1 引言
指紋是指手指末端正面皮膚上凸凹不平產(chǎn)生的紋路。盡管指紋只是人體皮膚的一小部分，但是，它蘊(yùn)涵大量的信息。這些皮膚的紋路在圖案、斷點(diǎn)和交叉點(diǎn)上是各不相同的，在信息處理中將它們稱作“特征”，依靠特征的唯一性，就可以把用戶同他的指紋對應(yīng)起來，通過比較輸入的指紋特征和預(yù)先保存的合法指紋特征，就可以驗(yàn)證用戶的真實(shí)身份。
以前的各種指紋識(shí)別系統(tǒng)屬于光學(xué)識(shí)別系統(tǒng)，由于光不能穿透皮膚表層，所以只能夠掃描手指皮膚的表面，或者掃描到死性皮膚層，但不能深入真皮層。在這種情況下，手指表面的干凈程度，直接影響到識(shí)別的效果。如果，用戶手指上粘了較多的灰塵，可能就會(huì)出現(xiàn)識(shí)別出錯(cuò)的情況。并且，如果人們按照手指，做一個(gè)指紋手模，也可能通過識(shí)別系統(tǒng)，對于用戶而言，使用起來不是很安全和穩(wěn)定。
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title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A" title="SPCE061A">SPCE061A單片機(jī)作為控制核心，SPCE061A不僅僅是具有單片機(jī)的控制功能，它還是一款運(yùn)算能力很強(qiáng)的DSP芯片；對于指紋的采集，本系統(tǒng)采用了富士通公司的新型指紋傳感器MBF300，這種電容傳感器發(fā)出的電子信號可以穿過手指的表面和死性皮膚層，達(dá)到手指皮膚的真皮層，直接讀取指紋圖案，從而大大提高了該系統(tǒng)的安全性。
2 系統(tǒng)設(shè)計(jì)
SPCE061A的指紋識(shí)別系統(tǒng)總體設(shè)計(jì)方案如圖1所示。
圖1 指紋識(shí)別系統(tǒng)總體設(shè)計(jì)方案
本系統(tǒng)采用凌陽公司的SPCE061A單片機(jī)，它是將控制功能、數(shù)據(jù)處理功能以及數(shù)字信號處理（DSP）功能集于一身的一種新型單片機(jī)。它的CPU采用凌陽最新推出的16位微處理芯片，工作頻率可達(dá)到40MHz。它的指令系統(tǒng)提供了16位乘法運(yùn)算指令和內(nèi)積運(yùn)算指令，可以對指紋模板進(jìn)行高速的DSP處理。它的內(nèi)部采用總線結(jié)構(gòu)，減少了各個(gè)功能部件之間的連線，提高了可靠性和抗干擾能力。它的結(jié)構(gòu)采用模塊化，易于系統(tǒng)的擴(kuò)展。它的中斷處理能力較強(qiáng)，適用于各種實(shí)時(shí)控制領(lǐng)域。它的地址線達(dá)到22根，可以擴(kuò)展4M空間的程序和數(shù)據(jù)存儲(chǔ)器，適合指紋識(shí)別系統(tǒng)對存儲(chǔ)器容量較大的要求。它的低功耗和低電壓工作模式也使它特別適合于電池供電的指紋識(shí)別系統(tǒng)。
MBF300是富士通開發(fā)出的一種微型指紋傳感器，系統(tǒng)利用MBF300將采樣指紋模板輸入到單片機(jī)中進(jìn)行比較分析。它是利用手指在傳感器表面滑動(dòng)進(jìn)行指紋的采樣，所以被稱為掃描型傳感器。
鍵盤和LCD都是I/O設(shè)備。鍵盤可以讓用戶修改信息和輸入ID號，增強(qiáng)該系統(tǒng)的安全性；LCD采用CHIPS65545，用于顯示界面信息,為防電磁干擾和信號衰減，LCD連接線必須作一些特殊處理。
