[Digikam-users] Re: Channel Mixer Question

[Elle Stone]

David, I just used the digikam-edit channel mixer in monochrome mode,
put the red at +200%, green at -200%, blue at -100%, with a tiff
rendered with digikam (saved as "raw" - no input or output profile
applied - the only way I can get the digikam raw converter to work the
way I want it to work) starting with a cr2 raw file.

The image does look IR-ish, kinda cool, but I'm not seeing any unusual
graininess.

I tried the same settings in photoshop, got the exact same results.
Tried again in Gimp - got the tiniest variation in mid-tone tonality,
hardly enough to even mention.

Gilles is right - the red channel is inherently noisier than the green
or blue channel. In cr2 files, at least for my camera, the red channel
is multiplied by a bit more than 2 to get the daylight white balance,
which means there is less information in the red channel to begin with
- it is underexposed compared to green or blue channel. The only way
to reduce that source of graininess is to use a magenta filter (an
honest to goodness physical filter in front of your lens - not a
software filter applied after the fact) to bring down the green
channel. Or shoot multiple exposures bracketing and take the red
channel from the over-exposed image.

Elle