RGB contribution from individual photos in a stack

[bruceleonard]

I've spent hours searching for this idea both here and on the greater interweb without success, but if I'm duplicating something I've missed please point me to it.  My other caveat is I'm totally new to trying any sort of sophisticated post-processing.  To date the extent of my "lab" work has been adjusting contrast, exposure, color levels, etc., so please keep in mind that I probably won't understand technical discussions without some supporting explanation.  My apologies and thanks.

So, to the crux of the matter.  I want to combine in some way 3 separate photos of the same scene (I don't care RAW or JPEG at this point though I've been working in RAW) such that each photo contributes only one color channel (red, green or blue) to the final composite image.  The end result being that if I shot three photos of a completely static scene, then the final composite image would be indistinguishable from any of the 3 original photos rendered in full color.

I've tried stacking them and then "turning off" 2 of the 3 channels on each photo, but I don't think I've actually "turned them off" in a contribution sense, I think I've just picked one of the channels to view by clicking the eyeball icon in the channels panel.  I've read that I need to convert them to greyscale first, but I don't understand how removing all the color information from 3 individual photos and then stacking them could possibly result in a color image.  When I try what I think is being described I just get a black result.  I've also played with (without really understanding what I'm doing) trying to create a spare channel from just one color channel for a photo and then applying (again I think) a greyscale mask layer(?) to the photo using the spare channel.  Then I just end up with a white image.

I know what I'm trying to achieve is possible, there was an article on one of the photo news/collaboration sites a couple of years ago describing this technique.  But I failed to save it, can't find it now and just don't know enough about what I'm doing to be able to form the query in such a way as to get the internet to cough anything up.

Thank you for any pointers or tips anyone can provide.  And thank you to Serif for creating such a wonderful alternative to Adobe which is really out of the price range of hobbyists such as myself.  I've really enjoyed working with Affinity so far and am looking forward to learning how to use it in depth.

[Old Bruce]

Open the pictures you as red, green and blue Save them as xxx-Red.jpeg xxx-Green.jpeg xxx-Blue.jpeg you should note the name of the layer, it will be Background for the rest of my explanation.  Go to the channels panel (for each of the Red Green and Blue pictures) and make sure the Pixel Selection channel is Black. Make a spare channel from that, it should be black, it has to be black.

Replace the Red Background layer's Green and Blue Channels with the black Spare Channel, do this by right clicking on the Spare Channel and choosing from the pop-up context menu. Do the same for the Green and Blue pictures. You now have three pictures one is Red etc. Make a new document and place the three then use blending of the layers or changing the transparency to your liking.

[lepr]

20 hours ago, bruceleonard said:

I want to combine in some way 3 separate photos of the same scene (I don't care RAW or JPEG at this point though I've been working in RAW) such that each photo contributes only one color channel (red, green or blue) to the final composite image.  The end result being that if I shot three photos of a completely static scene, then the final composite image would be indistinguishable from any of the 3 original photos rendered in full color.

I've tried stacking them and then "turning off" 2 of the 3 channels on each photo, but I don't think I've actually "turned them off" in a contribution sense, I think I've just picked one of the channels to view by clicking the eyeball icon in the channels panel.  I've read that I need to convert them to greyscale first, but I don't understand how removing all the color information from 3 individual photos and then stacking them could possibly result in a color image.  When I try what I think is being described I just get a black result.

Instead of disabling visibility or editability of channels of the document, you need to clear two channels of each image (when they are Pixel objects rather than Image objects) and then add the images together. When a Pixel object is selected, the Channels panel will list the channels of the Pixel object below the channels of the document composite. Right-clicking a channel of the Pixel object will pop open a menu where you can choose to clear that channel.

I've attached a macro that will do it all for you. Simply stack the three photos (as Image or Pixel objects) so the bottom one is to be the red contribution, the middle one is to be green and the top one is to be blue, and then run the macro.

RGB additive stack from 3 images.afmacro

 

[thomaso]

19 hours ago, bruceleonard said:

I've tried stacking them and then "turning off" 2 of the 3 channels on each photo, but I don't think I've actually "turned them off"

Just in case: An Affinity article about channels:  https://affinityspotlight.com/article/channels/

At its bottom a the list of tutorials, one about a quite complex workflow:
(which in a way also appears as a CMY separation)

"Manipulate an image's red, green and blue channels to emulate the Technicolor 3-strip process."
https://www.youtube.com/watch?v=y3ZBB4B7LH8&feature=youtu.be
 

33 minutes ago, anon2 said:

I've attached a macro that will do it all for you. Simply stack the three photos (as Image or Pixel objects) so the bottom one is to be the red contribution, the middle one is to be green and the top one is to be blue, and then run the macro.

 Handy macro, thank you!

[lepr]

22 minutes ago, thomaso said:

Handy macro, thank you!

You're welcome

 

[Lisbon]

Hi bruceleonard!

"I want to combine in some way 3 separate photos of the same scene"
Ok. But doing that by reconstructing the RGB channels can cause huge shifts in colour.

"I've read that I need to convert them to greyscale first"
That is one way of doing it. I will use a different way.

A) Select your top layer (first photo in stack).
B) Go to channels and fill with white the channels you want to "discard". In the example i kept the Green channel and filled with white, the Red and Blue channels.
After that, don't forget to press reset.

C) Turn off the visibility off your top layer and select the next layer.
D) Repeat step B) but this time "keep" a different channel.
E) After the 3 layers have been edited change top and middle layer to multiply.

For this to work you have to keep intact one Red, one green and one blue channel.
From top to bottom layer, it doesn't matter the order, you could have RGB, GRB, BRG,...

Good luck 🙂

 

[bruceleonard]

Thanks everyone for the great information!  I will definitely give all of these a try and report back on what I find.

[bruceleonard]

Good evening everyone,

My apologies for not getting back sooner, I work remotely from the machine that I run Affinity on and I had a power outage at that location which took down my router, so it took me a while to get things back up.

Anyway, I've tried all the suggestions here, and they all work in different ways to achieve the effect I'm looking for.  I think the best results came from doing it in a stack rather than trying to copy three individual "colorized" pics as Old Bruce suggested.  Doing it in a stack allowed AP to get the alignment between the photos correct so that fringing only showed up around the edge of the final image which could be cropped out.  Copying individual pics into a new document seemed to frequently result in fringing in lots of places within the final image because of subtle shifts in camera position between the shots.  But overall, the final result was much the same with each of the techniques suggested.

I've attached a sample of the effect I'm after.  It's really a poor example because there's really too much movement in the scene, but it gives the idea.  I've seen this technique used to great effect when the scene was a night scape of a city with clouds moving over it where there was a fringe of white-ish to the clouds so that when you finished with the editing you would have some clouds ringed with red, some with blue, and some with green, and where there's overlap between the images you get some really interesting color blends like I did in the attached image.

So thank you all so much for the help!  I should have asked sooner.  I was starting to get frustrated that I couldn't figure it out on my own and was ready to give it up when I found this forum.  Awesome resource!