LRGB combination in Affinity Photo - Forums

Topic starter

Jun 12, 2021 · Edited: Jun 12, 2021

Hi,

Since Affinity Photo has introduced the stacking feature, I've been working with it more often and also used it for a full LRGB combination process, i.e. combining the channels after stacking into a single image.

There are some online tutorials available including from Serif itself. In their examples, they're using the recolor adjustment and simply set the according tone of the color channel. However, I notice that they're not reducing the luminance to 50%. The effect of this is that saturated data in the respective color channel spills into the other colors. E.g., a saturated star in R would become white with L=100% and hence also the pixels in the G and B become saturated.

To me this approach doesn't seem very helpful since it makes the color balance much more difficult in the later steps. I guess users of Photoshop and Co. would observe the same behavior.

Any comments on this? Do you share my experience and recommendation (i.e., recolor with L reduced to 50%)?

Björn

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Prea

Jun 12, 2021

Hi Björn
I process most of my image in APP application, stacking noise reduction etc and use Affinity Photo for the final process using the layering tool ,curves, levels some colour adjustment and saturation.
I have been doing astrophotography for only 9 months and when I initially used Affinity Photo for stacking and processing the images were not that good.
I found Affinity Photo were having issues with new releases and sometimes the image process was disputed.
Using APP and Affinity Photo I processed my first image with is on Astrobin, the Leo triplet and I thought the colours were ok. I still use Affinity Photo as part of my processing but I don't seem to get the results I want relying solely Affinity Photo.
Affinity Photo is a good system which I intend to keep using as part of my processing I find it to be of use as part of the overall process not the only solution.
I hope it helps and as I said have been in the hobby on 9 months and my way might won't suit everyone and I look forward to learning from others on the forum
Peter

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Björn Arnold

Topic starter

Jun 12, 2021

Hi Peter,

I had a similar experience. I was happy to see the stacking persona in Affinity but in the beginning, it often crashed. Then I tried other applications and I ended up with APP + Affinity.
Just recently, I gave Affinity's stacking another try and produced the Messier 82 image, fully processed in Affinity. Although my experience with the new camera that I used to collect the data wasn't a lot, I think the overall result is "presentable".

Björn

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Prea

Jun 12, 2021

Hi Björn
Yes I have seen you M82 and liked it.
I think Affinity will get better and I intend to keep using it but I think using different systems and taking the parts we need is the best route for me and my final image.
I am just getting set up now for tonight it reported as clear all night where I live, well 3hrs of darkness only.
Peter

Björn Arnold

Topic starter

Jun 12, 2021

Hi Peter,

Thanks for your like!

Indeed, one takes the tools that give the workflow one is most satisfied with in the end (i.e., personal effort vs. result).
I like using Affinity for a full process as well as all steps (except stacking) are manual and I like to understand what's happening behind the curtains and fiddle around with these details.

According to the programmes, there is no darkness anymore at my 49N. Nevertheless, with the bad weather this year, I just don't care. I take what I can get.

Björn

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Prea

Jun 12, 2021

I agree Björn
Clear sky's

Michael Bate

Jun 12, 2021 · Edited: Jun 12, 2021

I watched the Serif tutorial you’re referring too as well and used that approach it for a while for combining my LRGB images but I do reduce the opacity of L normally to anywhere between 50-70% depending on the image.

There’s a slightly long winded approach for creating an LRGB image from individual subs by extracting the corresponding colour channel from each of the separate colour subs and assigning each one to a spare channel, then assigning the corresponding spare channels to the RGB layers in a new pixel layer and then inverting the alpha layer (not sure why this is needed but the colour image doesn’t manifest until after this step). Then I process the L normally and overlay with reduced opacity.

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Björn Arnold

Topic starter

Jun 13, 2021

Hi Michael,

Are you applying the Luminance as a stretched layer or are you combining LRGB and then de-linearise?
I also played around combining stretched L with RGB but there it helps to reduce the opacity as you do. If everything is linear still, I use the 100% and Luminance as blend mode.
there is one caveat (it’s the same for Affinity and Photoshop): everybody talks about luminance but one needs to be careful which definition is used. Affinity and PS use Luma which weighs the RGB channels to compute a „luminance“ value. Therefore, applying a luminance layer gives a color cast.

To your second method: that’s exactly doing what the recolor does by reducing luminance to 50%. You don’t need spare channels. For the red layer, you only need to delete the G and B channel. Respectively the same for the G and B. Blend mode is Add (like with recolour).
I would assume that the new pixel layer has an Alpha that’s is completely white which makes it transparent? I‘ll look at it myself the next time I‘ve Affinity at hand.
The recolour adjustment has a nice advantage: if you want to create HOO (or a flavor of it), you‘d assign Red (H=0 degree) to Ha and the tone of the O3 wavelength(H=153 degree) to the O3 data and voila.

There would be one significant improvement for the stacking: allow drag and drop for the files. The navigation is sometimes a bit annoying.
Also I wished that they’d extend the stacking settings a bit to the industry standard (I.e., there is no winsorized clipping)

But overall: it’s an excellent image editing application!

Björn

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Michael Bate

Jun 13, 2021

100% agree it's a great application and Serif are developing more astrophotography specific features which i hope continues with future releases.

I'll stick with the recolour method in that case then if there's no benefit as recolour is much quicker.

Re. when i add lumanince, i normally add as a stretched layer onto a combined RGB that I've finished processing rather than delinearising LRGB after combining. This is because I do additional processing to L, especially on sharpening and noise reduction and also tend to blur my rgb to soften the colour noise. I add L layer with luminosity blend mode and adjust opacity as well, how do you approach LRGB combination in your workflow, any tips?

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Björn Arnold

Topic starter

Jun 13, 2021

Michael Bate:
I add L layer with luminosity blend mode and adjust opacity as well, how do you approach LRGB combination in your workflow, any tips?

In most of the cases, I did the stacking and LRGB combination in APP including gradient removal, color calibration, stretch and some saturation. After this, I export a 16bit TIFF and work on this in Affinity (additional tone corrections, saturation, denoising, etc.).

When I stack everything in Affinity, I do the LRGB combination in the way of the youtube tutorials from Affinity (except that I set L=50% in the recolor adjustment). Then, the channels are all combined in linear fashion (incl. L in Luminance blend mode) and afterwards the stretch + cosmetic work.