Java PNG Library — Read, Write & Convert PNG Files

// Read a PNG with alpha into a BufferedImage
BufferedImage image = JDeli.read(pngFile);

// Detect if the image has alpha
boolean hasAlpha = image.getColorModel().hasAlpha();
// Type 2 = TYPE_INT_ARGB when PNG contains transparency
int imageType = image.getType();

// Write a BufferedImage to PNG with compression options
final PngEncoderOptions options = new PngEncoderOptions();

// Choose compression: ZLIB_BETTER_COMPRESSION | ZLIB_BETTER_SPEED | QUANTISED8BIT | NONE
options.setCompressionFormat(PngCompressionFormat.ZLIB_BETTER_COMPRESSION);

JDeli.write(myBufferedImage, options, outputFile);

// Or use QUANTISED8BIT for indexed 8-bit color — much smaller file size
options.setCompressionFormat(PngCompressionFormat.QUANTISED8BIT);

JDeli.write(myBufferedImage, options, outputFile);

// Convert PNG to JPEG with background fill for alpha
BufferedImage png = JDeli.read(pngFile);

// JPEG has no alpha — composite onto a white background
BufferedImage rgb = new BufferedImage(
    png.getWidth(), png.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics2D g = rgb.createGraphics();
g.setColor(Color.WHITE);
g.fillRect(0, 0, rgb.getWidth(), rgb.getHeight());
g.drawImage(png, 0, 0, null);
g.dispose();

JDeli.write(rgb, "jpeg", outputFile);

// Resize a PNG to fit within target dimensions (preserves aspect ratio)
ImageProcessingOperations operations = new ImageProcessingOperations();
operations.resizeToFit(targetWidth, targetHeight);

JDeli.convert(inputFile, outputFile, operations);

// Or generate a thumbnail
ImageProcessingOperations thumbOps = new ImageProcessingOperations();
thumbOps.thumbnail(150, 150);

JDeli.convert(inputFile, outputFile, thumbOps);

// Strip PNG metadata by reading and re-writing
BufferedImage image = JDeli.read(inputFile);

// Write back — produces a clean PNG without the original ancillary chunks
PngEncoderOptions options = new PngEncoderOptions();
JDeli.write(image, options, outputFile);

// Read a 16-bit PNG — JDeli supports 1, 2, 4, 8 and 16-bit per sample
BufferedImage image = JDeli.read(new File("16bit-photo.png"));

// Or use PngDecoder directly
PngDecoder decoder = new PngDecoder();
BufferedImage image = decoder.read(pngData);