Peak White Inversion On/Off; Backlight Compensation - ADEMCO ACM574TP Installation Instructions Manual

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Table of Contents

Peak white inversion is used to eliminate the effect of point sources of light, for example car

headlamps. These point sources of light are typically much brighter than the rest of the scene

and although relatively small in terms of area, they can dramatically affect the camera’s exposure

system and the lens iris. For example, car headlamps will cause the lens iris to close or the

cameras exposure time to be decreased. The rest of the scene will then become much darker

and thus it could prove impossible to read the vehicle licence plate.

Peak white inversion renders the highlights in such a scene above a specified brightness

threshold as black. This is performed before the signal is passed to the camera’s electronic iris

control, AGC control or the lens iris. Therefore point sources of light are effectively ignored and

the exposure and applied gain is correct for the rest of the scene. The inverted areas of the

scene are shown by the monitor as black. See also

When using peak white inversion, the AV-PK potentiometer (either on the camera for a DC lens,

or the lens itself for a video drive type lens), must be set to peak

The backlight compensation feature can be used to eliminate the effect of an area of strong

background lighting in a scene. If a strong background light such as a window exists in a

scene, the camera will try to compensate for it by reducing the overall exposure. This would

mean that the areas surrounding the window would become too dark.

By using the backlight compensation feature, it is possible to select areas of the scene which

may be used to control the exposure. The BLC feature is used in conjunction with the BLC

Window Selection switches (B, C and D, figure 1). These switches select one of eight predefined

BLC windows which the camera uses to calculate its exposure. The shaded area on the

diagram represents the area used within the scene for exposure control. Any part of the scene

outside of the shaded area is ignored. Default setting is Window 1.

Window 1

C D

Window 5

C D

The BLC feature is turned

function with a manual iris lens when the Electronic Iris feature is switched

and video drive lenses, BLC will still function even though the Electronic Iris feature is switched

off.

Window 2

C D

Window 6

C D

using switch K figure 1. Default setting is