It s the most convenient but also time consuming.
Cv mat set to zero.
Element i j i 0 based row index j 0 based column index of a matrix can be retrieved or modified using cv mat elem macro.
Uchar pixval cv mat elem grayimg uchar i j cv mat elem cameramatrix float 0 2 image width 0 5f.
The one régis mentioned is called on the fly ra in opencv tutorial.
Based on the tutorial s experiment it also lists performance differences in all the 4 methods.
Fully transparent pixels should have alpha set to 0 fully opaque pixels should have alpha set to 255 65535 see the code sample below.
Obviously providing a beta value of 1 0 would have made this example exactly the same as a regular add function with no transparency for the overlay text.
For cv mat the documentation says that.
However opencv crew are trying to support c features including templates.
It means that you can zero the matrix like this i couldn t find equivalent overloads for matx or sparsemat.
Inline void zero cv mat m m 0.
In fact there are 4 kinds of methods to get set a pixel value in a cv mat object as described in the opencv tutorial.
It passes the number of dimensions 1 to the mat constructor but the created array will be 2 dimensional with the number of columns set to 1.
If the format depth or channel order is different use mat convertto and cv cvtcolor to convert.
Matrix elements are stored row by row.
Otherwise it is set to zero.
Multiple images vector of mat can be saved in tiff format see the code sample below.
Use a copy constructor or assignment operator where there can be an array or expression on the right side see below.
To set all the matrix elements to the particular value after the construction use the assignment operator mat operator const scalar value.
So mat dims is always 2 can also be 0 when the array is empty.
In this kind of thresholding the destination pixel value is set to the corresponding source pixel value if the source pixel value is greater than the threshold.
To access multiple channel matrices you can use cv mat elem matrix.