java bufferedimage array data immediately changes

Question

    import javax.imageio.ImageIO;

    import org.bytedeco.javacv.FFmpegFrameGrabber;

    public class FrameData 
    {   
int count = 0;
int picWidth;
int picHeight;

BufferedImage img = null;

//GET FRAME COUNT
public int gf_count(int numofFrames, BufferedImage[] frameArray, String fileLocationsent, String videoNamesent) throws IOException
{        
    String fileLocation = fileLocationsent;
    String videoName = videoNamesent;

    int frameNums = numofFrames;
    int totFrames = 0;

            FFmpegFrameGrabber grab = new FFmpegFrameGrabber(fileLocation + videoName);

        try {   grab.start(); } 
        catch (Exception e) {   System.out.println("Unable to grab frames");  }

                    for(int i = 0 ; i < frameNums  ; i++) 
        {
            try 
            {                   
                frameArray[i]= grab.grab().getBufferedImage();
                totFrames = i;  
                File outputfile = new File(fileLocation + "GrayScaledImage" + i + ".jpg");
                ImageIO.write(frameArray[i], "jpg", outputfile);
            } 
            catch (Exception e) {   /*e.printStackTrace();*/    }
        }//END for

                return totFrames;

    }//END METHOD long getFrameCount()

Hope someone can explain this to me... I am just learning java so here goes... I wrote this code to count the number of frames in a .mov file and to test my buffered image array I generated files of the images. As the code is, it works as planned... The problem is immediately after the capturing, if I send the bufferedimages out as files, they all seem to be just the first image. see example below...

    for(int i = 0 ; i < frameNums  ; i++) 
        {
            try 
            {                   
                frameArray[i]= grab.grab().getBufferedImage();
                totFrames = i;  
                File outputfile = new File(fileLocation + "GrayScaledImage" + i + ".jpg");
                ImageIO.write(frameArray[i], "jpg", outputfile);
            } 
            catch (Exception e) {   /*e.printStackTrace();*/    }
        }//END for

And now if I change that to...

    for(int i = 0 ; i < frameNums  ; i++) 
        {
            try 
            {                   
                frameArray[i]= grab.grab().getBufferedImage();
                totFrames = i;  catch (Exception e) {   /*e.printStackTrace();*/    }}
    for(int j = 0; j < frameNums; j++)
    {
    File outputfile = new File(fileLocation + "GrayScaledImage" + j + ".jpg");
                ImageIO.write(frameArray[j], "jpg", outputfile);
    }

I don't understand why I am getting the same image repeatedly. If further information Is required, just lemme know, this is my first programming question online... Usually find what I am looking for that others have asked. Couldn't find this one. Thanks for your time Ken

Answer 1

The problem is that the grab().getBufferedImage() does its work in the same buffer every time. When you assign a reference to that buffer in your loop, you are assigning a reference to the same buffer numofFrames times. What you are writing then is not the first frame, but the last frame. In order to fix this you need to do a "deep copy" of the BufferedImage. See code below:

public class FrameData {
    BufferedImage img;
    Graphics2D g2; 
    // GET FRAME COUNT
    public int gf_count(int numFrames, BufferedImage[] frameArray, String fileLocation, String videoName) throws Exception, IOException {
        Java2DFrameConverter converter = new Java2DFrameConverter();
        int totFrames = 0;

        img = new BufferedImage(100, 50, BufferedImage.TYPE_INT_ARGB);
        g2 = img.createGraphics();

        FFmpegFrameGrabber grab = new FFmpegFrameGrabber(fileLocation + videoName);
        grab.start();
        for (int i = 0; i < numFrames; i++) {
            frameArray[i] = deepCopy(converter.convert(grab.grab()));
            totFrames = i;
        }
        for (int j = 0; j < totFrames; j++) {
            File outputfile = new File(fileLocation + "TImage" + j + ".jpg");
            ImageIO.write(frameArray[j], "jpg", outputfile);
        }
        return totFrames;
    }// END METHOD long getFrameCount()

    BufferedImage deepCopy(BufferedImage bi) {
        ColorModel cm = bi.getColorModel();
        boolean isAlphaPremultiplied = cm.isAlphaPremultiplied();
        WritableRaster raster = bi.copyData(null);
        return new BufferedImage(cm, raster, isAlphaPremultiplied, null);
    }
    // This does what the converter.convert seems to do, which
    // is decode an image into the same place over and over.
    // if you don't copy the result every time, then you end up
    // with an array of references to the same last frame.
    BufferedImage draw() {
        g2.setColor(new Color(-1));
        g2.fillRect(0, 0, 100, 50);
        g2.setColor(new Color(0));
        g2.drawLine(0, 0, (int)(Math.random()*100.0), (int)(Math.random()*50.0));        
        return img;
    }

    public static void main(String... args) throws Exception, IOException {
        new FrameData().run();        
    }
    private void run() throws Exception, IOException {
        BufferedImage images[] = new BufferedImage[50];
        gf_count(50, images, "C:/Users/karl/Videos/", "dance.mpg");
    }
}

I have included a draw() method that shows by example how work is done in the same BufferedImage repeatedly, in case you want to replicate the problem.

There are certainly other ways to do a deep copy and there may be issues with the one shown. Reference: How do you clone a BufferedImage.

PS> I updated the code to use the 1.1 version of the bytedeco library.