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

[Sean Walker <vze2c3z8@mail.verizon.net>]

Matt, when did you do LRGB?

Sean Walker

> From: Matt BenDaniel <matt@starmatt.com>
> Reply-To: astro-photo@seds.org
> Date: Wed, 10 Oct 2001 10:16:42 -0400
> To: astro-photo@seds.org
> Subject: Re: [APML] New Image: IC 1805 with Nikon Lens
> 
> 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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