Change image size & transform tool

[Michael Thaler]

On Thursday 23 June 2005 10:43, Casper Boemann wrote:

> Well it doesn't do filtering yet, so you are kind of right.
>
> But I think mine does implement 2-pass scaling and yours does not.
>
> Mine takes (m+n)*x*y step (when filtering is done)
> I think (have not checked 100% though) that yours take m*n*x*y

Are you sure? I think the main reason why my old filter code is slow is, 
because it reads single pixels. I think it would be a lot faster if it would 
read whole lines and scale them.

> I would like to know if you agree that that's the case, or if I'm just
> misreading your code (havn't looked that carefully)

I don't really know. The code is really not very clear and I did not look at 
it for a long time.

> Anyway mine is prepared for doing scale, shear, translate and rotate in one
> go, making it a lot faster in those cases.

But it also makes the code a lot more complicated, doesn't it? I think it is 
important to have high-quality zooming, shearing and rotating code. I don't 
say that you can write code that can do all this at once, but it is 
definitely beyond my understanding. Personally I would rather like to see 
seperate code for each of these actions that can then be optimised for 
quality and speed.

Would it not be better to use some e.g. scaling code with lower quality for 
the transform tool anyway and just apply a high-quality algorithm at the end? 
I think you can never do a full Mitchell filter in real time on large images 
and it is unecessary anyway. I remember that Mosfet once wrote something 
about a very fast, optimised scaling routine he wrote on kde-graphics. One 
can use a routine like this to rescale the image in real time and use a high 
quality scaling routine fopr the final result if you release the mouse 
button.

> Hower that means that no precalulation is possible

I don't really know how much speed gain precalculations get you, this should 
betested-

> Indeed yours looks better at the moment. As I said no filtering is done in
> mine.

I have a feeling that it looks even slightly better then the results from the 
GIMP, but I am not quite sure. Can someone scale pictures with GIMP and Krita 
and compare the results. Anyway, we should definitely aim to keep this 
quality.

> I would actually like it better if you would help implementing filtering
> code in the transform visitor instead.

As I said, I doubt that I understand enough about scaling, rotating and 
shearing to implement such a do everything at once algorithm.

Greetings,
Michael