# Backlight Unit Excessive Dimming Based on Perceptual Image Analysis
## 4 Simulation Results  
### SPBSS, SPS\({}_{\text{sat}}\), SPS\({}_{\text{overall}}\), and Their Effects  
This section identifies differences in influence in the process of maximizing dimming while preserving image quality, for each of SPBSS for image brightness recognition, SPS\({}_{\text{sat}}\) for contrast of saturated region, and SPS\({}_{\text{overall}}\) for contrast value of an image block, as shown in (6). For this purpose, the simulation results are described based on the result images that vary in only one characteristic among SPBSS, SPS\({}_{\text{sat}}\), and SPS\({}_{\text{overall}}\) with fixed values for the others. First, to make only the SPBSS in (6) vary, Figure 6a varied the pixel value in a bright image, whereas Figure 6c did so in a dark image. To make the SPS\({}_{\text{overall}}\) and SPS\({}_{\text{sat}}\) fixed, the pixel values vary within the same contrast range. To make SPBSS vary, which depends on brightness, the same excessive dimming was applied to the two images, and the results are shown in Figure 6b,d, respectively. As shown in the region indicated by the arrow, the pixel saturation by excessive dimming for low SPBSS shown in Figure 6d is larger than the saturation for high SPBSS shown in Figure 6b. Therefore, the smaller the brightness sensitivity slope value is, the less image quality deterioration humans perceive due to the excessive dimming. In Figure 7, only the SPS\({}_{\text{overall}}\) of was varied. To make the SPS\({}_{\text{overall}}\) vary, Figure 7a increased the image slope (contrast) by repeating the dark and bright regions with relatively small pixel distance or interval, whereas Figure 7c repeated with a large distance to reduce the image slope (contrast). To make SPBSS fixed, the maximum brightness and the number  
Figure 6: High Saturated Pixel Brightness Sensitivity Slope (SPBSS) vs. Low SPBSS. (**a**) High SPBSS original image; (**b**) High SPBSS image after excessive dimming; (**c**) Low SPBSS original image; (**d**) Low SPBSS image after excessive dimming. of pixels that are saturated during excessive dimming were held to be equal. The results of each of these two images with the same excessive dimming are shown in Figure 7b,d. For Figure 7c, where SPS\({}_{\text{overall}}\) is low, Figure 7d after the excessive dimming has zero contrast. This is because the contrast value is small before the dimming so perceived contrast deterioration is small and the contrast value is so low that the contrast difference cannot be noticed easily as well. However, it can be confirmed that Figure 7a with high SPS\({}_{\text{overall}}\) shows easily noticeable difference compared to Figure 7b, the image after the excessive dimming. Thus, as shown in (4), the smaller the SPS\({}_{\text{overall}}\), the more excessive dimming is possible. Figure 8 only varied SPS\({}_{\text{sat}}\) in (6). In order to make the SPS\({}_{\text{sat}}\) different with different image slope of the saturated pixel region, an excessive dimming was performed to ensure that saturation occurs starting from the same pixel value for the two images, where the two images have different image slopes within the same saturated pixel region. Figure 8a has two different pixel values alternatively with a smaller interval for high image slope value, while pixel values of Figure 8c varied slowly with a larger interval between the same two pixel-values of Figure 8a for low image slope. The results of the same excessive dimming applied to each image are shown in Figure 8b,d, respectively. Figure 7: High saturated pixel slope (SPS)\({}_{\text{overall}}\) vs. Low SPS\({}_{\text{overall}}\). (**a**) High SPS\({}_{\text{overall}}\) original image; (**b**) High SPS\({}_{\text{overall}}\) image after excessive dimming: (**c**) Low SPS\({}_{\text{overall}}\) original image; (**d**) Low SPS\({}_{\text{overall}}\) image after excessive dimming. Since both images belong to the saturated pixel region, the dimming results look the same.