Dual-ISO "Always ON" with ETTR for consistent timelapses

Started by AaronW, September 19, 2017, 07:49:01 PM

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I've been testing latest Nightly builds for shooting timelapses using ETTR together with it's auto-link to Dual-ISO and I've encountered quite significant nuisance while trying to process frames into final video.

Namely a resolution difference between Single-ISO frames (CR2's) and Dual-ISO ones merged with cr2hdr (DNG's).

I was doing a sunset timelapse, so there were hard changes in light and one segment of the recording came out as Dual-ISO (direct Sun) and remaining as Single-ISO.

I'm using 60D, so normal full CR2 resolution is 5184x3456 (as reported & exported by all Adobe's) and DNG's after Dual-ISO cr2hdr conversion are 5202x3465 (at least that's how Lightroom sees and treats them on export).
I've pixel-compared two consecutive frames when there was a method change and DNG's have more pixels on sides, CR2's must get an extra 18x9 crop and I haven't found a method to convert or open them without that crop, so the resolution would match DNG's.

To make those both frame types compatible I needed to manually crop DNG frames and if you ever tried to perform a pixel-precise crop either in ACR or Lightroom you must know that it's a complete bullsh** ... apparently Adobe considered such operation as unnecessary and there's no tool to help you do that.

Using a trial-and-error method and after many tries I managed to properly crop one frame in ACR, so now I got a .xmp with good crop that I can apply to other frames, however it would be much nicer to have better/easier/faster solution.

What I'm proposing is an option (ON/OFF) to make Dual-ISO always enabled while ETTR, so in cases when ETTR would want to turn off Dual-ISO, it would instead use smallest possible difference, for example Dual-ISO 100/200 instead of Single-ISO 100. In that way all frames would be Dual-ISO and problem solved.

With that way it would make all frames in this same resolution & details manner (like this same amount of let's say "effective" pixels - no 2x difference on vertical axis), so the whole timelapse would be more... consistent.
There is also a slight and very hard (!) to correct visual difference between frames on which the ISO method changes. After applying some manual corrections it's difficult to notice while the video is playing, but when you go frame by frame, you can still tell where are the method-changing points. It manifests in a sudden but subtle difference in colors and noise.

Alternative way would be to make cr2hdr to crop-output to the same resolution as CR2's, but I would prefer the first solution for more consistent timelapses (and couple steps less in post-production).



To avoid visual differences from method changes, my suggestion would be to fix Dual ISO to 100/800 or 100/1600 during the entire timelapse (disable ETTR link to Dual ISO). It's probably a bit suboptimal for aliasing when the scene doesn't require dual ISO, and will have the shadows noisier than plain ISO 1600, but at least I'd expect the overall look to stay consistent.

(wish I had some examples to show - maybe later)