2017-12-22 - shorterimage

Stacked, Aligned and Mean Averaged


In my previous post, Shooting on the Mean Streets of Noise, I went through the procedure on how you stack, align and mean average a series of images into one final composite image. That was done with a couple of quick test shots I made at home. Today I've taken this idea out into the real world to see what can be done in a real way. I've shot some that are on tripod and some that are hand held to get a flavor of what both can achieve.

I decided to try and shoot some moving water to see if you could use the stack, align, mean average technique as a replacement for ND Filters. I was surprised by how well this did. The first shots I made were at somewhat slow shutter speeds so I assumed that helped add blur to the multiple exposures. Then I purposely made another shot using much higher shutter speeds wondering if that would not give good results for water blur when combining multiple images. To my surprise it worked as well. Maybe not quite as much blur which seems normal but I had expected some kind of artifacts to show up making the water movement look objectionable in some way. But not so. The faster shutter speed test came out pretty good I think.


So here's my first real world test of water motion blur using the stack, align, mean averaged technique. This shot above is a composite of 25 images shot on a tripod at f11, 1/13th sec @ ISO 100. I tell you, I really can't tell much difference between the results here and the blur I got shooting some months earlier on this same creek with ND filters and about a 30  second exposure. They really do look quite the same when it comes to the water blur, except for maybe how much blur there is. But I think the quality of the blur is pretty comparable.

Compare this multi-image shot with the next shot below which was shot back mid summer, same creek, Rice Creek, Victoria Bryant State Park, GA, made with high quality ND filters. This shot was either a 25 or 30 second exposure. I think the quality of blur looks pretty comparable but think the multi exposure image probably would have needed another 10 exposures or so to look more identical to the long exposure with ND filters. You need to look past the overall look of the image and just assess the water blur as the image above was made in harsh, near winter solstice light while the image below was made in very nice mid summer light.



Back to the multi exposure method. This shot was 23 exposures, f11, 1/50th sec @ ISO 100 for the sequence. Once again, combined into one image in Photoshop using the stack, align, mean average method. This was shot on tripod.



There's no reason to use multiple exposures for this shot but I wanted to test multi exposures hand held and this park was not too far from our house. This was thirteen exposures hand held, f8, 1/250th sec @ ISO 640. Composite into one image using the stack, align, mean average method in photoshop. I wanted to see if a shot with detail would be reasonably sharp still with multi exposure combined. I think it did pretty well.


And because I wanted to see if it was feasible to do water motion blur using the stack, align, mean average method while hand holding -- a  couple of days later I went up to north GA and made this shot on the Soque River. First thing to know is it's fairly severely cropped because the longest focal length I had with me was 70mm and my shot was much looser than this with lots of extraneous junk. But thanks to the Sony A7RII's 42Mpx resolution I was able to crop it around 50% and still get this acceptably nice image (I think). This is 22 images hand held, combined using the stack, align, mean average method. F8, 1/250th sec @ ISO 640. I'd say not bad at all for hand held but I do think it would take around 35 exposures to get the best quality of blur to match a 30 second single shot with ND filters.


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