VV5430

Exposure Control

CD5430F-A

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7.3

Backlit Mode

The VV5430 can be configured to operate in two auto-exposure modes, selected by the BKLIT pin (pin28) state, or via the serial

interface (Setup Code_1, bit 0). The default mode (BKLIT = 0) provides exposure control for normally illuminated scenes. For

scenes where a bright background can cause the foreground subject to be severely under exposed, the ‘Backlit’ mode (BKLIT =

1) offers superior performance.

‘Backlit Mode’ (BKLIT=1) operates by using a higher threshold level for the exposure control comparator over the central area of

an image, which is therefore exposed for longer and so enhanced. The area in which the higher comparator threshold is used

when BKLIT=1 is illustrated below:

Figure 7 : Backlit exposure region

Note: The threshold level used for the central area is a preset mutiple of the normal mode reference level, and is not

alterable. In some circumstances this may not be sufficient difference to cause a noticable effect on the overall expo-

sure of the image.

10%

30%

80%

80%

25%

75%

Normal operation (BKLIT=0)

Higher threshold area (BKLIT=1)

Visible

25%

90%

image

Higher

Threshold

Exposure

control area