analyse and generate gamma ramps

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/src/gamma.c b/src/gamma.c
new file mode 100644
index 0000000..fa57fb4
--- /dev/null
+++ b/src/gamma.c
@@ -0,0 +1,72 @@
+/**
+ * crt-calibrator – Calibration utility for CRT monitors
+ * Copyright © 2014  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "gamma.h"
+
+#include <math.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;
+  
+  middle = (middle - min) / (max - min);
+  *gamma = log(middle) / log(2.0);
+}
+
+
+/**
+ * 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;
+  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] = y;
+    }
+}
+