色彩增強不同於彩色圖像增強,圖像增強的一般處理方式爲直方圖均衡化等,目的是爲了增強圖像局部以及整體對比度。而色彩增強的目的是爲了使的原有的不飽和的色彩信息變得飽和、豐富起來。對應於Photoshop裏面的“色相/飽和度”調節選項裏面對飽和度的操作。色彩增強的過程,並不改變原有彩色圖像的顏色以及亮度信息。
在我的色彩增強算法模塊裏面,始終只針對色彩飽和度(Saturation)信息做研究,調整。這樣的話,那就不得不介紹HSV顏色空間了,H代表Hue(色彩),S代表Saturation(飽和度),V代表Value,也可用B表示(Brightness,明度),HSV空間也可稱作HSB空間。
HSV空間在wikipedia上的介紹,https://en.wikipedia.org/wiki/HSL_and_HSV
下面根據自己的理解介紹一下HSV空間,以及其各通道在Matlab和OpenCV中的不同。
HSV的圓柱模型
HSV的圓錐模型
從上圖可以看出,在HSV空間中,Hue通道的取值從0-360°變化時,顏色從紅->黃->綠->青->藍逐步變化。Saturation從0->1變化時,色彩逐漸加深變成純色(pure)。Value值從0->1變化時,圖像整體亮度增加,V值爲0時,圖像爲全黑,V值爲1時,圖像爲全白。
Matlab RGB色彩空間向HSV轉換,採用函數rgb2hsv,轉換後的hsv各通道的元素取值範圍爲[0,1];OpenCV中彩色圖像向HSV空間中轉換,cvtColor(src,srcHsv,CV_BGR2HSV),轉換後H的取值範圍爲[0,180],S,V的取值範圍爲[0,255].
下面介紹自己的算法處理思路,後面會給出完整的Matlab代碼:
步驟一、給出一張原圖src,用PS進行飽和度(Saturation)+40處理後另存爲src_40;
步驟二、將以上兩張圖像分別轉換到hsv空間,提取出飽和度信息,分別爲S,S_40;
步驟三、統計飽和度增加40後,原色彩飽和度與飽和度增量之間的對應關係,即S -- (S_40-S);
步驟四、對關係S -- (S_40-S)進行二次多項式曲線擬合,得到二次曲線f(x) = p1*x^2 + p2*x + p3;
爲什麼是二次?1.對應關係呈現出拋物線形狀;2.更高次曲線並沒有明顯改善擬合性能,且計算消耗會變高。
步驟五、任意給定輸出圖像input,根據其色彩飽和度信息,即可進行色彩增強40處理,新的飽和度信息可以表示爲S'(x) = S(x) + f(x),得到增強後的色彩信息後返回RGB圖像輸出;
步驟六、分別對原圖+20,+40,+60後進行飽和度信息統計,並得到相應擬合參數,設置爲色彩增強的低、中、高三擋,在實際處理過程中,根據輸入圖像input自身色彩飽和度信息(均值)自適應選取相應參數進行色彩增強;
步驟七、按需對某一單獨顏色通道進行色彩增強處理,例如綠色範圍爲105°-135°,在對該範圍進行增強的同時,還需對75°-105°,135°-165°進行一半強度的增強,這樣纔會保證色彩的連續性,不會出現色斑;
步驟八、按需對色彩(Hue)進行轉換;
代碼部分:第一部分用作估計擬合參數,在Curve fitting tool裏面對X,Y進行擬合,得到曲線參數。
% Color Enhancement
clc,clear,close all
src1 = imread('src.bmp');
src2 = imread('src_40.bmp');
src1_hsv = rgb2hsv(src1);
src2_hsv = rgb2hsv(src2);
h1 = src1_hsv(:,:,1);
s1 = src1_hsv(:,:,2);
v1 = src1_hsv(:,:,3);
h2 = src2_hsv(:,:,1);
s2 = src2_hsv(:,:,2);
v2 = src2_hsv(:,:,3);
%
meanS1 = mean(s1(:));
varS1 = std2(s1);
%
meanS2 = mean(s2(:));
varS2 = std2(s2);
%
deltaS = s2 - s1;
deltaV = v2 - v1;
%% test1 : 觀測“原飽和度-飽和度調整增量”的關係 saturation and delta saturation
figure;
oriS = zeros(101,2);
s3 = s1;
j = 1;
for i = 0: 0.01 : 1
oriS(j,1) = i + 0.01;
oriS(j,2) = mean(deltaS(find(s1 > i & s1< i + 0.01)));
j = j + 1;
end
X = oriS(:,1);
Y = oriS(:,2);
XX = oriS(:,1) * 255;
YY = oriS(:,2) * 255;
plot(XX,YY)
第二部分,對輸入圖像進行高、中、低三級自適應增強處理
%% Color Enhancement Module -- Authored by HuangDao,08/17/2015
% functions: input a image of type BMP or PNG, the program will decide to
% do the Color Enhancement choice for you.There are four types of Enhanced
% intensity - 20,40,60,80.The larger number stands for stronger
% enhancement.
