The opencv Mat object (java)

java

asked 2015-03-13 02:49:58 -0600

Nawara
11 ●2 ●3

updated 2015-03-13 07:23:58 -0600

FooBar
2938 ●9 ●37 http://magazino.eu/

I'am new to opencv I want to understand the opencv Mat class

For the get method

I try the first one int get(int row, int col, byte[] data) with this example

  Mat mat = Mat.eye( 3, 3, CvType.CV_8UC1 );
  System.out.println(mat.dump());
  byte[] data = new byte[mat.cols() * mat.rows() * (int)mat.elemSize()];
  System.out.println(data.length);-->9
  System.out.println( mat.get(0, 0, data)); -->9

but I can't understand

1) the role of the third argument byte[] data

2) and the result

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answered 2015-03-13 04:59:13 -0600

dennisb
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The array "data" gives you the result of a single element of the Mat object. Thus, your initialization is wrong:

byte[] data = new byte[(int)mat.elemSize()];

However, if you're using a Mat with a single channel only you may also ignore the array:

System.out.println(mat.get(0, 0, new byte[(int) mat.elemSize()]));

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sorry, but you're wrong about this.

mat.get(0, 0, data) retrieves as many bytes as you allocate.

if you have an array of mat.elemSize(), it will retrieve a single element, if you have mat.elemSize() * mat.total() bytes, it will retrieve the whole Mat content.

e.g, a Mat(3,3,CV_32F) will have 3x3x4 bytes, and a Mat(3,3,CV_8UC3) will have 3x3x3 bytes.