examples.lisp

(defpackage "COLOURS.EXAMPLES"
  (:use "CL" "COLOURS.SPACES" "COLOURS.CONVERSIONS"))

(in-package "COLOURS.EXAMPLES")

(defun grayscaleize (png)
  (declare (optimize speed))
  (declare (type png:rgb-image png))
  (let* ((height (png:image-height png))
         (width (png:image-width png))
         (result (png:make-image height width 1))
         (toXYZ (convert 'RGB 'XYZ))
         (fromXYZ (convert 'XYZ 'RGB)))
    (declare (type (unsigned-byte 24) height width))
    (dotimes (i height)
      (dotimes (j width)
        (let ((Y (nth-value 1 (funcall toXYZ (aref png i j 0) (aref png i j 1) (aref png i j 2)))))
          (declare (type single-float Y))
          (setf (aref result i j 0)
                (nth-value 0 (funcall fromXYZ (alexandria:lerp Y 0 0.9505) Y (alexandria:lerp Y 0 1.089)))))))
    result))