This section presents the simulation work by evaluating four different types of still im- ages. The HR images reconstructed by Bilinear interpolation, frequency domain approach, IBP approach, conventional POCS approach and the proposed wavelet-based POCS plus
wavelet coefficient refinement SR reconstruction algorithm are presented subjectively. Figure 5.6 shows the SR reconstruction results based on the proposed algorithm as well as various existing algorithms. Figure 5.6(a) shows the original HR image Lena of size 256x256. Figure 5.6(b) shows one of the LR frames of size 64x64. There are 10 LR frames in total, which are generated by degrading the HR image with 9 randomly generated motion vectors and blurred by a Gaussian low-pass filter with size 4x4 and a standard deviation of 1. These 10 degraded images were then down-sampled both horizontally and vertically with a factor of 4. Gaussian noise was then added to these LR frames. In order to have a better visual comparison, the LR frame show in Figure 5.6(b) is magnified by nearest-neighborhood interpolation. In the actual SR reconstruction process however, the LR frames are in the size of 64x64. Figure 5.6(c) shows the SR image reconstructed by
using the bilinear interpolation. Figure 5.6(d) gives the result obtained from the frequency domain method. Figure 5.6(e) shows the result obtained by using the IBP method. Figure
5.6(f) is from the conventional POCS and Figure 5.6(g) shows the SR image reconstructed
by the proposed wavelet-based POCS method. The HR images reconstructed by different SR approaches are all of the same size as the original HR image.
In Figure 5.6,it is clearly seen that the proposed SR reconstruction presents more de-
tailed features such as "lips and feathers" textures than other SR reconstruction approaches. The features contained in HR image Lena are mixed with middle and low frequency
components. Figure 5.7 presents the results of image Baboon which contain mostly high frequency texture components. Figure 5.7(a) shows the original HR image Baboon with
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size 256x256. Figure 5.7(b) shows one of the LR frames with size 64x64. Figure 5.7(c)- (g) show the SR images reconstructed by using the Bilinear interpolation, the frequency
domain method, the IBP method, the conventional POCS and the proposed wavelet-based
POCS method, respectively. Again, the estimated HR images reconstructed by different SR approaches all have the same size as the original Baboon HR image. It is seen that the HR image reconstructed by the frequency domain approach has fairly good subjective results, but the proposed SR reconstruction process shows improvements on both image contrasty
and the resolution.
The HR image Lena and Baboon are natural images. Normally, the human eye has similar perception to natural images. Therefore, an artificial HR image is used as a differ- ent type of image for comparison. In the following SR simulation, the HR image Chart is employed. This image contains small font size numbers and different texture charts.
Thus, a different visual perception is provided by this type of image. Figure 5.8(a) shows
the original HR image Chart which contains artificial textures of size 256x320. Figure
5.8(b) shows one of the LR frames with size 64x80. Figure 5.8(c) shows the SR image
reconstructed by using the Bilinear interpolation. Figure 5.8(d)-(g) show the results ob- tained from the frequency domain method, the IBP method, the conventional POCS and the proposed wavelet-based POCS approach, respectively. The HR images reconstructed by different SR approaches all have the same size as the original HR image.
From Figure 5.8, the IBP approach seen to have better than the frequency domain and the conventional POCS approaches. The HR image reconstructed by the IBP approach presents more information on numbers such as character "2" in the middle bottom and
shows more textures on the vertical chart in the middle of the image. But overall, the HR
image reconstructed by the proposed algorithm has a better quality.
An image with only letters is also used to test the performance of the different SR reconstruction approaches on a class of images that have sharp transition edges. In the
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l,t 4. * · M B "I (g) ProposedHR image, letters with different font sizes are shown, hence the limitation of each SR
reconstruction approach can be presented. Figure 5.9(a) shows the original HR image Letters which contains only white background color and black English characters with size
256x256. Figure 5.9(b) shows one of the LR frames with size 128x 128. Different from the previous three experiments, the LR frames in the experiment are down-sampled from the original HR image in both horizontal and vertical directions with only a factor of 2. Figures 5.9(c)-(g) show the SR images reconstructed by using the bilinear interpolation,
the frequency domain method, the IBP method, the conventional POCS and the proposed method, respectively. It is noted that the estimated HR images have the same size as the
original HR image, the smallest words in the picture are hardly recognizable from the images reconstructed by the frequency domain and the conventional POCS approaches.
However, most characters still can be easily read in the images constructed by the IBP approach and the proposed SR reconstruction algorithm.