LL component of wavelet transform

Question

I applied the discrete wavelet transform to an image using dwt2 and displayed the LL component. It shows a brighter image instead of a blurred image. Can anyone please tell me why it is brighter?

My code is:

 I=im2double(imread('lena1.jpg'));
 [LL,LH,HL,HH] = dwt2(I,'db1');
 imshow(LL);

Answer 1

The reason why is because the LL component most likely has values that go beyond 1 since you converted with im2double . When trying to display that image, try doing this instead:

imshow(LL, []);

This will map the lowest value to 0 and the highest value to 255 and scaling everything linearly in between. Note that this won't change the actual LL variable. imshow with [] as the second parameter will internally scale the intensities so that the values get mapped between [0,255] respectively.