src/org/nutz/img/Images.java
private static BufferedImage createJPEG4(Raster raster) {
        int w = raster.getWidth();
        int h = raster.getHeight();
        byte[] rgb = new byte[w * h * 3];

        float[] Y = raster.getSamples(0, 0, w, h, 0, (float[]) null);
        float[] Cb = raster.getSamples(0, 0, w, h, 1, (float[]) null);
        float[] Cr = raster.getSamples(0, 0, w, h, 2, (float[]) null);
        float[] K = raster.getSamples(0, 0, w, h, 3, (float[]) null);

        for (int i = 0, imax = Y.length, base = 0; i < imax; i++, base += 3) {
            float k = 220 - K[i], y = 255 - Y[i], cb = 255 - Cb[i], cr = 255 - Cr[i];

            double val = y + 1.402 * (cr - 128) - k;
            val = (val - 128) * .65f + 128;
            rgb[base] = val < 0.0 ? (byte) 0 : val > 255.0 ? (byte) 0xff : (byte) (val + 0.5);

            val = y - 0.34414 * (cb - 128) - 0.71414 * (cr - 128) - k;
            val = (val - 128) * .65f + 128;
            rgb[base + 1] = val < 0.0 ? (byte) 0 : val > 255.0 ? (byte) 0xff : (byte) (val + 0.5);

            val = y + 1.772 * (cb - 128) - k;
            val = (val - 128) * .65f + 128;
            rgb[base + 2] = val < 0.0 ? (byte) 0 : val > 255.0 ? (byte) 0xff : (byte) (val + 0.5);
        }

        raster = Raster.createInterleavedRaster(new DataBufferByte(rgb, rgb.length),
                                                w,
                                                h,
                                                w * 3,
                                                3,
                                                new int[]{0, 1, 2},
                                                null);

        ColorSpace cs = ColorSpace.getInstance(ColorSpace.CS_sRGB);
        ColorModel cm = new ComponentColorModel(cs,
                                                false,
                                                true,
                                                Transparency.OPAQUE,
                                                DataBuffer.TYPE_BYTE);
        return new BufferedImage(cm, (WritableRaster) raster, true, null);
    }
private static BufferedImage createJPEG4(Raster raster) {
        int w = raster.getWidth();
        int h = raster.getHeight();
        byte[] rgb = new byte[w * h * 3];

        float[] Y = raster.getSamples(0, 0, w, h, 0, (float[]) null);
        float[] Cb = raster.getSamples(0, 0, w, h, 1, (float[]) null);
        float[] Cr = raster.getSamples(0, 0, w, h, 2, (float[]) null);
        float[] K = raster.getSamples(0, 0, w, h, 3, (float[]) null);

        for (int i = 0, imax = Y.length, base = 0; i < imax; i++, base += 3) {
            float k = 220 - K[i], y = 255 - Y[i], cb = 255 - Cb[i], cr = 255 - Cr[i];

            double val = y + 1.402 * (cr - 128) - k;
            val = (val - 128) * .65f + 128;
            rgb[base] = val < 0.0 ? (byte) 0 : val > 255.0 ? (byte) 0xff : (byte) (val + 0.5);

            val = y - 0.34414 * (cb - 128) - 0.71414 * (cr - 128) - k;
            val = (val - 128) * .65f + 128;
            rgb[base + 1] = val < 0.0 ? (byte) 0 : val > 255.0 ? (byte) 0xff : (byte) (val + 0.5);

            val = y + 1.772 * (cb - 128) - k;
            val = (val - 128) * .65f + 128;
            rgb[base + 2] = val < 0.0 ? (byte) 0 : val > 255.0 ? (byte) 0xff : (byte) (val + 0.5);
        }

        raster = Raster.createInterleavedRaster(new DataBufferByte(rgb, rgb.length),
                                                w,
                                                h,
                                                w * 3,
                                                3,
                                                new int[]{0, 1, 2},
                                                null);

        ColorSpace cs = ColorSpace.getInstance(ColorSpace.CS_sRGB);
        ColorModel cm = new ComponentColorModel(cs,
                                                false,
                                                true,
                                                Transparency.OPAQUE,
                                                DataBuffer.TYPE_BYTE);
        return new BufferedImage(cm, (WritableRaster) raster, true, null);
    }
Java's ImageIO can't process 4-component images and Java2D can't apply
AffineTransformOp either, so convert raster data to RGB. Technique due to
MArk Stephens. Free for any use.