+#include <GL/glew.h>
+#include <assert.h>
+#include <math.h>
#include <stdio.h>
#include <string.h>
-#include <assert.h>
+#include <Eigen/Core>
-#include <math.h>
+#include "init.h"
#include "util.h"
-#include "opengl.h"
+
+extern std::string *movit_data_directory;
void hsv2rgb(float h, float s, float v, float *r, float *g, float *b)
{
std::string read_file(const std::string &filename)
{
+ const std::string full_pathname = *movit_data_directory + "/" + filename;
+
static char buf[131072];
- FILE *fp = fopen(filename.c_str(), "r");
+ FILE *fp = fopen(full_pathname.c_str(), "r");
if (fp == NULL) {
- perror(filename.c_str());
+ perror(full_pathname.c_str());
exit(1);
}
return buf;
}
-void combine_two_samples(float w1, float w2, float *offset, float *total_weight)
+void combine_two_samples(float w1, float w2, float *offset, float *total_weight, float *sum_sq_error)
{
+ assert(movit_initialized);
assert(w1 * w2 >= 0.0f); // Should not have differing signs.
+ float z; // Just a shorter name for offset.
if (fabs(w1 + w2) < 1e-6) {
- *offset = 0.5f;
- *total_weight = 0.0f;
+ z = 0.5f;
} else {
- *offset = w2 / (w1 + w2);
- *total_weight = w1 + w2;
+ z = w2 / (w1 + w2);
}
+
+ // Round to the minimum number of bits we have measured earlier.
+ // The card will do this for us anyway, but if we know what the real z
+ // is, we can pick a better total_weight below.
+ z = lrintf(z / movit_texel_subpixel_precision) * movit_texel_subpixel_precision;
+
+ // Choose total weight w so that we minimize total squared error
+ // for the effective weights:
+ //
+ // e = (w(1-z) - a)² + (wz - b)²
+ //
+ // Differentiating by w and setting equal to zero:
+ //
+ // 2(w(1-z) - a)(1-z) + 2(wz - b)z = 0
+ // w(1-z)² - a(1-z) + wz² - bz = 0
+ // w((1-z)² + z²) = a(1-z) + bz
+ // w = (a(1-z) + bz) / ((1-z)² + z²)
+ //
+ // If z had infinite precision, this would simply reduce to w = w1 + w2.
+ *total_weight = (w1 * (1 - z) + w2 * z) / (z * z + (1 - z) * (1 - z));
+ *offset = z;
+
+ if (sum_sq_error != NULL) {
+ float err1 = *total_weight * (1 - z) - w1;
+ float err2 = *total_weight * z - w2;
+ *sum_sq_error = err1 * err1 + err2 * err2;
+ }
+
assert(*offset >= 0.0f);
assert(*offset <= 1.0f);
}