9

I'm using the new OpenCV Java bindings to read an image and do some processing on the image. I'm trying to convert C code to Java using the Java bindings but can't seem to find the relevant methods:

C code:

cv::Mat img = cv::imread(argv[1]);
cv::Mat gray;
cv::cvtColor(img, gray, CV_BGR2GRAY);
int erosion_size = 5;
cv::Mat element = cv::getStructuringElement(cv::MORPH_CROSS,
                                       cv::Size(2 * erosion_size + 1, 2 * erosion_size + 1),
                                       cv::Point(erosion_size, erosion_size) );
cv::erode(gray, gray, element);

I can't find:

  • imread
  • cvtcolor
  • getStructuringElement
  • erode

I looked around the api here: http://docs.opencv.org/java/

Unfortunately the sample java code provided doesn't even show how to read an image!

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4 Answers 4

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26

To read an image with OpenCV for Java:

OpenCV 2.x (JavaDoc)

Mat img = Highgui.imread("path/to/img");

OpenCV 3.x (JavaDoc)

Mat img = Imgcodecs.imread("path/to/img");

In both versions you can pass a second parameter specifying how to load the image:

  • CV_LOAD_IMAGE_ANYDEPTH: returns 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.
  • CV_LOAD_IMAGE_COLOR: always convert image to a color one.
  • CV_LOAD_IMAGE_GRAYSCALE: always convert image to a grayscale one.

Example:

// OpenCV 2.x   
Mat img = Highgui.imread("path/to/img", Highgui.CV_LOAD_IMAGE_GRAYSCALE);
// OpenCV 3.x
Mat img = Imgcodecs.imread("path/to/img", Imgcodecs.CV_LOAD_IMAGE_GRAYSCALE);
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2 Comments

This is a cleaner answer.
Seems in the current OpenCV the constant is Imgcodecs.CV_LOAD_IMAGE_GRAYSCALE
6

If you have correctly installed Opencv with support for Java desktop and included opencv-2.4.4.jar , your should import:

import org.opencv.imgproc.Imgproc;
import org.opencv.core.Point;
import org.opencv.core.Size;
import org.opencv.highgui.Highgui;

And your code will look like this:

Mat img = Highgui.imread(argv[1], Highgui.CV_LOAD_IMAGE_GRAYSCALE);
int erosion_size = 5;
Mat element  = Imgproc.getStructuringElement(
    Imgproc.MORPH_CROSS, new Size(2 * erosion_size + 1, 2 * erosion_size + 1), 
    new Point(erosion_size, erosion_size)
);
Imgproc.erode(img, img, element);
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2 Comments

I know this is an old post, but i configured open-cv and all, i try running your code andi get: "Exception in thread "main" java.lang.UnsatisfiedLinkError: org.opencv.highgui.Highgui.imread_0(Ljava/lang/String;I)J at org.opencv.highgui.Highgui.imread_0(Native Method) at org.opencv.highgui.Highgui.imread(Highgui.java:306) at pack.ColoredObjectTrack.main(ColoredObjectTrack.java:41)"
You have not correctly referenced native library. Follow the tutorial with more attention.
1

for macOs you can use :

import org.opencv.imgcodecs.Imgcodecs;


Mat logo = Imgcodecs.imread("resources/images/gambar.jpg");

for me, I use opencv_java320.dll

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0

There is an important update to answer by @David Miguel.

Imgcodecs.CV_LOAD_IMAGE_GRAYSCALE is no longer available in opencv 4.x. You should rather use Imgcodecs.imread("/resources/images/test.png", Imgcodecs.IMREAD_GRAYSCALE) to load gray-scale image.

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