40 lines
1.2 KiB
Plaintext
40 lines
1.2 KiB
Plaintext
-- demo\rosetta\Bitmap_Histogram.exw (runnable version)
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include ppm.e -- black, white, read_ppm(), write_ppm() (covers above requirements)
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function to_bw(sequence image)
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sequence hist = repeat(0,256)
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for x=1 to length(image) do
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for y=1 to length(image[x]) do
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integer pixel = image[x][y] -- red,green,blue
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sequence r_g_b = sq_and_bits(pixel,{#FF0000,#FF00,#FF})
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integer {r,g,b} = sq_floor_div(r_g_b,{#010000,#0100,#01}),
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lum = floor(0.2126*r + 0.7152*g + 0.0722*b)
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image[x][y] = lum
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hist[lum+1] += 1
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end for
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end for
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integer lo = 1, hi = 256,
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ltot = hist[lo],
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rtot = hist[hi]
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while lo!=hi do
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if ltot<rtot then
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lo += 1
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ltot += hist[lo]
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else
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hi -= 1
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rtot += hist[hi]
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end if
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end while
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integer lum = lo
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for i=1 to length(image) do
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for j=1 to length(image[i]) do
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image[i][j] = iff(image[i][j]<lum?black:white)
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end for
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end for
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return image
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end function
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sequence img = read_ppm("Lena.ppm")
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img = to_bw(img)
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write_ppm("LenaBW.ppm",img)
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