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Old 11-05-2011, 06:25 PM
Carl
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RGB and Luminance?

Might sound dumb but I understand where the RGB files and channels come from. But I'm shooting with a DSLR. Where does the Luminance layer or channel come from.
Is it shot with an additional filter then combined in photoshop?

I'm about to get into the buying filters game and any guidance would be appreciated appreciated.

Cheers
Carl
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Old 11-05-2011, 06:38 PM
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Octane (Humayun)
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DSLR's are one shot colour devices, meaning that RGB is captured along with whatever luminance data there is mixed in the one system.

H
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Old 11-05-2011, 06:45 PM
Carl
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L-rgb

Thanks Humayan
Would this mean; for example; that if i were to image a nebula with my modded DSLR using a UV/IR filter then used a 12nm H-Alpha filter to gain vital information in that nebula, would i then introduce the H-Alpha image as a channel or as a layer over my original image?

Any suggestions

Cheers Carl
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Old 11-05-2011, 08:13 PM
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troypiggo (Troy)
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Sounds like you're confusing mono camera techniques and DSLR techniques.

If you use a Ha filter on a DSLR, you're still capturing RGB data, it's just that the majority of that data is in the R channel because that's what the Ha filter is letting through. G and B data will just be noise.

Do you have a colour image and want to use Ha as a luminance layer? If so, just put the RGB image in one layer, the Ha in another. Set the Ha layer blend mode to luminance and the RGB one to colour.
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Old 11-05-2011, 08:27 PM
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You're welcome, Carl.

+1 what Troy said.

H
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Old 11-05-2011, 08:35 PM
Carl
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Combining images

Hi Troy
Thanks for the reply. So am i over complicating the issue? to be honest I just want to get one of those stunning images that we see on our site.

Is it simply a matter of; for example;Creating a finished 5x 5min stack (H-Alpha) and importing that finished file as a layer in Photoshop above my combined RGB image.Then using the layers palate to set the blending mode.

Or is there something special i have to do to create a luminance layer?

I've been using Photoshop for 10 years now and there are always things that dont sink in first, second or sometimes third time round.

regards
Carl
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Old 11-05-2011, 08:42 PM
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You've got the right idea, Carl.

If you had a monochrome system, you could even potentially mix some red into the hydrogen alpha to avoid the composition taking on that pale disgusting salmony-pink appearance that hydrogen alpha introduces as a pure luminance layer.

H
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Old 11-05-2011, 08:44 PM
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Carl

What version of ImagesPlus are you using, if you are using IP4+ you can make a Luminance image to work on using the Split Luminance command under the Colour Menu.

Cheers

Last edited by JohnG; 11-05-2011 at 09:00 PM.
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Old 11-05-2011, 08:48 PM
Carl
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Filters continued

Hi Humayan
I dont have a monochrome camera, mines a single shot DSLR canon modified.
So the H-Alpha will have a horrible Salmon hue, not good. So how do i get around that or am i better off just sticking with my UV/IR filetr

Regards
Carl
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Old 11-05-2011, 11:00 PM
Hagar (Doug)
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Hi Carl, There is a couple of ways to incorporate Ha into a one shot colour frame. No real easy way to get quick and acceptable results though. Using images plus you should be able to separate the luminance layer from the original image. Ha can be blended into this layer using Photoshop. You should also try to blend the Ha into the red channel after separating the RGB channels in IP. This will help to strengthen the red and prevent the image with only Ha in the luminance channel turning quite pink.
You can also blend a small amount of the Ha into the blue and even the green channels in varying amounts to ensure an even spread of colour throughout your image.

Ha blending is not as easy as just blending it into your luminance layer if you want premium results.
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