Re: Resizing changes sharpness

[Jakub Steiner <jimmac gmail com>]

On Mon, 2007-07-30 at 15:13 +0200, Anders Bo Rasmussen wrote:
> On 7/30/07, Stephane Delcroix <stephane delcroix org> wrote:
> > It's really easy to hook the sharpening filter on the exporters, bu twe
> > need to agree on the various sharpening factors...
> 
> I think it should be adjustable and not on by default. I would like to not
> have my photos modified with sharpening, contrast adjustment or things like
> that unless I specifically ask the tool to do so. How much sharpening should
> be applied might also depend on how much sharpening the camera has applied?

The thing is that you are getting your photos softened on scaling at the
moment, due to the filtering algorithm. So the current method is doing
something you weren't asking for. The sharpening is just a mean to
compensating the effect. 

It is true, however that using unsharp mask as a method of sharpening
will introduce shifts in hue and boost noise.

I would personally suggest not making this an option, but make the
sharpening algorithm more sophisticated. Only work on the luminosity
channel in LAB space, or Value channel in HSV, and only sharpen edges to
avoid boosting noise. This method is nicely illustrated in this tutorial
- http://www.gimpguru.org/Tutorials/SmartSharpening2/ 

cheers

-- 
Jakub Steiner <jimmac gmail com>