Contrast-sensitivity-based evaluation method of a surveillance camera's visual resolution: Improvement from the conventional slanted-edge spatial frequency response method

Visual resolution is an important specification of a surveillance camera, and it is usually quantified by linewidths per picture height (LW/PH). The conventional evaluation method adopts the slanted-edge spatial frequency response (e-SFR) and uses a fixed decision contrast ratio to determine LW/PH. However, this method brings about a considerable error with respect to subjectively judged results because the perceptibility of the human vision system (HVS) varies with spatial frequency. Therefore, in this paper, a systematic calculation method, which combines the contrast sensitivity function characterizing the HVS and e-SFR, is proposed to solve LW/PH. Eight 720P camera modules in day mode, four 720P modules in night mode, and two 1080P modules in day mode are actually adopted. Corresponding to the three modes, mean absolute error between objective and subjective LW/PH are suppressed to as low as 26 (3.6% of 720P), 27 (3.8% of 720P), and 49 (4.5% of 1080P), while those of the conventional method are 68 (9.4% of 720P), 95 (13.2% of 720P), and 118 (10.9% of 1080P).