# Backlight Unit Excessive Dimming Based on Perceptual Image Analysis
## 4 Simulation Results
### Real Image Samples  
Figure 9 shows the results of presented excessive dimming methodologies using \(\text{SPBSS}\), \(\text{SPS}_{\text{overall}}\), and \(\text{SPS}_{\text{sat}}\) of (6) with actual images rather than regularly patterned ones presented before. As discussed previously, smaller image block sizes can improve the excessive dimming with increased amount of hardware and processing time. In Figure 9a, the image frame is divided into six large inhomogeneous blocks that can be easily implemented with low display manufacturing cost. The excessive dimming is applied by twenty pixels for each block to show the validities of (6)-(8) with real photo images. Comparing the original image of Figure 9a to the result of Figure 9b, after applying the local excessive dimming, we can see several characteristics of our proposed method. The block Local_1 has a high SPBSS, and low \(\text{SPS}_{\text{overall}}\) and \(\text{SPS}_{\text{sat}}\), and excessive dimming occurs at bright areas, where contrast of the block and of saturated pixel region is low. Therefore, all the three characteristics show that more excessive dimming is possible. The excessive dimming results for the block Local_1 does not show much difference between the original block and the excessively dimmed one as expected. Local_2 is the case where \(\text{SPBSS}\) is lower than Local_1. Even though \(\text{SPBSS}\) is lower than Local_1, there is still no difference between the original and excessively dimmed one. Figure 9c is an enlarged image of the Local_3 block. Local_3, which has high \(\text{SPBSS}\), may enable more excessive dimming, but with high \(\text{SPS}_{\text{overall}}\) and \(\text{SPS}_{\text{sat}}\) less excessive dimming is allowed. Although with the same excessive dimming as other blocks, there is  
Figure 9: Real image simulation results. (**a**) Original image; (**b**) Excessively dimmed image; (**c**) Original “Local_3” block; (**d**) Excessively dimmed “Local_3” block. For the case of excessive local dimming shown in Figure 11 with the block size of 512 \(\times\) 256, compared to the existing method of relatively strict pixel count 95% dimming, the excessive dimming method proposed in this paper shows that an average of 11.9% more excessive dimming is possible, which reduces power consumption more. The eye test results show that the image quality degradation is unnoticeable. To measure perceptual image quality, twelve people of eight males and four females measured MOS scores to give ratings from 1 to 10, where high scores represent better image quality. For the blocks of Local 1, Local 3, and Local 5 with large SPBSS due to their darkness, relatively more dimming is possible, while the blocks Local 2, Local 4, and Local 6 have large \(\text{SPS}_{\text{overall}}\) and \(\text{SPS}_{\text{sat}}\), so there is a limit on the allowable excessive dimming. Local 3 and Local 5 have relatively few pixels in the pixel saturation region, so more dimming is possible. Furthermore, SSIM values of Figure 11b,c are 0.9591 and 0.9550, respectively, so we can see that the difference is small. Even though more optimal excessive dimming can be realized with smaller block sizes, a large block size of 512 \(\times\) 256 is used for the feasibility of commercial applications by sacrificing the homogeneity. Figure 12 shows the results of the excessive RGB global dimming, which separately adjusts the RGB values of backlight. Figure 12a-c respectively represent the original image, image with the existing dimming method, and the result of applying more excessive dimming of the proposed method. Figure 12c shows no significant noticeable degradation in the image quality. The blue component of Figure 12 has high max. pixel value, but most blue pixel has low values, so SPBSS is high and \(\text{SPS}_{\text{overall}}\) and \(\text{SPS}_{\text{sat}}\) are low. Only a small amount of excessive dimming is possible if max.