Examples of Matlab to OpenCV conversions

Question

From time to time I have to port some Matlab Code to OpenCV.

Almost always there is a way to do it and an appropriate function in OpenCV. Nevertheless its not always easy to find.

Therefore I would like to start this summary to find and gather some equivalents between Matlab and OpenCV.

I use the Matlab function as heading and append its description from Matlab help. Afterwards a OpenCV example or links to solutions are appreciated.

Answer 1

Repmat

Replicate and tile an array. B = repmat(A,M,N) creates a large matrix B consisting of an M-by-N tiling of copies of A. The size of B is [size(A,1)*M, size(A,2)*N]. The statement repmat(A,N) creates an N-by-N tiling.

B = repeat(A, M, N)

OpenCV Docs

Find

Find indices of nonzero elements. I = find(X) returns the linear indices corresponding to the nonzero entries of the array X. X may be a logical expression. Use IND2SUB(SIZE(X),I) to calculate multiple subscripts from the linear indices I.

Similar to Matlab's find

Conv2

Two dimensional convolution. C = conv2(A, B) performs the 2-D convolution of matrices A and B. If [ma,na] = size(A), [mb,nb] = size(B), and [mc,nc] = size(C), then mc = max([ma+mb-1,ma,mb]) and nc = max([na+nb-1,na,nb]).

Similar to Conv2

Imagesc

Scale data and display as image. imagesc(...) is the same as IMAGE(...) except the data is scaled to use the full colormap.

SO Imagesc

Imfilter

N-D filtering of multidimensional images. B = imfilter(A,H) filters the multidimensional array A with the multidimensional filter H. A can be logical or it can be a nonsparse numeric array of any class and dimension. The result, B, has the same size and class as A.

SO Imfilter

Imregionalmax

Regional maxima. BW = imregionalmax(I) computes the regional maxima of I. imregionalmax returns a binary image, BW, the same size as I, that identifies the locations of the regional maxima in I. In BW, pixels that are set to 1 identify regional maxima; all other pixels are set to 0.

SO Imregionalmax

Ordfilt2

2-D order-statistic filtering. B=ordfilt2(A,ORDER,DOMAIN) replaces each element in A by the ORDER-th element in the sorted set of neighbors specified by the nonzero elements in DOMAIN.

SO Ordfilt2

Roipoly

Select polygonal region of interest. Use roipoly to select a polygonal region of interest within an image. roipoly returns a binary image that you can use as a mask for masked filtering.

SO Roipoly

Gradient

Approximate gradient. [FX,FY] = gradient(F) returns the numerical gradient of the matrix F. FX corresponds to dF/dx, the differences in x (horizontal) direction. FY corresponds to dF/dy, the differences in y (vertical) direction. The spacing between points in each direction is assumed to be one. When F is a vector, DF = gradient(F)is the 1-D gradient.

SO Gradient

Sub2Ind

Linear index from multiple subscripts. sub2ind is used to determine the equivalent single index corresponding to a given set of subscript values.

SO sub2ind

backslash operator or mldivide

solves the system of linear equations A*x = B. The matrices A and B must have the same number of rows.

cv::solve