Wednesday, June 1, 2022

Landscape Bracketing Script: Update

Recently I've been focused on getting my M3 bracketing script updated, as well as refining my Canon R set up, which I've yet to write about.

In this post I'm pleased to say I've tweaked my CHDK, non-M3, bracketing script (downloadable on the right).

The script's runtime UI is less developed than on the M3, with feedback only available via the CHDK console. Nevertheless, the script allows you to carry out focus and exposure bracketing, covering many use cases.

The script's menus look like this:

@subtitle Focus Stuff
# focus_strat = 0 "Focus logic?" {None X2INF Min2INF H/x2INF Min2X}
# hfrac = 0 "H start" {H H/3 H/5 H/7 H/9}
# overlap = 0 "Overlap at" {CoC 2CoC/3 CoC/2}
# quality = 2 "Infinity quality?" {CoC/2 CoC/3 CoC/4}

@subtitle Exposure Stuff
# delta = 0 "Exposure logic?" {None 1Ev 2Ev 3Ev 800 1600 ZN4 ZN3 ZN2 A:x>H ...
...Wind A:S>H}
# logic = 0 "Bracketing logic?" {0/-/+ 0/-/-- 0/+/++}
# hilit = 0 "Over X Sensitivity" {Normal Medium High}
# bp = 0 "Black Level Sensitivity" {Normal Medium High}
# sky = 0 "Inf Bracketing?" {None Sky NDSim Both}
# NDF = 1 "ND (Ev) value" [1 5]

@subtitle Other Stuff
# delay = 3 "Script Delay (s)" [0 5]
# bookends = 1 "Bookends?" {No Yes}
# screen_off = 1 "Screen off?" {No Yes}
# bplevel = 0 "Check Black Level?" {No Yes}
# bpval = 30 "Black Level" [0 200]

The first section addresses focus bracketing, eg: none; from the current focus position to infinity (X2INF); from the camera's focus minimum to infinity (MIN2INF); from a user selectable fraction of the hyperfocal to infinity (H/x2INF); or from the camera's minimum to the current focus (MIN2X).

Infinity is user selected as either 2x, 3x or 4x the hyperfocal, ie an infinity blur of CoC/2, CoC/3 or CoC/4; where the circle of confusion is the CHDK value for the camera.

Finally, the user can select the focus overlap value in terms of the CHDK CoC blur, eg CoC, 2CoC/3 or CoC/2.

The second section of the script's menu covers exposure, eg: none; three brackets at either 1Ev, 2Ev or 3Ev; a single ISO bracket at either ISO800 or ISO1600; a single (Zero Noise) bracket at either 4Ev, 3Ev or 2Ev; an auto bracket set that will take brackets at 2Ev from a the current exposure to an ETTR exposure for the highlights; a single wind bracket at the same base exposure but with the shutter and ISO both adjusted by 3Ev; or an auto bracket set that will take brackets at 2Ev covering shadows and highlights, irrespective of the current exposure.

The user can also choose the bracketing logic when capturing three images, eg 0/-/+ etc.

The over exposure warning allows the user to tell the script how many histogram bins to use to set the ETTR exposure, ie Normal, Medium or High. The higher setting uses more bins of the histogram, thus the exposure is skewed away from the 'perfect' ETTR, ie providing more highlight exposure insurance.

The black level, used for the auto S>H option, is used in a similar fashion. The camera's black level can be checked at set by running the Check Black Level option with a lens cap on.

The user can tell the script to take two additional brackets at infinity, ie for the sky and/or to simulate an ND filter. The ND filter value is user selectable between 1 and 5 stops, with 5 generating 32 images for post processing.

The final menu section covers choosing: a capture delay time (0-5 seconds); selecting (dark image) bookends; and electing to have the screen off when the script is capturing images (recommended).

The script is initiated in the normal CHDK fashion, ie from ALT mode.

Once initiated, the script pauses and provides user feedback on the focus and, if X2INF is selected, an estimate of the number of images that will be captured in the focus bracket set. When paused the user can change focus and the shutter speed; but note that in some cameras one may see a clash between available buttons/functionality, that may require a tweak to the code ;-)

To capture the requested images, one only needs to carry out a half shutter press in the paused state. The right button,if pressed, will exit the script without capturing any images.

To illustrate the script's functionality, I used my G1X, at f/4, and selected the X2INF focus bracketing option and switched on sky bracketing. I focused on the nearest point of interest in the test scene and got the following bracket set:

Here we see the bookends are delineating six focus brackets and an ETTR/sky bracket.

After processing in Lightroom and Photoshop, here is the resultant test image:

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

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