How to edit/reading pixels from Mat(Vec3b) using Java

asked 2013-06-11 02:56:43 -0600

orochi
72 ●4 ●6 ●11

Hi guys, how to edit or reading pixels from Mat with type Vec3b using java. In c++ we can use something like this

matImage.at<Vec3b>(x,y)[0]; // for blue
matImage.at<Vec3b>(x,y)[1]; // for grey
matImage.at<Vec3b>(x,y)[2]; // for red

or we can use something like this

for(int i=0; i<A.rows; i++){
   for(int j=0; j<A.cols; j++){
           A.data[A.channels()*(A.cols*i + j) + 0] = 0;
           A.data[A.channels()*(A.cols*i + j) + 1] = 0;
           A.data[A.channels()*(A.cols*i + j) + 2] = 0;
    }
}

but how to do it using Java? i already search it, i got stuck, i still dont have clear idea how to edit/reading it in Java language.

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answered 2013-06-11 11:43:50 -0600

Daniil Osokin

2197 ●5 ●32

updated 2013-06-13 06:38:55 -0600

Hi! Try something like this:


// assume, that Mat with three channel
byte[] sourceBuffer = new byte[srcMat.total() * srcMat.channels()];
srcMat.get(0, 0, sourceBuffer);
int cols = srcMat.cols();
int rows = srcMat.rows();
for (int y = 0; y < rows; y++){
  for (int x = 0; x < cols * 3; x += 3){
    for (int channelId = 0; channelId < 3; channelId++){
          sourceBuffer[y * cols + x + channelId] = 0;
    }
  }
}
srcMat.put(0, 0, destinationBuffer);

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hi @Daniil Osokin, thanks for the answer, but i've another question, for the sourceBuffer, are we only need srcMat.total()? because from this tutorial http://answers.opencv.org/question/5/how-to-get-and-modify-the-pixel-of-mat-in-java/, he multiply it with srcMat.channel(). what is the difference?

orochi ( 2013-06-12 10:27:21 -0600 )edit

Mat.total() returns number of pixels, so here should be srcMat.total() * srcMat.channels().

Daniil Osokin ( 2013-06-13 06:51:23 -0600 )edit

Thank you @Daniil Osokin, if you have any good documentation or tutorial or example about developing an app using opencv and java, can you share it?

orochi ( 2013-06-13 08:44:16 -0600 )edit

You can look through android tutorials (http://opencv.org/android). In general developing is very similar with java apps. Here the docs for java: http://docs.opencv.org/java/

Daniil Osokin ( 2013-06-14 02:19:40 -0600 )edit

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answered 2013-06-11 12:03:02 -0600

gargsl
41 ●1 ●1 ●4

Hey, I was stuck on this yesterday too. There are two ways of doing this. Here, I have explained both the methods -

http://answers.opencv.org/question/14961/using-get-and-put-to-access-pixel-values-in-java/

Let me know if you have any other questions.

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hey @gargsl, thank you for the answer, i really appreciate it. actually i have a lot of question regarding opencv and java. if you have any good documentation or tutorial or example about developing an app using opencv and java, can you share it?

orochi ( 2013-06-13 09:01:00 -0600 )edit

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