java 缓冲图像像素操作

Buffered image pixel manipulation

提问by Lukasz Madon

I have this code:

我有这个代码：

public Image toNegative()
{
    int imageWidth =  originalImage.getWidth();
    int imageHeight = originalImage.getHeight();
    int [] rgb = null; // new int[imageWidth * imageWidth];
    originalImage.getRGB(0, 0, imageWidth, imageHeight, rgb, 0,imageWidth);

    for (int y = 0; y < imageHeight; y++)
    {
         for (int x = 0; x < imageWidth; x++)
         {
             int index = y * imageWidth + x;
             int R = (rgb[index] >> 16) & 0xff;     //bitwise shifting
             int G = (rgb[index] >> 8) & 0xff;
             int B = rgb[index] & 0xff;

             R = 255 - R;
             G = 255 - R;
             B = 255 - R;

             rgb[index] = 0xff000000 | (R << 16) | (G << 8) | B;                                
         }
    }


    return getImageFromArray(rgb, imageWidth, imageHeight);
}

It throws NPE or when array is used or ArrayOutOfBoundsException when I allocate array before passing it getRGB. I check in debugger and image has the size and is allocated.

当我在传递 getRGB 之前分配数组时，它会抛出 NPE 或使用数组时或 ArrayOutOfBoundsException。我签入调试器，图像具有大小并已分配。

UPDATE: The getRGB

更新：getRGB

 /**
 * Returns an array of integer pixels in the default RGB color model
 * (TYPE_INT_ARGB) and default sRGB color space,
 * from a portion of the image data.  Color conversion takes
 * place if the default model does not match the image
 * <code>ColorModel</code>.  There are only 8-bits of precision for
 * each color component in the returned data when
 * using this method.  With a specified coordinate (x,&nbsp;y) in the
 * image, the ARGB pixel can be accessed in this way:
 * </p>
 *
 * <pre>
 *    pixel   = rgbArray[offset + (y-startY)*scansize + (x-startX)]; </pre>
 *
 * <p>
 *
 * An <code>ArrayOutOfBoundsException</code> may be thrown
 * if the region is not in bounds.
 * However, explicit bounds checking is not guaranteed.
 *
 * @param startX      the starting X coordinate
 * @param startY      the starting Y coordinate
 * @param w           width of region
 * @param h           height of region
 * @param rgbArray    if not <code>null</code>, the rgb pixels are
 *          written here
 * @param offset      offset into the <code>rgbArray</code>
 * @param scansize    scanline stride for the <code>rgbArray</code>
 * @return            array of RGB pixels.
 * @see #setRGB(int, int, int)
 * @see #setRGB(int, int, int, int, int[], int, int)
 */
public int[] getRGB(int startX, int startY, int w, int h,
                    int[] rgbArray, int offset, int scansize) {
    int yoff  = offset;
    int off;
    Object data;
    int nbands = raster.getNumBands();
    int dataType = raster.getDataBuffer().getDataType();
    switch (dataType) {
    case DataBuffer.TYPE_BYTE:
        data = new byte[nbands];
        break;
    case DataBuffer.TYPE_USHORT:
        data = new short[nbands];
        break;
    case DataBuffer.TYPE_INT:
        data = new int[nbands];
        break;
    case DataBuffer.TYPE_FLOAT:
        data = new float[nbands];
        break;
    case DataBuffer.TYPE_DOUBLE:
        data = new double[nbands];
        break;
    default:
        throw new IllegalArgumentException("Unknown data buffer type: "+
                                           dataType);
    }

    if (rgbArray == null) {
        rgbArray = new int[offset+h*scansize];
    }

    for (int y = startY; y < startY+h; y++, yoff+=scansize) {
        off = yoff;
        for (int x = startX; x < startX+w; x++) {
            rgbArray[off++] = colorModel.getRGB(raster.getDataElements(x,
                                                                    y,
                                                                    data));
        }
    }

    return rgbArray;
}

采纳答案by Adamski

Your code will throw a NullPointerExceptionbecause you are never assigning a non-null reference to the rgbvariable. Hence, references to it (e.g. rgb[index]) will generate the exception. If you wish to pass in a null array to getRGB you need to ensure you assign the result array returned by the method; e.g.

您的代码将抛出 a，NullPointerException因为您从未为该rgb变量分配非空引用。因此，对它的引用（例如rgb[index]）将产生异常。如果您希望将空数组传递给 getRGB，您需要确保分配该方法返回的结果数组；例如

int[] rgb = originalImage.getRGB(0, 0, imageWidth, imageHeight, rgb, 0,imageWidth);

If you were to uncomment the code commented out there is a bug in that you are allocating the array as imageWidth * imageWidthinstead of imageWidth * imageHeight, which is why you're seeing an ArrayIndexOutOfBoundsException.

如果您要取消注释已注释掉的代码，则存在一个错误，即您将数组分配为 asimageWidth * imageWidth而不是imageWidth * imageHeight，这就是为什么您会看到ArrayIndexOutOfBoundsException.

回答by Aaron Digulla

There are two problems:

有两个问题：

1. The width of the array is not the width of the image but the "scan size" (some image sizes get padded with extra pixels)

2. If you call getRGB()with a nullarray, the method will create an array but it won't change the rgbreference - Java doesn't support "out parameters".

1. 数组的宽度不是图像的宽度，而是“扫描尺寸”（某些图像尺寸会填充额外的像素）

2. 如果您getRGB()使用null数组调用，该方法将创建一个数组，但不会更改rgb引用 - Java 不支持“输出参数”。

To make this work, use

要完成这项工作，请使用

rgb = originalImage.getRGB(0, 0, imageWidth, imageHeight, null, 0,imageWidth);