Re: [css3-background] Where we are with Blur value discussion

On Jul 26, 2010, at 8:58 PM, Sylvain Galineau wrote:

>> From: www-style-request@w3.org [mailto:www-style-request@w3.org] On
>> Behalf Of Tab Atkins Jr.
> 
> 
>> So, yeah, like Brad says, if the "range of pixels within which the
>> shadow becomes effectively invisible to the human eye" is a bit off at
>> very high shadow blur lengths, you'll never notice.  It's a pretty
>> unimportant point.
> 
> To the human eye, sure. Now, can we  talk about testing implementations 
> for conformance ?

I've been using an image editor (PhotoShop) with screen captures of the shadow to test implementations. The paint bucket tool can dump a contrasting color into the pure white or pure black (or other shadow color) areas. Then I can select the remaining blur area (or a region of set width/height) with the rectangular selection tool and glance at the info palette to see how many pixels wide or tall the selection is. If I am only interested in the outer part of the blend, I use a shadow with zero offsets. If the outermost blur pixel in a 200px region should be no lighter than 2% opacity, and the pixel outside that should be no darker than 2% opacity, then this can be confirmed with the eyedropper tool (if a black, 100% opaque shadow, I can just look at the brightness value. Otherwise some multiplication is still required). 

I don't have a way of automating this test, or doing it all within the browser.