📄 第4章 图象的半影调和抖动技术.htm
字号:
lang=EN-US>U<SUB>n</SUB></SPAN><SPAN style="FONT-FAMILY: 宋体">均为</SPAN><SPAN
lang=EN-US>2<SUP>n</SUP></SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>2<SUP>n</SUP></SPAN><SPAN style="FONT-FAMILY: 宋体">的方阵，</SPAN><SPAN
lang=EN-US>U<SUB>n</SUB></SPAN><SPAN style="FONT-FAMILY: 宋体">的所有元素都是</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN style="FONT-FAMILY: 宋体">。根据这个算法，可以得到</SPAN><SPAN
lang=EN-US>M<SUB>2</SUB>=<SUB> <IMG height=96
src="第4章 图象的半影调和抖动技术.files/image011.gif" width=120 v:shapes="_x0000_i1032">
</SUB></SPAN><SPAN style="FONT-FAMILY: 宋体">，为</SPAN><SPAN
lang=EN-US>16</SPAN><SPAN style="FONT-FAMILY: 宋体">级灰度的标准图案。</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN lang=EN-US>M<SUB>3</SUB>(8</SPAN><SPAN
style="FONT-FAMILY: 宋体">×</SPAN><SPAN lang=EN-US>8</SPAN><SPAN
style="FONT-FAMILY: 宋体">阵</SPAN><SPAN lang=EN-US>)</SPAN><SPAN
style="FONT-FAMILY: 宋体">比较特殊，称为</SPAN><SPAN lang=EN-US>Bayer</SPAN><SPAN
style="FONT-FAMILY: 宋体">抖动表。</SPAN><SPAN lang=EN-US>M<SUB>4</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体">是一个</SPAN><SPAN lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋体">×</SPAN><SPAN lang=EN-US>16</SPAN><SPAN
style="FONT-FAMILY: 宋体">的矩阵。</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN
style="FONT-FAMILY: 宋体">根据上面的算法，如果利用</SPAN><SPAN
lang=EN-US>M<SUB>3</SUB></SPAN><SPAN style="FONT-FAMILY: 宋体">一个象素要用</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">的图案表示，则一幅</SPAN><SPAN
lang=EN-US>N</SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>N</SPAN><SPAN style="FONT-FAMILY: 宋体">的图将变成</SPAN><SPAN
lang=EN-US>8N</SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>8N</SPAN><SPAN style="FONT-FAMILY: 宋体">大小。如果利用</SPAN><SPAN
lang=EN-US>M<SUB>4</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体">，就更不得了，变成</SPAN><SPAN lang=EN-US>16N</SPAN><SPAN
style="FONT-FAMILY: 宋体">×</SPAN><SPAN lang=EN-US>16N</SPAN><SPAN
style="FONT-FAMILY: 宋体">了。能不能在保持原图大小的情况下利用图案化技术呢？一种很自然的想法是：如果用</SPAN><SPAN
lang=EN-US>M<SUB>2</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体">阵，则将原图中每</SPAN><SPAN lang=EN-US>8</SPAN><SPAN
style="FONT-FAMILY: 宋体">×</SPAN><SPAN lang=EN-US>8</SPAN><SPAN
style="FONT-FAMILY: 宋体">个点中取一点，即重新采样，然后再应用图案化技术，就能够保持原图大小。实际上，这种方法并不可行。首先，你不知道这</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">个点中找哪一点比较合适，另外，</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN
style="FONT-FAMILY: 宋体">的间隔实在太大了，生成的图象和原图肯定相差很大，就象图</SPAN><SPAN
lang=EN-US>4.1</SPAN><SPAN style="FONT-FAMILY: 宋体">最右边的那幅图一样。</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN
style="FONT-FAMILY: 宋体">我们可以采用这样的做法：假设原图是</SPAN><SPAN lang=EN-US>256</SPAN><SPAN
style="FONT-FAMILY: 宋体">级灰度，利用</SPAN><SPAN lang=EN-US>Bayer</SPAN><SPAN
style="FONT-FAMILY: 宋体">抖动表，做如下处理</SPAN></P>
<P style="LINE-HEIGHT: 18pt; TEXT-ALIGN: center" align=center><SPAN
lang=EN-US>if (g[y][x]>>2) > bayer[y&7][x&7] then </SPAN><SPAN
