數(shù)字圖像處理第三章 空域圖像增強(qiáng)技術(shù)

1、It makes all the difference whether one sees darkness through the light or brightness through the shadows.第3章 空域圖像增強(qiáng)技術(shù)圖像增強(qiáng)的目的是使處理后的圖像更適合于具體的應(yīng)用，是面向問(wèn)題的，例如：適合于處理X射線的技術(shù)并不一定適合于處理空間探測(cè)器傳送的圖像。圖像增強(qiáng)是最有趣的和最生動(dòng)的圖像處理技術(shù)之一。判斷標(biāo)準(zhǔn)：人的主觀視覺(jué)圖像增強(qiáng)技術(shù)從總體上說(shuō)，可以分為兩大類：空域增強(qiáng)和頻域增強(qiáng)。空域增強(qiáng)是直接對(duì)圖像平面中的像素進(jìn)行處理，像前面已經(jīng)介紹過(guò)的直方圖均衡、匹配等方法，都屬于空域增強(qiáng)技術(shù)。

2、頻域增強(qiáng)則是將原定義在圖像空間中的圖像以某種形式轉(zhuǎn)換（Fourier 變換）到其它空間（頻率域）中，利用該空間的特有性質(zhì)方便地進(jìn)行圖像處理，最后再轉(zhuǎn)回原圖像空間中。另外，兩大類中的某些方法通常也被結(jié)合在一起來(lái)進(jìn)行增強(qiáng)操作。It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.1 基礎(chǔ)( , ) ( , )g x yT f x y空域增強(qiáng)的一般數(shù)學(xué)表達(dá)式：算子T操作在(x,y)的某個(gè)鄰域(neighborhood)上，例如33領(lǐng)域，或一

3、輸入圖像集上It makes all the difference whether one sees darkness through the light or brightness through the shadows.當(dāng)領(lǐng)域?yàn)?1，即只包含當(dāng)前象素自己時(shí)，T成為灰度級(jí)變換函數(shù)，此時(shí)的處理成為點(diǎn)處理。當(dāng)更大的鄰域被考慮時(shí)，往往成為掩碼處理(mask processing)或者濾波。( )sT r兩個(gè)常用的灰度級(jí)變換函數(shù)：對(duì)照度拉伸和閾值函數(shù)It makes all the difference whether one sees darkness through the light or b

4、rightness through the shadows.3.2 一些基本的灰度變換It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.2.1 負(fù)變換S=L-1-r, 這里圖像的灰度范圍為0, L-1It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.2.2 對(duì)數(shù)變換l

5、og(1),0scrr 其將使比較狹窄的低灰度級(jí)范圍變得更寬，而較寬的高灰度級(jí)范圍變得更窄，同時(shí)能夠壓縮象素值變化范圍很大的圖像，使之象素值分布范圍更小。Fourier譜(01.5*106)經(jīng)過(guò)對(duì)數(shù)變換后：06.2It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.2.3 冪律變換,0scrcc1，而變化 r 時(shí)的各種變換規(guī)律It makes all the difference whether one sees darkness

6、through the light or brightness through the shadows.冪律變換的一個(gè)最好應(yīng)用是伽馬校正(Gamma correction)被廣泛使用在圖像捕捉、打印和顯示設(shè)備上。2.50.4It makes all the difference whether one sees darkness through the light or brightness through the shadows.Gamma變換用于通常的對(duì)照度操作It makes all the difference whether one sees darkness through the

7、 light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.2.4 分段線性變換分段線性函數(shù)的主要有點(diǎn)是其形式可以任意復(fù)雜，主要缺點(diǎn)是其說(shuō)明需要更多的用戶輸入。對(duì)照度拉伸變換：a) 分段線性函數(shù)b) 低對(duì)照度放大約700倍的花粉SEM圖像c) 對(duì)照度拉伸結(jié)果d) 灰度閾值化處理It makes all the difference whether one se

