不同于普通座舱显示器，直升机平视显示器的背景画面为外界真实视景，显示画面可读性更易受到外界环境的影响。提出了一种基于最小可辨差异(PJND）理论的复杂视觉环境下直升机平视显示器的可读性评价方法。通过实验探究满足可读性的PJND值与背景因素(亮度、色度）的变化关系，以此为依据进行可读性设计工作，设计满足可读性的直升机平视显示器亮度控制曲线。实验结果表明，PJND值可综合反映亮度、色度对可读性的影响，以PJND值为标准设计出的直升机平视显示器亮度控制曲线能够满足可读性。

Different from the ordinary cockpit displays，the background of helicopter head-up display is the real outside scene and thus the readability of the displayed picture is easily disturbed by the outside environment. A method was proposed based on Perceived Just-Noticeable Difference (PJND) theory for evaluating the readability of helicopter HUD in complex visual environment.The relationship between the satisfactory PJND value and the environment factors (luminance and chrominance) was studied through experiments. On this basis，a luminance control curve satisfactory for the readability of HUD was designed. Experiment results showed that:1) The PJND value can synthetically reflect the effect of luminance and chrominance on the readability;and 2) The luminance control curve designed based on PJND value can satisfy the requirement on readability of the helicopter HUD.