% And we can also choose the simple color channel(eg.R,G,B) to do the
% enhancement.There are also four different types of enhanced intensity.
%
% parameters table
% ------------------------------------------------------------------------
% | Enhanced | MATLAB params | OpenCV params |
% | intensity |p1 p2 p3 | p1 p2 p3 |
% | 20 |-0.1661 0.2639 -0.003626 |-0.0006512 0.2639 -0.9246|
% | 40 |-0.4025 0.6238 -0.0005937 |0.001578 0.6238 -0.1514|
% | 60 |1.332 1.473 -0.01155 |-0.005222 1.473 -2.946 |
% | 80 |-4.813 3.459 -0.004568 |-0.01887 3.459 -1.165 |
% ------------------------------------------------------------------------
clc; clear ;close all
% 載入文件夾
pathName = '.\';
fileType = '*.bmp';
files = dir([pathName fileType]);
len = length(files);
for pic = 5%1:1:len
srcName = files(pic).name;
srcImg = imread(srcName);
srcHSV = rgb2hsv(srcImg);
srcH = srcHSV(:,:,1);
srcS = srcHSV(:,:,2);
srcV = srcHSV(:,:,3);
meanS = mean(srcS(:));
varS = std2(srcS);
%圖像整體進行色彩增強處理
if (meanS >= 0.5)
p1 = 0;p2 = 0;p3 = 0;
else if (meanS >= 0.35 && meanS < 0.5)
p1 = -0.1661;p2 = 0.2639;p3 = -0.003626;
else if (meanS >=0.2 && meanS <0.35)
p1 = -0.4025;p2 = 0.6238;p3 = -0.0005937;
else
p1 = 1.332;p2 = 1.473;p3 = -0.01155;
end
end
end
dstS = srcS + p1*srcS.*srcS + p2*srcS + p3 ;
dstHSV = srcHSV;
dstHSV(:,:,2) = dstS;
dstImg = hsv2rgb(dstHSV);
figure;imshow(srcImg);
figure;imshow(dstImg);
%指定R,G,B通道進行色彩增強處理,紅色範圍([225-255]),綠色範圍(75-[105-135]-165),藍色範圍([-15-15])
p11 = -0.4025;p21 = 0.6238;p31 = -0.0005937;%周邊雜色調整係數,40
p12 = 1.332; p22 = 1.473; p32 = -0.01155; %純色區域調整係數,60
compHue = srcH;
GcompS = dstS;
RcompS = dstS;
BcompS = dstS;
channel = 'B';
switch channel
case 'G'
I1 = find(compHue > 0.2083 & compHue <0.2917);
GcompS(I1) = dstS(I1) + dstS(I1).*dstS(I1)*p11 + dstS(I1)*p21 + p31;
I2 = find(compHue >= 0.2917 & compHue <= 0.3750);
GcompS(I2) = dstS(I2) + dstS(I2).*dstS(I2)*p12 + dstS(I2)*p22 + p32;
I3 = find(compHue > 0.3750 & compHue <0.4583);
GcompS(I3) = dstS(I3) + dstS(I3).*dstS(I3)*p11 + dstS(I3)*p21 + p31;
compHSV = dstHSV;
compHSV(:,:,2) = GcompS;
dstImgG = hsv2rgb(compHSV);
figure;imshow(dstImgG);
case 'R'
I1 = find(compHue > 0.875 & compHue <0.9583);
RcompS(I1) = dstS(I1) + dstS(I1).*dstS(I1)*p11 + dstS(I1)*p21 + p31;
I2 = find(compHue >= 0.9583 | compHue <= 0.0417);
