On Thu, 26 Apr 2007 18:47:42 +0200, Sven Neumann <[EMAIL PROTECTED]> wrote:

> Hi,
>
> On Thu, 2007-04-26 at 12:38 +0200, [EMAIL PROTECTED] wrote:
>> I said some time back that the use of gint() rather than round is
>> fairly indemic in gimp and is an area that needs following up.
>
> Yes, and I said in response that we are well aware of the fact that a
> lot of the algorithms used in GIMP just plain suck and that there's a
> lot to do all over the place.

It's not the algorithms that suck (to use your term) it's way it's coded.  
Not the same thing.

Now what's your point in repeating that
> over and over again? Please point out specific problems and, preferably,
> come up with patches.
>

Over and over , I think not. I repeated it here since you were suggesting  
this sort of thing was unavoidable and saying it was the algorithms. I  
disagree, so I explained why.

>> > What you describe sounds like a very artifical test.
>>
>> That is a comment that you often put forward in replies to bugs but it  
>> is
>> necessary to develop specific test cases to pinpoint and quantify a
>> problem.
>
> Artificial was the wrong term to use here. Sorry about that. What I
> meant to say is that the proposed test is not well chosen since it
> doesn't test the problem pointed out here. Instead it focuses on the
> behavior at the image border which is a different problem.
>
>> I described a large image not affected by border issues and posted a
>> histogram showing the mean 112 grey level . Since it is not too  
>> disimilar
>>  from your test case it's surprising that the results are so different.
>
> I couldn't reproduce your test, probably because you didn't provide all
> parameters (like for example the blur radius). But I think it suffers
> from the same problem. In order to blur two large areas in a way that
> yields a single (almost) solid colored area, you need to use a large
> blur radius. Your test image is then small compared to the blur radius
> and again you are mainly looking at the border behaviour.
>
>> Maybe you could post your test image somewhere so that we can compare  
>> the
>> results and see why there is a clear difference.
>
> Any image with a test pattern that is smaller than the blur radius will
> do. You can use the Stripes pattern or create a pattern using the Grid
> or Checkerboard plug-ins.

>
> I have reduced the rounding errors in our blur plug-ins today. The
> results are a lot more stable now, even after multiple iterations.
>
>
> Sven
>

Excellent work! I just reran my test case (which was centred on the b/w  
boundry in the middle of the image) and it works almost perfectly after a  
very large number of reps.

Now the mean grey values are 129.9 , a very credible result for 8bit  
processing.

The gimp now has a much better implementation of the gaussian blur  
algorithm. Great news.

and thanks to Jasper Schalken for bringing up the whole blur darkening  
issue.

/gg
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