ADV7196A datasheet(21/36 Pages) AD

21 / 36 page

REV. 0

ADV7196A

–21–

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, 224.

Location 0, 16, 240, and 255 are fixed and can not 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 at points:

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

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

the gamma correction register.

Example:

y32 = [(16/22

4)0.

2 24] + 16 = 76

y64 = [(48/22

4)0.

224] + 16 =120

y96 = [(80/22

4)0.

224] + 16 = 150

y128 = [(112/22

4)0.

224] + 16 = 147

*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

SIGNAL OUTPUT

SIGNAL INPUT

0.5

GAMMA CORRECTION BLOCK OUTPUT

TO A RAMP INPUT

100

150

200

250

LOCATION

Figure 35. Signal Input (Ramp) and Signal Output for

Gamma 0.5

FILTER GAIN

FG (FG7–FG0)

(Address (SR4–SR0) = 10H)

Figure 34 shows the various operations under the control of the

Filter Gain register.

FG7

FG6

FG5

FG4

FG3

FG2

FG1

FG0

FG7–FG4

FILTER GAIN B

0000

0001

0010

0011

0100

0101

0110

0111

1000

–8

1001

–7

1010

–6

1011

–5

1100

–4

1101

–3

1110

–2

1111

–1

FG3–FG0

FILTER GAIN A

0000

0001

0010

0011

0100

0101

0110

0111

1000

–8

1001

–7

1010

–6

1011

–5

1100

–4

1101

–3

1110

–2

1111

–1

Figure 34. Filter Gain Register

FG BIT DESCRIPTION

Filter Gain A (FG3–FG0)

These bits are used to program the gain A value, which varies

from response –8 to response +7 and are applied to Filter A.

Filter Gain B (FG4–FG7)

These bits are used to program the gain B value, which varies

from response –8 to response +7 and are applied to Filter B.

Refer to Sharpness Filter Control and Adaptive Filter Control

section for more detail.

GAMMA CORRECTION REGISTERS 0–13

(GAMMA CORRECTION 0–13)

(Address (SR5–SR0) = 14H–21H)

The Gamma Correction Registers are fourteen 8-bit-wide register.

They are used to program the gamma correction Curves A and B.

Generally, 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

nonlinear processing is used.

Gamma correction uses the function:

SignalOUT = (SignalIN )

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.

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