@Override
  public LuminanceSource crop(int left, int top, int width, int height) {
    return new PlanarYUVLuminanceSource(yuvData,
                                        dataWidth,
                                        dataHeight,
                                        this.left + left,
                                        this.top + top,
                                        width,
                                        height,
                                        false);
  }
This object extends LuminanceSource around an array of YUV data returned from the camera driver,
with the option to crop to a rectangle within the full data. This can be used to exclude
superfluous pixels around the perimeter and speed up decoding.

It works for any pixel format where the Y channel is planar and appears first, including
YCbCr_420_SP and YCbCr_422_SP.

The code for this class was adapted from the ZXing project: http://code.google.com/p/zxing
OCRTest/src/main/java/edu/sfsu/cs/orange/ocr/PlanarYUVLuminanceSource.java