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  #76  
Old 21st February 2019
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DekHog DekHog is offline
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Re: My latest foray into FF mirrorless - and why I'm sticking with m43

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Originally Posted by pdk42 View Post
OK, maybe a bit of explanation is needed...



1) Stacking of images with the same exposure to reduce noise



When you stack multiple images of the same exposure, you blend them such that each contributes its own proportion to the final image. So, with 4 exposures, each gives 25%. This is performed automatically using "median" blending in Photoshop. You can do the same with pretty much any software that can handle layers with varying opacity, such as GIMP etc. The resulting image will have lower noise, because the random effect of noise means that when stacked it will cancel out. The signal on the other hand will not cancel out.



The end result is that the image noise will be as if the stacked images were taken at a lower ISO. The final effective ISO will be halved for each image stacked - so 8 stacked images will reduce the ISO by 1/2*8 = 1/16. Hence, ISO 6400 will appear like ISO 400.



Another way of looking at this is to imagine that instead of capturing 8 shorter images that you capture 1 longer one. So, 8 images at 1/800 sec each is the same as 1 image at 1/100 sec. It's as if you've increased the exposure and hence reduced the ISO.



So why do it? Well, if the subject is static and you're shooting handheld you will be able to take 8 short shots and keep the subject sharp, but a shot 8 times longer would be blurred due to camera shake.



Doing it is fairly easy and quick on the E-M1ii:



- Use 60-fps electronic shutter

- Set the frame limiter to the desired number of frames

- Press the shutter - you'll capture 8 shots (or whatever) in no time

- Import, align and stack in Photoshop as per Dave's instructions above



Voila!



You can do it on any camera of course, but having a very high FPS and a frame limiter as the E-M1ii does makes it much easier.



Stacking of images with bracketed exposure for HDR



This is more often used of course. In the case, the stacking is more complex since the images need analysing to find the bright and dark areas and the stacking then needs to vary the opacity by these areas. However, it's a technique that works well if done sensitively.





Stacking of images with same exposure to increase resolution



The technique above for reducing noise can be tweaked to increase resolution if there is a little "dithering" between shots (i.e. slight movement of the subject in the image). In this case, you do exactly the same as above, but you upscale the images before stacking. This will increase the apparent resolution since movement of the subject will be across the pixel boundaries resulting in slightly improved resolution when the image is de-mosaiced.



You'll also get noise reduction for the reasons discussed above.



This is what's happening with hand held hi-res. The camera is taking up to 16 shots and arranging for the IBIS to be off between shots to introduce some dither. The upscaling, aligning and stacking is then done in camera to produce a single file. Very clever!



You can do the same using Photoshop, but in my experience of trying it, the resolution increase is not as good as I observed from my playing around with the E-M1x (see my other post on this in E-M1x section).







Hope that helps!
It certainly does help. Thanks, Paul......
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  #77  
Old 21st February 2019
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Re: My latest foray into FF mirrorless - and why I'm sticking with m43

I'll just add that the tripod-variant of hi-res is somewhat different since in that version the camera is using the IBIS to move the subject by pixel-level amounts between 8 separate shots. The stacking is then done using some fancy algorithm that accounts for the CFA (Bayer filter). I assume this will also reduce noise, but I haven't tried looking for it. TBH, I have very seldom used this feature because I find that even slight movement (e.g. wind) ruins the end result. I think it's something that really needs a very good tripod and a studio environment.
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  #78  
Old 6th April 2019
Internaut Internaut is offline
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Re: My latest foray into FF mirrorless - and why I'm sticking with m43

Full frame.... Different format..... Larger format. I suppose itís something many of us need to get out of our systems. My view is that the larger format makes sense if i) you need to shoot in low light or ii) if you need 40+ megapixels of data. I have an A7 II that Iím very happy with, in addition to my Olympus System. I regard Four Thirds as my main system. An incomplete/disjointed set of examples based on my experience:

Spear Street with the Sony:


Spear Street
by Jason Hindle, on Flickr

And with Olympus (I prefer this):


Spear Street
by Jason Hindle, on Flickr

Hong Kong with the Sony (Olympus attempts were messy - my fault - and never published.


Lockhart Road
by Jason Hindle, on Flickr


Causway Bay at Night
by Jason Hindle, on Flickr

I never regarded myself as switcher, so am more happy than most as a two system user.

At the moment, my focus is in Four Thirds, with a Pen F in the bag and a desire for an E-M1 mk II and 12-100.
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  #79  
Old 7th April 2019
Harold Gough Harold Gough is offline
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Re: My latest foray into FF mirrorless - and why I'm sticking with m43

Quote:
Originally Posted by Internaut View Post
I regard Four Thirds as my main system.
Me too but I bought my A7r (1) for legacy UWAs. It could also be said that my many other legacy 35mm film lenses are used fully on the frame they were designed for, rather than the outer parts cropped, by the sensor, and discarded.

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  #80  
Old 7th April 2019
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Re: My latest foray into FF mirrorless - and why I'm sticking with m43

Yes, I use my A7S quite a bit for that. I enjoy the feel of a well engineered direct manual focus ring on my small collection of OM, Rokkor and Leitz lenses from the 50s - early 80s. Iíve learned their 35mm angles of view over the years and it feels odd having them on m4/3.

Iím currently on the train to London for a dayís street photography with some friends. Iíve got an E-M1ii which Iíll mainly use, but Iíve also brought the Sony plus Zeiss 35mm f2.8 which Iím going to use in some indoor markets.

It focuses like a sluggish brick on Valium, but in that environment you can zone focus close at f8 or 11 and wick up the iso to wherever necessary to give a shutter speed of 1/250, then just concentrate on spotting good compositions. ISO52k is perfectly OK for my purposes.

The Oly is also fully usable in situations like that, but to keep the ISO & shutter speed manageable you have to be at f1.2 and use the killer CAF while moving the focus points on the rear screen, so itís suitable for entirely different-looking images.

Horses for courses.

I donít find I get confused between the Oly and Sony controls, or not nearly as often as I do between the 1ii and the 10ii, presumably because they are more similar.
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