m1-ENSL/seam-carving
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Correct indices and near equality

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augustin64 2025-03-26 15:36:25 +01:00
parent 1d28489c11
commit 7c2f9b36d7
1 changed files with 33 additions and 25 deletions
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58
src/seam-carving.cpp
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@ -19,6 +19,11 @@ int min(int a, int b) {
return a < b ? a : b; return a < b ? a : b;
} }
bool nearly_equal(float a, float b) {
return std::nextafter(a, std::numeric_limits<float>::lowest()) <= b
&& std::nextafter(a, std::numeric_limits<float>::max()) >= b;
}
void export_image(const char* filename, const void* data, int width, int height, int nbChannels) { void export_image(const char* filename, const void* data, int width, int height, int nbChannels) {
if (!silent) std::cout << "Exporting to \"" << filename << "\".." << std::endl; if (!silent) std::cout << "Exporting to \"" << filename << "\".." << std::endl;
int errcode = stbi_write_png(filename, width, height, nbChannels, data, nbChannels*width); int errcode = stbi_write_png(filename, width, height, nbChannels, data, nbChannels*width);
@ -67,15 +72,15 @@ std::vector<int> optimal_vertical_seam(std::vector<float> energy, int width, int
std::vector<float> dyn_energy(width*height); std::vector<float> dyn_energy(width*height);
//* Find an end of the minimal connected vertical/horizontal seam //* Find an end of the minimal connected vertical/horizontal seam
for (auto i=1; i < height; i++) { for (auto i=0; i < width; i++) {
dyn_energy[width*i] = energy[width*i]; dyn_energy[i] = energy[i];
} }
for (auto j=1; j < width; j++) { for (auto i=1; i < height; i++) {
for (auto i=0; i < height; i++) { for (auto j=0; j < width; j++) {
float bot_center = (i > 0) ? dyn_energy[width*(i-1)+j] : __FLT_MAX__; float bot_center = dyn_energy[width*(i-1) + j];
float bot_left = (i > 0 && j > 0) ? dyn_energy[width*(i-1)+(j-1)] : __FLT_MAX__; float bot_left = (j > 0) ? dyn_energy[width*(i-1) + (j-1)] : __FLT_MAX__;
float bot_right = (i > 0 && j+1 < width) ? dyn_energy[width*(i-1)+(j+1)] : __FLT_MAX__; float bot_right = (j+1 < width) ? dyn_energy[width*(i-1) + (j+1)] : __FLT_MAX__;
dyn_energy[width*i+j] = fmin( dyn_energy[width*i+j] = fmin(
bot_center, bot_center,
@ -83,7 +88,7 @@ std::vector<int> optimal_vertical_seam(std::vector<float> energy, int width, int
bot_left, bot_left,
bot_right bot_right
) )
) + energy[width*i+j]; ) + energy[width*i + j];
} }
} }
@ -92,9 +97,9 @@ std::vector<int> optimal_vertical_seam(std::vector<float> energy, int width, int
int min_idx = -1; int min_idx = -1;
float min_val = __FLT_MAX__; float min_val = __FLT_MAX__;
for (auto j=0; j < width; j++) { for (auto j=0; j < width; j++) {
if (min_val > dyn_energy[width*(height-1)+j]) { if (min_val > dyn_energy[width*(height-1) + j]) {
min_idx = j; min_idx = j;
min_val = dyn_energy[width*(height-1)+j]; min_val = dyn_energy[width*(height-1) + j];
} }
} }
result[height-1] = min_idx; result[height-1] = min_idx;
@ -102,22 +107,25 @@ std::vector<int> optimal_vertical_seam(std::vector<float> energy, int width, int
//* Backtracking to find the path //* Backtracking to find the path
for (auto i=height-1; i > 0; i--) { for (auto i=height-1; i > 0; i--) {
// We want to find either (bot_l, bot_c, bot_r) with dyn_energy[.] = min_val - energy[cur] // We want to find either (bot_l, bot_c, bot_r) with dyn_energy[.] = min_val - energy[cur]
float objective_energy = min_val - energy[i*width+min_idx]; //! With float, do we always have x + y - y = x ? float objective_energy = min_val - energy[width*i + min_idx];
if (dyn_energy[(i-1)+height*min_idx] == objective_energy) { //! With float, we don't always have x + y - y = x
// min_idx does not change if (nearly_equal(dyn_energy[width*(i-1) + min_idx], objective_energy)) {
min_val = dyn_energy[(i-1)+height*min_idx]; // min_idx does not change
} else if (min_idx > 0 && dyn_energy[(i-1)+height*(min_idx-1)] == objective_energy) { min_val = dyn_energy[(i-1)*width + min_idx];
min_val = dyn_energy[(i-1)+height*(min_idx - 1)]; } else if (min_idx > 0 && nearly_equal(dyn_energy[(i-1)*width + (min_idx-1)], objective_energy)) {
min_idx = min_idx - 1; min_val = dyn_energy[(i-1)*width + (min_idx-1)];
} else if (min_idx+1 < width && dyn_energy[(i-1)+height*(min_idx+1)] == objective_energy) { min_idx = min_idx - 1;
min_val = dyn_energy[(i-1)+height*(min_idx + 1)]; } else if (min_idx+1 < width && nearly_equal(dyn_energy[(i-1)*width + (min_idx+1)], objective_energy)) {
min_idx = min_idx + 1; min_val = dyn_energy[(i-1)*width + (min_idx+1)];
} else { min_idx = min_idx + 1;
std::cerr << "Unable to backtrack path !" << std::endl; } else {
exit(1); std::cerr << dyn_energy[(i-1)*width + min_idx] <<", "<< dyn_energy[(i-1)*width + (min_idx-1)]
} <<", "<< dyn_energy[(i-1)*width + (min_idx+1)] <<" != "<< objective_energy << std::endl;
result[i-1] = min_idx; std::cerr << "Unable to backtrack path !" << std::endl;
exit(1);
}
result[i-1] = min_idx;
} }
return result; return result;