B

Task/Bitmap-Histogram/Lua/bitmap-histogram.lua

@@ -0,0 +1,52 @@
+function Histogram( image )
+    local size_x, size_y = #image, #image[1]
+
+    local histo = {}
+    for i = 0, 255 do
+        histo[i] = 0
+    end
+
+    for i = 1, size_x do
+        for j = 1, size_y do
+            histo[ image[i][j] ] = histo[ image[i][j] ] + 1
+        end
+    end
+
+    return histo
+end
+
+function FindMedian( histogram )
+    local sum_l, sum_r = 0, 0
+    local left, right = 0, 255
+
+    repeat
+        if sum_l < sum_r then
+            sum_l = sum_l + histogram[left]
+            left = left + 1
+        else
+            sum_r = sum_r + histogram[right]
+            right = right - 1
+        end
+    until left == right
+
+    return left
+end
+
+
+bitmap = Read_PPM( "inputimage.ppm" )
+gray_im = ConvertToGrayscaleImage( bitmap )
+histogram = Histogram( gray_im )
+median = FindMedian( histogram )
+
+for i = 1, #gray_im do
+    for j = 1, #gray_im[1] do
+        if gray_im[i][j] < median then
+            gray_im[i][j] = 0
+        else
+            gray_im[i][j] = 255
+        end
+    end
+end
+
+bitmap = ConvertToColorImage( gray_im )
+Write_PPM( "outputimage.ppm", bitmap )