代码里面设置像素为255，可结果为什么是205？

int lineByte=(m_nBitCount*m_imgWidth/8+3)/4*4;
    m_pImgDataOut=new unsigned char[lineByte*m_imgHeight];
    int pixelByte=m_nBitCount/8;
    int i,j,k,t;
    for (i=1;i<m_imgHeight-1;i++)
    {
        for (j=1;j<m_imgWidth-1;j++)
        {
            for (k=0;k<pixelByte;k++)
            {
                t=  8* *(m_pImgData+i*lineByte+j*pixelByte+k)
                    -1* *(m_pImgData+(i-1)*lineByte+j*pixelByte+k)
                    -2**(m_pImgData+(i+1)*lineByte+j*pixelByte+k)
                    -0* *(m_pImgData+i*lineByte+(j-1)*pixelByte+k)
                    -0**(m_pImgData+i*lineByte+(j+1)*pixelByte+k)
                    -0**(m_pImgData+(i+1)*lineByte+(j+1)*pixelByte+k)
                    -0**(m_pImgData+(i-1)*lineByte+(j+1)*pixelByte+k)
                    -0**(m_pImgData+(i+1)*lineByte+(j-1)*pixelByte+k)
                    -0**(m_pImgData+(i-1)*lineByte+(j-1)*pixelByte+k);

                t=abs(t)+0.5;
                if(t>160)
                    t=0;
                else
                    t=255;
                *(m_pImgDataOut+i*lineByte+j*pixelByte+k)=t;
            }
        }
    }