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imgproc: optimise local cost computation in IntelligentScissorsMB::buildMap

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This commit is contained in:
Christine Poerschke 2022-05-08 21:22:13 +01:00
parent 6b53fe8f7b
commit f597838685
1 changed files with 65 additions and 44 deletions
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109
modules/imgproc/src/intelligent_scissors.cpp
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@ -40,7 +40,7 @@ static const int neighbors_encode[8] = {
}; };
#define ACOS_TABLE_SIZE 64 #define ACOS_TABLE_SIZE 64
// acos_table[x + ACOS_TABLE_SIZE] = acos(x / ACOS_TABLE_SIZE) / CV_PI (see local_cost) // acos_table[x + ACOS_TABLE_SIZE] = acos(x / ACOS_TABLE_SIZE) / CV_PI (see add_local_cost)
// x = [ -ACOS_TABLE_SIZE .. ACOS_TABLE_SIZE ] // x = [ -ACOS_TABLE_SIZE .. ACOS_TABLE_SIZE ]
float* getAcosTable() float* getAcosTable()
{ {
@ -495,55 +495,76 @@ struct IntelligentScissorsMB::Impl
// details: see section 3.1 of the article // details: see section 3.1 of the article
const float* acos_table = getAcosTable(); const float* acos_table = getAcosTable();
float local_cost(const Point& p, const Point& q) const const float sqrt2_inv = 0.7071067811865475f; // 1.0 / sqrt(2)
/** @brief Adds local_cost(p, q) to cost_p.
*
* local_cost(p, q) is computed as
weight_non_edge_compute * non_edge_feature.at<uchar>(q) +
weight_gradient_direction * fD +
weight_gradient_magnitude * fG
*
* @param p point p (input)
* @param q point q (input)
* @param cost_p cost for p (input/output)
* @param cost_q cost for q (input)
*
* @return The boolean result of the (cost_p < cost_q) comparison.
*
* @note The computed output cost_p can be partial if (cost_p < cost_q) is false.
*/
bool add_local_cost(const Point& p, const Point& q, float& cost_p, const float cost_q) const
{ {
const bool isDiag = (p.x != q.x) && (p.y != q.y); if ((cost_p += weight_non_edge_compute * non_edge_feature.at<uchar>(q)) < cost_q)
float fG = gradient_magnitude.at<float>(q);
const Point2f diff((float)(q.x - p.x), (float)(q.y - p.y));
const Point2f Ip = gradient_direction(p);
const Point2f Iq = gradient_direction(q);
const Point2f Dp(Ip.y, -Ip.x); // D(p) - 90 degrees clockwise
const Point2f Dq(Iq.y, -Iq.x); // D(q) - 90 degrees clockwise
float dp = Dp.dot(diff); // dp(p, q)
float dq = Dq.dot(diff); // dq(p, q)
if (dp < 0)
{ {
dp = -dp; // ensure dp >= 0 const bool isDiag = (p.x != q.x) && (p.y != q.y);
dq = -dq;
}
const float sqrt2_inv = 0.7071067811865475f; // 1.0 / sqrt(2) float fG = gradient_magnitude.at<float>(q);
if (isDiag) if (!isDiag)
{ {
dp *= sqrt2_inv; // normalize length of (q - p) fG *= sqrt2_inv;
dq *= sqrt2_inv; // normalize length of (q - p) }
}
else if ((cost_p += weight_gradient_magnitude * fG) < cost_q)
{ {
fG *= sqrt2_inv;
} const Point2f diff((float)(q.x - p.x), (float)(q.y - p.y));
const Point2f Ip = gradient_direction(p);
const Point2f Iq = gradient_direction(q);
const Point2f Dp(Ip.y, -Ip.x); // D(p) - 90 degrees clockwise
const Point2f Dq(Iq.y, -Iq.x); // D(q) - 90 degrees clockwise
float dp = Dp.dot(diff); // dp(p, q)
float dq = Dq.dot(diff); // dq(p, q)
if (dp < 0)
{
dp = -dp; // ensure dp >= 0
dq = -dq;
}
if (isDiag)
{
dp *= sqrt2_inv; // normalize length of (q - p)
dq *= sqrt2_inv; // normalize length of (q - p)
}
#if 1 #if 1
int dp_i = cvFloor(dp * ACOS_TABLE_SIZE); // dp is in range 0..1 int dp_i = cvFloor(dp * ACOS_TABLE_SIZE); // dp is in range 0..1
dp_i = std::min(ACOS_TABLE_SIZE, std::max(0, dp_i)); dp_i = std::min(ACOS_TABLE_SIZE, std::max(0, dp_i));
int dq_i = cvFloor(dq * ACOS_TABLE_SIZE); // dq is in range -1..1 int dq_i = cvFloor(dq * ACOS_TABLE_SIZE); // dq is in range -1..1
dq_i = std::min(ACOS_TABLE_SIZE, std::max(-ACOS_TABLE_SIZE, dq_i)); dq_i = std::min(ACOS_TABLE_SIZE, std::max(-ACOS_TABLE_SIZE, dq_i));
const float fD = acos_table[dp_i + ACOS_TABLE_SIZE] + acos_table[dq_i + ACOS_TABLE_SIZE]; const float fD = acos_table[dp_i + ACOS_TABLE_SIZE] + acos_table[dq_i + ACOS_TABLE_SIZE];
#else #else
const float CV_PI_inv = static_cast<float>(1.0 / CV_PI); const float CV_PI_inv = static_cast<float>(1.0 / CV_PI);
const float fD = (acosf(dp) + acosf(dq)) * CV_PI_inv; // TODO optimize acos calls (through tables) const float fD = (acosf(dp) + acosf(dq)) * CV_PI_inv; // TODO optimize acos calls (through tables)
#endif #endif
float cost = cost_p += weight_gradient_direction * fD;
weight_non_edge_compute * non_edge_feature.at<uchar>(q) + }
weight_gradient_direction * fD + }
weight_gradient_magnitude * fG; return cost_p < cost_q;
return cost;
} }
struct Pix struct Pix
@ -625,8 +646,8 @@ struct IntelligentScissorsMB::Impl
CV_DbgCheckLE(cost_q, cost_r, "INTERNAL ERROR: sorted queue is corrupted"); CV_DbgCheckLE(cost_q, cost_r, "INTERNAL ERROR: sorted queue is corrupted");
#endif #endif
float cost = cost_q + local_cost(q, r); // TODO(opt): compute partially until cost < cost_r float cost = cost_q;
if (cost < cost_r) if (add_local_cost(q, r, cost, cost_r))
{ {
#if 0 // avoid compiler warning #if 0 // avoid compiler warning
if (cost_r != FLT_MAX) if (cost_r != FLT_MAX)