QString img_path = "C:\\Users\\Yajun Dou\\Desktop\\test.bmp";

 QImage buff(img_path);

 QImage image;

 uchar* pImageData1 = NULL,*pImageData2 = NULL;

 pImageData1 = buff.bits();

 image = buff.convertToFormat(QImage::Format_Indexed8);

 QVector<QRgb> table();

 for( int i = ; i < ; ++i )

 {

 table[i] = qRgb(i,i,i);

 }

 image.setColorTable(table);

 for(int i =; i< image.width();i++)

 {

 for(int j=; j< image.height();j++)

 {

 QRgb pix_value = image.pixel(i,j);

 image.setPixel(i,j,qGray(pix_value));

 }

 }

 pImageData2 = image.bits();

 image.save("D:\\out.bmp",,);