VV6501 datasheet(18/60 Pages) STMICROELECTRONICS

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Functional Description

VV6501

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3.1.9

Dark calibration

In order to produce a high quality output image from the VV6501, it is necessary to accurately

control the black level of the video signal. There are two main sources of error:

Dark current

Offsets in the output path.

The black level is corrected by using dark pixel rows to “learn” the offset so that it can then be

subtracted from the image data. Dark rows have the same exposure setting as the visible lines but

are shielded from incident light.

For 10-b data the ideal “black” code is set to be 64 (when viewing 8-b data the ‘black’ code should

be 16). The aim of the dark calibration algorithm is to “learn” the offset required such that “black”

image lines have code 64.

Figure 15: Overview of dark offset cancellation

Figure 16: Role of dark offset calibration

Dpix

Vpix

Column

ADC element

+ offset

Dpix

Vpix

10-b

Column

ADC element

+ offset

10-b

Normal pixel

Idark

Dark pixel

Ilight

Idark

Offset

cancellation

Learn offset

+ Idark

Digital Logic

Dark Line

typ. value = 400

Image Line

typ. value: 400 - 1360

Dark calibration

dark offset = 336

Dark Line

typ. value = 64

Image Line

typ. value: 64-1024

processed image

raw image

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