8、es darkness through the light or brightness through the shadows.灰度切割(slicing):主要用于突出某個(gè)特定的灰度范圍，從而增強(qiáng)某個(gè)專門的特征，如衛(wèi)星圖像中的水團(tuán)。It makes all the difference whether one sees darkness through the light or brightness through the shadows.位平面切割(bit-plane slicing):該操作主要是為突出圖像中的某個(gè)具體的位對(duì)整個(gè)圖像外表的貢獻(xiàn)?？梢园岩桓睌?shù)字圖像分解成位平面的組合，分析圖像

9、每個(gè)位的相對(duì)重要性，從而在圖像量化時(shí)可以幫助決定所使用的位數(shù)是否足夠，這種分解在圖像壓縮中也有很大的作用。It makes all the difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.3 直方圖處理直方圖是大量的空域處理技術(shù)的基礎(chǔ)，直方圖處理可以有效

10、地用于圖像增強(qiáng)。除了能提供有關(guān)圖像的統(tǒng)計(jì)特征外，其所包含的信息還能用于其他很多的圖像處理技術(shù)，如圖像分割、圖像壓縮等。其軟件實(shí)現(xiàn)簡(jiǎn)單，可以做成固件，使其在實(shí)時(shí)圖像處理中成為最受歡迎的工具。定義：性質(zhì)：It makes all the difference whether one sees darkness through the light or brightness through the shadows.直方圖描述了每個(gè)灰度級(jí)具有的像素的個(gè)數(shù)，反映的是圖像灰度的統(tǒng)計(jì)信息，但丟失了所有這些像素點(diǎn)的空間信息，即像素點(diǎn)的相對(duì)位置。因此，任一特定的圖像有唯一的直方圖，但反之并不成立。It make

11、s all the difference whether one sees darkness through the light or brightness through the shadows.直方圖反映的總體性質(zhì)：明暗程度、細(xì)節(jié)是否清晰、動(dòng)態(tài)范圍大小等It makes all the difference whether one sees darkness through the light or brightness through the shadows.四種典型灰度圖像的直方圖特征：(a)暗圖像；(b)亮圖像；(c)低對(duì)照度圖像；(e)高對(duì)照度圖像It makes all the

12、difference whether one sees darkness through the light or brightness through the shadows.直方圖的計(jì)算：通過(guò)面積求直方圖（做實(shí)驗(yàn)）：It makes all the difference whether one sees darkness through the light or brightness through the shadows.直方圖的用途：1）數(shù)字化參數(shù)的選擇：2）邊界閾值的選取：例：It makes all the difference whether one sees darkness

13、through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.3.1 直方圖均衡處理(equalization)用于直方圖均衡化的函數(shù)s=T(r)必須滿足兩個(gè)條件:a) T(r)是一個(gè)單調(diào)遞增的單值函數(shù)b) 0 T(r) 1， 對(duì)0 r 1;以上s和r；分別表示輸入和輸出圖像的規(guī)一化灰度，即在0,1范圍可以證明，概率累計(jì)分布函數(shù)就是所要的直

14、方圖均衡函數(shù)：0( )( ),1( )( )( )1,1rrrsrsT rp w dwrp rdrp sp rTdss It makes all the difference whether one sees darkness through the light or brightness through the shadows.在離散情況下：00( )( )( ),krkkkkrjjkkjnp rkLnsT rp rnkLn 以上，k表示某個(gè)灰度級(jí)，L是整個(gè)灰度級(jí)的數(shù)目，在通常的8位圖像下，為256。以上的方程就是通常所說(shuō)的直方圖均衡化或者線性化。很顯然，該方程滿足前面所說(shuō)的兩個(gè)條件。特點(diǎn)：

15、雖然不象連續(xù)情況下時(shí)輸出灰度完全滿足均勻分布，但從該方程明顯可以看出，均衡化后的圖像比原圖像所跨越的灰度級(jí)范圍更寬。另外，直方圖處理是完全“自主”性質(zhì)的，即該過(guò)程所需的參數(shù)完全來(lái)自圖像本身，不需要任何額外的參數(shù)，是一種有力的自適應(yīng)增強(qiáng)工具。還有，該技術(shù)實(shí)現(xiàn)起來(lái)也很簡(jiǎn)單。It makes all the difference whether one sees darkness through the light or brightness through the shadows.rjrj+rsjsj+sIt makes all the difference whether one sees da

