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OpenCV

Resources

Basic Data Types

What are the basic data types in OpenCV?
  • Template class cv::Point<> with aliases in form of cv::Point{2,3}{i,f,d}
  • Class cv::Scalar<> a four dimensional point derived from cv::Vec<double, 4>
  • Template class cv::Vec<> known as fixed vector classes with aliases in form of cv::Vec{2,3,4,6}{b,w,s,i,f,d}
  • Template class cv::Matx<> known as fixed matrix classes with aliases in form of cv::Matx{1,2,3,4,6}{1,2,3,4,6}{f,d}
  • Template class cv::Size<> with aliases in form of cv::Size{2,3}{i,f,d}
  • Class cv::Rect<>
  • Class cv::RotatedRect<>

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::Point<> template class?

The point class is a container of two or three values of one of the primitive types and are derived from their own template.

Operation Example
Default constructors cv::Point2i{} cv::Point3f{}
Copy constructor cv::Point3f{p}
Value constructor cv::Point2i{x0, x1} cv::Point3d{x0, x1, x2}
Cast to fixed vector (cv::Vec3d) cv::Point3d{}
Member access p.x p.y
Dot product float x = p1.dot(p2)
Double-precision dot product double x = p1.ddot(p2)
Cross product p1.cross(p2)
Query if Point is inside Rect p.inside(r)

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::Scalar class?

Description

A four-dimensional point class derived from cv::Vec<double, 4> inheriting all of the vector algebra operations, member access functions, and other properties.

Operation Example
Default constructor cv::Scalar{}
Copy constructor cv::Scalar{s}
Value constructor cv::Scalar{x0} cv::Scalar{x0, x1, x2, x3}
Element-wise multiplication s1.mul(s2)
Conjugation s.conj()
Real test s.isReal()

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::Size class?

The size classes are similar to point classes, and can be cast to and from them. The primary difference is that the point data members are named x and y, while the size data members are named width and height.

Operation Example
Default constructor cv::Size{} cv::Size2i{} cv::Size2f{}
Copy constructor cv::Size{s}
Value constructor cv::Size2f{w, h}
Member access sz.width sz.height
Compute area sz.area()

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::Rect class?

Description

Similar to cv::Point class there are x and y data members in cv::Rect class. Additionally, there are width and height data members.

Operation Example
Default constructor cv::Rect{}
Copy constructor cv::Rect{r}
Value constructor cv::Rect{x, y, w, h}
Construct from origin and size cv::Rect{p, sz}
Construct from two corners cv::Rect{tl, br}
Member access r.x r.y r.width r.height
Compute area r.area()
Extract upper-left corner r.tl()
Extract bottom-right corner r.br()
Determine if a point is inside r.contains(p)
Intersection of rectangles r1 &= r2
Minimum area rectangle `r1
Translate rectangle by an amount r += x
Enlarge rectangle by size r += s
Compare rectangles for exact quality r1 == r2
Compare rectangles for inequality r1 != r2

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::RotatedRect class?

Description

A non-template class holding a cv::Point2f member called center, a cv::Size2f called size, and one additional float called angle, with the latter representing the rotation of the rectangle around center.

Operation Example
Default constructor cv::RotatedRect{}
Copy constructor cv::RotatedRect{rr}
Value constructor cv::RotatedRect{p, sz, theta}
Construct from two corners cv::RotatedRect{p1, p2}
Member access rr.center rr.size rr.angle
Return a list of corners rr.points{pts[4]}

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::Matx template class?

Description

A matrix whose dimensions are known at compile time. The fixed vector class derives from the fixed matrix class, and other classes either derive frmo the fixed vector class or they rely on casting to the fixed vector class for many important operations.

Operation Example
Default constructor cv::Matx33f{} cv::Matx43d{}
Copy constructor cv::Matx22d{n22d}
Value constructor cv::Matx21f{x0, x1} cv::Matx22d{x0,x1,x2,x3}
Matrix of identical elements cv::Matx33f::all(x)
Matrix of zeros cv::Matx23d::zeros()
Matrix of ones cv::Matx16f::ones()
Unit matrix cv::Matx33f::eye()
Diagonal of matrix m31f = cv::Matx33f::diag()
Matrix of uniformly distributed entries m33f = cv::Matx33f::randu(min, max)
Matrix of normally distributed entries m33f = cv::Matx33f::nrandn(mean, variance)
Member access m(i,j) m(i)
Matrix algebra m1 = m0 m0 * m1 m0 + m1 m0 - m1
Singelton algebra m * a a * m m / a
Comparison m1 == m2 m1 != m2
Dot product m1.dot(m2)
Double-precision dot product m1.ddot(m2)
Reshape matrix m91f = m33f.reshape<9, 1>()
Extract submatrix m44f.get_minor<2, 2>(i, j)
Extract row m41f = m44f.row(i)
Extract column m14f = m44f.col(j)
Extract diagonal m41f = m44f.diag()
Matrix Transpose n44f = m44f.t()
Invert Matrix n44f = m44f.inv(method = cv::DECOMP_LU)
Solve linear system m31f = m33f.solve(rhs31f, method)
Per-element multiplication m1.mul(m2)

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::Vec template class?

The fixed vector classes are derived from fixed matrix classes.

Alias templates are cv::Vec{2,3,4,6}{b,s,w,i,f,d}

Operation Example
Default constructor cv::Vec2s{} cv::Vec6d{}
Copy constructor cv::Vec3f{v3f}
Value constructor cv::Vec2f{x0, x1} cv::Vec6d{x0,x1,x2,x3,x4,x5}
Member access v4f[i] v3w(j)
Cross-product v3f.cross(u3f)

Resources

  • Learning OpenCV 3 - Chapter 3

References

What operations are supported by cv::Complex<> class template?

The cv::Complex template class is not indentical to, but is compatible with, and can be cast to and from, the std::complex<>.

In std::complex<> the real and imaginary parts are accessed through the member functions real() and imag(), while in cv::Complex<> they are directly accessible as public members re and im.

Operation Example
Default constructor cv::Complexf{} cv::Complexd{}
Copy constructor cv::Complexd{c}
Value constructor cv::Complexd{re) cv::Complexd{re, im}
Member access z1.re z2.im
Complex conjugate z2 = z1.conj()

Resources

  • Learning OpenCV 3 - Chapter 3

References

Drawing

Annotating