September 2017 Update

Task/Color-quantization/Common-Lisp/color-quantization.lisp

@@ -0,0 +1,66 @@
+(defpackage #:quantize
+  (:use #:cl
+        #:opticl))
+
+(in-package #:quantize)
+
+(defun image->pixels (image)
+  (check-type image 8-bit-rgb-image)
+  (let (pixels)
+    (do-pixels (y x) image
+      (push (pixel* image y x) pixels))
+    pixels))
+
+(defun greatest-color-range (pixels)
+  (loop for (r g b) in pixels
+        minimize r into r-min
+        minimize g into g-min
+        minimize b into b-min
+        maximize r into r-max
+        maximize g into g-max
+        maximize b into b-max
+        finally
+           (return (let* ((r-range (- r-max r-min))
+                          (g-range (- g-max g-min))
+                          (b-range (- b-max b-min))
+                          (max-range (max r-range g-range b-range)))
+                     (cond ((= r-range max-range) 0)
+                           ((= g-range max-range) 1)
+                           (t                     2))))))
+
+(defun median-cut (pixels target-num-colors)
+  (assert (zerop (mod (log target-num-colors 2) 1)))
+  (if (or (= target-num-colors 1) (null (rest pixels)))
+      (list pixels)
+      (let* ((channel (greatest-color-range pixels))
+             (sorted (sort pixels #'< :key (lambda (pixel) (nth channel pixel))))
+             (half (floor (length sorted) 2))
+             (next-target (/ target-num-colors 2)))
+        (nconc (median-cut (subseq sorted 0 half) next-target)
+               (median-cut (subseq sorted half) next-target)))))
+
+(defun quantize-colors (pixels target-num-colors)
+  (let ((color-map (make-hash-table :test #'equal)))
+    (dolist (bucket (median-cut pixels target-num-colors) color-map)
+      (loop for (r g b) in bucket
+            sum r into r-sum
+            sum g into g-sum
+            sum b into b-sum
+            count t into num-pixels
+            finally (let ((average (list (round r-sum num-pixels)
+                                         (round g-sum num-pixels)
+                                         (round b-sum num-pixels))))
+                      (dolist (pixel bucket)
+                        (setf (gethash pixel color-map) average)))))))
+
+(defun quantize-image (input-file output-file target-num-colors)
+  (let* ((image (read-png-file input-file))
+         (pixels (image->pixels image))
+         (color-map (quantize-colors pixels target-num-colors))
+         (result-image (with-image-bounds (height width) image
+                         (make-8-bit-rgb-image height width :initial-element 0))))
+    (set-pixels (y x) result-image
+      (let* ((original (multiple-value-list (pixel image y x)))
+             (quantized (gethash original color-map)))
+        (values-list quantized)))
+    (write-png-file output-file result-image)))

Task/Color-quantization/Python/color-quantization.py

@@ -0,0 +1,6 @@
+from PIL import Image
+
+if __name__=="__main__":
+	im = Image.open("frog.png")
+	im2 = im.quantize(16)
+	im2.show()