private void rgb_gray_convert(byte[][] input_buf, int input_row, byte[][][] output_buf, int output_row, int num_rows)
{
int num_cols = m_cinfo.m_image_width;
for (int row = 0; row < num_rows; row++)
{
int columnOffset = 0;
for (int col = 0; col < num_cols; col++)
{
int r = input_buf[input_row + row][columnOffset + JpegConstants.RGB_RED];
int g = input_buf[input_row + row][columnOffset + JpegConstants.RGB_GREEN];
int b = input_buf[input_row + row][columnOffset + JpegConstants.RGB_BLUE];
columnOffset += JpegConstants.RGB_PIXELSIZE;
/* Y */
output_buf[0][output_row][col] = (byte)((m_rgb_ycc_tab[r + R_Y_OFF] + m_rgb_ycc_tab[g + G_Y_OFF] + m_rgb_ycc_tab[b + B_Y_OFF]) >> SCALEBITS);
}
output_row++;
}
}