m=512;

X=meshgrid(1:m);

r=imresize(rand(6),m/6).*127;

s=sign(sin(X./8));

imshow(interp2(X,X',128+127.*(s.*s'),0.7*X+r,0.7*X'+r),gray(256))

m=768; n=512;

sfs=logspace(0.5,log10(m/3),m);

[X,Y]=meshgrid(linspace(0,1,m).*sfs,logspace(-2.5,0,n));

imshow(128+127.*Y.*sin(X),gray(256));

C=imread('peppers.png');

[m n p]=size(C);

t=double(rgb2gray(C));

b=double(imresize(imresize(C,[m n]./32),[m n]));

s=32; w=2; M=2*max([m n]);

[X Y]=meshgrid([1:n], [1:m]);

g=(mod(X,m/s)<w)|(mod(Y,m/s)<w);

im=cat(3,t,t,t).*(1-g)+b.*g;

imshow(im./256,gray(256));

m=512;

[X,Y]=meshgrid(1:m);

a=255.*rand(6);

r=imresize(a,m/6)./2;

imshow(interp2(X,Y,imresize(a,m/6,'bilinear'),0.7*X+r,0.7*Y+r),gray(256))

Recipe for strong brightness illusion: add oblique square wave to lower freq vertical square wave. "Light" stripes on the left and "dark" stripes on the right of the result are phys. identical(!) We see "paint" (oblique grating) and ignore "lighting" (low freq grating).