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

[Chuck Vaughn <aa6g@aa6g.org>]

Gene,
 
> 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.

I have run the tests for my filters and LRGB makes pink nebulas so
I don't think that's the problem. What I think the problem is that
saturation needs to be increased along with Luminance. Increasing
Luminance alone de-saturates the image.
 
> 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.

I don't know about this. I'm sure the people at Adobe have a good
rationale why they implemented it as they did.
 
> 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.

Yes, I am aware of that but I'd still like to see a real RGB.
 
>> 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.

That's why I said "RGB of some sort." I didn't mean true color.
I meant they don't do LRGB.

Chuck <aa6g@aa6g.org>


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