[Digikam-users] D-Lightning" tool.

[Jean-François Rabasse]

On Tue, 28 Feb 2012, Robert Zeller wrote:

> I am using Enhance -> Local contrast in the DK editor with fairly good
> results; I don't think that it is possible to implement exactly Nikon's
> dD-Lightning because it is their proprietary knowledge.

Right, using Local contrast (or playing with density curves) gives
similar good results, but it's impossible to reproduce exactly the
original effect, for technical reasons :

Nikon's D-lightning technology is implemented at camera hardware level
and consists of local electronic gain tweaking *before* the analog to 
digital conversion.
Roughly, it works as if we were able to use different ISO settings for 
different parts of the image, e.g. ISO 100 for highlights, ISO 400 for 
mediumlights, ISO 1600 for lowlights.
Thus, the detection can enhance dark parts of the image without 
enhancing (!!) the noise too much (D-lightning increases signal/noise ratio 
in dark areas).
And unfortunately, this can't be achieved after image has been acquired with
a fixed uniform gain and original scene photometry has been degraded.

But, lucky of us, the visual difference between true D-lighting before ADC
and D-lightning-like effects from post processing software, is subtle in 
most cases.
(And for very difficult images, consider using HDR or hand working.)

However, the reverse effect (un-D-lightning ?) is always possible with 
processing software, Local contrast et al. So my personal philosophy
for Nikon owners, is to always have D-lightning set to ON on the camera
and should one dislike the effect for such of such image, one can correct
back to an « almost without D-lightning » result.

Regards,
Jean-François