VV6501 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

View to exact match

VV6501

VGA CMOS Color Image Sensor

STMicroelectronics 

Functional Description

VV6501

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:

q Dark current

q 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.

Figure 15: Overview of dark offset cancellation

Normal pixel

Ilight

+

Idark

Vpix

Dpix

Dark pixel

Idark

Vpix

Dpix

Column 10-b

ADC element

+ offset

Digital Logic

Offset

cancellation

Column 10-b

ADC element

+ offset

Learn offset

+ Idark

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 16: Role of dark offset calibration

Dark Line

typ. value = 400

Dark calibration

dark offset = 336

Dark Line

typ. value = 64

Image Line

typ. value: 400 - 1360

Image Line

typ. value: 64-1024

raw image

processed image

18/60

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