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

[Sven Burmeister]

Am Donnerstag, 23. Juni 2011, 11:48:20 schrieb Martin:
> 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 have pictures from a Nikon D90 and a Panasonic LX3, so it might indeed use 
rawspeed for those.

> 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.

You can try this. In digikam, open a RAW image that has visible highlights 
with the demosaicing tool and set highlights to "rebuild" or "blend". You will 
get a very dark image and thus need gamma. In darktable you get the same 
results regarding highlights (or better) but without a dark image or having to 
apply gamma and I would like to understand why because it would make RAW 
demosaicing in digikam easier if it worked as it does in darktable, regarding 
colours and highlights.

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

Yes, it's that base curve. Is this the equivalent of the curve in digikam's 
demosaicing tool? Did you ever use any curves in digikam? When I tried 
handling the points on the curve, i.e. placing them by dragging, seemed very 
hard to me and I often get lines curves that have sharp bends whereas the 
"sliders" in darktable's curve-tool seem to work better for me. If I'm not the 
only one, I would file a request to enhance the usage of digikam's curves.

And I noticed that darktable has presets for different kind of cameras for 
that curve. Having that in digikam would also be helpful I think.

> 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'll try that out. Equaliser did not sound like anything noise-related to me. 
RAW denoise is marked as obsolete which is why I did not try it. The third 
option is not present in my 0.8 package.

Sven