Re: [Pixman] [PATCH v13 10/14] pixman-filter: Gaussian fixes

2016-03-04 Thread Bill Spitzak 
On Fri, Mar 4, 2016 at 3:39 PM, Søren Sandmann 
wrote:

>
>
> On Wed, Feb 10, 2016 at 1:25 AM,  wrote:
>
>> From: Bill Spitzak 
>>
>> The SIGMA term drops out on simplification.
>>
>
> But SIGMA has a meaning here: it's the standard deviation for the normal
> distribution corresponding to the Gaussian in question, so unless there is
> some good argument for reducing the formula, I think it should stay the way
> it is.
>

The simplification does not happen due to inexact math.



>
> Expanding the size is fine with me
>

This is based on checking other software for the widths it uses for such
filters.

There is a bit of hf at the cutoffs, enlarging the size reduces this. It is
very common for "gaussian" to actually be this function multiplied by a
sinc window to avoid this, but I did not think that change was a good idea.
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Re: [Pixman] [PATCH v13 10/14] pixman-filter: Gaussian fixes

2016-03-04 Thread Søren Sandmann 
On Wed, Feb 10, 2016 at 1:25 AM,  wrote:

> From: Bill Spitzak 
>
> The SIGMA term drops out on simplification.
>

But SIGMA has a meaning here: it's the standard deviation for the normal
distribution corresponding to the Gaussian in question, so unless there is
some good argument for reducing the formula, I think it should stay the way
it is.

Expanding the size is fine with me.


Søren
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