You are not logged in. [Login] Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar

Astrophotography and Sketching >> CCD Imaging & Processing Previous   Index   Next   Threaded

Pages: 1 | 2 | 3 | (show all) Peter in Reno Post Laureate Reged: 07/15/08 Loc: Reno, NV Re: Do we need Luminance for imaging? or only RGB? [Re: Inverted]       #5681594 - 02/15/13 02:03 PM Edit   Reply   Quote Quick Reply   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:       Inverted sage Reged: 01/19/13 Loc: LP Land Re: Do we need Luminance for imaging? or only RGB? [Re: Peter in Reno]       #5681655 - 02/15/13 02:26 PM Edit   Reply   Quote Quick Reply   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:       Peter in Reno Post Laureate Reged: 07/15/08 Loc: Reno, NV Re: Do we need Luminance for imaging? or only RGB? [Re: Inverted]       #5681669 - 02/15/13 02:31 PM Edit   Reply   Quote Quick Reply   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:       Inverted sage Reged: 01/19/13 Loc: LP Land Re: Do we need Luminance for imaging? or only RGB? [Re: Peter in Reno]       #5681697 - 02/15/13 02:45 PM Edit   Reply   Quote Quick Reply   That's stunning. And very interesting usage of SCNR Post Extras:       HunterofPhotons scholastic sledgehammer Reged: 04/26/08 Loc: Rhode Island, USA Re: Do we need Luminance for imaging? or only RGB? [Re: Inverted]       #5682116 - 02/15/13 06:30 PM Edit   Reply   Quote Quick Reply   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:       Alex McConahay Carpal Tunnel Reged: 08/11/08 Loc: Moreno Valley, CA Re: Do we need Luminance for imaging? or only RGB? [Re: HunterofPhotons]       #5682156 - 02/15/13 06:46 PM Edit   Reply   Quote Quick Reply   >>>>>Take a look at Hanny's Voorwerp. Or any of the classic Martians or other little green men. Alex Post Extras:       Inverted sage Reged: 01/19/13 Loc: LP Land Re: Do we need Luminance for imaging? or only RGB? [Re: HunterofPhotons]       #5682184 - 02/15/13 07:09 PM Edit   Reply   Quote Quick Reply   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:       Inverted sage Reged: 01/19/13 Loc: LP Land Re: Do we need Luminance for imaging? or only RGB? [Re: Alex McConahay]       #5682186 - 02/15/13 07:10 PM Edit   Reply   Quote Quick Reply   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:       pfile Carpal Tunnel Reged: 06/14/09 Re: Do we need Luminance for imaging? or only RGB? [Re: Inverted]       #5682281 - 02/15/13 08:24 PM Edit   Reply   Quote Quick Reply   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:       neptun2 professor emeritus Reged: 03/04/07 Loc: Bulgaria Re: Do we need Luminance for imaging? or only RGB? [Re: pfile]       #5682759 - 02/16/13 02:26 AM Edit   Reply   Quote Quick Reply   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:       mmalik Carpal Tunnel Reged: 01/13/12 Loc: USA Re: Do we need Luminance for imaging? or only RGB? [Re: kfir Simon]       #5682886 - 02/16/13 07:04 AM Edit   Reply   Quote Quick Reply   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:       Inverted sage Reged: 01/19/13 Loc: LP Land Re: Do we need Luminance for imaging? or only RGB? [Re: neptun2]       #5682967 - 02/16/13 08:40 AM Edit   Reply   Quote Quick Reply   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:       neptun2 professor emeritus 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 Edit   Reply   Quote Quick Reply   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:       bill w Postmaster Reged: 03/26/05 Loc: southern california Re: Do we need Luminance for imaging? or only RGB? [Re: Inverted]       #5683361 - 02/16/13 12:04 PM Edit   Reply   Quote Quick Reply   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:       blueman Vendor Blue Sky Accessories Reged: 07/20/07 Loc: California Re: Do we need Luminance for imaging? or only RGB? [Re: blueman]       #5683564 - 02/16/13 01:49 PM Attachment (4 downloads) Edit   Reply   Quote Quick Reply   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:       blueman Vendor Blue Sky Accessories Reged: 07/20/07 Loc: California Re: Do we need Luminance for imaging? or only RGB? [Re: blueman]       #5683569 - 02/16/13 01:52 PM Attachment (4 downloads) Edit   Reply   Quote Quick Reply   Here is the Synthetic Luminance, small size due to image size constaints. Blueman Post Extras:       kfir Simon Vendor-PowerNewt Reged: 09/21/10 Re: Do we need Luminance for imaging? or only RGB? [Re: blueman]       #5684646 - 02/17/13 05:24 AM Edit   Reply   Quote Quick Reply   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:       Pages: 1 | 2 | 3 | (show all)

Previous   Index   Next   Threaded

Extra information 22 registered and 38 anonymous users are browsing this forum. Moderator:  Oldfield, bilgebay  Print Thread Forum Permissions       You cannot start new topics       You cannot reply to topics       HTML is disabled       UBBCode is enabled Thread views: 1544 Jump to *Announcements and News* -----   Cloudy Nights Announcements   Discussion of CN Articles, Reviews, and Reports   Celestial Events*General Astronomy* -----   Beginners Forum   General Observing and Astronomy   Outreach   Light Pollution*Equipment Discussions* -----   ATM, Optics and DIY Forum   Binoculars   Binoviewers   Cats & Casses   Classic Telescopes   Equipment   Eyepieces   Mounts   Observatories   Reflectors   Refractors    Video and Electronically Assisted Astronomy*Astrophotography and Sketching* -----   Beginning and Intermediate Imaging   Film Astrophotography   DSLR & Digital Camera Astro Imaging & Processing   CCD Imaging & Processing   Solar System Imaging & Processing   Sketching   Astro Imaging/Sketching Contest *Observing* -----   NEO   Planetary and Solar System Observing   Lunar Observing   Deep Sky Observing   Double Star Observing   Solar   Variable Star Observing and Radio Astronomy*Telescope Specific Forums* -----   Celestron NexStar    NexStar GPS / CPC Telescopes   Questar Forum   Meade ACF/RCX / LX / GPS    Meade ETX*Speciality Forums* -----   Arizona Science and Astronomy Expo   NEAF (Northeast Astronomy Forum) and NEAIC (Northeast Astro Imaging Conference)   AstroArt   Astronomy Clubs and Star Parties   Astronomy Software & Computers   AstroWebsites   Science! Astronomy & Space Exploration, and Others   Space Rocks   Stellar Media*Swap and Shop* -----   Shop and Swap Audio Components*CN Feedback and Vendor Announcements* -----   Vendor and Group Announcements*International Year of Astronomy 2009 - Forums are now closed.* -----   IYA Archive Info

CN Forums Home