PngjWriter

README.md

Java's ImageIO PNGImageWriter is slow in Java <9 (see also JDK-6488522). This snipped uses PNGJ to encode a BufferedImage. Requires Java 8 for the Stream API.

PngjWriter.java

import ar.com.hjg.pngj.FilterType;
import ar.com.hjg.pngj.ImageInfo;
import ar.com.hjg.pngj.ImageLineByte;
import ar.com.hjg.pngj.PngWriter;
import ar.com.hjg.pngj.PngjException;

import java.awt.image.BufferedImage;
import java.awt.image.DataBuffer;
import java.awt.image.Raster;
import java.awt.image.SinglePixelPackedSampleModel;
import java.io.OutputStream;

/**
 * Writes {@link BufferedImage} using PNGJ {@link PngWriter}.
 */
class PngjWriter {

    private PngjWriter() {
    }

    /**
     * Writes the image {@code bi} to {@code os} using PNGJ {@link PngWriter}.
     * @param bi the image to write
     * @param os the stream to write to
     */
    static void writeARGB(BufferedImage bi, OutputStream os) {
        if (bi.getType() != BufferedImage.TYPE_INT_ARGB) {
            throw new PngjException("This method expects BufferedImage.TYPE_INT_ARGB");
        }
        writeARGB(bi.getRaster(), os);
    }

    private static void writeARGB(Raster raster, OutputStream os) {
        final SinglePixelPackedSampleModel sampleModel = (SinglePixelPackedSampleModel) raster.getSampleModel();
        final DataBuffer dataBuffer = raster.getDataBuffer();
        if (dataBuffer.getNumBanks() != 1) {
            throw new PngjException("This method expects one bank");
        }

        final ImageInfo info = new ImageInfo(raster.getWidth(), raster.getHeight(), 8, true);
        final PngWriter writer = new PngWriter(os, info);
        writer.setCompLevel(5);
        writer.setFilterType(FilterType.FILTER_ADAPTIVE_FAST);
        for (int row = 0; row < info.rows; row++) {
            final byte[] bytes = new byte[4 * info.cols];
            int i = 0;
            for (int col = 0; col < info.cols; col++) {
                final int sample = dataBuffer.getElem(sampleModel.getOffset(col, row));
                bytes[i++] = (byte) ((sample & 0xFF0000) >> 16); //R
                bytes[i++] = (byte) ((sample & 0xFF00) >> 8); //G
                bytes[i++] = (byte) (sample & 0xFF); //B
                bytes[i++] = (byte) ((sample & 0xFF000000) >> 24); //A
            }
            writer.writeRow(new ImageLineByte(info, bytes), row);
        }
        writer.end();
    }
}