1 files changed, 57 insertions, 0 deletions
diff --git a/gamma.c b/gamma.c
new file mode 100644
index 0000000..d15f3b6
--- /dev/null
+++ b/gamma.c
@@ -0,0 +1,57 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+/**
+ * Analyse a gamma ramp
+ * 
+ * @param  stops       The number of stops in the gamma ramp
+ * @param  ramp        The gamma ramp
+ * @param  gamma       Output parameter for the gamma
+ * @param  contrast    Output parameter for the contrast
+ * @param  brightness  Output parameter for the brightness
+ */
+void gamma_analyse(size_t stops, const uint16_t *restrict ramp, double *restrict gamma,
+                   double *restrict contrast, double *restrict brightness)
+{
+	double min, middle, max;
+	*brightness = min = (double)(ramp[0])         / (double)0xFFFF;
+	*contrast   = max = (double)(ramp[stops - 1]) / (double)0xFFFF;
+	middle            = (double)(ramp[stops / 2]) / (double)0xFFFF;
+
+	if (!(stops % 2)) {
+		middle += (double)(ramp[stops / 2 - 1]) / (double)0xFFFF;
+		middle /= (double)2;
+	}
+
+	middle = (middle - min) / (max - min);
+	*gamma = -log((double)2) / log(middle);
+}
+
+
+/**
+ * Generate a gamma ramp
+ * 
+ * @param  stops       The number of stops in the gamma ramp
+ * @param  ramp        Memory area to where to write the gamma ramp
+ * @param  gamma       The gamma
+ * @param  contrast    The contrast
+ * @param  brightness  The brightness
+ */
+void gamma_generate(size_t stops, uint16_t *restrict ramp, double gamma, double contrast, double brightness)
+{
+	double diff = contrast - brightness;
+	double gamma_ = (double)1 / gamma;
+	size_t i;
+	int32_t y;
+	double y_;
+
+	for (i = 0; i < stops; i++) {
+		y_ = (double)i / (double)stops;
+		y_ = pow(y_, gamma_) * diff + brightness;
+		y = (int32_t)(y_ * 0xFFFF);
+		if (y < 0x0000)  y = 0x0000;
+		if (y > 0xFFFF)  y = 0xFFFF;
+		ramp[i] = (uint16_t)y;
+	}
+}