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How to pull red channel from one image and blend it into another RGB image in Photoshop

Rudy_Pohl
31 Jan, 2019 20:47
Hi there,

I have just received as a gift a full spectrum modified Canon T3i camera with a clip-in UV/IR filter, and I have been using an unmodified Nikon D5500 camera for astrophotography for two years. I would like to produce an HaRGB image of the Orion and Running Man Nebula in the surrounding dust and other HaRGB images.

I have been advised to pull the Ha (red channel I presume) from the T3i and blend it into the RGB image from the D5500.  The problem is that even though I have lots of experience in Photoshop and Pixinsight, I'm not sure how to do this.

Can someone briefly explain this to me or supply me with a link to a tutorial that explains how to do it?

Thanks very much,
Rudy
dciobota
31 Jan, 2019 23:03
Hi Rudy,

 The easiest for me is to use the channel mixer.  To convert the image to a "monochrome" with red only, open the channel mixer, and for each color choose red at 100 percent, setting all the other colors to zero.  Voila!  Red only as a "monochrome" rgb.

Then you can copy that image and paste it over your RBG image as a luminance layer.

Hope this helps.

Daniel
Rudy_Pohl
01 Feb, 2019 10:33
dciobota
Hi Rudy, The easiest for me is to use the channel mixer.  To convert the image to a "monochrome" with red only, open the channel mixer, and for each color choose red at 100 percent, setting all the other colors to zero.  Voila!  Red only as a "monochrome" rgb.

Then you can copy that image and paste it over your RBG image as a luminance layer.

Hope this helps.

Daniel

Wow, very cool and easy solution!

So just to double-check on this: You take the T3i image and convert it to monochrome all channels red, and then you paste that altered T3i image into the RGB image of my D5500 and set the Luminance blend of the monochrome image layer to Luminance, correct?

Rudy
carastro
01 Feb, 2019 12:59
I would in photoshop, go to the channel's tab and then from the drop down menu (pile of lines), select split channels.  That will split them into Red, Green and Blue, so you can take your red channel and blend it into the images where you want to add the Ha.

You can blend by splitting the channels in the image you want to add it to in the same way.  Add it to the red channel in layers and then use blend mode lighten.
then go back to the channels tab - select merge channel, then select RGB and it will recombine the channels.

HTH

Carole
Rudy_Pohl
01 Feb, 2019 13:17
Hi Carole,

Thanks for taking the time to answer. This sounds like a straightforward and easy solution… I'll try it out later today.

By the way, I had a quick peek at your image gallery and I must say, they are stunning!

Thanks again and best regards,
Rudy
dciobota
01 Feb, 2019 16:34
What Carole said works as well.  Probably more intuitive too, but I keep forgetting about the split channels function.

If you use my example, you don't have to convert the image to monochrome.  When you select all channels in the channel mixer to use red 100% that makes the image monochrome (actually it's rgb with all channels set to the red values).  Then you can vary how much Ha to apply to each color by using levels and adjusting the levels for each channel in the Ha image.

Hope this helps.
Rudy_Pohl
01 Feb, 2019 17:10
Thanks for this Daniel. I will be trying all the various ways that people have suggested to me for doing Photoshop, plus the one way someone gave me for PIxinsight in the Pixinsight forum. Much appreciated.

Cheers,
Rudy
astrobrandy
02 Feb, 2019 09:21
Hi Rudi,

I also tried to mix Ha and red-channel via photoshop and I had used the following informations from Rob Gendler, a well known astrophotographer. Have a look:

                                                                                           http://www.robgendlerastropics.com

I hope that you will find some practical hints for your workflow.

best regards
Stefan
Rudy_Pohl
02 Feb, 2019 22:21
astrobrandy
Hi Rudi,I also tried to mix Ha and red-channel via photoshop and I had used the following informations from Rob Gendler, a well known astrophotographer. Have a look:

                                                                                           http://www.robgendlerastropics.com

I hope that you will find some practical hints for your workflow.

best regards
Stefan

Hi Stefan,

Thanks very much for this link. I read Rob Gendler's article and it is very good.

Best regards,
Rudy
JerHetrick
03 Feb, 2019 11:07
Go into layers panel > channels, select and right click red channel and duplicate. Make sure you select new file from the drop down. Now name and save. You now have a file with only red channel data that you can import into and blend into you RGB image. There are a million and one different blending techiques that you can use to blend that data into the other. This all seems like allot of work for nothing though, because you modified camera is collecting all the data your non-modified camera is collecting then some, it's just that it's collecting a wider spectrum of light than the non modified camera. The red channel from the modified DSLR is not h-alpha data, a portion of it may be , though if you want  h-alpha data specifically you need to use an h-alpha filter, astronomik makes a decent clip in EOS filter actually I believe they manufacture a +-6nm as well as a +-12nm.
Rudy_Pohl
03 Feb, 2019 11:38
Jer Hetrick
Go into layers panel > channels, select and right click red channel and duplicate. Make sure you select new file from the drop down. Now name and save. You now have a file with only red channel data that you can import into and blend into you RGB image. There are a million and one different blending techiques that you can use to blend that data into the other. This all seems like allot of work for nothing though, because you modified camera is collecting all the data your non-modified camera is collecting then some, it's just that it's collecting a wider spectrum of light than the non modified camera. The red channel from the modified DSLR is not h-alpha data, a portion of it may be , though if you want  h-alpha data specifically you need to use an h-alpha filter, astronomik makes a decent clip in EOS filter actually I believe they manufacture a +-6nm as well as a +-12nm.

Hi Jer, thanks so much for your reply, I appreciate it!
Best regards,
Rudy
 
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