3 MBF300傳感器的基本原理及特點(diǎn)
電容式傳感器可以將物體、圖形、文字等具有二維的圖象轉(zhuǎn)換成電信號。MBF300屬于電容式傳感器。它由一個(gè)2維金屬電極陣列構(gòu)成。一端為固定極板，而人的手指皮膚則作為活動(dòng)極板。當(dāng)手指置于感應(yīng)器上時(shí)，一個(gè)微細(xì)的信號從驅(qū)動(dòng)環(huán)耦合到手指真皮表層上，并隨著指紋的紋脊和紋谷的變化而變化。感應(yīng)器偵測這種細(xì)微變化，對感應(yīng)信號放大，經(jīng)模數(shù)轉(zhuǎn)換后，從而最終形成精確的指紋圖象。
3．1 MBF300傳感器的基本原理
MBF300電容式傳感器的基本原理如圖2所示。
圖2 MBF300傳感器的基本原理圖
S是固定極板，H為活動(dòng)極板，即用戶的手指指紋。當(dāng)活動(dòng)極板因被測參數(shù)的改變而引起移動(dòng)時(shí)，兩極板間的距離d發(fā)生變化，從而改變了兩極板之間的電容量。設(shè)兩極板相互覆蓋的有效面積為A(M2)，兩極板間的距離為d（M），板極間介質(zhì)的介電常數(shù)為ε(F·m-1)，在忽略板極邊緣影響的條件下，其靜態(tài)電容量C（F）為：
3．2
MBF300傳感器的特點(diǎn)
MBF300表面保護(hù)膜異常堅(jiān)硬，使得該傳感器經(jīng)久耐用。它的工作電壓為2.8V～5V，所以可以利用電池進(jìn)行供電。它具有256*32像素感應(yīng)矩陣，使得指紋的特征采樣數(shù)據(jù)更精確。它的總線接口分別支持USB1.1、增強(qiáng)型8位微處理器接口和SPI串行接口。SPCE061A利用USB接口芯片PDIUSBD12和MBF300指紋傳感器進(jìn)行通信。
4軟件設(shè)計(jì)
4．1指紋識(shí)別算法
人類的指紋由緊密相鄰的凹凸紋路構(gòu)成，根據(jù)公式3-2，通過對每個(gè)像素點(diǎn)上利用標(biāo)準(zhǔn)參考放電電流，便可檢測到指紋的紋路狀況，具體算法分為四部分。
4．1．1指紋識(shí)別預(yù)處理算法
指紋識(shí)別預(yù)處理的目的是使指紋圖像更清晰，邊緣更明顯，以便提取指紋的特征點(diǎn)進(jìn)行識(shí)別。本文采取極值濾波和改進(jìn)的平滑濾波進(jìn)行噪聲消除，使圖像不失真；采取拉普拉斯銳化對指紋進(jìn)行紋線增強(qiáng)，突出邊緣信息，為背景分離算法提供方便。
4．1．2背景分離
采用迭代閥值的方法對指紋圖像進(jìn)行閥值分割。在圖像處理中，反復(fù)地用一種運(yùn)算直至條件滿足而得到輸出圖像的方法稱為迭代。迭代閥值方法如下：
①設(shè)定初始灰度閾值T（如令T=127），指指紋圖像的灰度值分為兩組R1和R2。
②計(jì)算兩組的平均灰度值u1和u2。
③重新設(shè)定新的灰度閾值T。新的T定義為：T=（u1+u2）/2。
④依據(jù)新的T對指紋圖像進(jìn)行閥值分割。
這種方法是以自適應(yīng)的閥值對指紋圖像進(jìn)行二值化處理。實(shí)驗(yàn)結(jié)果表明，該方法比設(shè)定固定閥值進(jìn)行處理更有普遍意義，且行之有效。
4.1．3 特征點(diǎn)提取
采用脊跟蹤法，其基本思想是直接對圖象進(jìn)行脊線跟蹤，在跟蹤過程中檢測和提取特征點(diǎn)。
4.1．4分類算法
指紋被分成5大類：拱類、做環(huán)類、右環(huán)類、尖拱類和旋渦類，預(yù)先使用全局特征排序，可以加速指紋的匹配服務(wù)。
