File:WX20211211-012754@2x.png

Figure 3. DWT plays a significant role in reducing the dimension of an image and extract the features by decomposing an image in frequency domain into sub-bands at different scales. The DWT of an image is created as follows: in the first level of decomposition, the image is split into four sub-bands, namely HH1, HL1, LH1, and LL1, as shown in the figure. The HH1, HL1 and LH1 sub-bands represent the diagonal details, horizontal features and vertical structures of the image, respectively. The LL1 sub-band is the low resolution residual consisting of low frequency components and it is this sub-band which is further split at higher levels of decomposition.