just did a simple test

* 16x16 rgb image
* select half (vertically in my case) and fill in
* run the Gaussian blur, 1 blur pixel
* Hold  Ctrl+F to rerun the filter many times

- Image will eventually turn black
- Happens for RLE and IIR

If its a rounding error, you could see if theres some way to give a more 
accurate result (cast to float?) - you probably alredy do that..

At worst, you could dither so every second pixel rounds up.

> On Tue, 24 Apr 2007 20:57:43 +0200, Sven Neumann <[EMAIL PROTECTED]> wrote:
>> Hi,
>> On Wed, 2007-04-25 at 02:41 +1000, Jasper Schalken wrote:
>>> This is what I thought was a bug (I posted
>>> herehttp://bugzilla.gnome.org/show_bug.cgi?id=432978) but Sven Neumann
>>> says I should discuss it on here first.
>> Your video shows the blur tool being used on large areas of black color
>> and small areas of white color. The average of this is a dark gray. Now
>> when you continue to blur, you are mixing a dark gray with black. If you
>> go further, you end up with all black.
>> But there could very well be rounding errors in the blur tool code.
>> There are even most definitely rounding errors as we are only working
>> with 8bit per channel and rounding errors are unavoidable then. But
>> please take a look at the code and see if there's anything we could
>> change to improve this.
>> Sven
> Jasper , your bug says:
>>> It's algorithm
>>> appears to favour dark colours when they are included in the blur.
> Why do you say that? Does it still favour dark colours if the image is  
> predominantly white?
>>> From my understanding, the average lightness of a given image should  
>>> always
>>> remain constant as it is blurred.
> What is your understanding , of what blur tool?
> Is there some specific blur algorithm that you believe does preserve  
> lightness or is this just an assumption you were making?
> Maybe you could be more precise about what blur you are refering to ,  
> there are several IIRC.
> Please try to be a little more specific about what you are reporting.
> Thanks.
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