[ptx] Display gamma (was:Vignetting correction in nona)

[douglas wilkins]

Hi there!

--- Pablo d'Angelo <pablo.dangelo at web.de> wrote:

> Hi Doug,
> 
> >>Wouldnt Display gamma be a toppic to do together with colour management, as
> > 
> > Douglas Wilkins allready planed?
> > 
> > I would have thought so :-)
> > And now that 0.5 has been released, I think it is time to put some thought into
> > the colour management in hugin.
> > 
> > As I see it, there are two areas that need to be addressed. Firstly, ensuring
> > that embedded ICC profiles are passed through correctly. Unlike an normal image
> > editing application, there is no need for hugin to modify the embedded ICC
> > profile or add one if there is no profile. 
> 
> This is the most important thing, I guess. Enblend already supports this. 
> I'd like to add this soon, but I have both enblend and hugin contain their 
> own, forked version of the vigra library, especially of the image loading 
> functions. I've started to get the modifications back into the main vigra 
> distribution, and hopefully I'll have enought time to do so in the next 
> month. Then it should be quite simple to add support like that.

Andrew has only implemented the "pass-through" of ICC profiles for tiff images, but the
framework is in place in his code for other types of images. Pass-through for jpeg images
should be relatively easy to implement as well. My thought was to extract the relevant code
from enblend, incorporate it into hugin and extend it as neccessary. These changes could then
possibly be merged upstream as a whole. 
 
> 
> > Secondly, to colour manage the actual images in hugin for accurate display.
> > Modifying the display gamma "on the fly" would fall into this area I guess.
> > Again, hugin is slightly different and would probably only require an input and
> > display profile since we are not doing any colour manipulation, but I welcome
> > input on this.
> 
> Actually since hugin is not really a photo editor it is not terribly 
> important that the color display is 100% accurate, but if it can be done 
> easily (and without performance issues), why not.
> I guess it would mean that the displayed images need to be transformed with 
> lcms while loading. Shouldn't be too hard to add.

Not at all hard :-)
As far as the performance is concerned, I'd have to do some tests, but I would not expect a
large performance hit.

> 
> I'm not an expert in color management, but for stuff like the vignetting 
> correction it would be great to work with a linear (intensity proportional 
> to gray values) image.
> It would be nice if the image could be transformed into a linear colorspace 
> for this. I'm not sure if this can be done if images with good input 
> profiles are given.

Indeed it could be done, and even if we don't have a good input profile, an assumed sRGB input
profile should give reasonable results

> 
> > Finally, I was thinking of using lcms for the colour management, mostly because
> > I am familiar with it ;-), but also because it is reasonably mature and
> > complete. It will add an additional dependancy though.
> 
> Hmm, shouldn't be that bad, lcms is not an exotic library.
> 

And works on all of the supported platforms :-). 

regards,
Doug



	
	
		
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