[LRflex] Re: Was: Concentration; Now: Colour of light.

Hi David,

Sorry for the "late" reply, as I'm on the digest only. You've received lots
of good information and suggestions from Ted, Etienne, and Aram, so what I
have to offer is a little expansion on your general quest to color correct
the light from various sources. Unfortunately, the link to your comparison
images didn't work this morning, so my comments are very general.

> Date: Wed, 16 Jul 2008 07:03:32 -0700
> From: David Young <dsy@xxxxxxxxxxxxxxx>
> [...]
> The light on the Ball mill side is provided by some sort of lamps,
> the likes of which I've not seen before.  The images have a yellow
> cast similar to that provided to daylight film when shot under
> tungsten light, but much more so.
>
> Experimentation has shown that the colours can be restored to some
> semblance of what I remember by reducing the colour temperature to
> 2000 Kelvin  (my RAW software, Silkypix, will not permit going any
> lower).  However, if I do this, although the colours come closer to
> what I saw, they take on a surreal look. While the mill's walls are
> starting to come close to their "natural" colour, the greens are
> still too weak, and the yellows much too strong.  Not to mention that
> in spots, they disappear all together, when they really were there,
> in the mill!
>
[...]

The main problem is that there has to be color content in order to adjust
it! While many light sources "color" a scene by having spikes at one or more
location in the color spectrum, they also emit light energy across much of
the rest of the spectrum. So, filtering out the spike(s) leaves a more
balanced scene because of the content in the rest of the spectrum.

Light sources that only emit a narrow band of light will not provide
significant illumination (if any) in the rest of the color spectrum, so
there is nothing in the recorded image to adjust! making broad-based
adjustments such as changing the overall color temperature will only result
in filtering the light in the range of the illumination, so the image can
take on a posterized look.

Just as our minds can "fill in the blanks" when viewing a b/w image, the
same happens under other monochromatic lighting conditions. I suspect that
there are details that aren't recorded in the b/w version of your image as
well, but the expectations may be different.

Best regards,

Neil Gould

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