Well, I don't know if this is intentional, but every new image in the loop gets filtered by a different kernel because refback never gets reset to zero and just keeps accumulating in the line,
refback = refback + im2double(Y);
If the filter kernel is supposed to be constant, the creation of Y should be pulled out of the loop, as below. Also, since Y is generated using FFTs, it is recommendable to ensure that Y is real-valued.
infolder = 'C:\Users\91894\Desktop\matlab\Dataset\images_001\images'
outfolder = 'C:\Users\91894\Desktop\matlab\Dataset\images_001\processed image'
imgFiles = dir([infolder,filesep,'\*.png']) ;
N = length(imgFiles) ;
refback = zeros(25, 25);
for f = 1:4
SpatDog = fspecial('gaussian',25,0.732) - fspecial('gaussian',25,0.785);
FreqDog = fftshift(fft2(fftshift(SpatDog)));
Y = abs(FreqDog)
refback = refback + im2double(Y);
end
refback = (1/4) * refback;
Y = fftshift(ifft2(fftshift(refback)));
Y=real(Y);
for i = 1:N
thisFile = [infolder,filesep,imgFiles(i).name] ;
[filepath,name,ext] = fileparts(thisFile) ;
outFile = [outfolder,filesep,[name,ext]] ;
I = imread(thisFile) ;
J = imresize(I,[256 256]);
conv = convn(J,Y);
imwrite(conv,outFile) ;
end
