Dwt is the algorithm used to reduce dimensionality of image so it used for image compression, feature extraction process. DWT algorithm decomposes the image into 4 subband (subimage) ie,LL,LH,HL,HH. dwt output extract the detailed ouput of input image. LL is the approximate image of input image it is low frequency subband so it is used for further decomposition process.. LH subband extract the horizontal features of original image HL subband gives vertical features HH subband gives diagonal features
LH,HL,HH are high frequency subbands
[LL,LH,HL,HH] = DWT2(X,'db5') % x is input image
figure;imshow(LH); % shows LH subband