Friday, October 15, 2021

M3 Landscape Bracketing Script: Now with ND and Super-Resolution bracketing

I've discussed multi image bracketing for ND and Super-Resolution in previous posts: that is taking a bracket set of images for post processing to simulate a long exposure or provide the data to create an up-scaled and/or noise reduced image.

The idea is simple. For LEs just divide the required time by the shutter speed and take this many images for 'averaging' in post, eg to simulate movement in water. This feature works well when you either don't have an ND filter with you, or you don't have a stronger enough one.

For Super-Resolution processing the procedure is similar, but we need to introduce small amounts of sensor movement between images. That is take at least 4 images, or as many as you wish, that are up-scaled and statistically averaged in post. This technique is best applied to images with little/no movement. The Super-Resolution bracketing exploits the focus breathing that occurs when changing focus, ie to simulate pixel shifting at the sensor. But note, this effect may not manifest itself on every lens or at every focus position or focal length, as it is dependent on the lens exhibiting lens breathing, ie a change in the angle of view, in the area of focus. However, even with no movement, you will still have a noise reduction bracket set.

I'm pleased to announce that I've incorporated both bracketing schemes into my M3 Landscape Bracketing Script: which can be downloaded from the right as usual. The top part of the menu now looks like this:

@subtitle Bracketing Options
#mode = 0 "Focus bracket?" {Off X2INF Min2INF Manual Min2X SupRes}
#bracket = 0 "Exposure bracket?" {Off 1(4Ev) 1(3Ev) 1(2Ev) 2(2Ev) 3(2Ev) ISO Auto Wind3Ev Wind4Ev}
#sky = 0 "Sky Bracket?" {Off 2Ev 3Ev 4Ev 5Ev 6Ev ETTR}
#ndf = 0 "ND?" [-5 30]

@subtitle Bracketing Settings
#infinity = 3 "Infinity Focus (xH)" [2 4]
#overlap = 15 "Overlap (um)" [5 30]
#hilit = 5 "% Histo HiLit" [1 30]
#start = 1 "Histo Upper Quartiles" [1 4]
#pmag = 1 "Assumed Pupil Mag" [1 6]
#isoval = 0 "ISO Bracketing Value" {400 800 1600 3200}
#supres = 4 "# SupRes shots?" [4 16]

To use the ND/LE feature, simply set ND to a non-zero number. If the number is negative the bracket set will simulate that ND value, eg -2 will take 4 images for processing a simulated 2 stop ND filter; whereas -5 will take 32 images to simulate a 5 stop filter.

Note that the negative mode can also be used to create a noise reduction bracket subset. That is a value of -4 will create 16 images, for a NR of 4 after processing in post.

If the ND value is positive, eg 2, this is asking the script to take the required number of images to simulate a 2s exposure. In order to keep the number of images to a minimum, the script first adjusts the aperture to the maximum it can, ie up to f/22 if the base shutter allows. The shutter is then adjusted to ensure the exposure is the same as the base. 

The Super-Resolution technique will only work on a lens whose focus motor can be controlled, eg the EFM lenses. This new feature works best when you set the base focus at the hyperfocal, as the lens moves towards infinity, at the smallest step it can, to simulate sensor pixel shifting.

The number of images is set in the supres menu item, ie between 4 and 16. Also, the super-resolution bracket set can only realised with focus bracketing set to manual. Whereas the ND/LE/NR bracket set will be created as part of a focus bracket capture, eg X2INF.

Both bracket sets are post processed in, say, photoshop, using the following workflows:

  • For LE/ND processing ingest the images into Photoshop and stack into a single image. Align the images then either use the Photoshop Merge script on the right or manually adjust the individual image's opacity, ie halving the opacity each time with the bottom image at 100%. Then flatten the image.
  • For Super-Resolution the process is similar, however,after stacking and before aligning, upscale the image by 200%. After processing you can then export the Super-Resolution image back to Lightroom, or downscale first. See here for more information on the Super-Resolution technique.

You can also use Smart Object statistics, eg median, but this route is slow if you have a large number of objects.

The following is a Super-Resolution test image I just took with my M3 using the 11-22mm M lens at 11mm. The aperture was set to f/8 and the shutter to 1/40s. I requested a 10 image Super-Res bracket set on this occasion, and was lucky that there was nearly no wind to ruin the test.

If you zoom in on the image it is easy to see the lack of noise in the shadows and the general cleanness of the image, noting that no NR was used in post.

With the two new bracketing features, it is easy to create complex bracket sets via one or two button pushes. For example you could set up focus bracketing for a deep focus capture, plus taking an ND/LE bracket set to layer in in post, plus an ETTR sky shot to, once again, layer in in post.

I will discuss post processing in a future post.

As usual I welcome any comments on this post or any of my posts.

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