September 2017 Update

Task/Bitmap-Histogram/Common-Lisp/bitmap-histogram.lisp

@@ -0,0 +1,46 @@
+(defpackage #:histogram
+  (:use #:cl
+        #:opticl))
+
+(in-package #:histogram)
+
+(defun color->gray-image (image)
+  (check-type image 8-bit-rgb-image)
+  (let ((gray-image (with-image-bounds (height width) image
+                      (make-8-bit-gray-image height width :initial-element 0))))
+    (do-pixels (i j) image
+      (multiple-value-bind (r g b) (pixel image i j)
+        (let ((gray (+ (* 0.2126 r) (* 0.7152 g) (* 0.0722 b))))
+          (setf (pixel gray-image i j) (round gray)))))
+    gray-image))
+
+(defun make-histogram (image)
+  (check-type image 8-bit-gray-image)
+  (let ((histogram (make-array 256 :element-type 'fixnum :initial-element 0)))
+    (do-pixels (i j) image
+      (incf (aref histogram (pixel image i j))))
+    histogram))
+
+(defun find-median (histogram)
+  (loop with num-pixels = (loop for count across histogram sum count)
+        with half = (/ num-pixels 2)
+        for count across histogram
+        for i from 0
+        sum count into acc
+        when (>= acc half)
+          return i))
+
+(defun gray->black&white-image (image)
+  (check-type image 8-bit-gray-image)
+  (let* ((histogram (make-histogram image))
+         (median (find-median histogram))
+         (bw-image (with-image-bounds (height width) image
+                     (make-1-bit-gray-image height width :initial-element 0))))
+    (do-pixels (i j) image
+      (setf (pixel bw-image i j) (if (<= (pixel image i j) median) 1 0)))
+    bw-image))
+
+(defun main ()
+  (let* ((image (read-jpeg-file "lenna.jpg"))
+         (bw-image (gray->black&white-image (color->gray-image image))))
+    (write-pbm-file "lenna-bw.pbm" bw-image)))

Task/Bitmap-Histogram/Zkl/bitmap-histogram-1.zkl

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+fcn histogram(image){
+   hist:=List.createLong(256,0);	// array[256] of zero
+   image.data.howza(0).pump(Void,'wrap(c){ hist[c]+=1 });  // byte by byte loop
+   hist;
+}
+fcn histogramMedian(hist){
+   from,to:=0,(2).pow(8) - 1; // 16 bits of luminance
+   left,right:=hist[from],hist[to];
+   while(from!=to){
+      if(left<right){ from+=1; left +=hist[from]; }
+      else 	    { to  -=1; right+=hist[to];   }
+   }
+   from
+}

Task/Bitmap-Histogram/Zkl/bitmap-histogram-2.zkl

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+img:=PPM.readPPMFile("lenaGrey.ppm"); // a grey scale image
+median:=histogramMedian(histogram(img));
+median.println();
+
+bw:=PPM(img.w,img.h);
+  // stream bytes from orginal, convert to black/white, write to new image
+  // each pixel is 24 bit RGB
+img.data.pump(bw.data.clear(),'wrap(c){ if(c>median) 0xff else 0  });
+
+bw.write(File("foo.ppm","wb"));