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Linear image interpolation for timelapse video (amongst other things) http://sites.google.com/site/timelap…
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Stacking HOWTO ============== Copyright --------- The stack.py and stack-32bit.py scripts are copyright (C) Tim Haynes 2010 and may be used and distributed under the terms of the GNU General Public License (GPL) version 3 or higher. What? ---- Stacking is the process of taking multiple source images and generating a result where each pixel is the simple average (mean) of the corresponding pixels from all the sources. Why? --- There are at least two situations in which this is useful: 1) Reducing effective ISO noise: all digital images suffer from thermal sensor noise, which can be regarded as random small offsets in pixel values - so if the image signal says a pixel should be a particular (r,g,b) value, the recorded pixel might have a small offset (r+dr, g+dg, b+db). As ISO sensitivity increases, fewer photons are required to cause the same change in recorded pixels, which means that the fixed number of thermal photons contributes a greater proportion of the image - so the apparent noise increases. However, because the noise is effectively random, the more times a pixel is read the more accurate the reading becomes: specifically the effective ISO drops as 1/2^N where N is the number of frames. For example, four images taken at ISO 1600, averaged together, have the same effective signal:noise ratio as one image at ISO 400. 2) Simulating long exposures: some scenes require quite long exposures to achieve desired motion-blur effects (for example, choppy seas at the coast often run to a minute or more). If the lighting is bright daylight, it might not be practical to carry sufficient filters to reduce the exposure to such an extent, and even if it's possible to reduce the aperture small enough, it might not be desirable as diffraction will degrade image-quality significantly. Hence, with an intervalometer, one can take several photos of a scene over a prolonged period and by averaging the results, simulate the effect of one longer exposure. How? --- The scripts stack.py and stack-32bit.py operate identically except that stack-32bit.py maintains a running average with 32-bit precision internally. Requirements: python (tested with 2.6); Python Image Library (PIL) compiled with support for whatever format your source images come in (typically JPEG, PNG and/or TIFF). Usage: stack.py *.JPG --> results in out.png stack-32bit.py *.png --> results in files out32.png, out-r32.png, out-g32.png, out-b32.png Optional: The file =adjustment.json= may be used to specify a tone curve, applied to each image immediately after it's opened, before averaging takes place. When run without any parameters, the script gen-curve.py generates a greyscale spectrum, greyscale-strip.png. This can be opened in the Gimp or Photoshop alongside one of the sample input images, levels and curves operations applied in parallel and then the greyscale-strip.png saved out again. When run a second time, with an image file as argument, the script emits a JSON mapping of the image: ./gen-curve.py greyscale-strip.png > adjustment.json This is useful where the source images are 8-bit and you want a dramatic tone curve (for example, lightening dark shadow areas).