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

[Chuck Vaughn <aa6g@aa6g.org>]

Rob,

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

I have seen LRGB images that appear to have "normal" color. What
are others doing to achieve this? Is the saturation turned back
up until the color looks "right?" How is the block-up problem
being handled?

I did some of my own experiments with RGB vs. LRGB with some
tricolors. I have some tricolor and B&W (L) photos of the same
objects now. I found that the L image needs to be low contrast
so as not to cause the final image to block up. I could find no
way to bring the LRGB colors back to the colors of the RGB alone
other than increasing saturation of the LRGB image. You have to
be careful though because it is easy to block up the image again
by increasing saturation.

One thing I noticed in my experiments was that the LRGB image
had higher contrast than the RGB image. I found that it was possible
to apply a curve in Photoshop to achieve contrast similar to the
LRGB but without the block-up problem. All that was required was
to fix a point on the curve in the range of 16,16 to 32,32
(depending on the image) and then sharply raise the curve somewhat
above that, say around level 50-60. Some additional raising
at the top end was sometimes useful.

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. 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.

Chuck <aa6g@aa6g.org>

--------------------------------------------------

> Hi,
> I've uploaded a new image of the emission nebula IC 1805.
> This was taken with my F2.8 300mm Nikon Lens at F4 and ST10.
> The luminance was 80 minutes H-alpha and 40 minutes "red filtered",
> RGB= 10:10:10. The image is large so if you're at 56K like me walk
> away from computer for awhile. I kept it large since there's much detail
> in the image. The image is at
> http://robgendler.astrodigitals.com/1805.html
> Enjoy!
> Rob Gendler
> Email: robgendler@att.net
> Web site: http://robgendler.astrodigitals.com


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