Created
October 9, 2018 15:25
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Code for median filter based on 'A coarse-to-fine algorithm for fast median filtering of image data with a huge number of levels' by Alparone et al.
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using Images, TestImages, Statistics, BenchmarkTools, Test | |
img = testimage("lena_gray") | |
function median_filter_multilevel(img::Array{Gray{Normed{T,f}}, 2}, window_size::Tuple{Int64,Int64}) where {T,f} | |
nlevels = 2^f | |
course_nlevels = 2^(f>>1) | |
bin_bits = f>>1 | |
function update_median(median_val, lt_median, course_median_val, lt_course_median, hist, course_hist, half_pixels) | |
if lt_median <= half_pixels | |
for val in course_median_val:course_nlevels | |
if lt_course_median + course_hist[val] > half_pixels | |
course_median_val = val | |
break | |
else | |
lt_course_median += course_hist[val] | |
end | |
end | |
if (median_val - 1) >> bin_bits + 1 != course_median_val | |
median_val = (course_median_val - 1) << bin_bits + 1 | |
lt_median = lt_course_median | |
end | |
for val in median_val:nlevels | |
if lt_median + hist[val] > half_pixels | |
median_val = val | |
break | |
else | |
lt_median += hist[val] | |
end | |
end | |
elseif lt_median > half_pixels | |
if lt_course_median <= half_pixels | |
for val in median_val-1:-1:1 | |
lt_median -= hist[val] | |
if lt_median <= half_pixels | |
median_val = val | |
break | |
end | |
end | |
else | |
for val in course_median_val-1:-1:1 | |
lt_course_median -= course_hist[val] | |
if lt_course_median <= half_pixels | |
course_median_val = val | |
break | |
end | |
end | |
median_val = (course_median_val - 1) << bin_bits + 1 | |
lt_median = lt_course_median | |
for val in median_val:nlevels | |
if lt_median + hist[val] > half_pixels | |
median_val = val | |
break | |
else | |
lt_median += hist[val] | |
end | |
end | |
end | |
end | |
return median_val, lt_median, course_median_val, lt_course_median | |
end | |
result = copy(img) | |
if iseven(window_size[1]) || iseven(window_size[2]) | |
error("window width and height must be odd.") | |
end | |
half_window_size = window_size.>>1 | |
img_size = size(img) | |
half_pixels = (window_size[1]*window_size[2])>>1 | |
for j in 1 + half_window_size[2]: img_size[2] - half_window_size[2] | |
hist = zeros(Int, nlevels) | |
course_hist = zeros(Int, course_nlevels+1) | |
for I in CartesianIndices((1:window_size[1], j-half_window_size[2]:j+half_window_size[2])) | |
hist[img[I].val.i+1] += 1 | |
course_hist[(img[I].val.i)>>bin_bits+1] += 1 | |
end | |
median_val, lt_median, course_median_val, lt_course_median = update_median(1, 0, 1, 0, hist, course_hist, half_pixels) | |
result[1+half_window_size[2], j] = Gray{Normed{T,f}}((median_val-1)/(nlevels-1)) | |
for i in 2 + half_window_size[1]: img_size[1] - half_window_size[1] | |
for I in CartesianIndices((i-half_window_size[1]-1, j-half_window_size[2]:j+half_window_size[2])) | |
hist[img[I].val.i+1] -= 1 | |
course_hist[(img[I].val.i)>>bin_bits+1] -= 1 | |
if img[I].val.i + 1 < median_val | |
lt_median -= 1 | |
end | |
if (img[I].val.i)>>bin_bits+1 < course_median_val | |
lt_course_median -= 1 | |
end | |
end | |
for I in CartesianIndices((i+half_window_size[1], j-half_window_size[2]:j+half_window_size[2])) | |
hist[img[I].val.i+1] += 1 | |
course_hist[(img[I].val.i)>>bin_bits+1] += 1 | |
if img[I].val.i + 1 < median_val | |
lt_median += 1 | |
end | |
if (img[I].val.i)>>bin_bits+1 < course_median_val | |
lt_course_median += 1 | |
end | |
end | |
median_val, lt_median, course_median_val, lt_course_median = update_median(median_val, lt_median, course_median_val, lt_course_median, hist, course_hist, half_pixels) | |
result[i, j] = Gray{Normed{T,f}}((median_val-1)/(nlevels-1)) | |
end | |
end | |
result[1+half_window_size[1]:img_size[1]-half_window_size[1], 1+half_window_size[2]:img_size[2]-half_window_size[2]] | |
end | |
#Testing | |
@test median_filter_multilevel(img, (3,3)) == mapwindow(median, img, (3,3))[2:255, 2:255] | |
@test median_filter_multilevel(img, (5,5)) == mapwindow(median, img, (5,5))[3:254, 3:254] | |
#Benchmarking | |
@btime median_filter_multilevel($img, (3,3)); | |
@btime median_filter_multilevel($img, (5,5)); | |
@btime median_filter_multilevel($img, (7,7)); | |
@btime median_filter_multilevel($img, (11,11)); | |
@btime median_filter_multilevel($img, (21,21)); | |
@btime mapwindow($median, $img, (3,3)); | |
@btime mapwindow($median, $img, (5,5)); | |
@btime mapwindow($median, $img, (7,7)); | |
@btime mapwindow($median, $img, (11,11)); | |
@btime mapwindow($median, $img, (21,21)); | |
high_resolution_img = convert(Array{Gray{Normed{UInt32,32}}, 2}, img) | |
@btime median_filter_multilevel($high_resolution_img, (3,3)); | |
@btime median_filter_multilevel($high_resolution_img, (5,5)); | |
@btime median_filter_multilevel($high_resolution_img, (7,7)); | |
@btime median_filter_multilevel($high_resolution_img, (11,11)); | |
@btime median_filter_multilevel($high_resolution_img, (21,21)); | |
@btime mapwindow($median, $high_resolution_img, (3,3)); | |
@btime mapwindow($median, $high_resolution_img, (5,5)); | |
@btime mapwindow($median, $high_resolution_img, (7,7)); | |
@btime mapwindow($median, $high_resolution_img, (11,11)); | |
@btime mapwindow($median, $high_resolution_img, (21,21)); |
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