Example Image Enhancement

• 

  Dark image before histogram adjustment

• 

  Image after its histogram has been globally adjusted

• 

  Image after its edges are enhanced

Demonstration of different image enhancement operations. If an image is excessively dark or light the visibility of features can be improved by adjusting its histogram. Another technique makes the edges in an image more pronounced by.

Example Code:

• ExampleImageEnhancement.java

Concepts:

• Visibility

Relevant Examples:

• Image Blur

Example Code

/**
 * Demonstration of various ways an image can be "enhanced". Image enhancement typically refers to making it easier
 * for people to view the image and pick out its details.
 *
 * @author Peter Abeles
 */
public class ExampleImageEnhancement {

	static String imagePath = "enhance/dark.jpg";
//	static String imagePath = "enhance/dull.jpg";

	static ListDisplayPanel mainPanel = new ListDisplayPanel();

	/**
	 * Histogram adjustment algorithms aim to spread out pixel intensity values uniformly across the allowed range.
	 * This if an image is dark, it will have greater contrast and be brighter.
	 */
	public static void histogram() {
		BufferedImage buffered = UtilImageIO.loadImageNotNull(UtilIO.pathExample(imagePath));
		GrayU8 gray = ConvertBufferedImage.convertFrom(buffered, (GrayU8)null);
		GrayU8 adjusted = gray.createSameShape();

		int[] histogram = new int[256];
		int[] transform = new int[256];

		ListDisplayPanel panel = new ListDisplayPanel();

		ImageStatistics.histogram(gray, 0, histogram);
		EnhanceImageOps.equalize(histogram, transform);
		EnhanceImageOps.applyTransform(gray, transform, adjusted);
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null), "Global");

		EnhanceImageOps.equalizeLocal(gray, 50, adjusted, 256, null);
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null), "Local");

		panel.addImage(ConvertBufferedImage.convertTo(gray, null), "Original");

		panel.setPreferredSize(new Dimension(gray.width, gray.height));
		mainPanel.addItem(panel, "Histogram");
	}

	/**
	 * Same as above but on a color image.
	 */
	public static void histogramColor() {
		BufferedImage buffered = UtilImageIO.loadImageNotNull(UtilIO.pathExample(imagePath));
		Planar<GrayU8> color = ConvertBufferedImage.convertFrom(buffered, true, ImageType.PL_U8);
		Planar<GrayU8> adjusted = color.createSameShape();

		int[] histogram = new int[256];
		int[] transform = new int[256];

		ListDisplayPanel panel = new ListDisplayPanel();

		// Apply the correction to each color band independently. Alternatively, you could compute the adjustment
		// on a gray scale image then apply the same transform to each band
		for (int bandIdx = 0; bandIdx < color.getNumBands(); bandIdx++) {
			ImageStatistics.histogram(color.getBand(bandIdx), 0, histogram);
			EnhanceImageOps.equalize(histogram, transform);
			EnhanceImageOps.applyTransform(color.getBand(bandIdx), transform, adjusted.getBand(bandIdx));
		}
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null, true), "Global");

		GEnhanceImageOps.equalizeLocal(color, 50, adjusted, 256, null);
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null, true), "Local");
		panel.addImage(buffered, "Original");

		panel.setPreferredSize(new Dimension(color.width, color.height));
		mainPanel.addItem(panel, "Histogram Color");
	}

	/**
	 * When an image is sharpened the intensity of edges are made more extreme while flat regions remain unchanged.
	 */
	public static void sharpen() {
		BufferedImage buffered = UtilImageIO.loadImageNotNull(UtilIO.pathExample(imagePath));
		GrayU8 gray = ConvertBufferedImage.convertFrom(buffered, (GrayU8)null);
		GrayU8 adjusted = gray.createSameShape();


		ListDisplayPanel panel = new ListDisplayPanel();

		EnhanceImageOps.sharpen4(gray, adjusted);
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null), "Sharpen-4");

		EnhanceImageOps.sharpen8(gray, adjusted);
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null), "Sharpen-8");

		panel.addImage(ConvertBufferedImage.convertTo(gray, null), "Original");

		panel.setPreferredSize(new Dimension(gray.width, gray.height));
		mainPanel.addItem(panel, "Sharpen");
	}

	/**
	 * Same as above but on a color image
	 */
	public static void sharpenColor() {
		BufferedImage buffered = UtilImageIO.loadImageNotNull(UtilIO.pathExample(imagePath));
		Planar<GrayU8> color = ConvertBufferedImage.convertFrom(buffered, true, ImageType.PL_U8);
		Planar<GrayU8> adjusted = color.createSameShape();

		ListDisplayPanel panel = new ListDisplayPanel();

		GEnhanceImageOps.sharpen4(color, adjusted);
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null, true), "Sharpen-4");

		GEnhanceImageOps.sharpen8(color, adjusted);
		panel.addImage(ConvertBufferedImage.convertTo(adjusted, null, true), "Sharpen-8");

		panel.addImage(buffered, "Original");

		panel.setPreferredSize(new Dimension(color.width, color.height));
		mainPanel.addItem(panel, "Sharpen Color");
	}

	public static void main( String[] args ) {
		histogram();
		histogramColor();
		sharpen();
		sharpenColor();
		ShowImages.showWindow(mainPanel, "Enhancement", true);
	}
}