* @exception IllegalArgumentException
	 *                <ul>
	 *                <li>ERROR_NULL_ARGUMENT - if pixels is null</li>
	 *                <li>ERROR_INVALID_ARGUMENT - if x or y is out of bounds</li>
	 *                <li>ERROR_INVALID_ARGUMENT - if getWidth is negative</li>
	 *                </ul>
	 */
	public void getAlphas(int x, int y, int getWidth, byte[] alphas,
			int startIndex) {
		if (alphas == null)
			SWT.error(SWT.ERROR_NULL_ARGUMENT);
		if (getWidth < 0 || x >= width || y >= height || x < 0 || y < 0)
			SWT.error(SWT.ERROR_INVALID_ARGUMENT);
		if (getWidth == 0)
			return;

		if (alphaData == null) {
			int endIndex = startIndex + getWidth;
			for (int i = startIndex; i < endIndex; i++) {
				alphas[i] = (byte) 255;
			}
			return;
		}
		// may throw an IndexOutOfBoundsException
		System.arraycopy(alphaData, y * width + x, alphas, startIndex, getWidth);
	}