Rotate gray scale image

ImageOperator.cpp

void ImageOperator::rotate(const unsigned char* input,
                           const int width,
                           const int height,
                           const int channel,
                           unsigned char*& output){

    unsigned char* tmp = new unsigned char[width*height*channel];
    for (int row = 0; row < height; ++row) {
        for (int col = 0; col < width; col+=1) {
            tmp[col*width+width-1-row] = input[row*width+col];
        }
    }
    output = tmp;
}