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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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49
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
// 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 ]
float* getAcosTable()
{
@ -495,11 +495,38 @@ struct IntelligentScissorsMB::Impl
// details: see section 3.1 of the article
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
{
if ((cost_p += weight_non_edge_compute * non_edge_feature.at<uchar>(q)) < cost_q)
{
const bool isDiag = (p.x != q.x) && (p.y != q.y);
float fG = gradient_magnitude.at<float>(q);
if (!isDiag)
{
fG *= sqrt2_inv;
}
if ((cost_p += weight_gradient_magnitude * fG) < cost_q)
{
const Point2f diff((float)(q.x - p.x), (float)(q.y - p.y));
@ -517,16 +544,11 @@ struct IntelligentScissorsMB::Impl
dq = -dq;
}
const float sqrt2_inv = 0.7071067811865475f; // 1.0 / sqrt(2)
if (isDiag)
{
dp *= sqrt2_inv; // normalize length of (q - p)
dq *= sqrt2_inv; // normalize length of (q - p)
}
else
{
fG *= sqrt2_inv;
}
#if 1
int dp_i = cvFloor(dp * ACOS_TABLE_SIZE); // dp is in range 0..1
@ -539,11 +561,10 @@ struct IntelligentScissorsMB::Impl
const float fD = (acosf(dp) + acosf(dq)) * CV_PI_inv; // TODO optimize acos calls (through tables)
#endif
float cost =
weight_non_edge_compute * non_edge_feature.at<uchar>(q) +
weight_gradient_direction * fD +
weight_gradient_magnitude * fG;
return cost;
cost_p += weight_gradient_direction * fD;
}
}
return cost_p < cost_q;
}
struct Pix
@ -625,8 +646,8 @@ struct IntelligentScissorsMB::Impl
CV_DbgCheckLE(cost_q, cost_r, "INTERNAL ERROR: sorted queue is corrupted");
#endif
float cost = cost_q + local_cost(q, r); // TODO(opt): compute partially until cost < cost_r
if (cost < cost_r)
float cost = cost_q;
if (add_local_cost(q, r, cost, cost_r))
{
#if 0 // avoid compiler warning
if (cost_r != FLT_MAX)