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-rw-r--r--gamma.c57
1 files changed, 57 insertions, 0 deletions
diff --git a/gamma.c b/gamma.c
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index 0000000..d15f3b6
--- /dev/null
+++ b/gamma.c
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+/* 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;
+ }
+}