Conversion to Java of OpenCVUtils class and some classes from chapter 04

[saudet]

If you could send a pull request for OpenCVUtilsJava.java (and maybe name it just OpenCVUtils.java) on the repo for JavaCV, I'd merge that it there (along with a port of OpenCVUtilsTest.scala would be nice too). Then we could also use it from Scala in the examples. @jpsacha what do you think?

[jpsacha]

@saudet it is fine with me if OpenCVUtils goes to JavaCV. After the next release I can remove corresponding methods from the javacv-examples.

@johngodoi the Ex2ComputeHistogramGraphJava example can be simplified. No need to extend JFrame or create a separate thread:

package opencv2_cookbook.chapter04;

import org.bytedeco.javacpp.opencv_core.Mat;

import java.awt.image.BufferedImage;
import java.io.File;

import static opencv2_cookbook.OpenCVUtils.loadAndShowOrExit;
import static opencv2_cookbook.OpenCVUtils.show;
import static org.bytedeco.javacpp.opencv_imgcodecs.IMREAD_GRAYSCALE;

/**
 * The second example for section "Computing the image histogram" in Chapter 4, page 92.
 * Displays a graph of a histogram created using utility class [[opencv2_cookbook.chapter04.Histogram1D]].
 */
public class Ex2ComputeHistogramGraphJava {

    public static void main(final String[] args) {
        Mat src = loadAndShowOrExit(new File("data/group.jpg"), IMREAD_GRAYSCALE);

        // Calculate histogram
        Histogram1DJava h = new Histogram1DJava();
        BufferedImage histogram = h.getHistogramImage(src);
        // Display the graph
        show(histogram, "Histogram");
    }
}

There is also an unnecessary canvas.waitKey() in OpenCVUtilsJava#show(BufferedImage, String).

[johngodoi]

@saudet OpenCVUtils is not totally translated to Java, should I still send a pull to javacv?

@jpsacha I removed JFrame extension and the thread initialization.

[saudet]

It would need to be in Java, yes. Please send a pull request if you make a Java version.

[saudet]

Or do you mean that you didn't translate the whole OpenCVUtils class? That's fine, you can start by sending what you have.

[johngodoi]

@saudet I didn't translate the whole class

[saudet]

That's fine, please send what you have! Thanks

[jpsacha]

@johngodoi Thank you for proving the Java versions. They are now merged.

[johngodoi]

I would like to thank you too, for the support and dedication. I will keep doing it but, sadly, I can't focus on it and do it as frequent as I wish.