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

On Jul 27, 2010, at 3:03 PM, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:

> On Tue, Jul 27, 2010 at 2:29 PM, Brad Kemper <brad.kemper@gmail.com> wrote:
>> On Jul 27, 2010, at 9:44 AM, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:
>> 
>>> We can automate it, we just have to build the automation manually -
>>> screenshot and then run pixel comparisons.
>> 
>> So what would you use for for the screen shot? The approximate Gaussian or the true Gaussian?
> 
> You'd compare it against a true gaussian.  You don't actually have to
> do a screenshot *comparison* - just take the one screenshot, and
> compare each pixel's value against the predicted value given by the
> gaussian distribution.

If you have a picture of what it is supposed to look like, with the predicted values rendered, then you could more easily make an initial visual comparison. 

> (My previous complaint against Aryeh's suggestion along these lines
> was arguing against requiring a gaussian precisely.  The gaussian
> approximation I'm advocating will probably allow physically accurate
> shadows.)

But the approximation would fail your test, because you're comparing each pixel's value against the value of an actual gaussian distribution. Firefox would fail, because it has noticeable banding, whereas an actual gaussian distribution presumably wouldn't.