4．2程序流程
當(dāng)系統(tǒng)處于空閑狀態(tài)時(shí)，SPCE061A利用P_SystemClock單元寫入CPUCLK STOP控制字，使系統(tǒng)從運(yùn)行狀態(tài)轉(zhuǎn)入睡眠狀態(tài)，關(guān)閉系統(tǒng)時(shí)鐘（PLL振蕩器）。當(dāng)用戶有指紋或按鍵輸入時(shí)， 系統(tǒng)接收到喚醒信號后接通PLL振蕩器，同時(shí)CPU會(huì)響應(yīng)喚醒事件的處理并進(jìn)行初始化。利用IRQ3_KEY為觸鍵喚醒源，利用FIQ為MBF300指紋傳感器輸入喚醒源。下面是程序流程圖3和IRQ3_KEY喚醒程序的部分代碼。
圖3 程序流程圖
R1=0x0000； //設(shè)置A口為帶下拉電阻的輸入口
[P_IOA_Attrib]=R1； //設(shè)置3個(gè)屬性向量
[P_IOA_Dir]=R1；
[P_IOA_Data]=R1； //中斷設(shè)置(允許IRQ3_KEY觸鍵中斷)
INT OFF； //關(guān)中斷
R1=0x0080； //設(shè)置中斷標(biāo)置
[P_Int_Ctrl]=R1；
INT IRQ； //開中斷
//讀P_IOA_Latch單元，以鎖存IOA[0～7]的數(shù)據(jù)，用于觸鍵喚醒
R1=[P_IOA_Latch]； //鎖存A口低8位的數(shù)據(jù)
//將P_SystemClock(寫)7013H單元的第0~2位置為“111”，使系統(tǒng)進(jìn)入睡眠狀態(tài)，
R1=0x0007； //系統(tǒng)進(jìn)入睡眠狀態(tài)
[P_SystemClock]=R1；
//IRQ3子程序(端口A的觸鍵喚醒源被觸發(fā)后，調(diào)用IRQ3 中斷服務(wù)子程序)：
.TEXT
.PUBLIC _IRQ3
_IRQ3:
R1 = 0x0100； //比較是否為L_IRQ3_Ext1中斷
TEST R1,[P_INT_Ctrl]；
JNZ L_IRQ3_Ext1； //是，則進(jìn)入；否，進(jìn)行下面的判斷
R1 = 0x0200；
TEST R1,[P_INT_Ctrl]； //是否為L_IRQ3_Ext2中斷
JNZ L_IRQ3_Ext2； //是，進(jìn)入該中斷；否，執(zhí)行下面的程序
L_IRQ3_KeyChange_WakeUp: //不是上面的兩種中斷則一定為鍵喚醒中斷
R1 = 0x0080； //清除IRQ3觸鍵中斷請求
[P_INT_Clear]= R1；
:
(處理系統(tǒng)被喚醒后的任務(wù))
:
RETI
L_IRQ3_Ext2:
[P_INT_Clear] = R1； //清除IRQ3_EXT2中斷請求
RETI
L_IRQ3_Ext1:
[P_INT_Clear] = R1； //清除IRQ3_EXT1中斷請求
RETI
相對于其它指紋識(shí)別系統(tǒng)控制核心大多數(shù)是DSP運(yùn)算能力強(qiáng)，但控制能力差的缺點(diǎn)，本系統(tǒng)最大的創(chuàng)新點(diǎn)是控制核心采用了既具有單片機(jī)的控制功能，又具有強(qiáng)大的DSP運(yùn)算能力于一體的16位SOC芯片SPCE061A，使本系統(tǒng)在進(jìn)行簡單的擴(kuò)展后即可以在指紋鎖、無鑰汽車、PDA設(shè)備、大型門禁系統(tǒng)等各種需要指紋控制的領(lǐng)域進(jìn)行廣泛的應(yīng)用。