Return to the Cloudy Nights Telescope Reviews home page


Astrophotography and Sketching >> CCD Imaging & Processing

Pages: 1 | 2 | 3 | (show all)
Peter in Reno
Postmaster
*****

Reged: 07/15/08

Loc: Reno, NV
Re: Do we need Luminance for imaging? or only RGB? new [Re: Inverted]
      #5681594 - 02/15/13 02:03 PM

You might be thinking of PixInsight's SCNR which removes unwanted green cast caused by LP from the images. You can also select to remove red or blue as well with this tool. Be careful when using this tool because it can also remove "good" green as well.

Peter


Post Extras: Print Post   Remind Me!   Notify Moderator  
Inverted
sage
*****

Reged: 01/19/13

Loc: LP Land
Re: Do we need Luminance for imaging? or only RGB? new [Re: Peter in Reno]
      #5681655 - 02/15/13 02:26 PM

Yeah, that's it. And I'm not providing any opinion or recommendation, just describing how it is described in the PI documentation.
http://pixinsight.com/doc/legacy/LE/21_noise_reduction/scnr/scnr.html

From it:
"The rationale for SCNR is quite simple. We know that, with the exception of some planetary nebulae, there is no green object in the deep-sky. There are no green stars. Emission nebulae are deeply red. Reflection nebulae are blue. Oxygen III emission corresponds to a mix of blue and green. We may conclude that if we find green pixels on a color balanced, deep-sky astrophoto, they are noise. Fortunately, removing green noisy pixels from most deep-sky images is not difficult and can be accomplished very efficiently."


Post Extras: Print Post   Remind Me!   Notify Moderator  
Peter in Reno
Postmaster
*****

Reged: 07/15/08

Loc: Reno, NV
Re: Do we need Luminance for imaging? or only RGB? new [Re: Inverted]
      #5681669 - 02/15/13 02:31 PM

I use SCNR to remove excessive green when I was processing Hubble Palette of Bubble Nebula since Ha is mapped to Green channel. You can adjust the amount of green to reduce. This simple tool did a neat trick. You can see my result at Bubble Nebula in HST .

Peter


Post Extras: Print Post   Remind Me!   Notify Moderator  
Inverted
sage
*****

Reged: 01/19/13

Loc: LP Land
Re: Do we need Luminance for imaging? or only RGB? new [Re: Peter in Reno]
      #5681697 - 02/15/13 02:45 PM

That's stunning. And very interesting usage of SCNR

Post Extras: Print Post   Remind Me!   Notify Moderator  
HunterofPhotons
Pooh-Bah


Reged: 04/26/08

Loc: Rhode Island, USA
Re: Do we need Luminance for imaging? or only RGB? new [Re: Inverted]
      #5682116 - 02/15/13 06:30 PM

Quote:

.... We know that, with the exception of some planetary nebulae, there is no green object in the deep-sky. ....




Take a look at Hanny's Voorwerp.

dan k.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alex McConahay
Carpal Tunnel


Reged: 08/11/08

Loc: Moreno Valley, CA
Re: Do we need Luminance for imaging? or only RGB? new [Re: HunterofPhotons]
      #5682156 - 02/15/13 06:46 PM

>>>>>Take a look at Hanny's Voorwerp.

Or any of the classic Martians or other little green men.

Alex


Post Extras: Print Post   Remind Me!   Notify Moderator  
Inverted
sage
*****

Reged: 01/19/13

Loc: LP Land
Re: Do we need Luminance for imaging? or only RGB? new [Re: HunterofPhotons]
      #5682184 - 02/15/13 07:09 PM

Quote:

Quote:

.... We know that, with the exception of some planetary nebulae, there is no green object in the deep-sky. ....




Take a look at Hanny's Voorwerp.

dan k.




They mentioned O-III in the paragraphs I quoted "Oxygen III emission corresponds to a mix of blue and green. "

If I remember correctly, it tends to fall end up registering twice in OSC cameras for that reason, because it ends op on the blue and green pixels. So, that is sort of a false color even without luminance as your doubly counting it (or triply maybe as green is counted twice on an OSC). So, there is false color without a luminance layer


Post Extras: Print Post   Remind Me!   Notify Moderator  
Inverted
sage
*****

Reged: 01/19/13

Loc: LP Land
Re: Do we need Luminance for imaging? or only RGB? new [Re: Alex McConahay]
      #5682186 - 02/15/13 07:10 PM

Quote:

>>>>>Take a look at Hanny's Voorwerp.

Or any of the classic Martians or other little green men.

Alex




Everyone knows that's a myth, the Martians are grey duh


Post Extras: Print Post   Remind Me!   Notify Moderator  
pfile
Post Laureate


Reged: 06/14/09

Re: Do we need Luminance for imaging? or only RGB? new [Re: Inverted]
      #5682281 - 02/15/13 08:24 PM

oh on the PI thing, it actually extracts L* which is the perceptual lightness. if you leave your rgb image in it's original weighting and gamma then L* is as in the CIE model. but by setting the rgb weights to 1:1:1 you get something closer to luminance, rather than being green weighted to match the response of the human eye.

Post Extras: Print Post   Remind Me!   Notify Moderator  
neptun2
scholastic sledgehammer


Reged: 03/04/07

Loc: Bulgaria
Re: Do we need Luminance for imaging? or only RGB? new [Re: pfile]
      #5682759 - 02/16/13 02:26 AM

In photoshop you can easily control the ratios of R, G, B, yellow, cyan and magenta. Every channel can be set from -200 to +300%. The default configuration is as follows:

R - 40%
Yellow - 60%
G - 40%
Cyan - 60%
Blue - 20%
Magenta - 80%

This is maybe the so called "visual" convertion. There is also option for 0% on all channels called "Maximum black" which looks like the 1:1:1 ratio. There are also other presets and you can create and save your own. All this is accessible from Image->Adjustments->Black & White menu. This is with latest photoshop cs6. I don't know if the older versions have all these options.


