Question

Consider two Images of same dimensions where one image is an original image and other should be a degraded image.   

Write a matlab program to measure picture quality using objective assessment validation criteria for the degraded image and original image. Calculate MSE, PSNR, Normalized absolute error, Maximum Difference, Structural content, Average difference, Normalized cross correlation for the images.

  

Explain the importance of Objective assessment in Image processing

Answer 1

function img = correctLighting(img, method)
if nargin<2, method='rgb'; end
switch lower(method)
case 'rgb'
%# process R,G,B channels separately
for i=1:size(img,3)
img(:,:,i) = LinearShading( img(:,:,i) );
end
case 'hsv'
%# process intensity component of HSV, then convert back to RGB
HSV = rgb2hsv(img);
HSV(:,:,3) = LinearShading( HSV(:,:,3) );
img = hsv2rgb(HSV);
case 'lab'
%# process luminosity layer of L*a*b*, then convert back to RGB
LAB = applycform(img, makecform('srgb2lab'));
LAB(:,:,1) = LinearShading( LAB(:,:,1) ./ 100 ) * 100;
img = applycform(LAB, makecform('lab2srgb'));
end
end

function I = LinearShading(I)
%# create X-/Y-coordinate values for each pixel
[h,w] = size(I);
[X Y] = meshgrid(1:w,1:h);

%# fit a linear plane over 3D points [X Y Z], Z is the pixel intensities
coeff = [X(:) Y(:) ones(w*h,1)] \ I(:);

%# compute shading plane
shading = coeff(1).*X + coeff(2).*Y + coeff(3);

%# subtract shading from image
I = I - shading;

%# normalize to the entire [0,1] range
I = ( I - min(I(:)) ) ./ range(I(:));
end

img = im2double( imread('http://i.stack.imgur.com/JmHKJ.jpg') );
subplot(411), imshow(img)
subplot(412), imshow( correctLighting(img,'rgb') )
subplot(413), imshow( correctLighting(img,'hsv') )
subplot(414), imshow( correctLighting(img,'lab') )