VD5377 datasheet(33/88 Pages) STMICROELECTRONICS

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VD5377

Key features

6.4

Automatic exposure control

Figure 16 describes the automatic exposure control function. This routine is performed

every EXPO_FRAME_UPDATE (register 0x4B).The auto-exposure control algorithm works

by adjusting exposure until the brightest (max exposed(a)) pixel in the frame lies within a

specified target range. This is to ensure that no part of the frame is saturated.

Figure 16. Automatic exposure algorithm

Manual or automatic exposure control can be selected. This is controlled using register

EXPOSURE_CONTROL 0x43 bit 0 (see Table 18). Bits [6:4] give the exposure status and

bit 7 is the exposure limit flag. In automatic exposure control mode, register EXPOTIME

a. In fact the second brightest pixel is used. Note that AEC operates on the exposed frame, that is, before noise

cancellation. Processing is done on the CDS frame which is derived from the exposed frame as follows:

CDS frame = Exposed frame - Black frame + 8

MEP = 255?

Expo = Min(0,

Expo - SatDecStep)

Status = SATURATED

MEP > MEP_HighT

Expo = Min(0,

Expo - DecStep)

Status = HIGH

(overexposed)

MEP < MEP_LowT

Expo = Max(255,

Expo + IncStep)

Status = LOW

(underexposed)

Status = STABLE

Expo > ExpoMax

Expo = ExpoMax

LimitFlag = 1

Expo < ExpoMin

Expo = ExpoMin

END

Programmable parameters shown in red

START

Yes

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