## 3 Halo Effect  
The halo artifact usually appears around a bright object on a black background due to the light leakage and the zone crosstalk in an mLCD panel. The experimental procedure to quantitatively characterize the halo effect is illustrated in Figure 8. We first inputted a test pattern with a white cross on a black background [28]. Then, we used the LMK to obtain a luminance distribution image. A halo image could finally be generated by excluding the luminance pattern of the cross from the luminance distribution image, where the halo artifacts surrounding the cross were more visible. Based on the measured RMS and SD values, we could quantitatively analyze and compare the halo effect for the generated halo images. The values of the RMS and SD for the mLCD driven in the HDR1000 and HDR600 modes and the OLED display were [0.2379, 0.2339], [0.1916, 0.1893], and [0.1830, 0.1811], respectively. The halo of an OLED display is caused by the measurement instrument, such as an imaging lens. Such a halo is analogous to the eye halo [29]. So far, we have characterized and compared the halo effect by obtaining the images on the CMOS sensor. The cross-section luminance profiles are shown in Figure 9a, where the luminance profile for the OLED display is non-ideal and the lines are all broadened due to a gradient drop in the 1D luminance distribution caused by the imaging instruments. To obtain the real luminance profiles for the displayed images, the non-ideal luminance profile for the OLED display can be used as a background reference and accordingly subtracted in the region outside the displayed line. In this way, an ideal luminance profile for the OLED display should be a rectangular function from zero to the maximum luminance. For the mLCD, its luminance profile was also narrowed to a rectangular line with the same method. The difference lies that the luminance outside the line will not quickly drop to zero, depending on how many zones are lit, because the contrast ratio in those lit zones is still limited by the LC layer. Figure 9b shows the real luminance profiles for the mLCDs driven in the HDR1000 and HDR600 modes. Taking the HDR600 driving mode as an example, the maximum and minimum luminances in the lit zones were 490 nits and 0.2 nits, respectively, indicating a contrast ratio of 2450:1. This contrast ratio was quite close to that of the FFS mode, whose CR was about 2500:1, which validated our methods for obtaining the real luminance profiles from imaging instruments. Furthermore, it can be inferred that five zones were lit in this selected cross-section due to the nearly constant value of 0.2 nits, ranging approximately from \(-\)20 mm to 20 mm. The five lit zones were possible if the selected cross-section was very close to the center portion of the cross. It should be mentioned that for the HDR1000 driving mode, a scaling luminance factor should be considered due to a significant luminance difference between the mLCD driven in the HDR1000 mode and the OLED display. Figure 8: Measurement procedure for the halo effect. As mentioned before, the contrast ratio inside the lit zones is limited by the intrinsic CR of the LC mode. In the boundary areas between lit zones and closed zones, it is also hard to obtain a sharp transition of the luminance profile due to the zone crosstalk characterized by the point spread function. To measure the point spread function of the backlight module, we first inputted a display pattern of two thin lines to make sure that just one zone was lit in the direction perpendicular to the line. Next, we adopted a novel strategy without requiring the physical separation between the LC layer and the backlight module. This method takes advantage of a limited contrast ratio of the FFS mode and a very bright backlight. Furthermore, this method is enabled because the backlight is independent of the LC driving signal.