16、rkness through the light or brightness through the shadows.例例例例例例例：設(shè)圖象有例：設(shè)圖象有6464* *6464=4096=4096個(gè)象素，有個(gè)象素，有8 8個(gè)灰度級(jí)，灰度個(gè)灰度級(jí)，灰度分布如表所示。進(jìn)行分布如表所示。進(jìn)行直直方圖均衡化方圖均衡化。rkr0=0r1=1/7r2=2/7r3=3/7r4=4/7r5=5/7r6=6/7r7=1 nk 790102385065632924512281p(rk) 0.190.250.210.160.080.060.030.02It makes all the difference whet

17、her one sees darkness through the light or brightness through the shadows.步驟：步驟：rkr0=0r1=1/7r2=2/7r3=3/7r4=4/7r5=5/7r6=6/7r7=1 nk 790102385065632924512281p(rk) 0.190.250.210.160.080.060.030.02例例例例例例It makes all the difference whether one sees darkness through the light or brightness through the shad

18、ows.1. 1. 由（由（2-22-2）式計(jì)算）式計(jì)算s sk k。rkr0=0r1=1/7r2=2/7r3=3/7r4=4/7r5=5/7r6=6/7r7=1 nk 790102385065632924512281p(rk) 0.190.250.210.160.080.060.030.02sk計(jì)算計(jì)算 0.190.440.650.810.890.950.981.00例例例例例例It makes all the difference whether one sees darkness through the light or brightness through the shadows.rk

19、r0=0r1=1/7r2=2/7r3=3/7r4=4/7r5=5/7r6=6/7r7=1 nk 790102385065632924512281p(rk) 0.190.250.210.160.080.060.030.02sk計(jì)算計(jì)算 0.190.440.650.810.890.950.981.00sk舍入舍入 1/73/75/76/76/71112. 2. 把計(jì)算的把計(jì)算的s sk k就近安排到就近安排到8 8個(gè)個(gè)灰度級(jí)中?；叶燃?jí)中。例例例例例例It makes all the difference whether one sees darkness through the light or

20、brightness through the shadows.rkr0=0r1=1/7r2=2/7r3=3/7r4=4/7r5=5/7r6=6/7r7=1 nk 790102385065632924512281p(rk) 0.190.250.210.160.080.060.030.02sk計(jì)算計(jì)算 0.190.440.650.810.890.950.981.00sk舍入舍入 1/73/75/76/76/7111sk nsk 7901023850985448p(sk) 0.190.250.210.240.113. 3. 重新命名重新命名s sk k，歸并相同灰度歸并相同灰度級(jí)的象素?cái)?shù)。級(jí)的象素?cái)?shù)

21、。例例例例例例It makes all the difference whether one sees darkness through the light or brightness through the shadows.均衡化前后直方圖比較例例例例例例It makes all the difference whether one sees darkness through the light or brightness through the shadows.例：It makes all the difference whether one sees darkness through t

22、he light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows. 直方圖均衡化實(shí)質(zhì)上是減少圖象的灰度級(jí)以換取對(duì)比度的加大。在均衡過(guò)程中，原來(lái)的直方圖上頻數(shù)較小的灰度級(jí)被歸入很少幾個(gè)或一個(gè)灰度級(jí)內(nèi)，故得不到增強(qiáng)（？?。?。若這些灰度級(jí)所構(gòu)成的圖象細(xì)節(jié)比較重要，則需采用局部區(qū)域直方圖均衡。It makes all the difference whether one

23、sees darkness through the light or brightness through the shadows.3.3.2 直方圖匹配/規(guī)定(specification)n 另外，直方圖的規(guī)定沒(méi)有什么規(guī)則可循。一般，可以根據(jù)特定的增強(qiáng)任務(wù)，采用試錯(cuò)的方法來(lái)得到想要的直方圖規(guī)定。It makes all the difference whether one sees darkness through the light or brightness through the shadows.連續(xù)灰度的直方圖原圖It makes all the difference whether

