fastClip.java

/**
 * How to create a BufferedImage from a sub rectangle of another BufferedImage, a.k.a. 'clipping'.
 * inspired by :
 * http://stackoverflow.com/questions/2825837/java-how-to-do-fast-copy-of-a-bufferedimages-pixels-unit-test-included
 *
 * Does an arraycopy of the relevant part of the rasters.
 * 
 */
BufferedImage src = ImageIO.read(new File("SomeFile.png"));

Rectangle clip = new Rectangle((src.getWidth() - 200) / 2, (src.getHeight() - 200) / 2, 200, 200);

BufferedImage dst = new BufferedImage(clip.width, clip.height, src.getType());

Object srcbuf = null;
Object dstbuf = null;

int mpx = src.getWidth() * src.getHeight();
int factor = 1;
DataBuffer buff = src.getRaster().getDataBuffer();
/**
 * Different type of image have different type of underlying buffer. Each type has a different number of cells
 * dedicated to a single pixel.
 */
if (buff instanceof DataBufferByte) {
	srcbuf = ((DataBufferByte) buff).getData();
	dstbuf = ((DataBufferByte) dst.getRaster().getDataBuffer()).getData();
	factor = ((DataBufferByte) buff).getData().length / mpx;
}
if (buff instanceof DataBufferDouble) {
	srcbuf = ((DataBufferDouble) buff).getData();
	dstbuf = ((DataBufferDouble) dst.getRaster().getDataBuffer()).getData();
	factor = ((DataBufferDouble) buff).getData().length / mpx;
}
if (buff instanceof DataBufferFloat) {
	srcbuf = ((DataBufferFloat) buff).getData();
	dstbuf = ((DataBufferFloat) dst.getRaster().getDataBuffer()).getData();
	factor = ((DataBufferFloat) buff).getData().length / mpx;
}
if (buff instanceof DataBufferInt) {
	srcbuf = ((DataBufferInt) buff).getData();
	dstbuf = ((DataBufferInt) dst.getRaster().getDataBuffer()).getData();
	factor = ((DataBufferInt) buff).getData().length / mpx;
}
if (buff instanceof DataBufferShort) {
	srcbuf = ((DataBufferShort) buff).getData();
	dstbuf = ((DataBufferShort) dst.getRaster().getDataBuffer()).getData();
	factor = ((DataBufferShort) buff).getData().length / mpx;
}
if (buff instanceof DataBufferUShort) {
	srcbuf = ((DataBufferUShort) buff).getData();
	dstbuf = ((DataBufferUShort) dst.getRaster().getDataBuffer()).getData();
	factor = ((DataBufferUShort) buff).getData().length / mpx;
}

int srcOffset = src.getWidth() * clip.y * factor + clip.x * factor;
int dstOffset = 0;

final int dstLineOffset = clip.width * factor;
final int srcLineOffset = src.getWidth() * factor;

/** Actually copying the pixel data from src to dst.*/
for (int y = 0; y < clip.height; y++) {
	System.arraycopy(srcbuf, srcOffset, dstbuf, dstOffset, clip.width * factor);
	srcOffset += srcLineOffset;
	dstOffset += dstLineOffset;
}
//done !