A psychovisual experiment with 80 observers determined the amount of additive noise an observer could tolerate in resolving 36 different bar targets. The results show that the detection threshold noise can be represented by a simple analytical expression with contrast and spatial frequency as variables. The expression that closely matched the data is Vnoise (6.4C + 0.68)/v' , where Vnoise IS the amount of noise that can be tolerated, C is the contrast, and is the spatial frequency in cycles! radian. The numerical values are a function of the monitor used and are readily obtained by a simple measurement.