24、 one sees darkness through the light or brightness through the shadows.連續(xù)灰度的直方圖規(guī)定It makes all the difference whether one sees darkness through the light or brightness through the shadows. 令P(r) 為原始圖象的灰度密度函數(shù)，P(z)是期望通過(guò)匹配的圖象灰度密度函數(shù)。對(duì)P(r) 及P(z) 作直方圖均衡變換，通過(guò)直方圖均衡為橋梁，實(shí)現(xiàn)P(r) 與P(z) 變換。It makes all the differe

25、nce whether one sees darkness through the light or brightness through the shadows.rjzkIt makes all the difference whether one sees darkness through the light or brightness through the shadows. 步驟： （1）由 將各點(diǎn)灰度由 r映射成s。 （2）由 將各點(diǎn)灰度由 z映射成v。 rrdrrprTs010)()(zzdzzpzGv010)()(It makes all the difference wheth

26、er one sees darkness through the light or brightness through the shadows. 步驟： （3）根據(jù)v=G(z), z=G-1(v) 由于v, s有相同的分布，逐一取 v=s，求出與r對(duì)應(yīng)的z=G-1(s)。It makes all the difference whether one sees darkness through the light or brightness through the shadows.離散灰度級(jí)情況： 由（1）、（2）計(jì)算得兩張表，從中選取一對(duì), ，使，并從兩張表中查得對(duì)應(yīng)的rj，zk。于是，原始

27、圖象中灰度級(jí)為的所有象素均映射成灰度級(jí)。最終得到所期望的圖象。It makes all the difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness thr

28、ough the light or brightness through the shadows.3.3.3 局部增強(qiáng)前面所說(shuō)的兩種處理技術(shù)都是全局處理，用于整體增強(qiáng)。在某些情況下，用于增強(qiáng)某個(gè)小區(qū)域細(xì)節(jié)的局部增強(qiáng)技術(shù)是需要的。局部增強(qiáng)其實(shí)就是基于鄰域的空間域操作（更詳細(xì)的討論在3.5節(jié)），前面的方法同樣可以使用，但此時(shí)處理的是一副圖像中的某個(gè)子區(qū)域。簡(jiǎn)單實(shí)例：It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.3.4 直方圖統(tǒng)計(jì)量

29、用于增強(qiáng)1010011220( )()( )( )0( )()(LnniiiLiiiLiiinrrmp rm=r p rrrrrmp r階中心矩：）均值：）顯然：1，二階中心矩（方差）：）m是圖像平均灰度級(jí)的測(cè)度；而方差，通常表示為2，則代表了圖像的平均對(duì)照度。這兩個(gè)量的更有力的應(yīng)用是在局部增強(qiáng)中，不僅簡(jiǎn)單、靈活性大，而且局部均值和方差與圖像的外觀存在緊密的、可預(yù)測(cè)的對(duì)應(yīng)關(guān)系。例：02( , ),and( , ), otherwisexyxysG1GsGE f x ymk Mk Dk Dg x yf(x,y)It makes all the difference whether one see

30、s darkness through the light or brightness through the shadows.繞在支撐物上鎢絲的SEM圖像（放大130倍）使用統(tǒng)計(jì)量的局部增強(qiáng)結(jié)果It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.4 代數(shù)和邏輯運(yùn)算增強(qiáng)n 邏輯操作(二進(jìn)制掩膜，binary masking)基于點(diǎn)運(yùn)算，對(duì)兩副圖像的單個(gè)象素進(jìn)行操作（此時(shí)每個(gè)象素的值都被看成邏輯值），基本包括與、或、非三者，其他任何邏輯

31、操作都可通過(guò)三者之間的組合來(lái)完成。邏輯操作通常用于選擇ROI (region of interest)，也常與形態(tài)學(xué)處理相結(jié)合。It makes all the difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.4.1 圖像加It makes all th

32、e difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shado

33、ws.3.4.2 圖像減圖像減的重要作用之一是突出圖像間的差異，最成功的商業(yè)應(yīng)用是醫(yī)學(xué)圖像中的掩碼模式X光成像。It makes all the difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.4.3 圖像乘It makes all the differ

34、ence whether one sees darkness through the light or brightness through the shadows.3.4.4 圖像乘It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.4.5 代數(shù)運(yùn)算的應(yīng)用平均去噪It makes all the difference whether one sees darkness through the light or brightness

