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lang=ZH-CN style='font-size:10.5pt'>能够说明差影法的原理。</span><span style='font-size:
10.5pt;font-family:"Times New Roman"'><o:p></o:p></span></p>
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mso-padding-alt:0cm 0cm 0cm 0cm'>
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<p style='text-align:justify;text-justify:inter-ideograph;line-height:18.0pt'><span
style='font-size:10.5pt;font-family:"Times New Roman"'><!--[if gte vml 1]><v:shape
id="_x0000_i1030" type="#_x0000_t75" alt="" style='width:138pt;height:111pt'>
<v:imagedata src="./chp8.files/image006.jpg" o:href="http://www-scf.usc.edu/~flv/ipbook/chap08.files/image011.jpg"/>
</v:shape><![endif]--><![if !vml]><img width=184 height=148
src="./chp8.files/image006.jpg" v:shapes="_x0000_i1030"><![endif]><o:p></o:p></span></p>
<p align=center style='text-align:center;line-height:18.0pt'><b><span
lang=ZH-CN style='font-size:10.5pt'>图</span></b><b><span style='font-size:
10.5pt;font-family:"Times New Roman"'>8.6 </span></b><b><span
lang=ZH-CN style='font-size:10.5pt'>前景</span></b><b><span style='font-size:
10.5pt;font-family:"Times New Roman"'>+</span></b><b><span lang=ZH-CN
style='font-size:10.5pt'>背景</span></b><span style='font-size:10.5pt;
font-family:"Times New Roman"'><o:p></o:p></span></p>
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<td width=184 valign=top style='width:138.0pt;padding:0cm 0cm 0cm 0cm'>
<p style='text-align:justify;text-justify:inter-ideograph;line-height:18.0pt'><span
style='font-size:10.5pt;font-family:"Times New Roman"'><!--[if gte vml 1]><v:shape
id="_x0000_i1031" type="#_x0000_t75" alt="" style='width:139.5pt;height:112.5pt'>
<v:imagedata src="./chp8.files/image007.jpg" o:href="http://www-scf.usc.edu/~flv/ipbook/chap08.files/image013.jpg"/>
</v:shape><![endif]--><![if !vml]><img width=186 height=150
src="./chp8.files/image007.jpg" v:shapes="_x0000_i1031"><![endif]><o:p></o:p></span></p>
<p align=center style='text-align:center;line-height:18.0pt'><b><span
lang=ZH-CN style='font-size:10.5pt'>图</span></b><b><span style='font-size:
10.5pt;font-family:"Times New Roman"'>8.7 </span></b><b><span
lang=ZH-CN style='font-size:10.5pt'>背景</span></b><span style='font-size:10.5pt;
font-family:"Times New Roman"'><o:p></o:p></span></p>
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<td width=184 valign=top style='width:138.0pt;padding:0cm 0cm 0cm 0cm'>
<p style='text-align:justify;text-justify:inter-ideograph;line-height:18.0pt'><span
style='font-size:10.5pt;font-family:"Times New Roman"'><!--[if gte vml 1]><v:shape
id="_x0000_i1032" type="#_x0000_t75" alt="" style='width:139.5pt;height:112.5pt'>
<v:imagedata src="./chp8.files/image008.jpg" o:href="http://www-scf.usc.edu/~flv/ipbook/chap08.files/image015.jpg"/>
</v:shape><![endif]--><![if !vml]><img width=186 height=150
src="./chp8.files/image008.jpg" v:shapes="_x0000_i1032"><![endif]><o:p></o:p></span></p>
<p align=center style='text-align:center;line-height:18.0pt'><b><span
lang=ZH-CN style='font-size:10.5pt'>图</span></b><b><span style='font-size:
10.5pt;font-family:"Times New Roman"'>8.8 </span></b><b><span lang=ZH-CN
style='font-size:10.5pt'>图</span></b><b><span style='font-size:10.5pt;
font-family:"Times New Roman"'>8.6</span></b><b><span lang=ZH-CN
style='font-size:10.5pt'>、图</span></b><b><span style='font-size:10.5pt;
font-family:"Times New Roman"'>8.7</span></b><span style='font-size:10.5pt;
font-family:"Times New Roman"'><o:p></o:p></span></p>
<p align=center style='text-align:center;line-height:18.0pt'><b><span
lang=ZH-CN style='font-size:10.5pt'>相减的结果</span></b><span style='font-size:
10.5pt;font-family:"Times New Roman"'><o:p></o:p></span></p>
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<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span lang=ZH-CN style='font-size:10.5pt'>图</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'>8.6</span><span
lang=ZH-CN style='font-size:10.5pt'>是前景图</span><span style='font-size:10.5pt;
font-family:"Times New Roman"'>(</span><span lang=ZH-CN style='font-size:10.5pt'>猫</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'>)</span><span
lang=ZH-CN style='font-size:10.5pt'>加背景图</span><span style='font-size:10.5pt;
font-family:"Times New Roman"'>(</span><span lang=ZH-CN style='font-size:10.5pt'>木星</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'>)</span><span
