cximage SetPixelColor有关问题

cximage SetPixelColor问题
用cximage类加载位图后，用SetPixelColor设置为红色时，为什么效果不是红色？请高手指点谢谢。下面是代码：
for (int i=0;i<widthThree;i++)
{
for (int j=0;j<heightThree;j++)
{
if (pDoc->m_imageThree.GetPixelGray(i,j)!=pDoc->m_imageThree.GetPixelGray(i-1,j)||
pDoc->m_imageThree.GetPixelGray(i,j)!=pDoc->m_imageThree.GetPixelGray(i+1,j)||
pDoc->m_imageThree.GetPixelGray(i,j)!=pDoc->m_imageThree.GetPixelGray(i,j-1)||
pDoc->m_imageThree.GetPixelGray(i,j)!=pDoc->m_imageThree.GetPixelGray(i,j+1))
{
// MemDC.SetPixel(i,heightThree-j,RGB(255,0,0));
pDoc->m_imageThree.SetPixelColor(i,heightThree-j,RGB(255,0,0));
}
}
}
  pDoc->m_imageThree.Draw(MemDC.GetSafeHdc(),logicX,logicY);

------解决方案--------------------
加个断点，看SetPixelColor执行到了没有
------解决方案--------------------
m_imageThree是怎么定义的？它本身正确吗？
m_imageThree.SetPixelColor(i,heightThree-j,RGB(255,0,0));
或
m_imageThree->SetPixelColor(i,heightThree-j,RGB(255,0,0));
使用是正确的，是可以将图像全部设为红色的
或者是其它地方的错误