More CMUCam Exposure Register Info

Register 24- rw: AEC Auto Exposure White Pixel Ratio


Registers 24 and 25 together control the AEC target values for image brightness.
For a brighter image, increase register 24 and decrease register 25.
For a darker image, decrease register 24 and decrease register 25.
AEW<7:0>- used to calculate the white pixel ratio. OV7620 AEC algorithm counts the
whole field/frame white pixel (its luminance level is higher than a fixed level) and black
pixel (its luminance level is lower than a fixed level) number. When white/black pixel ratio
is same as the ratio defined by registers [25] and [26], image stable. This register is used
to define the white pixel ratio, default is 25%, each LSB represent step: Interlaced: 1.3%;
Progressive Scan: 0.7%. Change range is: Interlaced: [01] ~ [4A]; Progressive Scan: [01]
~ [96]. Increase AEW<7:0> will increase the white pixel ratio. For same light condition,
the image brightness will increase if AEW<7:0> increase.
Note: AEW<7:0> must combined with register [26] AEB<7:0>. Keep the relation always
true: AEW<7:0> + AEB<7:0> > [4A] for Interlaced; AEW<7:0> + AEB<7:0> > [90].

Register 25- rw: AEC Auto Exposure Black Pixel Ratio


AEB<7:0>- used to calculate the black pixel ratio. OV7620 AEC algorithm is count whole
field/frame white pixel (its luminance level is higher than a fixed level) and black pixel (its
luminance level is lower than a fixed level) number. When white/black pixel ratio is same
as the ratio defined by registers [25] and [26], image stable. This register is used to
define black pixel ratio, default is 75%, each LSB represent step: Interlaced: 1.3%;
Progressive Scan: 0.7%. Change range is: Interlaced: [01] ~ [4A]; Progressive Scan: [01]
~ [96]. Increase AEB<7:0> will increase black pixel ratio. For same light condition, the
image brightness will decrease if AEB<7:0> increase.
Note: AEB<7:0> must combined with register [25] AEW<7:0>. Keep the relation always
true: AEW<7:0> + AEB<7:0> > [4D] for Interlaced; AEW<7:0> + AEB<7:0> > [90].

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