Finished pi-pan-tilt post part 3

posts/2016-10-04-pi-pan-tilt-2.md

@@ -139,8 +139,8 @@ However, you can look up close and see how well the details came
 through - which I find quite impressive for cheap optics and a cheap
 sensor.
 
-Further posts will follow on some other details, and hopefully other
+[Part 3](./2016-10-12-pi-pan-tilt-3.html) delves into the image
-images!
+processing workflow.
 
 [ArduCam]: http://www.arducam.com/camera-modules/raspberrypi-camera/
 [forum-raw-images]: https://www.raspberrypi.org/forums/viewtopic.php?p=357138

posts/2016-10-12-pi-pan-tilt-3.md

@@ -8,7 +8,8 @@ tags: photography, electronics, raspberrypi
 This is the third part in this series, continuing on from
 [part 1][part1] and [part 2][].  The last post was about integrating
 the hardware with Hugin and PanoTools.  This one is similarly
-technical and without as many pretty pictures, so be forewarned.
+technical, and without any pretty pictures (really, it has no concern
+at all for aesthetics), so be forewarned.
 
 Thus far (aside from my first stitched image) I've been using a raw
 workflow where possible.  That is, all images arrive from the camera
@@ -156,26 +157,54 @@ These were done with 16-bit TIFFs rather than 8-bit ones:
 In theory, the 16-bit ones should be retaining two extra bits of data
 from the 10-bit sensor data, and thus two extra stops of dynamic
 range, that the 8-bit image cannot keep.  I can't see the slightest
-difference myself.  Perhaps those two bits are just well below the
+difference myself.  Perhaps those two bits are below the noise floor;
-noise floor; perhaps if I used a brighter scene, it would be more
+perhaps if I used a brighter scene, it would be more apparent.
-apparent.
 
 Regardless, starting from raw sensor data rather than the JPEG image
 gets some additional dynamic range.  That's hardly surprising - JPEG
 isn't really known for its faithful reproduction of darker parts of an
-image.  Regardless, bracketing exposures and merging them later (as
+image.
-Hugin will do) is probably a better idea than pretending the sensor is
-going to give 10 bits of resolution.
 
 Here's another comparison, this time a 1:1 crop from the center of an
-image (shot with [this lens][12-40mm], whose Amazon price mysteriously
+image (shot at 40mm with [this lens][12-40mm], whose Amazon price
-is now $146 instead of the $23 I actually paid).  Click for a lossless
+mysteriously is now $146 instead of the $23 I actually paid).  Click
-PNG view, as JPEG might eat some of the finer details.
+the preview for a lossless PNG view, as JPEG might eat some of the
+finer details, or [here][leaves-full] for the full JPEG file
+(including raw, if you want to look around).
 
 [![JPEG & raw comparison](../assets_external/2016-10-12-pi-pan-tilt-3/leaves_test_preview.jpg){width=100%}](../assets_external/2016-10-12-pi-pan-tilt-3/leaves_test.png)
 
+The JPEG image seems to have some aggressive denoising that cuts into
+sharper detail somewhat, as denoising algorithms tends to do.  Of
+course, another option exists too, which is to shoot many images from
+the same point, and then average them.  That's only applicable in a
+static scene with some sort of rig to hold things in place, which is
+convenient, since that's what I'm making...
+
+[![Shot setup](../assets_external/2016-10-12-pi-pan-tilt-3/IMG_20161016_141826_small.jpg){width=100%}](../assets_external/2016-10-12-pi-pan-tilt-3/IMG_20161016_141826_small.jpg)
+
+I used that (messy) test setup to produce the below comparison between
+a JPEG image, a single raw image, 4 raw images averaged, and 16 raw
+images averaged.  These are again 1:1 crops from the center to show
+noise and detail.
+
+[![JPEG, raw, and averaging](../assets_external/2016-10-12-pi-pan-tilt-3/penguin_compare.jpg){width=100%}](../assets_external/2016-10-12-pi-pan-tilt-3/penguin_compare.png)
+
+Click for the lossless version, and take a look around finer details.
+4X averaging has clearly reduced the noise from the un-averaged raw
+image, and possibly has done better than the JPEG image in that regard
+while having clearer details.  The 16X definitely has.
+
+Averaging might get us the full 10 bits of dynamic range by cleaning
+up the noise.  However, if we're able to shoot enough images at
+exactly the same exposure to average them, then we could also shoot
+them at different exposures (i.e. [bracketing][]), merge them into an
+HDR image (or [fuse them][exposure fusion]), and get well outside of
+that limited dynamic range while still having much of that same
+averaging effect.
+
 I'll cover the remaining two steps I noted - Hugin & PanoTools
-stitching, and postprocessing - in the next post.
+stitching and HDR merging, and postprocessing - in the next post.
 
 [part1]: ./2016-09-25-pi-pan-tilt-1.html
 [part2]: ./2016-10-04-pi-pan-tilt-2.html
@@ -197,3 +226,6 @@ stitching, and postprocessing - in the next post.
 [picamera-raw]: https://picamera.readthedocs.io/en/release-1.10/recipes2.html#bayer-data
 [picamera]: https://www.raspberrypi.org/documentation/usage/camera/python/README.md
 [12-40mm]: https://www.amazon.com/StarDot-Vari-Focal-Camera-Lens-Black/dp/B00IPR1YSC
+[leaves-full]: ../assets_external/2016-10-12-pi-pan-tilt-3/leaves_test_full.jpg
+[exposure fusion]: https://en.wikipedia.org/wiki/Exposure_Fusion
+[bracketing]: https://en.wikipedia.org/wiki/Bracketing