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

[Matt BenDaniel <matt@starmatt.com>]

Chuck,

I agree.  When I do LRGB combine, I take a look at the RGB image's L
channel (after converting to lab mode).  Then I take the hi-rez
greyscale image and, by eye, adjust (i.e. lower) its contrast/brightness
to match the RGB's luminance channel.  Then I paste the new luminance
over the RGB's L channel.  This yields more natural color.

Matt

Chuck Vaughn wrote:
> 
> 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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-- 
Matt BenDaniel
http://starmatt.com

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