boofcv.alg.filter.binary.GThresholdImageOps Java Examples

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Example #1
Source File: ContourHelper.java    From cineast with MIT License 6 votes vote down vote up 
/**
 * Applies a contour-detection algorithm on the provided image and returns a list of detected contours. First, the image
 * is converted to a BinaryImage using a threshold algorithm (Otsu). Afterwards, blobs in the image are detected using
 * an 8-connect rule.
 *
 * This method provides the best results if the image is a black & white, i.e. factually binary, image!
 * See {@link ContourHelper#segmentImageByColour(BufferedImage,float[])} to convert a coloured image to a binary image.
 *
 * @param image BufferedImage in which contours should be detected.
 * @return List of contours.
 */
public static List<Contour> getContours(BufferedImage image) {
    /* Draw a black frame around to image so as to make sure that all detected contours are internal contours. */
    BufferedImage resized = new BufferedImage(image.getWidth() + 4, image.getHeight() + 4, image.getType());
    Graphics g = resized.getGraphics();
    g.setColor(Color.BLACK);
    g.fillRect(0,0,resized.getWidth(),resized.getHeight());
    g.drawImage(image, 2,2, image.getWidth(), image.getHeight(), null);

    /* Convert to BufferedImage to Gray-scale image and prepare Binary image. */
    GrayF32 input = ConvertBufferedImage.convertFromSingle(resized, null, GrayF32.class);
    GrayU8 binary = new GrayU8(input.width,input.height);
    GrayS32 label = new GrayS32(input.width,input.height);

    /* Select a global threshold using Otsu's method and apply that threshold. */
    double threshold = GThresholdImageOps.computeOtsu(input, 0, 255);
    ThresholdImageOps.threshold(input, binary,(float)threshold,true);

    /* Remove small blobs through erosion and dilation;  The null in the input indicates that it should internally
     * declare the work image it needs this is less efficient, but easier to code. */
    GrayU8 filtered = BinaryImageOps.erode8(binary, 1, null);
    filtered = BinaryImageOps.dilate8(filtered, 1, null);

    /* Detect blobs inside the image using an 8-connect rule. */
    return BinaryImageOps.contour(filtered, ConnectRule.EIGHT, label);
}