RcompS(I2) = dstS(I2) + dstS(I2).*dstS(I2)*p12 + dstS(I2)*p22 + p32;
I3 = find(compHue > 0.0417 & compHue <0.125);
RcompS(I3) = dstS(I3) + dstS(I3).*dstS(I3)*p11 + dstS(I3)*p21 + p31;
compHSV = dstHSV;
compHSV(:,:,2) = RcompS;
dstImgR = hsv2rgb(compHSV);
figure;imshow(dstImgR);
case 'B'
I1 = find(compHue > 0.5417 & compHue <0.625);
BcompS(I1) = dstS(I1) + dstS(I1).*dstS(I1)*p11 + dstS(I1)*p21 + p31;
I2 = find(compHue >= 0.625 & compHue <= 0.7083);
BcompS(I2) = dstS(I2) + dstS(I2).*dstS(I2)*p12 + dstS(I2)*p22 + p32;
I3 = find(compHue > 0.7083 & compHue <0.7917);
BcompS(I3) = dstS(I3) + dstS(I3).*dstS(I3)*p11 + dstS(I3)*p21 + p31;
compHSV = dstHSV;
compHSV(:,:,2) = BcompS;
dstImgB = hsv2rgb(compHSV);
figure;imshow(dstImgB);
end
%進行R,G,B通道之間的互換
convH = zeros(size(srcH,1),size(srcH,2)); %convert
deltaHue = 240;
switch deltaHue
case 120
disp('R -> G')
convH = srcH + 1/3;
convH(find(convH >= 1)) = convH(find(convH >= 1)) - 1;
case 240
disp('R -> B')
convH = srcH + 2/3;
convH(find(convH >= 1)) = convH(find(convH >= 1)) - 1;
end
convHSV = dstHSV;
convHSV(:,:,1) = convH;
convImg = hsv2rgb(convHSV);
figure;imshow(convImg)
pause();
end
添加OpenCV代碼段:
Mat srcHSV,sat,satAdj,dstMerge,dst; //sat - saturation飽和度分量
Mat imageAwb = imread("m_ImageAwb.bmp");
vector<Mat> channels,channels1;
double p1,p2,p3;
cvtColor(imageAwb,srcHSV,CV_BGR2HSV);
split(srcHSV,channels);
split(srcHSV,channels1);
sat = channels.at(1);
Scalar m = mean(sat);
if (m(0) <= 51.5)
{p1 = -0.002714 , p2 = 0.9498, p3 = -0.5073; AfxMessageBox("High Color Enhancement!"); }//高
else if (m(0) > 38.5 && m(0) <= 89.5)
{p1 = -0.001578 , p2 = 0.6238, p3 = -0.1514;AfxMessageBox("Middle Color Enhancement!"); }//中
else if (m(0) > 89.5 && m(0) <=127.5)
{p1 = -0.0006512, p2 = 0.2639, p3 = -0.9246;AfxMessageBox("Low Color Enhancement!");}//低
else
{p1 = 0,p2 = 0,p3 =0;AfxMessageBox("No Color Enhancement!");}
satAdj = sat;
for (int i = 0 ; i < sat.rows;i ++)
{
for (int j = 0;j < sat.cols;j ++)
{
uchar val = sat.at<uchar>(i,j);
satAdj.at<uchar>(i,j) = (val + p1 * val * val + p2 * val + p3) ;
}
}
channels1.at(1) = satAdj;
merge(channels1,dstMerge);
cvtColor(dstMerge,dst,CV_HSV2BGR);
imwrite("m_ImageCE.bmp",dst);
最後給出算法效果圖:
Group1.原圖->增強後
Group2.原圖->R通道增強->顏色通道改變R2B
Group3.原圖->增強後->顏色通道改變R2B
完!下篇講Local Tone Mapping。