35、 through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.5 空間濾波It makes all the difference whether one sees darkness through the light or brightness through the shadows.基本步驟：不過(guò)當(dāng)模板的邊界超出圖像的邊界時(shí)，要注意邊界問(wèn)題的處理，最常用的方法是填充(padding)，但其會(huì)影響圖像

36、的邊界，影響程度隨模板尺寸的增大而增加。It makes all the difference whether one sees darkness through the light or brightness through the shadows.也稱做濾波器(filter)、核(kernel)、模板(template)、窗口(window)。對(duì)mn的掩碼（通常要求m,n必須是奇數(shù)）：( , )( , ) (,)absa tbg x yw s t f xs yt 這里：a=(m-1)/2，b=(n-1)/2，這種線性空間濾波也通常指“把圖像與掩碼進(jìn)行卷積”，掩碼也叫“卷積掩碼”。從濾波器響

37、應(yīng)的角度講，上式也可以簡(jiǎn)寫稱：1 1221mnmnmniiiRw zw zw zw zIt makes all the difference whether one sees darkness through the light or brightness through the shadows.3.5.1 空間平滑濾波器a) 線性平滑濾波器平滑濾波通常被用作模糊圖像和減少噪聲。模糊處理通常用在預(yù)處理階段，如在目標(biāo)抽取前用于移除小的細(xì)節(jié)，或者把線和曲線間的間隙連接起來(lái)。噪聲減少可以用可以用線性的或非線性的濾波器來(lái)完成。It makes all the difference whether on

38、e sees darkness through the light or brightness through the shadows.鄰域平均相當(dāng)于模板的元素全為1的情況，當(dāng)還包含其他整數(shù)時(shí)，更適合的叫法是加權(quán)平均。( , )( , ) (,)/( , )ababsa tbsa tbg x yw s t f xs ytw s t 平均法在一定程度上抑制了噪聲，但同時(shí)也會(huì)引起模糊線性，其程度與鄰域半徑成正比。It makes all the difference whether one sees darkness through the light or brightness through

39、the shadows.從左至右，從上到下分別為500500象素的原圖像，和用大小分別為3、5、9、15和35的平方平均濾波器模板對(duì)原圖像平滑的結(jié)果。It makes all the difference whether one sees darkness through the light or brightness through the shadows.超限（基于閾值的）鄰域平均法：It makes all the difference whether one sees darkness through the light or brightness through the shadow

40、s.b) 排序統(tǒng)計(jì)濾波器是一種非線性操作，其響應(yīng)是基于模板所包含圖像區(qū)域內(nèi)象素的排序結(jié)果來(lái)定的，用得最多的是中值濾波器，此外還有最大、最小濾波器等。中值濾波對(duì)脈沖噪聲和椒鹽噪聲(salt-and pepper noise)特別有效。It makes all the difference whether one sees darkness through the light or brightness through the shadows.中值濾波的基本步驟：It makes all the difference whether one sees darkness through the li

41、ght or brightness through the shadows.一般來(lái)講：It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.5.2 空間銳化濾波器一階導(dǎo)數(shù)和二階導(dǎo)數(shù)的特征：1)一階導(dǎo)數(shù)產(chǎn)生更厚的邊緣；2）二階導(dǎo)數(shù)對(duì)細(xì)的細(xì)節(jié)，如細(xì)線和孤立點(diǎn)的響應(yīng)更強(qiáng)；3）一階導(dǎo)數(shù)對(duì)灰度的階躍變化響應(yīng)更強(qiáng)烈，而二階導(dǎo)數(shù)則會(huì)在此產(chǎn)生雙響應(yīng)；4）二階導(dǎo)數(shù)在灰度變化相似時(shí)，其對(duì)線的響應(yīng)要強(qiáng)于階躍變化，對(duì)點(diǎn)的響應(yīng)又強(qiáng)于線。It makes all

42、 the difference whether one sees darkness through the light or brightness through the shadows.It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.5.2.1 二階導(dǎo)數(shù)增強(qiáng)Laplacian算子22222fffxy2 (1, )(1, )( ,1)( ,1)4 ( , )ff xyf xyf x yf x yf x y具有各向同性特征的線性變

