ADV7342 datasheet(60/88 Pages) AD

60 / 88 page

ADV7342/ADV7343

Rev. 0 | Page 60 of 88

When changing the adaptive filter mode to Mode B

(Subaddress 0x35, Bit 6), the output shown in Figure 76

can be obtained.

Figure 76. Output Signal from ED/HD Adaptive Filter (Mode B)

SD DIGITAL NOISE REDUCTION

Subaddress 0xA3 to Subaddress 0xA5

Digital noise reduction (DNR) is applied to the Y data only.

A filter block selects the high frequency, low amplitude compo-

nents of the incoming signal (DNR input select). The absolute

value of the filter output is compared to a programmable

threshold value (DNR threshold control). There are two DNR

modes available, DNR mode and DNR sharpness mode.

In DNR mode, if the absolute value of the filter output is smaller

than the threshold, it is assumed to be noise. A programmable

amount (coring gain border, coring gain data) of this noise

signal is subtracted from the original signal. In DNR sharpness

mode, if the absolute value of the filter output is less than the

programmed threshold, it is assumed to be noise. Otherwise, if

the level exceeds the threshold, now identified as a valid signal,

a fraction of the signal (coring gain border, coring gain data) is

added to the original signal to boost high frequency components

and sharpen the video image.

In MPEG systems, it is common to process the video information

in blocks of 8 pixels × 8 pixels for MPEG2 systems, or 16 pixels ×

16 pixels for MPEG1 systems (block size control). DNR can be

applied to the resulting block transition areas that are known to

contain noise. Generally, the block transition area contains two

pixels. It is possible to define this area to contain four pixels

(border area).

It is also possible to compensate for variable block positioning

or differences in YCrCb pixel timing with the use of the DNR

block offset.

The digital noise reduction registers are three 8-bit registers.

They are used to control the DNR processing.

BLOCK SIZE CONTROL

BORDER AREA

BLOCK OFFSET

CORING GAIN DATA

CORING GAIN BORDER

GAIN

DNR CONTROL

FILTER

OUTPUT

> THRESHOLD?

INPUT FILTER

BLOCK

FILTER OUTPUT

< THRESHOLD

DNR OUT

MAIN SIGNAL PATH

ADD SIGNAL

ABOVE

THRESHOLD

RANGE FROM

ORIGINAL SIGNAL

DNR

SHARPNESS

MODE

NOISE

SIGNAL PATH

Y DATA

INPUT

BLOCK SIZE CONTROL

BORDER AREA

BLOCK OFFSET

CORING GAIN DATA

CORING GAIN BORDER

GAIN

DNR CONTROL

FILTER

OUTPUT

< THRESHOLD?

INPUT FILTER

BLOCK

FILTER OUTPUT

> THRESHOLD

DNR OUT

MAIN SIGNAL PATH

SUBTRACT

SIGNAL IN

THRESHOLD

RANGE FROM

ORIGINAL SIGNAL

DNR MODE

NOISE

SIGNAL PATH

Y DATA

INPUT

–

Figure 77. SD DNR Block Diagram

Coring Gain Border—Subaddress 0xA3, Bits[3:0]

These four bits are assigned to the gain factor applied to border

areas. In DNR mode, the range of gain values is 0 to 1 in

increments of 1/8. This factor is applied to the DNR filter

output that lies below the set threshold range. The result is then

subtracted from the original signal.

In DNR sharpness mode, the range of gain values is 0 to 0.5 in

increments of 1/16. This factor is applied to the DNR filter

output that lies above the threshold range. The result is added to

the original signal.

Coring Gain Data—Subaddress 0xA3, Bits[7:4]

These four bits are assigned to the gain factor applied to the luma

data inside the MPEG pixel block. In DNR mode, the range of

gain values is 0 to 1 in increments of 1/8. This factor is applied

to the DNR filter output that lies below the set threshold range.

The result is then subtracted from the original signal.

In DNR sharpness mode, the range of gain values is 0 to 0.5 in

increments of 1/16. This factor is applied to the DNR filter

output that lies above the threshold range. The result is added to

the original signal.

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