new method based on sensor dimensions and focal length

gopro_8:7/unfish_gopro_8:7.glsl

@@ -1,14 +1,15 @@
 // RozK
 // Fisheye removal for GoPro 11+, 8:7 ratio, without hypersmooth
-// Adapted from https://github.com/duducosmos/defisheye
-// itself based on http://www.fmwconcepts.com/imagemagick/defisheye/index.php
 
 #extension GL_ARB_texture_rectangle: enable
 
 // TODO: investigate
 // precision highp float;
 
+// #define debug_borders
+
 // uniforms
+
 uniform sampler2DRect myTextureY;
 uniform sampler2DRect myTextureU;
 uniform sampler2DRect myTextureV;
@@ -16,25 +17,47 @@ uniform vec2 myResolution;
 uniform float pts;
 
 // parameters
-const float input_fov = 156.0;
+
-const float output_fov = 124.45;
+const vec2 sensor_dimensions = vec2(5.949440, 5.205760);
-const vec2 pixel_scale = vec2(0.652485, 1.0);
+const float fisheye_focal_length = 2.92;
+const float rectilinear_focal_length = 2.102263;
 const int subsampling = 4;
 
-// subsampling constants
+// constants
-const float substep = 1.0 / float(subsampling);
+
-const float substart = substep * 0.5 - 0.5;
+const float subsampling_step = 1.0 / float(subsampling);
-const float subscale = 1.0 / float(subsampling * subsampling);
+const float subsampling_start = subsampling_step * 0.5 - 0.5;
+const float subsampling_denominator = 1.0 / float(subsampling * subsampling);
 
 // variables
-vec2 center;
-float diameter;
-float input_len;
-float inv_output_len;
 
-vec4 unfish(const in vec2 coord) {
+vec2 texture_center;
-    float len = max(0.001, length(coord));
+vec2 texture_to_sensor;
-    vec2 y_coord = center + coord * ((input_len / len) * atan(len * inv_output_len));
+vec2 sensor_to_texture;
+
+void initialize() {
+    texture_center = myResolution * 0.5;
+    texture_to_sensor = (sensor_dimensions / myResolution);
+    sensor_to_texture = (myResolution / sensor_dimensions);
+}
+
+vec2 unfish_coord(const in vec2 coord) {
+    float rectilinear_distance = length(coord);
+    float rectilinear_angle = atan(rectilinear_distance / rectilinear_focal_length);
+    float fisheye_distance = rectilinear_angle * fisheye_focal_length;
+    return coord * (fisheye_distance / rectilinear_distance);
+}
+
+vec4 unfish_pixel(const in vec2 coord) {
+    vec2 unfished = unfish_coord((coord - texture_center) * texture_to_sensor);
+    vec2 y_coord = texture_center + unfished * sensor_to_texture;
+
+#ifdef debug_borders
+    if (y_coord.x < 0.0 || y_coord.y < 0.0 || y_coord.x > myResolution.x || y_coord.y > myResolution.y) {
+        return vec4(1.0, 1.0, 1.0, 1.0);
+    }
+#endif
+
     vec2 uv_coord = y_coord * 0.5;
     return vec4(
         texture2DRect(myTextureY, y_coord).r,
@@ -45,21 +68,18 @@ vec4 unfish(const in vec2 coord) {
 }
 
 void main() {
-    center = myResolution * 0.5;
+    initialize();
-    diameter = length(myResolution);
-    input_len = diameter / radians(input_fov);
-    inv_output_len = (2.0 * tan(radians(output_fov * 0.5))) / diameter;
 
-    vec2 coord = gl_TexCoord[0].xy - center;
+    vec2 coord = gl_TexCoord[0].xy;
     vec4 pixel = vec4(0.0, 0.0, 0.0, 0.0);
 
-    float x, y = substart;
+    float x, y = subsampling_start;
-    for (int column = 0; column < subsampling; column++, y += substep) {
+    for (int column = 0; column < subsampling; column++, y += subsampling_step) {
-        x = substart;
+        x = subsampling_start;
-        for (int row = 0; row < subsampling; row++, x += substep) {
+        for (int row = 0; row < subsampling; row++, x += subsampling_step) {
-            pixel += unfish((coord + vec2(x, y)) * pixel_scale);
+            pixel += unfish_pixel(coord + vec2(x, y));
         }
     }
 
