[Digikam-users] Re: Processing RAW images to get to the look of the jpg preview

[Martin (KDE)]

Am Donnerstag, 23. Juni 2011 schrieb Sven Burmeister:
> Am Sonntag, 19. Juni 2011, 16:40:26 schrieb Martin:
> > For raw processing I use a specialist in this area (ufraw in the
> > past, darktable since about a half a year). These programs have
> > much more options to get a pleasing photo. All the other stuff
> > (organizing and tagging) I do with digikam.
> 
> I tried darktable and I like the default results. It performs
> better at handling highlights (even when clipping! and even if one
> uses unclipping there is no need to apply gamma) and its colours
> are better. Since if I understood correctly it also uses libdcraw,
> how come its results are better?

Not exactly. Darktable uses two different raw libs (libraw and 
rawspeed). Usage depends on the camera. Raw development is a very 
complex process. I only know part of this, but the main author of 
darktable build a postscript picture of the modules a raw picture will 
pass until it gets a final jpeg. It is big and very 
complicated/confusing but alas it works.

I don't think your problem is gamma only. The gamma curve only depends 
on the colour model you use to view the picture (sRBG, Adobe RBG, 
Apple RGB ...). It should almost never be necessary to adjust this by 
hand. But I have no clue what the problem of digikam is here.

Darktable uses a good sets of defaults and by default the base curve 
is not linear. this may be one main difference.

> 
> Or to put it the other way around. Why do I not have to use gamma
> when working with highlights and why is there no way for me to get
> the colours the same way with digikam's demosaicing?
> 
> I noticed that using the camera's whitebalance shows three sliders
> for the colours, i.e. it seems to read values for red, green and
> blue from the camera's whitebalance. Does digikam maybe fail at
> doing so?

I don't think so. This sliders results from the colour temperature and 
the tint slider, which are present in darktable as well. Internally 
all dcraw based software will use this three colour sets (afaik). But 
it is way to complicated to set these by hand so on most systems the 
temperature (for red-blue) and the tint for green setup is used. 
Usually one value is always set to 1 (in most cases this is green). 
red and blue values are set "relative" to green. If you want to 
increase green you will in fact reduce blue and red.

> 
> Also, there is a noise reduction module but it is labeled as
> obsolete and it seems that there is no other module for noise
> reduction yet the noise reduction works very well nonetheless.

Ah, there is a noise reduction plugin. There are at least three ways 
to reduce the noise.
- Raw denoise
- Equalizer (a preset for denoise is available)
- denoise (very slow) (may be available in git only)

Equalizer is the most complex one thou. Here you can play with luma 
and chroma noise independently.

I don't know if I mentioned it: darktable can store presets of almost 
all modules. So if you took the time to find a really good equalizer 
setup you can store this and later on use this on other photos without 
fiddling with the values.

Regards
Martin

> 
> Sven