Post Extras: Print Post   Remind Me!   Notify Moderator  
mmalik
Postmaster
*****

Reged: 01/13/12

Loc: USA
Re: Do we need Luminance for imaging? or only RGB? new [Re: kfir Simon]
      #5682886 - 02/16/13 07:04 AM

Quote:

Do we need Luminance for imaging? or only RGB?




According to an S&T article (Dec. 2012, page 71)...

"You create the color image by aligning and combining these (RGB) color-filtered stacks into a master RGB image called chrominance.

Although the chrominance image provides the beautiful color, it's the luminance image (shot without color filters) that can contribute some of the sharpest detail."


Post Extras: Print Post   Remind Me!   Notify Moderator  
Inverted
sage
*****

Reged: 01/19/13

Loc: LP Land
Re: Do we need Luminance for imaging? or only RGB? new [Re: neptun2]
      #5682967 - 02/16/13 08:40 AM

Quote:

In photoshop you can easily control the ratios of R, G, B, yellow, cyan and magenta.




For sure, but then you have "false color". As mentioned we can think of an image in 2 parts, luminance and chrominance. An nebula or galaxy etc.. has a certain ratio of color "chrominance". And we then perceive that color based on the relative intensities and sensitivity of our eyes to that color this is "luminance.

So, by definition, an image should have a certain amount of luminance which by definition should match "chrominance" in a specific ratio. In our hobby we modify luminance (and "chromonance") to enhance visualization of features and detail in the image. So, I think we are really generally always working with "false color" images. That is why I don't think there is a strong argument to using RGB to begin with and extracting the luminance (unless you just prefer processing that way, or like the results better).. Unless we only do a linear stretch of the data, equally on all channels (once white balanced), and maintain the luminance in a 3:59:11 ratio, then we really do have false color.

So, there are two benefits to using L i think. If we collect a separate luminance image, this allows us to increase the SNR of the image, as no light is being blocked by the filters for the L. And two, we can work on a luminance image, which is essentially adjusted to remove the limitations of our vision. with respect to sensitivity to and perception of certain colors.

So, yeah, we do sort of end up with a false color image, but I seems that the way we proccess images in the hobby, we do regardless. Also, as mentioned, we are again only really increasing the SNR of the L, not the color, but do we care if it looks better? The L is where the detail is, and the RGB is distorted either ways.... So, to me, I'm perfectly happy distorting it a bit more to sample the detail a bit better.


Post Extras: Print Post   Remind Me!   Notify Moderator  
neptun2
scholastic sledgehammer


Reged: 03/04/07

Loc: Bulgaria
Re: Do we need Luminance for imaging? or only RGB? [Re: Inverted]
      #5683162 - 02/16/13 10:30 AM

Yes i completely agree that luminance should be used. I wonder if we will get any improvement if we extract another luminance from the combined R + G + B channels with 1:1:1 ratio and stack it with the normal luminance creating one let's say "super luminance". After this we can normally process the "super luminance" and RGB frames as ususal. I think that the added "color" luminance should create higher SNR combined "super" luminance. Of course this will be valid only if you take L , R , G and B frames with equal rsolution and duration and not binned the color.

Post Extras: Print Post   Remind Me!   Notify Moderator  
bill w
Postmaster
*****

Reged: 03/26/05

Loc: southern california
Re: Do we need Luminance for imaging? or only RGB? new [Re: Inverted]
      #5683361 - 02/16/13 12:04 PM

Quote:

Quote:

Quote:

.... We know that, with the exception of some planetary nebulae, there is no green object in the deep-sky. ....




Take a look at Hanny's Voorwerp.

dan k.




They mentioned O-III in the paragraphs I quoted "Oxygen III emission corresponds to a mix of blue and green. "





if memory serves, the voor werp is "red shifted" towards pure green

clearly an exception to the rule


Post Extras: Print Post   Remind Me!   Notify Moderator  
blueman
Photon Catcher
*****

Reged: 07/20/07

Loc: California
Re: Do we need Luminance for imaging? or only RGB? new [Re: blueman]
      #5683564 - 02/16/13 01:49 PM Attachment (5 downloads)

Here is an RGB image, using the RGB to make luminace in CCDStack using my own process.

I can not compare it to LRGB, but I have done that with other images and I can not tell the difference.

The synthetic luminance is from 63 10 minute RGB images.

http://www.astrophotogallery.org/showfull.php?photo=10984

Blueman


Post Extras: Print Post   Remind Me!   Notify Moderator  
blueman
Photon Catcher
*****

Reged: 07/20/07

Loc: California
Re: Do we need Luminance for imaging? or only RGB? new [Re: blueman]
      #5683569 - 02/16/13 01:52 PM Attachment (6 downloads)

Here is the Synthetic Luminance, small size due to image size constaints.
Blueman


Post Extras: Print Post   Remind Me!   Notify Moderator  
kfir Simon
Vendor-PowerNewt


Reged: 09/21/10

Re: Do we need Luminance for imaging? or only RGB? new [Re: blueman]
      #5684646 - 02/17/13 05:24 AM

Thank you all for such great inputs.
As I understand, it isn't as "Black and White" in favor of LRGB over RGB as I suspected in the beginning.

Keep on the good ideas!

Kfir


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
16 registered and 23 anonymous users are browsing this forum.

Moderator:  Oldfield, droid, bilgebay, WOBentley, dr.who 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 2137

Jump to

CN Forums Home




Cloudy Nights Sponsor: Astronomics