STV0672 データシートの表示（PDF） - STMicroelectronics

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STV0672

USB CIF/VGA Digital Camera Chipset

STMicroelectronics 

STV0672-chipsetf-3-1.fm

Introduction

modified) once per frame, where a frame consists of 2 video fields. The video fields are identical in length, that is they do not

contain any of the half line detail of the analogue video standards like CCIR or NTSC. Two fields per frame are required by the

internal sensor video timing model. Integration time, sensor analogue gain and STV0672 digital gain are all used to control the

overall exposure. The STV0672 exposure algorithm uses an asymptotic approach in calculating the change required in the

present exposure value to approach the requested exposure target.

2.2.3 Defect Correction

STV0672 automatically detects and corrects for pixel defects, without the need for any additional components or additional

sensor calibration procedures. This greatly simplifies camera assembly and test, when compared with previous EEPROM-based

defect correction schemes. The pixel defect correction scheme in STV0672 ensures that VV6410+STV0672 and

VV6500+STV0672 are ‘defect free’ chipsets.

2.2.4 Interpolation

The Bayer pattern from the sensor provides under-sampled trichromatic data. Interpolation up-samples these undersampled data

streams to restore a bandlimited (effectively blurred) version of the original, using simple two-dimensional filtering templates.

Signal components aliased in the under-sampling process remain aliased after interpolation. The green channel (no longer

containing notions of even and odd rows) is treated differently from red and blue, being interpolated into two output

representations, one ‘sharper’ (containing more high-frequency detail) than the other. The smoother of the two green signals is

output along with red and blue to the matrix block.

2.2.5 Unsharp masking

Subtraction of these two green representations creates an ‘unsharp mask’, which can be further processed before adding back

into the main colour flow. The unsharp signal undergoes variable coring (a central thresholding operation for noise reduction) and

intensity (gain operation on the cored signal). The strain parameter from the housekeeper acts as both a coring threshold and an

attenuator on the user intensity setting, achieving a softening of image appearance in low-light conditions.

FPN Vector

(644x14)

Defect Map

(128x32)

Line Store

(9x644x10)

FPN Cancel

Defect

Detect & Correct

Control

Address Gen (All Sub Blocks)

QVGA FIFO

IN

Input Processor

Set-Up

Registers

6/41

House Keeper

(AEC,AGC,

AWB etc)

RAM

ROM

interpolation Matrix

+

YCbCr

Gamma 4:2:2

Encoder

OUT

Peaking

Key

===

Ram/Data Storage

Logic

Figure 2 : STV0672 VP Block Diagram

29 November 2000

Commercial in confidence

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