[Gimp-developer] Downscaling quality.

[Guillermo Espertino]

A couple of weeks ago somebody commented about the quality of the 
downscaling in Gimp.
iirc there was a patch that improved the quality (that was bumped for 
future releases) and there was a discussion about the pertinence of the 
different names of the algorithms in the interface.
Well, I know that this kind of requests are not welcome when a new 
release is so near, but I've been using Gimp a little more this days for 
small images (my previous works were for print or signs, so I didn't 
find this issue to be critic), but now I do and I'd like to share my 
experiences and my concerns.
I'm working in a website right now, and one of the most frequent 
operations is to reduce images. I coudn't get a decent reduction using 
the different algorithms.
If you have to reduce a very large image to, say 800 px, you can use 
oversampling and you get a decent result, but when you're working on 
images for the web, which are frequently smaller than 100px, the results 
are very bad.
If you use oversampling, the result is a blurred image. If you don't you 
get jagged edges.This is particularly visible when you work with type, 
logotipes or high contrast images.
If you perform the transformation just once, the imperfections are 
visible. But the big problem comes when you have to perform 
transformations a couple of times.
And this operations are not rare. It's very common to scale down an 
image, rotate it and then tweak the size again.

The last time I mentioned this, Sven replied:

> I might be wrong but I think the current algorithms are basically the
> same as the ones used in GIMP 2.2. So there's really no point in
> addressing this long-standing but minor issue before 2.4.

I thought then that it was ok, but I've changed my mind.
It's not minor at all. Since Gimp doesn't support CMYK, it is not a 
viable tool for image processing for print, so we have a tool mostly for 
screen works. One of the main professional applications for that is 
preparing images for the web, and this issue is critic for that kind of 
work.
As a little example, I had to create a button for changing a website's 
language. I had a high resolution flag of the UK and wanted to reduce it.
I coudn't get the image right, by any means. I had to re-draw it using 
single pixels (I know that diagonal lines are difficult to represent in 
small sizes, so don't start to call me stupid. I made the same work 
before with other software and got better results).

The release of the 2.4 will be a huge event. The program went through 
very important changes, and it's becoming a truly professional 
application. If you compare 2.3.x with 2.2.x the difference is 
impressive. Now Gimp looks and feel professional.
It would be a shame to inherit that limitation from 2.2 series and have 
to wait until the next version (which, considering the whole GEGL thing. 
won't be ready  soon).
Please don't take this comments as another stupid user request. This is 
very important and for me is the major issue that obstaculizes my 
migation to Gimp.
I'd like to have CMYK, of course, but color management is enough for 
now, since CMYK is not a small change. I'm not telling that's a small 
change either, but I think it's critic enough to take a look before 2.4
I've discussed this with several users and they share my point of view. 
I'd like to know what you guys think about it, and if it's possible, 
revise the situation before 2.4

Thanks in advance,
Gez.