How to fill Matrix with zeros in OpenCV

Question

The code below causes an exception  Why    include  lt opencv2 core core hpp gt   include  lt iostream gt   using namespace cv  using namespace std   void main          try           Mat m1   Mat 1 1  CV 64F  0           m1 at lt double gt  0 0    0            catch cv  Exception  amp e            cerr  lt  lt  e what    lt  lt  endl             Error is follows   OpenCV Error  Assertion failed  dims  lt   2  amp  amp  data  amp  amp   unsigned i0  lt   unsigned size p 0   amp  amp   unsigned  i1 DataType lt  Tp gt   channels   lt   unsigned  size p 1  channels     amp  amp      sizeof size t  lt  lt 28  0x8442211   gt  gt    DataType lt  Tp gt   depth   amp    1  lt  lt  3   - 1   4   amp  15     elemSize1    in unknown function  file  OPENCV DIR  build include opencv2 core mat hpp  line 537   UPDATE  If tracing this code  I see that constructor line calls the constructor  inline Mat  Mat int  rows  int  cols  int  type  void   data  size t  step    Why  This prototype has 5 parameters  while I am providing 4 arguments

User · Answer

You can choose filling zero data or create zero Mat.

Filling zero data with setTo():
```
img.setTo(Scalar::all(0));
```
Create zero data with zeros():
```
img = zeros(img.size(), img.type());
```

The img changes address of memory.

User · Answer

Because the last parameter is optional and also the data pointer should point somewhere appropriate     inline Mat  Mat int  rows  int  cols  int  type  void   data  size t  step  double mydata 1   Mat m1   Mat 1 1  CV 64F  mydata    m1 at lt double gt  0 0    0    But better do it directly with this template-based constructor     inline Mat  Mat int  rows  int  cols  int  type  const Scalar amp   s  Mat m1   Mat 1 1  CV 64F  cvScalar 0        or even Mat m1   Mat 1 1  CV 64F  double 0

User · Answer

If You are more into programming with templates  You may also do it this way     template lt typename  Tp gt      some algo     cv  Mat mat   cv  Mat  lt  Tp gt   zeros rows  cols   mat at lt  Tp gt  i  j    val

User · Answer

I presume you are talking about filling zeros of some existing mat  How about this      mat    0

User · Answer

use cv  mat  setto  img setTo cv  Scalar redVal greenVal blueVal

User · Answer

You can use this to fill zeroes in a Mat object already containing data   image1   Scalar  all 0     For eg  if you use it this way   Mat image image1  image   imread  IMG 20160107 185956 jpg   CV LOAD IMAGE COLOR        Read the file  if   image data                                   Check for invalid input       cout  lt  lt    Could not open or find the image   lt  lt  std  endl       return -1    cvtColor image image1 CV BGR2GRAY   image1   Scalar  all 0     It will work fine  But you cannot use this for uninitialised Mat  For that you can go for other options mentioned in above answers  like  Mat drawing   Mat  zeros  image size    CV 8UC3

User · Answer

Mat img   img Mat  zeros size of image CV 8UC3    if you want it to be of an image img1  img Mat  zeros img1 size CV 8UC3

User · Answer

How to fill Matrix with zeros in OpenCV    To fill a pre-existing Mat object with zeros  you can use Mat  zeros    Mat m1        m1   Mat  zeros 1  1  CV 64F     To intialize a Mat so that it contains only zeros  you can pass a scalar with value 0 to the constructor   Mat m1   Mat 1 1  CV 64F  0 0                                 double literal   The reason your version failed is that passing 0 as fourth argument matches the overload taking a void  better than the one taking a scalar

[c++] How to fill Matrix with zeros in OpenCV?

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