'Speriment #1: ISO 100, Aperture Priority
So, stepped out the front door and took three pictures, ISO100, Aperture Priority exposure at F8, just tried to get overlap between adjacent shots. I’m not a pano-guy, so first lesson learned: 24mm is too wide a focal length! The far parts of the image aligned, so that’s good enough for brightness considerations.
Here’s the camera info for each:
DSZ_4013.NEF: 1/640sec f8 ISO100 EV15.3 LV 15.3
DSZ_4014.NEF: 1/320sec f8 ISO100 EV14.3 LV14.3
DSZ_4015.NEF: 1/250sec f8 ISO100 EV14.0 LV14.0
Okay, got shutter speed variation, so that’s good. BTW, the metering mode I use is highlight-weighted matrix, so the images you’ll see in a bit are dark, by design. Oh, and that goes with a EC of +1, which stayed the same for all three images.
The first interesting thing of note is that the brightest image out-of-the-box is the LV14.0 one, next-brightest is 14.3, and the darkest is 15.3. This corresponds to the EV definition, per Wikipedia: “Each increment of 1 in exposure value corresponds to a change of one “step” (or, more commonly, one “stop”) in exposure, i.e., half as much exposure” (I bolded the last part). In bear-of-little-brain terms, larger EVs got less light.
Of interest but of less importance is that in these images, EV=LV. Yes, since the ISO remained the same, and it shows that the exiftool equation performs identically to the Wikipedia EV equation for aperture and shutterspeed. Well and good, so far…
So, using the 14.0 image as the anchor brightness, I determined that the 14.3 image needs a 0.3 stop EC boost, and the 15.3 image needs a 1.3 stop boost. So, in rawproc, I opened each image, processed it to demosaic, and applied the corresponding exposure compensations. Then, I “stitched” the images together with rawproc-butt (I just slid the windows around to overlap each other at the relevant points…) and took this screenshot:
Look at the sky transitions; TLAR, IISSM…
So, without rawproc, one could run the following exiftool command to get the LVs from all the raws in a directory:
$ exiftool -LightValue *.NEF
======== DSZ_4013.NEF
Light Value : 15.3
======== DSZ_4014.NEF
Light Value : 14.3
======== DSZ_4015.NEF
Light Value : 14.0
3 image files read
Pick the brightest (lowest LV) image, and subtract that LV from the other LVs to get their ECs…