k496PMI08690@djwhome.demon.co.uk>
To: www-style@w3.org

> This RGB to grayscale translation is a subject of holy wars on the Net, like is 
> it
> luminance or what... And what if this GIF contains transparent color...

We are talking about zero chrominance, so to get a grayscale image with 
the same gamma as the the full image, one simply selects any channel,
as they are all the same.

Someone else mentioned gamma issues with PNG.  I'm not familiar with this
problem, but I am aware that one of the most common defects on the web
is using images in GIF and JPEG which are corected for a gamma of around 1.0 or 
around 1.6 (Mac) when images for the web should be sRGB (gamma 2.2) images, so
I would say that the designers of most web pages don't understand gamma.
(Also a lot of text anti-aliasing fails to temporarily convert to gamma 1
before averaging.)

Of course, alpha masks are not grayscale images, so if one uses a nominally
grayscale image format for them, I would expect the software to actually
assume a linear encoding for the mask.


> It is better to use just PNG and JPEGs (JPEG 2000) with alpha to be short.

Not at the moment, and in the time frames of new CSS standards, one cannot
assume what image formats will be available, as the actual formats don't matter,
only the capabilities.
Received on Tuesday, 9 May 2006 19:50:46 GMT

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