OK thanks for specifying what filters are doing this .

I just did a test with a rect that was just under half black half white  
with 2.2 . Using gaussian blur
repeatedly it ended up an even grey (114,114,114) after about 20 cntl-F  
reps. After 100 or so it was at 112.

It should have been lighter than 128 , this does seem to be consistant  
with a rounding error.


On Wed, 25 Apr 2007 01:08:21 +0200, Campbell Barton <[EMAIL PROTECTED]>  

> 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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