@Override
    public void writeImage(final BufferedImage src, final OutputStream os, final IcnsImagingParameters params) throws ImagingException, IOException {
        final IcnsType imageType;
        if (src.getWidth() == 16 && src.getHeight() == 16) {
            imageType = IcnsType.ICNS_16x16_32BIT_IMAGE;
        } else if (src.getWidth() == 32 && src.getHeight() == 32) {
            imageType = IcnsType.ICNS_32x32_32BIT_IMAGE;
        } else if (src.getWidth() == 48 && src.getHeight() == 48) {
            imageType = IcnsType.ICNS_48x48_32BIT_IMAGE;
        } else if (src.getWidth() == 128 && src.getHeight() == 128) {
            imageType = IcnsType.ICNS_128x128_32BIT_IMAGE;
        } else {
            throw new ImagingException("Invalid/unsupported source width " + src.getWidth() + " and height " + src.getHeight());
        }

        try (AbstractBinaryOutputStream bos = AbstractBinaryOutputStream.bigEndian(os)) {
            bos.write4Bytes(ICNS_MAGIC);
            bos.write4Bytes(4 + 4 + 4 + 4 + 4 * imageType.getWidth() * imageType.getHeight() + 4 + 4 + imageType.getWidth() * imageType.getHeight());

            bos.write4Bytes(imageType.getType());
            bos.write4Bytes(4 + 4 + 4 * imageType.getWidth() * imageType.getHeight());
            for (int y = 0; y < src.getHeight(); y++) {
                for (int x = 0; x < src.getWidth(); x++) {
                    final int argb = src.getRGB(x, y);
                    bos.write(0);
                    bos.write(argb >> 16);
                    bos.write(argb >> 8);
                    bos.write(argb);
                }
            }

            final IcnsType maskType = IcnsType.find8BPPMaskType(imageType);
            bos.write4Bytes(maskType.getType());
            bos.write4Bytes(4 + 4 + imageType.getWidth() * imageType.getWidth());
            for (int y = 0; y < src.getHeight(); y++) {
                for (int x = 0; x < src.getWidth(); x++) {
                    final int argb = src.getRGB(x, y);
                    bos.write(argb >> 24);
                }
            }
        }
    }
Constructs a new instance with the big-endian byte order.
src/main/java/org/apache/commons/imaging/formats/icns/IcnsImageParser.java