make Mat from buffer byte

asked 2013-03-23 11:55:03 -0600

pocahentez
63 ●1 ●1 ●9

Hi,

I have a Byte buffer and i want to make a Mat.How can i achieve it using a java code?Should i make a bitmap with the byte buffer first then transform it to Mat?

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answered 2013-03-25 03:04:04 -0600

Andrey Pavlenko
1808 ●3 ●18 ●39

You need to allocate a Mat of the appropriate size and type and then use Mat.put() method:

byte buf[] = new byte[100];
//...
Mat m = new Mat(1, 100, CvType.CV_8UC1);
m.put(0, 0, buf);

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@AndreyPavlenko Is there a way to create a Mat backed by a NIO ByteBuffer allocated by us. Alternatively, is there a way to get the Buffer of a Mat ?

TimeManx ( 2013-09-12 11:10:05 -0600 )edit

@TimeManx No, it's not possible: Mat reallocates its buffer on native level when needed, so it's hard to share it between native and java without copying...

Andrey Pavlenko ( 2013-09-14 10:27:17 -0600 )edit

In JavaCV's OpenCV wrapper, the IplImage has a "getDirectByteBuffer" native method that will from JNI create a new ByteBuffer with the address of the data of the Mat. In my tests modifying pixels like that performs much better than copying byte arrays to and from the Mat.