43、換算子:Laplacian算子（相當(dāng)于線性高通濾波器）離散實(shí)現(xiàn)：其具有90度旋轉(zhuǎn)不變性，當(dāng)對(duì)角方向的不變性（45度方向）也加上時(shí)，即得到如下右圖的掩碼：It makes all the difference whether one sees darkness through the light or brightness through the shadows.通過(guò)把原圖像與銳化處理結(jié)果相減，可以既保留銳化效果，同時(shí)能恢復(fù)圖像的背景特征。2( , )( , )( , )g x yf x yf x yIt makes all the difference whether one sees dar

44、kness through the light or brightness through the shadows.反銳化掩膜和高提升濾波（unsharp masking and high-boost filtering)見(jiàn)教材p132，自學(xué)It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.5.2.2 一階導(dǎo)數(shù)增強(qiáng)梯度算子1/222/()()xyGfxGfyfffxy f梯度算子：梯度矢量的幅度：xyfGG 9586fzzzz 在

45、不再特殊說(shuō)明時(shí)，通常把梯度矢量的幅度稱為梯度。其具有旋轉(zhuǎn)不變性。實(shí)際實(shí)現(xiàn)時(shí)通常采用如下近似：盡管其計(jì)算簡(jiǎn)單，也能反映灰度變化，但喪失了各向同性特征一階導(dǎo)數(shù)算子的數(shù)字近似：a) Robert 交叉梯度算子b) Sobel梯度算子789123369147(2)(2)(2)(2)fzzzzzzzzzzzz It makes all the difference whether one sees darkness through the light or brightness through the shadows.33掩模圖：It makes all the difference whether o

46、ne sees darkness through the light or brightness through the shadows.一階導(dǎo)數(shù)檢測(cè)隱形眼鏡邊緣缺陷It makes all the difference whether one sees darkness through the light or brightness through the shadows.3.6 空間增強(qiáng)方法的聯(lián)合應(yīng)用（實(shí)驗(yàn)）Frequently, a given enhancement task will require application of several complementary enhan

47、cement techniques in order to achieve an acceptable result. The image shown left is a nuclear whole body bone scan, used to detect diseases such as bone infection and tumors. The objective is to enhance this image by sharpening it and by bringing out more of the skeletal detail. The narrow dynamic r

48、ange of the low gray levels and high noise content make this image difficult to enhance.It makes all the difference whether one sees darkness through the light or brightness through the shadows.The StrategyUtilize the Laplacian to highlight fine detailUtilize the gradient to enhance prominent edgesC

49、ombine Laplacian and gradient to get the detail-enhanced and noise-compressed imageIncrease the contrast of low gray levels by using a gray-level transformation.It makes all the difference whether one sees darkness through the light or brightness through the shadows.Laplacian EnhancementA rather noi

50、sy sharpened image is expected. Median filter is incapable of removing noise in such medical images),(),(2yxfyxfIt makes all the difference whether one sees darkness through the light or brightness through the shadows.Smoothed Gradient as a MaskThe response of the gradient to noise and fine detail i

51、s lower than the Laplacians and can be lowered further by smoothing the gradient with an averaging filter.We can smooth the gradient and multiply it by the Laplacian enhanced image. In this case the smoothed gradient may be viewed as a mask image.5 x 5 box smoothmask imageIt makes all the difference

52、 whether one sees darkness through the light or brightness through the shadows.The Sharpen Enhanced ImageThe final sharpen enhanced image can be obtained from the sum of original image and the sharpened image which comes from the product of Laplacian enhanced image and the smoothed Sobel gradient.ad

53、d to theoriginalsharpen enhanced image Laplacianenhancedsmoothed Sobel gradientsharpened image strong edges and the relative lack of visible noiseIt makes all the difference whether one sees darkness through the light or brightness through the shadows.Contrast Stretch and the final ResultThe final s

54、tep in this enhancement task is to increase the contrast of the sharpened image.There are a number of gray level transformation functions that can accomplish this objective. The dark characteristics of the images lend themselves to a power-law transformation.Significant new detail is visible in the result, including the faint definition of the outline of the body, and of body tissue.c = 1 = 0.5It makes all the difference whether one sees darkness through the light or