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Re: [APML] A Curves Exercise [was: Histograms, curving and layers]
Here is my take on using a curve layer. (My first attempt at using a
separate curve layer)I created a curve layer and adjusted using Curves then
I flattened the image and adjusted the color balance and brightness on the
RGB image and the red channel. I did see that I lost some data at
the dark and light ends on the RED channel of the levels histogram.
http://www.starfillednights.com/image_data/01121504_image_data.htm
Joe Schaefer
----- Original Message -----
From: "Matt BenDaniel" <matt@starmatt.com>
To: <astro-photo@seds.org>
Sent: Thursday, December 05, 2002 1:37 PM
Subject: RE: [APML] A Curves Exercise [was: Histograms, curving and layers]
> Greg,
>
> The levels tool is useful but not as versatile as curves.
>
> Yes, my image is somewhat clipped on the low end. I did that to suppress
grain noise. Perhaps now that I know how to use SGBNR, I should fix the
clipping and deal with the grain by smoothing it away.
>
> To load a curves file, open a curves dialog in PS (Image->Adjust Curves
or Layer->New Adjustment Layer->Curves) and click on the Load button.
>
> Matt
>
> At 13:28 05-12-02 -0500, Greg Hartke wrote:
>
> >This is an excellent exercise to PS neophytes like me and I really
> >appreciate your effort in helping us, Matt.
> >
> >I downloaded both the uncurved and curved image and did some diddling. I
> >confess that after spending some time playing with the curves adjustment
to
> >the individual color channels, I got very frustrated at my inability to
get
> >a good image. I proceeded to go in a direction more familiar to me,
working
> >with levels. This may be the wrong approach but I was curious what would
> >happen. I suspect it's less versatile than curves but I don't enough to
say
> >that for sure.
> >
> >I looked at the information in the individual color channels and adjusted
> >the sliders on the low and high ends so that the range was more
compressed.
> >I moved them on either end such that they were right at the end of the
> >significant parts of the curves. I then adjusted the black point to 15,
15,
> >22 and looked at the result. After comparison to Matt's curved version, I
> >adjusted the center red slider for a little more red. The result was much
> >more like Matt's image, though not identical.
> >
> >I'm sure this isn't the right way, it's just what I could do. An
interesting
> >consequence was that the resulting histograms were all clearly quantized.
I
> >would assume that's the result of a compressed range and working with
only 8
> >bits of info.
> >
> >The curved version had interesting features. Am I mistaken or are the
blue
> >and green histograms clipped at the low end? My efforts resulted in
similar
> >clipping but I thought we were trying to avoid this?
> >
> >I really wanted to look at Matt's curves file but I'm embarrassed to say
I
> >couldn't figure out how to import and look at it. This must be simple but
I
> >couldn't manage it. Matt would you please elucidate? Sigh. Somebody point
me
> >at a command line Unix system so I can grep 'em to death. ;)
> >
> >Thanks.
> >
> >Greg Hartke
> >Sykesville, MD
> >
> >
> >
> >> -----Original Message-----
> >> From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On
> >> Behalf Of Matt BenDaniel
> >> Sent: Wednesday, December 04, 2002 9:39 PM
> >> To: astro-photo@seds.org
> >> Subject: [APML] A Curves Exercise [was: Histograms, curving and layers]
> >>
> >>
> >> Alan,
> >>
> >> The most important skill to master in image processing is curves.
> >> By far, you'll get more bang out of curves than any other tool.
> >> Both Photoshop and PictureWindow have good curves tools.
> >>
> >> I made an exercise for you (and anyone else who might be interested).
> >>
> >> I place an uncurved image of Central Auriga on my web site. Save
> >> the uncurved image onto your disk. Using solely a curves layer,
> >> try to make the color balance and contrast of the uncurved
> >> picture look like my curved one. All you need concern yourself
> >> with at this point is adjusting the R, G, and B curves in a
> >> single adjustment layer. That's it. I already took care of
> >> stacking, AV-ing and star shaping the uncurved image, so you
> >> don't need to worry about any of that with this image.
> >>
> >> Now, I don't claim that this exercise is easy. But if you do it
> >> right, you should be able to make the uncurved image look just
> >> like the curved one on my web page. The link to the uncurved
> >> image is at the bottom of the page:
> >>
> >> http://starmatt.com/gallery/astro/central_auriga.html
> >>
> >> I hope this exercise is helpful to you and others. Please let me
> >> know if you have questions, problems or have results to share.
> >>
> >> Matt
> >>
> >> At 17:45 04-12-02 -0800, Alan Voetsch wrote:
> >> >Hi Matt,
> >> >
> >> >--- Matt BenDaniel <matt@starmatt.com> wrote:
> >> >> Thanks. I'm always looking for suggestions for more
> >> >> articles.
> >> >
> >> >How about: making a copy to work on, setting black
> >> >points (whatever that is), making or using layers. All
> >> >I feel partially proficient at is adjusting contrast,
> >> >lightness and watching how much the image changes as I
> >> >move the curves slider around.
> >> >
> >> >> The order matters a lot. If one layer clips the
> >> >> image, nothing above it in the layer stack will
> >> >> rescue the lost info. I find that an AV layer works
> >> >> best if it is right above the source layer. When
> >> >> doing AV, I'll alternate adjustments to the AV layer
> >> >> and to the main curves layer. Their adjustment is
> >> >> intertwined.
> >> >
> >> >I understand the concept, but this sounds like there
> >> >are a lot of ways to learn a lesson the hard way.
> >> >Maybe another article on the sequential steps to use
> >> >throughout the whole process.
> >> >
> >> >Thanks Matt,
> >> >Alan
> >>
> >> --
> >> Matt BenDaniel
> >> matt@starmatt.com
> >> http://starmatt.com
>
>
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