style="FONT-FAMILY: 宋体">打一白点</SPAN><SPAN lang=EN-US> else </SPAN><SPAN
style="FONT-FAMILY: 宋体">打一黑点</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN style="FONT-FAMILY: 宋体">其中，</SPAN><SPAN
lang=EN-US>x,y</SPAN><SPAN style="FONT-FAMILY: 宋体">代表原图的象素坐标，</SPAN><SPAN
lang=EN-US>g[y][x]</SPAN><SPAN
style="FONT-FAMILY: 宋体">代表该点灰度。首先将灰度右移两位，变成</SPAN><SPAN
lang=EN-US>64</SPAN><SPAN style="FONT-FAMILY: 宋体">级，然后将</SPAN><SPAN
lang=EN-US>x</SPAN><SPAN style="FONT-FAMILY: 宋体">，</SPAN><SPAN
lang=EN-US>y</SPAN><SPAN style="FONT-FAMILY: 宋体">做模</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">运算，找到</SPAN><SPAN
lang=EN-US>Bayer</SPAN><SPAN
style="FONT-FAMILY: 宋体">表中的对应点，两者做比较，根据上面给出的判据做处理。</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN style="FONT-FAMILY: 宋体">我们可以看到，模</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">运算使得原图分成了一个个</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">的小块，每个小块和</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">×</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN style="FONT-FAMILY: 宋体">的</SPAN><SPAN
lang=EN-US>Bayer</SPAN><SPAN
style="FONT-FAMILY: 宋体">表相对应。小块中的每个点都参与了比较，这样就避免了上面提到的选点和块划分过大的问题。模</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN
style="FONT-FAMILY: 宋体">运算实质上是引入了随机成分，这就是我们下面要讲到的抖动技术。</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN style="FONT-FAMILY: 宋体">图</SPAN><SPAN
lang=EN-US>4.5</SPAN><SPAN style="FONT-FAMILY: 宋体">就是利用了这个算法，使用</SPAN><SPAN
lang=EN-US>M<SUB>3</SUB>(Bayer</SPAN><SPAN
style="FONT-FAMILY: 宋体">抖动表</SPAN><SPAN lang=EN-US>)</SPAN><SPAN
style="FONT-FAMILY: 宋体">阵得到的；图</SPAN><SPAN lang=EN-US>6</SPAN><SPAN
style="FONT-FAMILY: 宋体">是使用</SPAN><SPAN lang=EN-US>M<SUB>4</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体">阵得到的，可见两者的差别并不是很大，所以一般用</SPAN><SPAN
lang=EN-US>Bayer</SPAN><SPAN style="FONT-FAMILY: 宋体">表就可以了。</SPAN></P>
<P style="LINE-HEIGHT: 18pt; TEXT-ALIGN: center" align=center><SPAN
lang=EN-US><IMG height=259 src="第4章 图象的半影调和抖动技术.files/image012.gif" width=409
v:shapes="_x0000_i1033"> </SPAN></P>
<P style="LINE-HEIGHT: 18pt; TEXT-ALIGN: center" align=center><B><SPAN
style="FONT-FAMILY: 宋体">图</SPAN>4.5 </B><B><SPAN
style="FONT-FAMILY: 宋体">利用</SPAN><SPAN lang=EN-US>M3</SPAN></B><B><SPAN
style="FONT-FAMILY: 宋体">抖动生成的图</SPAN><SPAN lang=EN-US></SPAN></B></P>
<P style="LINE-HEIGHT: 18pt; TEXT-ALIGN: center" align=center><B><SPAN
lang=EN-US><IMG height=259 src="第4章 图象的半影调和抖动技术.files/image013.gif" width=409
v:shapes="_x0000_i1034"> </SPAN></B></P>
<P style="LINE-HEIGHT: 18pt; TEXT-ALIGN: center" align=center><B><SPAN
style="FONT-FAMILY: 宋体">图</SPAN>4.6 </B><B><SPAN
style="FONT-FAMILY: 宋体">利用</SPAN><SPAN lang=EN-US>M4</SPAN></B><B><SPAN
style="FONT-FAMILY: 宋体">抖动生成的图</SPAN><SPAN lang=EN-US></SPAN></B></P>
<P style="LINE-HEIGHT: 18pt"><SPAN
style="FONT-FAMILY: 宋体">下面是算法的源程序，是针对</SPAN><SPAN lang=EN-US>Bayer</SPAN><SPAN
