Re: [APML] New Image: IC 1805 with Nikon Lens

[Gene Horr <genehorr@texas.net>]

Chuck, I'm going to jump in here.

> I couldn't help but notice that the image is pink and portions are
> blocked up. These are typical results from the LRGB process.

>From my limited experience I have seen two problems consistent with
LRGB that may be what is bothering you.  Neither problem is really
an indictment against LRGB itself.

The problem of colour of midlevel pixels (generally the object being
photographed) is generally because very few people run a calibration
test of the exact throughput of each filter.  There are some noteable
exceptions (Al Kelly) but the average imager is more worried about 
vignetting or "dust donuts."  But from what I see there is no reason
why the LRGB process itself should not produce "accurate" colours
as long as the correct ratios for a particular filter set are used.

The second problem has to do with the tools being used.  This mainly
effects star colours.  Photoshop translates a 255 reading (100% @
8 bits) on the L channel as "white" no matter what the RGB ratio
is.  There is supposed to be a workaround, and I have a description
buried somewhere, but I have never tested it myself.  This is why
so many stars in LRGB images have no colour.  But again, this is
not a problem with LRGB itself, but a defect in the software being
used.

> There is one thing I'm still waiting to see from the amateur CCD
> world: a real RGB image, where each exposure is high S/N and of
> the proper exposure ratios. 

Well, but that defeats the main selling point of LRGB.  Laziness <g>.
A proper colour CCD image takes far longer to expose than a film
image.  LRGB allows one to get the exposure times down to below
that which film requires.

> Offhand, I can't remember seeing any
> professional LRGB images. They're always RGB of some sort. It
> must be possible for amateurs to do the same.

But most professional images that I have seen are not RGB either.
They are generally taken in specific narrowband wavelengths and
then translated to RGB.  Their colours are generally not what a
"true" RGB returns.

Gene Horr
genehorr@texas.net

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