色彩空間轉換：爲什麼lab2rgb（rgb2lab（RGB））無法完全恢復RGB圖像？

完成從RGB到LAB的色彩空間轉換後，我想通過LAB-> RGB轉換恢復原始RGB圖像。色彩空間轉換：爲什麼lab2rgb（rgb2lab（RGB））無法完全恢復RGB圖像？

但是，當嘗試：RGB --rgb2lab --> LAB -- lab2rgb --> RGB2, 輸出RGB2比輸入RGB更輕，爲什麼？

Matlab代碼：imshow(lab2rgb(rgb2lab(imread('peppers.png'))))

詳細

：

RGB = imread('peppers.png'); 
LAB = rgb2lab(RGB); %convert RGB to LAB 
RGB2 = lab2rgb(LAB); %try to recovery RGB 
figure, 
subplot(121); imshow(RGB); 
subplot(122); imshow(RGB2);

環境：Matlab的R2015a

來源

2016-05-15 応振強

對於我圖像Matlab的2015B幾乎相同。下面的命令給你什麼（數字差別）：'max（abs（double（RGB（：）） - 255 * RGB2（:)））'？ –

謝謝你的評論，我嘗試在MATLAB R2015a和max（ABS（雙（RGB（：）） - 255 * RGB2（:)）） ANS = 73.2527 –

我已經發現的錯誤。錯誤是由默認的'rgb2lab'的覆蓋版本引起的。再次感謝您。 –

由MATLAB提供不會產生該錯誤的默認功能。

此錯誤是由用戶定義函數rgb2lab覆蓋默認函數引起的。其可產生該錯誤的重寫功能是如下，請參閱GeometricContext\src\tools\misc

function [L,a,b] =rgb2lab(R,G,B) 
% function [L, a, b] = RGB2Lab(R, G, B) 
% RGB2Lab takes matrices corresponding to Red, Green, and Blue, and 
% transforms them into CIELab. This transform is based on ITU-R 
% Recommendation BT.709 using the D65 white point reference. 
% The error in transforming RGB -> Lab -> RGB is approximately 
% 10^-5. RGB values can be either between 0 and 1 or between 0 and 255. 
% By Mark Ruzon from C code by Yossi Rubner, 23 September 1997. 
% Updated for MATLAB 5 28 January 1998. 

if (nargin == 1) 
    B = double(R(:,:,3)); 
    G = double(R(:,:,2)); 
    R = double(R(:,:,1)); 
end 

if ((max(max(R)) > 1.0) | (max(max(G)) > 1.0) | (max(max(B)) > 1.0)) 
    R = R/255; 
    G = G/255; 
    B = B/255; 
end 

[M, N] = size(R); 
s = M*N; 

% Set a threshold 
T = 0.008856; 

RGB = [reshape(R,1,s); reshape(G,1,s); reshape(B,1,s)]; 

% RGB to XYZ 
MAT = [0.412453 0.357580 0.180423; 
     0.212671 0.715160 0.072169; 
     0.019334 0.119193 0.950227]; 
XYZ = MAT * RGB; 

X = XYZ(1,:)/0.950456; 
Y = XYZ(2,:); 
Z = XYZ(3,:)/1.088754; 

XT = X > T; 
YT = Y > T; 
ZT = Z > T; 

fX = XT .* X.^(1/3) + (~XT) .* (7.787 .* X + 16/116); 

% Compute L 
Y3 = Y.^(1/3); 
fY = YT .* Y3 + (~YT) .* (7.787 .* Y + 16/116); 
L = YT .* (116 * Y3 - 16.0) + (~YT) .* (903.3 * Y); 

fZ = ZT .* Z.^(1/3) + (~ZT) .* (7.787 .* Z + 16/116); 

% Compute a and b 
a = 500 * (fX - fY); 
b = 200 * (fY - fZ); 

L = reshape(L, M, N); 
a = reshape(a, M, N); 
b = reshape(b, M, N); 

if ((nargout == 1) | (nargout == 0)) 
    L = cat(3,L,a,b); 
end

來源

2016-05-15 14:58:37

色彩空間轉換：爲什麼lab2rgb（rgb2lab（RGB））無法完全恢復RGB圖像？

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