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Re: [fxtf-drafts] [filter-effects] Why can't opacity() filter function ever increase opacity?

From: Amelia Bellamy-Royds via GitHub <sysbot+gh@w3.org>
Date: Fri, 26 May 2017 21:51:20 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issue_comment.created-304395573-1495835478-sysbot+gh@w3.org>
>  I think it's kinda weird to do it multiplicatively; in particular, it means that something which is currently 0% opacity can't ever become visible, but something that's 1% can be

That's exactly the functionality I want!
You can currently apply multiplicative alpha with `<feComponentTransfer>` and I use it to make blurred edges more opaque (without also suddenly creating a solid background out of nothing).  

And as far as weirdness goes, I'd say it's even less intuitive for `brightness`, which also works as a multiplicative factor: you can use `brightness(255)` to turn every shade of gray that isn't pure black into white, but black itself will never get any brighter.  (Also true for pure saturated colors with one channel at 0; that channel never gets any brighter.)

> To have >100% opacity work, you'd need to allow the alpha channel of the pixels to be an unbounded value, which is very inconsistent with current models of pixel color.

I'm not saying that the end result should be something greater than 100% opacity.  The output of the filter operator would be clipped to the allowable range, just like it is for every other operator.


It would be nice to also have an additive option for both `opacity` and `brightness`.  Maybe a second parameter to the function (which would then be the `intercept` in the `<feComponentTransfer>` function).  But that's a separate feature, I think.

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Received on Friday, 26 May 2017 21:51:26 UTC

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