如何在BufferedImage中设置RGB像素以显示16位深度的PNG？

Question

我正在尝试阅读并显示PNG文件。我对处理8位深度的图像没有问题。我进行如下操作：

BufferedImage result = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

然后我读取每个像素的3 * 8 = 24位，将它们保存在字节data的数组中，并使用以下命令将它们放入图像中：

for (int y = 0; y < height; y++)
   for (int x = 0; x < width; x++)
     result.setRGB(x, y, ((data[x * 3 + 0] & 0xff) << 16)
                       + ((data[x * 3 + 1] & 0xff) << 8)
                       + ((data[x * 3 + 2] & 0xff)));

现在问题出在16位深度图像上。当然，data现在更大了，对于每个RGB三元组，它包含48位（分为6个字节）：来自调试器的data具有我期望的值。如何设置RGB像素？我是否需要更改BufferedImage声明？也许与：

BufferedImage result = new BufferedImage(width, height, BufferedImage.TYPE_USHORT_565_RGB);

非常感谢！

P.S .：使用PNG标准图像后，图像的颜色类型为2（RGB不带alpha）。

---

也许我必须使用http://docs.oracle.com/javase/7/docs/api/java/awt/image/ColorModel.html

Answer 1

@@ haraldK指出了正确的方向。我提供了一些工作代码，这些代码来自Java图像库“ icafe”的“ PNGReader”。

if(bitsPerPixel == 16) {
    if(interlace_method==NON_INTERLACED)
       spixels = generate16BitRGBPixels(compr_data, false);
    else {
       spixels = generate16BitRGBInterlacedPixels(compr_data, false);
               }
    int[] off = {0, 1, 2}; //band offset, we have 3 bands
    int numOfBands = 3;
    boolean hasAlpha = false;
    int trans = Transparency.OPAQUE;
    int[] nBits = {16, 16, 16}; 
    if(alpha != null) { // Deal with single color transparency
       off = new int[] {0, 1, 2, 3}; //band offset, we have 4 bands
       numOfBands = 4;
       hasAlpha = true;
       trans = Transparency.TRANSLUCENT;
       nBits = new int[] {16, 16, 16, 16};                      
    }
    db = new DataBufferUShort(spixels, spixels.length);
    raster = Raster.createInterleavedRaster(db, width, height, width*numOfBands, numOfBands, off, null);
    cm = new ComponentColorModel(colorSpace, nBits, hasAlpha, false, trans, DataBuffer.TYPE_USHORT);
}
return new BufferedImage(cm, raster, false, null);

这里是generate16BitRGBPixels（）方法：

private short[] generate16BitRGBPixels(byte[] compr_data, boolean fullAlpha) throws Exception {
     //
     int bytesPerPixel = 0;
     byte[] pixBytes;

     if (fullAlpha)
         bytesPerPixel = 8;
     else 
         bytesPerPixel = 6;

     bytesPerScanLine = width*bytesPerPixel;         

     // Now inflate the data.
     pixBytes = new byte[height * bytesPerScanLine];

     // Wrap an InflaterInputStream with a bufferedInputStream to speed up reading
     BufferedInputStream bis = new BufferedInputStream(new InflaterInputStream(new ByteArrayInputStream(compr_data)));

     apply_defilter(bis, pixBytes, height, bytesPerPixel, bytesPerScanLine);

     short[] spixels = null;

     if(alpha != null) { // Deal with single color transparency
         spixels = new short[width*height*4];
         short redMask = (short)((alpha[1]&0xff)|(alpha[0]&0xff)<<8);
         short greenMask = (short)((alpha[3]&0xff)|(alpha[2]&0xff)<<8);;
         short blueMask = (short)((alpha[5]&0xff)|(alpha[4]&0xff)<<8);

         for(int i = 0, index = 0; i < pixBytes.length; index += 4) {
             short red = (short)((pixBytes[i++]&0xff)<<8|(pixBytes[i++]&0xff));
             short green = (short)((pixBytes[i++]&0xff)<<8|(pixBytes[i++]&0xff));
             short blue = (short)((pixBytes[i++]&0xff)<<8|(pixBytes[i++]&0xff));
             spixels[index] = red;
             spixels[index + 1] = green;
             spixels[index + 2] = blue;
             if(spixels[index] == redMask && spixels[index + 1] == greenMask && spixels[index + 2] == blueMask) {
                 spixels[index + 3] = (short)0x0000;                               
             } else {
                 spixels[index + 3] = (short)0xffff;
             }
         }
     } else
         spixels = ArrayUtils.toShortArray(pixBytes, true);

     return spixels;         
 }

和ArrayUtils.toShortArray（）方法：

public static short[] toShortArray(byte[] data, int offset, int len, boolean bigEndian) {

    ByteBuffer byteBuffer = ByteBuffer.wrap(data, offset, len);

    if (bigEndian) {
        byteBuffer.order(ByteOrder.BIG_ENDIAN);
    } else {
        byteBuffer.order(ByteOrder.LITTLE_ENDIAN);
    }

    ShortBuffer shortBuf = byteBuffer.asShortBuffer();
    short[] array = new short[shortBuf.remaining()];
    shortBuf.get(array);

    return array;
}

Answer 2

无法使用BufferedImage.TYPE_...来创建每个样本16位（或每个像素48位）的图像（没有这样的常数）。 TYPE_USHORT_565_RGB创建一个每像素16位的图像，分别具有5位（红色），6位（绿色）和5位（蓝色）的样本。我认为这些USHORT RGB值是某些计算实际上具有16位显示（也称为“数千种颜色”）选项时的剩余值。

要实际创建每个样本具有16位的图像，您需要做的是：

ColorModel cm;
WritableRaster raster;

BufferedImage result = new BufferedImage(cm, raster, cm.isAlphaPremultiplied(), null);

[栅格是从类型为DataBufferUShort的数据缓冲区创建的，该数据缓冲区具有3个存储区和具有3个波段的BandedSampleModel，或者使用单个存储区和PixelInterleavedSampleModel的pixelStride为3，scanLineStride为3 * width和bandOffsets {0, 1, 2}。

这里是完整的样本，使用交错样本模型：

ColorSpace sRGB = ColorSpace.getInstance(ColorSpace.CS_sRGB)
ColorModel cm = new ComponentColorModel(sRGB, false, false, Transparency.OPAQUE, DataBuffer.TYPE_USHORT);
WritableRaster raster = Raster.createInterleavedRaster(DataBuffer.TYPE_USHORT, w, h, 3, null);
BufferedImage rgb = new BufferedImage(cm, raster, cm.isAlphaPremultiplied(), null);

PS：露出数据缓冲区后，您可以直接访问short样本，以操纵像素。这比使用BufferedImage.getRGB(...)/setRGB(...)快得多，并且每个样本的精度将保持原始的16位。 BufferedImage.getRGB(...)将把每个样本的像素值转换为32位像素/ 8位，从而失去额外的精度。