Example Interpolation

• Enlarging a small image with different interpolation methods
• 

  Nearest Neighbor

• 

  Bilinear

• 

  Bicubic

• 

  Polynomial

BoofCV provides abstract interfaces to apply different interpolation methods to all of its images. Bilinear is by far the most widely used interpolation method in computer vision.

Example Code:

• ExampleInterpolation.java

Concepts:

• Interpolation
• Image Distortion

Example Code

/**
 * Interpolation is used to convert an image, which is discrete by its nature, into a (piecewise) smooth function.
 * Interpolation is in many CV applications, such as feature detection, and when distorting images.  In this
 * example a low resolution is scaled up using several different techniques to make the differences easily visible.
 * For computer vision applications bilinear interpolation is almost always used.
 *
 * @author Peter Abeles
 */
public class ExampleInterpolation {
	public static void main( String[] args ) {
		String imagePath;
		imagePath = "eye01.jpg";
//		imagePath = "small_sunflower.jpg";

		BufferedImage buffered = UtilImageIO.loadImage(UtilIO.pathExample(imagePath));
		ListDisplayPanel gui = new ListDisplayPanel();

		gui.addImage(buffered, "Original");

		// For sake of simplicity assume it's a gray scale image.  Interpolation functions exist for planar and
		// interleaved color images too
		GrayF32 input = ConvertBufferedImage.convertFrom(buffered, (GrayF32)null);
		GrayF32 scaled = input.createNew(500, 500*input.height/input.width);

		for (InterpolationType type : InterpolationType.values()) {
			// Create the single band (gray scale) interpolation function for the input image
			InterpolatePixelS<GrayF32> interp = FactoryInterpolation.
					createPixelS(0, 255, type, BorderType.EXTENDED, input.getDataType());

			// Tell it which image is being interpolated
			interp.setImage(input);

			// Manually apply scaling to the input image.  See FDistort() for a built in function which does
			// the same thing and is slightly more efficient
			for (int y = 0; y < scaled.height; y++) {
				// iterate using the 1D index for added performance.  Altertively there is the set(x,y) operator
				int indexScaled = scaled.startIndex + y*scaled.stride;
				float origY = y*input.height/(float)scaled.height;

				for (int x = 0; x < scaled.width; x++) {
					float origX = x*input.width/(float)scaled.width;

					scaled.data[indexScaled++] = interp.get(origX, origY);
				}
			}

			// Add the results to the output
			BufferedImage out = ConvertBufferedImage.convertTo(scaled, null, true);
			gui.addImage(out, type.toString());
		}

		ShowImages.showWindow(gui, "Example Interpolation", true);
	}
}