lang=ZH-CN style='font-size:10.5pt'>。图</span><span style='font-size:10.5pt;
font-family:"Times New Roman"'>8.7</span><span lang=ZH-CN style='font-size:
10.5pt'>是背景图。图</span><span style='font-size:10.5pt;font-family:"Times New Roman"'>8.6</span><span
lang=ZH-CN style='font-size:10.5pt'>减图</span><span style='font-size:10.5pt;
font-family:"Times New Roman"'>8.7</span><span lang=ZH-CN style='font-size:
10.5pt'>的结果如图</span><span style='font-size:10.5pt;font-family:"Times New Roman"'>8.8</span><span
lang=ZH-CN style='font-size:10.5pt'>所示，这样就得到了前景</span><span style='font-size:
10.5pt;font-family:"Times New Roman"'>(</span><span lang=ZH-CN
style='font-size:10.5pt'>不完全是前景，因为背景的灰度值并不为零，但至少可以得到前景的形状</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'>)</span><span
lang=ZH-CN style='font-size:10.5pt'>。</span><span style='font-size:10.5pt;
font-family:"Times New Roman"'><o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span lang=ZH-CN style='font-size:10.5pt'>差影法是非常有用的，比如说可以用在监控系统中。在银行金库内，摄像头每隔一小段时间，拍摄一幅图，与上一幅图做差影；如果差别超过了预先设置的阈值，说明有人，这时就应该拉响警报。</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'><o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span lang=ZH-CN style='font-size:10.5pt'>我们在介绍灰度窗口变换时，曾经提到了电影“阿甘正传”特技中应用了“蓝幕”技术，其实也包含了差影法的原理。</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'><o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span lang=ZH-CN style='font-size:10.5pt'>以下是差影法的源程序。要注意的是，第一幅图的文件名为</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'>c:\test.bmp</span><span
lang=ZH-CN style='font-size:10.5pt'>，第二幅图的文件名是</span><span style='font-size:
10.5pt;font-family:"Times New Roman"'>c:\backgnd.bmp</span><span lang=ZH-CN
style='font-size:10.5pt'>。它们有着相同的灰度值和调色板。执行时，这两个文件都已经准备好。我们针对的虽然是二值图，但为了处理的方便，用的是</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'>256</span><span
lang=ZH-CN style='font-size:10.5pt'>级灰度图，不过只用到了</span><span style='font-size:
10.5pt;font-family:"Times New Roman"'>0</span><span lang=ZH-CN
style='font-size:10.5pt'>和</span><span style='font-size:10.5pt;font-family:
"Times New Roman"'>255</span><span lang=ZH-CN style='font-size:10.5pt'>两种灰度级。</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'><o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>BOOL Subtraction(HWND hWnd)<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>{<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'> DWORD
OffBits,BufSize;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>LPBITMAPINFOHEADER lpImgData;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
LPSTR
lpPtr;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
HGLOBAL
hSecond;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
LPBITMAPINFOHEADER lpSecondImgData;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
LPSTR
lpSecondPtr;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
HLOCAL
hTempImgData;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
LPBITMAPINFOHEADER lpTempImgData;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
LPSTR
lpTempPtr;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
HDC
hDc;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
HFILE
hf;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
LONG
x,y;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>
int
num,pos;<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>//</span><span lang=ZH-CN style='font-size:10.5pt'>用的是</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'>256</span><span
lang=ZH-CN style='font-size:10.5pt'>级灰度图，不过只用到了</span><span style='font-size:
10.5pt;font-family:"Times New Roman"'>0</span><span lang=ZH-CN
style='font-size:10.5pt'>和</span><span style='font-size:10.5pt;font-family:
"Times New Roman"'>255</span><span lang=ZH-CN style='font-size:10.5pt'>两种灰度级。</span><span
style='font-size:10.5pt;font-family:"Times New Roman"'><o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'> if( NumColors!=256){<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
inter-ideograph;line-height:18.0pt'><span style='font-size:10.5pt;font-family:
"Times New Roman"'>MessageBox(hWnd,"Must be a mono bitmap with grayscale
palette!",<o:p></o:p></span></p>
<p style='margin:0cm;margin-bottom:.0001pt;text-align:justify;text-justify:
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