44 lines
2.0 KiB
Bash
Executable File
44 lines
2.0 KiB
Bash
Executable File
#! /bin/sh
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# Given the input illegible scan of the Macintosh SE Main Logic Board
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# Page 1 schematic, apply some image processing magic on it to make it
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# somewhat more legible.
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# Here's how our image processing operations work.
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#
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# 1. The original scanned image is monochrome. Gradation is expressed
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# linearly through the means of error-diffusion half-toning.
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#
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# 2. To convert to grayscale, we simply convert to 8-bit grayscale and
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# then resize to 80%, using a cubic resize image filtering
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# algorithm. The resulting 8-bit intensity values will be
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# expressed in a linear sample space. We then resize by 250% to
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# get a grayscale image, linear intensity samples, that is twice
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# the spatial resolution of the original.
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#
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# The second resizing step is mainly to ease looking at zoomed in
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# copies of the image, which you must do almost all the time due to
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# the illegibility of the original.
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#
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# 3. If the image is displayed directly on sRGB displays, it will
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# appear artificially dark because it is currently using linear
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# intensity samples, but an sRGB display uses a curve
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# (approximately gamma = 2.2) to map the image samples to linear
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# light intensities. Just leave it this way because the source
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# image is already pretty light to begin with. The artificial
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# darkening makes the image easier to read.
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#
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# To get a gamma-correct image, we would need to apply a `gamma =
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# 0.45` curve to the image. Or, in other words, "gamma-correct" by
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# a factor of `1/0.45 = 2.2`. Alternatively, we could use the more
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# precise sRGB colorspace conversion function.
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set -e # Exit on errors.
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# N.B. We use two conversion command lines because I think otherwise
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# ImageMagick just replaces the previous resize command with the new
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# resize command and would only end up resizing the image once.
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convert -depth 8 -resize 80% -filter cubic se_mlb_p1.gif se_mlb_p1_tmp.png
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convert -resize 250% -filter cubic se_mlb_p1_tmp.png se_mlb_p1_proc.png
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rm se_mlb_p1_tmp.png
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