Java tutorial
//package net.gqu.utils; import java.awt.Color; import java.awt.Graphics2D; import java.awt.Image; import java.awt.RenderingHints; import java.awt.Toolkit; import java.awt.geom.AffineTransform; import java.awt.image.BufferedImage; import java.io.FileOutputStream; import java.io.OutputStream; import javax.swing.ImageIcon; import com.sun.image.codec.jpeg.JPEGCodec; import com.sun.image.codec.jpeg.JPEGImageEncoder; public class Thumbnail { /** * Reads an image in a file and creates a thumbnail in another file. * largestDimension is the largest dimension of the thumbnail, the other dimension is scaled accordingly. * Utilises weighted stepping method to gradually reduce the image size for better results, * i.e. larger steps to start with then smaller steps to finish with. * Note: always writes a JPEG because GIF is protected or something - so always make your outFilename end in 'jpg'. * PNG's with transparency are given white backgrounds */ public String createThumbnail(String inFilename, String outFilename, int largestDimension) { try { double scale; int sizeDifference, originalImageLargestDim; if (!inFilename.endsWith(".jpg") && !inFilename.endsWith(".jpeg") && !inFilename.endsWith(".gif") && !inFilename.endsWith(".png")) { return "Error: Unsupported image type, please only either JPG, GIF or PNG"; } else { Image inImage = Toolkit.getDefaultToolkit().getImage(inFilename); if (inImage.getWidth(null) == -1 || inImage.getHeight(null) == -1) { return "Error loading file: \"" + inFilename + "\""; } else { //find biggest dimension if (inImage.getWidth(null) > inImage.getHeight(null)) { scale = (double) largestDimension / (double) inImage.getWidth(null); sizeDifference = inImage.getWidth(null) - largestDimension; originalImageLargestDim = inImage.getWidth(null); } else { scale = (double) largestDimension / (double) inImage.getHeight(null); sizeDifference = inImage.getHeight(null) - largestDimension; originalImageLargestDim = inImage.getHeight(null); } //create an image buffer to draw to BufferedImage outImage = new BufferedImage(100, 100, BufferedImage.TYPE_INT_RGB); //arbitrary init so code compiles Graphics2D g2d; AffineTransform tx; if (scale < 1.0d) //only scale if desired size is smaller than original { int numSteps = sizeDifference / 100; int stepSize = sizeDifference / numSteps; int stepWeight = stepSize / 2; int heavierStepSize = stepSize + stepWeight; int lighterStepSize = stepSize - stepWeight; int currentStepSize, centerStep; double scaledW = inImage.getWidth(null); double scaledH = inImage.getHeight(null); if (numSteps % 2 == 1) //if there's an odd number of steps centerStep = (int) Math.ceil((double) numSteps / 2d); //find the center step else centerStep = -1; //set it to -1 so it's ignored later Integer intermediateSize = originalImageLargestDim, previousIntermediateSize = originalImageLargestDim; Integer calculatedDim; for (Integer i = 0; i < numSteps; i++) { if (i + 1 != centerStep) //if this isn't the center step { if (i == numSteps - 1) //if this is the last step { //fix the stepsize to account for decimal place errors previously currentStepSize = previousIntermediateSize - largestDimension; } else { if (numSteps - i > numSteps / 2) //if we're in the first half of the reductions currentStepSize = heavierStepSize; else currentStepSize = lighterStepSize; } } else //center step, use natural step size { currentStepSize = stepSize; } intermediateSize = previousIntermediateSize - currentStepSize; scale = (double) intermediateSize / (double) previousIntermediateSize; scaledW = (int) scaledW * scale; scaledH = (int) scaledH * scale; outImage = new BufferedImage((int) scaledW, (int) scaledH, BufferedImage.TYPE_INT_RGB); g2d = outImage.createGraphics(); g2d.setBackground(Color.WHITE); g2d.clearRect(0, 0, outImage.getWidth(), outImage.getHeight()); g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY); tx = new AffineTransform(); tx.scale(scale, scale); g2d.drawImage(inImage, tx, null); g2d.dispose(); inImage = new ImageIcon(outImage).getImage(); previousIntermediateSize = intermediateSize; } } else { //just copy the original outImage = new BufferedImage(inImage.getWidth(null), inImage.getHeight(null), BufferedImage.TYPE_INT_RGB); g2d = outImage.createGraphics(); g2d.setBackground(Color.WHITE); g2d.clearRect(0, 0, outImage.getWidth(), outImage.getHeight()); tx = new AffineTransform(); tx.setToIdentity(); //use identity matrix so image is copied exactly g2d.drawImage(inImage, tx, null); g2d.dispose(); } //JPEG-encode the image and write to file. OutputStream os = new FileOutputStream(outFilename); JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(os); encoder.encode(outImage); os.close(); } } } catch (Exception ex) { String errorMsg = ""; errorMsg += "<br>Exception: " + ex.toString(); errorMsg += "<br>Cause = " + ex.getCause(); errorMsg += "<br>Stack Trace = "; StackTraceElement stackTrace[] = ex.getStackTrace(); for (int traceLine = 0; traceLine < stackTrace.length; traceLine++) { errorMsg += "<br>" + stackTrace[traceLine]; } return errorMsg; } return ""; //success } }