style="FONT-FAMILY: 宋体">表的。因为它是个常用的表，我们不再利用</SPAN><SPAN
lang=EN-US>Limb</SPAN><SPAN style="FONT-FAMILY: 宋体">公式，而是直接给出。针对</SPAN><SPAN
lang=EN-US>M<SUB>4</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体">阵的算法是类似的，不同的地方在于，要用</SPAN><SPAN
lang=EN-US>Limb</SPAN><SPAN style="FONT-FAMILY: 宋体">公式得到</SPAN><SPAN
lang=EN-US>M<SUB>4</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体">阵，灰度也不用右移</SPAN><SPAN lang=EN-US>2</SPAN><SPAN
style="FONT-FAMILY: 宋体">位。要注意的是，为了处理的方便，我们的结果图仍采用</SPAN><SPAN
lang=EN-US>256</SPAN><SPAN style="FONT-FAMILY: 宋体">级灰度图，不过只用到了</SPAN><SPAN
lang=EN-US>0</SPAN><SPAN style="FONT-FAMILY: 宋体">和</SPAN><SPAN
lang=EN-US>255</SPAN><SPAN style="FONT-FAMILY: 宋体">两种灰度。</SPAN></P>
<P style="LINE-HEIGHT: 18pt">BYTE BayerPattern[8][8]={
0,32,8,40,2,34,10,42,</P>
<P style="LINE-HEIGHT: 18pt"><SPAN
lang=EN-US>48,16,56,24,50,18,58,26,</SPAN></P>
<P
style="LINE-HEIGHT: 18pt"><SPAN>
</SPAN>
12,44,4,36,14,46,6,38,</P>
<P
style="LINE-HEIGHT: 18pt"><SPAN>
</SPAN>
60,28,52,20,62,30,54,22,</P>
<P
style="LINE-HEIGHT: 18pt"><SPAN>
</SPAN>
3,35,11,43,1,33,9,41,</P>
<P
style="LINE-HEIGHT: 18pt"><SPAN>
</SPAN>
51,19,59,27,49,17,57,25,</P>
<P
style="LINE-HEIGHT: 18pt"><SPAN>
</SPAN>
15,47,7,39,13,45,5,37,</P>
<P
style="LINE-HEIGHT: 18pt"><SPAN>
</SPAN>
63,31,55,23,61,29,53,21};</P>
<P style="LINE-HEIGHT: 18pt"><SPAN lang=EN-US>BOOL LimbPatternM3(HWND
hWnd)</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN lang=EN-US>{</SPAN></P>
<P
style="LINE-HEIGHT: 18pt">DWORD
OffBits,BufSize</P>
<P style="LINE-HEIGHT: 18pt">LPBITMAPINFOHEADER lpImgData;</P>
<P
style="LINE-HEIGHT: 18pt">LPSTR
lpPtr;</P>
<P
style="LINE-HEIGHT: 18pt">HLOCAL
hTempImgData;</P>
<P style="LINE-HEIGHT: 18pt">LPBITMAPINFOHEADER lpTempImgData;</P>
<P
style="LINE-HEIGHT: 18pt">LPSTR
lpTempPtr;</P>
<P
style="LINE-HEIGHT: 18pt">HDC
hDc;</P>
<P
style="LINE-HEIGHT: 18pt">HFILE
hf;</P>
<P
style="LINE-HEIGHT: 18pt">LONG
x,y;</P>
<P style="LINE-HEIGHT: 18pt">unsigned
char
num;</P>
<P style="LINE-HEIGHT: 18pt"><SPAN
lang=EN-US>OffBits=bf.bfOffBits-sizeof(BITMAPFILEHEADER);</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN
lang=EN-US>BufSize=OffBits+bi.biHeight*LineBytes;//</SPAN><SPAN
style="FONT-FAMILY: 宋体">要开的缓冲区大小</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN
lang=EN-US>if((hTempImgData=LocalAlloc(LHND,BufSize))==NULL)</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN lang=EN-US>{</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN lang=EN-US>MessageBox(hWnd,"Error alloc
memory!","Error Message",MB_OK|</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN lang=EN-US>MB_ICONEXCLAMATION);</SPAN></P>
<P style="LINE-HEIGHT: 18pt"><SPAN> </SPAN>return FALSE;</P>
<P style="LINE-HEIGHT: 18pt"><SPAN lang=EN-US>}</SPAN></P>
<P
style="LINE-HEIGHT: 18pt">lpImgData=(LPBITMAPINFOHEADER)GlobalLock(hImgData);
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