Көру қабілетінің заңдары және Рикко заңы

Laws of sight

Riccò's law, discovered by astronomer Annibale Riccò, is one of several laws that describe a human's ability to visually detect targets on a uniform background. It says that for visual targets below a certain size, threshold visibility depends on the area of the target, and hence on the total light received. The "certain size" (called the "critical visual angle"), is small in daylight conditions, larger in low light levels. The law is of special significance in visual astronomy, since it concerns the ability to distinguish between faint point sources (e. g. stars) and small, faint extended objects ("DSOs").

Suppose that an achromatic target of angular area is viewed against a uniform background luminance (e. g. a disc of white light is projected on a white screen, or a nebula is seen through a telescope). For the target to be visible at all, there must be sufficient luminance contrast; i. e. the target must be brighter (or darker) than the background by some amount If the target is at threshold (i. e. only just visible) then the threshold contrast is defined as Riccò's law states that for targets below a certain size, threshold contrast is inversely proportional to target area, i. e.

for some constant Different values of background luminance will yield different values of
This can be seen in contrast threshold data for different levels of background luminance, plotted on a single graph as versus In each case (i. e. for each background ), the threshold curve for small targets is a straight line of gradient −1, i. e.

Targets for which the law holds are indistinguishable from point sources. Reading towards the right of each threshold curve, there is a target size at which the law begins to break down, i. e. the slope deviates from 1. This is called the "critical visual angle". Therefore, the contrast threshold required for detection is proportional to the signal to noise ratio multiplied by the noise divided by the area. This leads to the above equation.

Suppose that an achromatic target of angular area is viewed against a uniform background luminance (e. g. a disc of white light is projected on a white screen, or a nebula is seen through a telescope). For the target to be visible at all, there must be sufficient luminance contrast; i. e. the target must be brighter (or darker) than the background by some amount If the target is at threshold (i. e. only just visible) then the threshold contrast is defined as Riccò's law states that for targets below a certain size, threshold contrast is inversely proportional to target area, i. e.

for some constant Different values of background luminance will yield different values of
This can be seen in contrast threshold data for different levels of background luminance, plotted on a single graph as versus In each case (i. e. for each background ), the threshold curve for small targets is a straight line of gradient −1, i. e.

Targets for which the law holds are indistinguishable from point sources. Reading towards the right of each threshold curve, there is a target size at which the law begins to break down, i. e. the slope deviates from 1. This is called the "critical visual angle". Therefore, the contrast threshold required for detection is proportional to the signal to noise ratio multiplied by the noise divided by the area. This leads to the above equation.