-    gl_FragColor = pixel * subscale;
+    gl_FragColor = pixel * subsampling_denominator;
 }

gopro_8:7/unfish_gopro_8:7.py

@@ -0,0 +1,86 @@
+# RozK
+
+import math
+
+print("\n--- sensor size (millimeters) ---\n")
+
+# https://www.sony-semicon.com/files/62/pdf/p-13_IMX677-AAPH5-J_Flyer.pdf
+
+sensor_total_array_width    = 5700 # p
+sensor_total_array_height   = 5160 # p
+sensor_total_array_diagonal = math.hypot(sensor_total_array_width, sensor_total_array_height)
+
+sensor_pixel_size = 1.12 * 0.001 # mm
+
+sensor_total_width    = sensor_total_array_width * sensor_pixel_size
+sensor_total_height   = sensor_total_array_height * sensor_pixel_size
+sensor_total_diagonal = math.hypot(sensor_total_width, sensor_total_height)
+
+# sensor_total_diagonal = 8.35 # mm
+# sensor_total_width    = sensor_total_diagonal * (sensor_total_array_width  / sensor_total_array_diagonal)
+# sensor_total_height   = sensor_total_diagonal * (sensor_total_array_height / sensor_total_array_diagonal)
+
+print("sensor  total: width = %.6f, height = %.6f, diagonal = %.6f" % (
+    sensor_total_width,
+    sensor_total_height,
+    sensor_total_diagonal))
+
+sensor_active_array_width    = 5599 # p
+sensor_active_array_height   = 4927 # p
+sensor_active_array_diagonal = math.hypot(sensor_active_array_width, sensor_active_array_height)
+
+sensor_active_width    = (sensor_active_array_width    / sensor_total_array_width)    * sensor_total_width
+sensor_active_height   = (sensor_active_array_height   / sensor_total_array_height)   * sensor_total_height
+sensor_active_diagonal = (sensor_active_array_diagonal / sensor_total_array_diagonal) * sensor_total_diagonal
+
+print("sensor active: width = %.6f, height = %.6f, diagonal = %.6f" % (
+    sensor_active_width,
+    sensor_active_height,
+    sensor_active_diagonal))
+
+# https://community.gopro.com/s/article/HERO11-Black-Video-Settings-And-Resolutions
+
+gopro_array_width    = 5312 # p
+gopro_array_height   = 4648 # p
+gopro_array_diagonal = math.hypot(gopro_array_width, gopro_array_height)
+
+gopro_sensor_width    = (gopro_array_width    / sensor_total_array_width)    * sensor_total_width
+gopro_sensor_height   = (gopro_array_height   / sensor_total_array_height)   * sensor_total_height
+gopro_sensor_diagonal = (gopro_array_diagonal / sensor_total_array_diagonal) * sensor_total_diagonal
+
+print("gopro  active: width = %.6f, height = %.6f, diagonal = %.6f" % (
+    gopro_sensor_width,
+    gopro_sensor_height,
+    gopro_sensor_diagonal))
+
+# https://thinglabs.io/gopro-focal-length-guide
+
+gopro_focal_length = 2.92 # mm
+
+print("\n--- fisheye field of view (degrees) ---\n")
+
+# https://en.wikipedia.org/wiki/Fisheye_lens
+
+equidistant_angle  = lambda length: math.degrees(length / gopro_focal_length)
+
+gopro_fov_width    = 2.0 * equidistant_angle(gopro_sensor_width    * 0.5)
+gopro_fov_height   = 2.0 * equidistant_angle(gopro_sensor_height   * 0.5)
+gopro_fov_diagonal = 2.0 * equidistant_angle(gopro_sensor_diagonal * 0.5)
+
+print("gopro fov: width = %.6f, height = %.6f, diagonal = %.6f" % (
+    gopro_fov_width,
+    gopro_fov_height,
+    gopro_fov_diagonal))
+
+print("\n--- rectilinear focal length (mm) ---\n")
+
+rectilinear_focal_length = lambda length: length * math.tan(math.radians(90.0 - equidistant_angle(length)))
+
+rectilinear_focal_length_width    = rectilinear_focal_length(gopro_sensor_width    * 0.5)
+rectilinear_focal_length_height   = rectilinear_focal_length(gopro_sensor_height   * 0.5)
+rectilinear_focal_length_diagonal = rectilinear_focal_length(gopro_sensor_diagonal * 0.5)
+
+print("rectilinear focal length: width = %.6f, height = %.6f, diagonal = %.6f" % (
+    rectilinear_focal_length_width,
+    rectilinear_focal_length_height,
+    rectilinear_focal_length_diagonal))