Gamma correct pixels before writing out

src/camera.c

@@ -4,6 +4,7 @@
 #include "rng.h"
 
 #include <float.h>
+#include <math.h>
 #include <threads.h>
 
 #define MAX_ITER 10
@@ -13,6 +14,8 @@
 #define SAMPLE_WEIGHT (1.0 / (double)NSAMPLES)
 #define SAMPLE_STDDEV 0.333
 
+#define GAMMA 2.2
+
 #define NTHREADS 40
 
 typedef struct {
@@ -52,17 +55,22 @@ trace(ray_t ray, const obj_t *scene, unsigned scene_count, rng_t *rng)
 		}
 
 		ray = scatter(hit, rng);
-		coeff *= 0.5;
+		coeff *= 0.3;
 	}
 
 	return black;
 }
 
+static double linear_to_gamma(double channel)
+{
+	return pow(fmin(channel, 1.0), 1.0 / GAMMA);
+}
+
 static void setpix(vec3_t col, pix_t *out)
 {
-	out->r = UINT16_MAX * col.x;
-	out->g = UINT16_MAX * col.y;
-	out->b = UINT16_MAX * col.z;
+	out->r = UINT16_MAX * linear_to_gamma(col.x);
+	out->g = UINT16_MAX * linear_to_gamma(col.y);
+	out->b = UINT16_MAX * linear_to_gamma(col.z);
 	out->a = UINT16_MAX;
 }