Image stacking/Merging

[Tutster]

Hello. I'm new to Affinity having recently bought Affinity Photo, and to this forum but could I please get some advice from someone?

I plan to do some astrophotography soon which will entail taking several shots. I then plan to edit them and then stack or merge the images together to form one image. My question is, is there a limit to how many images can Affinity edit simultaneously and then how many can be stacked or merged together?

 

Many thanks in advance.

[Callum]

Hi Tutster,

 

Welcome to the forums

 

As far as I am aware there is no limit built into the software as to how many photos can be edited at once. It will depend on the specifications of your computer. 

 

Thanks

C

[James Ritson]

On 10/11/2017 at 10:30 PM, Tutster said:

Hello. I'm new to Affinity having recently bought Affinity Photo, and to this forum but could I please get some advice from someone?

I plan to do some astrophotography soon which will entail taking several shots. I then plan to edit them and then stack or merge the images together to form one image. My question is, is there a limit to how many images can Affinity edit simultaneously and then how many can be stacked or merged together?

 

Many thanks in advance.

 

Hi Tutster, I've created and edited 40-50 image astrophotography stacks without issue (using preprocessed 16-bit TIFFs). Whether you're stacking for noise reduction (Mean/Median) or for a star trail effect (Maximum), I would recommend you do a Merge Visible (from the Layer menu), which will create a single pixel layer from your stacked layers, then hide the stacked layer group. It will make editing much smoother, as Photo won't have to re-render your stack every time you change zoom level or add a new layer.

 

The one thing you should be mindful of is memory - the machine I'm using has 24GB RAM so I can comfortably edit large stacks (especially in 16-bit where the memory requirement is much higher). If your document requires more memory than you have installed, you'll find it starts eating into the swap space on your hard drive, which will slow things down considerably.

 

You can check memory usage via the Info panel (go to View>Studio>Info to toggle it) - look at Memory pressure. If it goes near or above 100% you're in trouble  (and it means you'll probably need more RAM if you intend to edit documents that large on a regular basis).

[Tutster]

Hello. Many thanks for the replies. Im hoping to trial merging for a star spiral image and Im thinking its gonna be in the region of about 20 images to start just so can get a feel for it.. Ive only got 4GB RAM so I may struggle a bit but we'll see.

 

Thanks very much again.

[WBRgroups]

I'm hoping I put this in the right topic, but there's a chance since I'm trying to stack a series of shots (between 10 and 50) into a single one for noise reduction (so explicitly no star trails).

The thing is, I can't get the alignment to work. There is absolutely no difference in the outcome, whether I check the box for alignment or not.

On the one hand, that creates the kind of nice star trails I often see around here, but that is exactly the opposite of what I was trying to achieve.

I tried different kinds of shots (few stars or a lot of stars in the frame) and various filetypes (raw / tiff / jpeg). I also tried the two different options concerning the alignment. The outcome is always the same: No alignment at all (Please see attached picture. The mode in the layer stack is set to maximum on purpose so you can see the startrails I didn't want to create). I'm pretty sure I'm doing something wrong. Maybe someone can help me with this. Please =)

 

[John Rostron]

One possible problem is the contrast is insufficient for the alignment algorithm. Could you boost the contrast before trying to align?

Another possibility which other astro-stackers in this forum have had is that there are objects on the horizon which, although they are a different shade of black from the sky, they seem to be the subjects that the alignment algorithm focusses on. If these are present, perhaps you could

• either reduce the contrast in the shadows (using Curves or Levels),
• or you could try blurring the edges of these objects.

You might have to use batch processing. This should work for using Curves or Levels, but probably not for blurring.

John

[WBRgroups]

Thank you John for the quick reply.

I think there are no other objects within the frame, so the alignment algorithm should not be confused by that. Or at least I could not find those objects.

Enhancing contrast before stacking sounds like a smart thing to do. I'm going to try that and report back. Thank you!

[WBRgroups]

Well unfortunately, enhancing contrast before stacking didn't do the trick, please see screenshot.

I used batch processing to apply a recorded macro to 10 pictures so they would have sufficient contrast.

I included the resulting images. Maybe you could check if they are so particularly bad, they are unusable for stacking with AP.

And if you can get them to be aligned properly, please let me know how you did it =)

Thank you!

ND5_0084.tif

ND5_0085.tif

ND5_0086.tif

ND5_0087.tif

ND5_0088.tif

ND5_0089.tif

ND5_0090.tif

ND5_0091.tif

ND5_0092.tif

ND5_0093.tif

[John Rostron]

I stacked your thirteen images and aligned by hand. Because of the subject matter, it did not take much time at all. I then averaged them by setting the opacities to 1/13, 1/12... and merging the layers. I also increased the contrast in the final image. Works well for this set, but I would guess it would be much more fiddly for 30-40+ images!

John

 

[WBRgroups]

Thank you so much! I greatly appreciate this. How did you align the images by hand? I thought about zooming in on one star (or star trail) and then pretty much dragging and dropping the other layers on it, so the positions match.

I‘m going to try this tonight with a large stack of 50 images. It‘s a pity though, that AP can‘t do this with the automatic alignment of layers.

I‘m going to report back, when I‘m done dragging and dropping lots of layers =)

Thank you again, John.

[John Rostron]

I opened the first image, labelling the layer 84, and zoomed in; then for each of the others:

1. I named the layer with a number (85 ...)
2. I selected and copied the layer (Ctrl-A, Ctrl-C)
3. I pasted this onto my start image (Ctrl-V), and reduced the opacity to 50%
4. I selected the move tool, then re-positioned the top layer so that the brightest star was superimposed.

I then adjusted the opacities to average the layers. (100%/13, 100%/12, .... 100%/2, 100%)

 

John

[lepr]

.

[John Rostron]

7 minutes ago, owenr said:

Another way that doesn't require setting a diminishing opacity for each layer is to create a new Live Stack document with all the images but with alignment disabled so the software doesn't waste time trying and failing to align.

Set the Live Stack's mode to one where you clearly see the superimposed images, such as Total or Standard Deviation, and then drag each image into alignment.

Finally, set the mode to Mean to average away the noise.

 

I recall trying to manually align layers in a Live Stack some time ago and I could not get it to work. It could well be that it now works as you describe. It is easier to align if you just have the one visible layer that is out of alignment. This means that you would need to set all layers but the bottom one to invisible, then make each layer visible in turn.

John

[lepr]

.

[John Rostron]

14 minutes ago, owenr said:

I found it very easy to align the stars with all layers visible as long as a suitable mode was in effect, such as Max or Total or Standard Deviation, and being well zoomed in.

 

I shall try it and see.

John

[WBRgroups]

Thank you all for the greatly appreciated input. I tried both methods and they both work with a nearly identical outcome (at least to my eyes).

The only thing I stumbled upon is that my Macbook gets seriously slow when I use the manual alignment in a live stack method by owenr. Maybe thats just my machine, but it seemed to me, that using separate layers like John does is somehow easier on the hardware resources, because not all images need to be visible at the same time.

Here's what I ended up with after stacking 50 shots and some final fiddling around =)

 

[lepr]

.

[WBRgroups]

Yes, of course, I did not think of it that way (duh...). I had all layers visible when dragging the images in the live stack. When I did it layer by layer, only two were visible at the same time. Thank you for this insight!

[Guest]

Try Deep Sky Stacker (free) to do your stacking, then edit in Affinity.

[RogerWehage]

If the image averaging process is linear it seems that one should be able to divide a set of images into a few groups and first average each group. Then average the resulting set of averages into one final average. Has anyone done this or is there some reason why this would not work?