ADV7191KST datasheet(42/69 Pages) AD

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ADV7190/ADV7191

–42–

REV. 0

GAMMA CORRECTION REGISTERS 0–13

(GAMMA CORRECTION 0–13)

(Address (SR5–SR0) = 26H–32H)

The Gamma Correction Registers are fourteen 8-bit-wide regis-

ters. They are used to program the gamma correction Curves A

and B.

Gamma correction is applied to compensate for the nonlinear

relationship between signal input and brightness level output (as

perceived on the CRT). It can also be applied wherever nonlin-

ear processing is used.

Gamma correction uses the function:

SignalOUT = (SignalIN )γ

where

γ = gamma power factor

Gamma correction is performed on the luma data only. The

user has the choice to use two different curves, Curve A, or

Curve B. At any one time only one of these curves can be used.

The response of the curve is programmed at seven predeﬁned

locations. In changing the values at these locations the gamma

curve can be modiﬁed. Between these points linear interpolation

is used to generate intermediate values. Considering the curve

to have a total length of 256 points, the seven locations are at:

32, 64, 96, 128, 160, 192, and 224.

Values at Location 0, 16, 240, and 255 are ﬁxed and cannot be

changed.

For the length of 16 to 240 the gamma correction curve has to

be calculated as below:

y = xγ

where

y = gamma corrected output

x = linear input signal

γ = gamma power factor

To program the gamma correction registers, the seven values for

y have to be calculated using the following formula:

yn = [x(n–16) /(240–16) ]γ

× (240–16) + 16

where

x(n-16) = Value for x along x-axis

Value for y along the y-axis, which has to be written

into the gamma correction register

= 32, 64, 96, 128, 160, 192, or 224

Example:

y32 = [(16/224)

.5 × 224] + 16 = 76*

y64 = [(48/224)

.5 × 224] + 16 =120*

y96 = [(80/224)

.5 × 224] + 16 = 150*

y128 = [(112/224)

.5 × 224] + 16 = 174*

*Rounded to the nearest integer.

The above will result in a gamma curve shown below, assuming

a ramp signal as an input.

250

200

150

100

300

250

200

150

100

300

SIGNAL OUTPUT

SIGNAL INPUT

0.5

GAMMA CORRECTION BLOCK OUTPUT

TO A RAMP INPUT

100

150

200

250

LOCATION

Figure 85. Signal Input (Ramp) and Signal Output for

Gamma 0.5

250

200

150

100

300

SIGNAL OUTPUTS

SIGNAL

INPUT

0.5

GAMMA CORRECTION BLOCK OUTPUT

TO A RAMP INPUT FOR VARIOUS GAMMA VALUES

100

150

200

250

LOCATION

0.3

1.5

1.8

Figure 86. Signal Input (Ramp) and Selectable Gamma

Output Curves

The gamma curves shown above are examples only, any user-

deﬁned curve is acceptable in the range of 16–240.

DNR27

DNR26

DNR25

DNR24

DNR23

DNR22

DNR21

DNR20

BLOCK OFFSET

DNR DNR DNR DNR

0000

0 PIXEL OFFSET

0001

1 PIXEL OFFSET

0010

2 PIXEL OFFSET

••••

•

••••

•

••••

•

1101

13 PIXEL OFFSET

1110

14 PIXEL OFFSET

1111

15 PIXEL OFFSET

DNR INPUT SELECT

DNR DNR DNR

FILTER A

FILTER B

FILTER C

FILTER D

DNR MODE

DNR

SHARPNESS

MODE

DNR23

DNR MODE

CONTROL

Figure 84. DNR Register 2

ADV7191KST Datasheet(PDF) 42 Page - Analog Devices

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