The effect of ambient illumination on handheld display image quality

Abstract

Handheld devices such as smartphones and tablets are becoming useful in the medical field, as they allow physicians, radiologists, and researchers to analyze images with the benefit of mobile accessibility. However, for handheld devices to be effective, the display must be able to perform well in a wide range of ambient illumination conditions. We conducted visual experiments to quantify user performance for testing the image quality of two current-generation devices in different ambient illumination conditions while measuring ambient light levels with a real-time illuminance meter. We found and quantified that due to the high reflectivity of handheld devices, performance deteriorates as the user moves from dark areas into environments of greater ambient illumination. The quantitative analysis suggests that differences in display reflection coefficients do not affect the low illumination performance of the device but rather the performance at higher levels of illumination.

Fig. 1

Experimental setup

Fig. 2

Average illuminance (lx) for each test subject under each bin for both devices. Each experiment took place in a controlled environment (either in a dark lab, office, or outside space) with increasing illuminance beginning in the dark environment. The illuminance distribution was binned into ten illuminance levels (x axis). Each bin consists of three points representing the average illuminance for each of the three subjects in that particular illuminance range. Each point was displayed along all individual illuminance measurement data points

Fig. 3

Experimental setup. The handheld device was attached to the face of the T-10 such that the sensor was able to capture illuminance readings of the background. The T-10 was connected to a laptop computer through a proprietary RS232 cable because due to Android OS limitations, the handheld devices were not able to directly interface with the T-10. The T-10 reading and writing program was run on the laptop so that it was able to read data from the T-10 and write measurements into a text file which was used for data analysis. A time stamp synchronized each user response from the DENOTE application with the exact illuminance measurement

Fig. 4

Ratio of correct to total responses comparison of the two devices

Fig. 5

Difference of ratio of correct to total responses of device A and device B. The illuminance distribution was binned into 10 illuminance levels (x axis). The negative points show that in almost all cases, the user performed better when using device B than when using device A