CS7622 datasheet(13/36 Pages) CIRRUS

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CS7622

DS322PP1

backlighting conditions. Details in dark areas stay

visible, even in very complex lighting conditions.

These three modes can be selected through 2 regis-

ter bits in operational control.

In the 12-bit clipped mode, any input above 4095

gets clipped to 4095. In the 10-bit companded

mode, the input gets companded through a four

segment, three knees, fully programmable curve.

To program the curve, the placement of the three

knees in the companding curve must be deter-

mined. The next step is to determine the slope of

the four segments created by the three knees (slope

for each segment is defined as delta y / delta x). Fi-

nally, offsets must be calculated to keep the com-

panding curve continuous.

A fourth knee exists in the curve, which represents

the black level value. There are two options for the

10-bit black value. In case one, a linear mapping is

employed such that “blacker-than-black” pixel in-

formation is kept, with black (code 64 in the 13 bit

data) being defined as code 8 in the 10 bit domain.

The second option clips all pixel values less than

black (code 64 in the 13 bit data) to a programma-

ble offset value, offset1. This may be set to 0 if de-

sired. This option will lose the “blacker-than-

black” pixel information, but allow for slightly

more dynamic range. Note: If using the linear mode

(option 1), offset1 must be set to 8.

Registers x1 through x3 should be programmed

with the x coordinates of each one of the three

knees.

Registers slope1 through slope4 should be pro-

grammed with 256 multiplied by the calculated

slopes.

Finally, the offsets can be programmed following

the formulas below:

y1 = slope1/256 × (x1-64) + offset1

y2 = slope2/256 × (x2-x1) + y1

y3 = slope3/256 × (x3-x2) + y2

offset2 = y1 - (x1 × slope2 / 256)

offset3 = y2 - (x2 × slope3 / 256)

offset4 = y3 - (x3 × slope4 / 256)

(use integer division and discard the remainder)

When using the 10 bit companded output, be aware

of the non-linearity of the output data. If linear out-

put is needed to perform Auto White Balance

(AWB) or Automatic Gain Control (AGC), a linear

curve can be implemented to gather statistics. This

can be achieved by writing 8191 to x1 (set register

Bits_out register bits

Output mode

10 bits companded

13 bits

12 bits (clipped)

Table 1.

1023

CODE_IN

CODE_OUT

8191

SLOPE1

SLOPE2

SLOPE3

SLOPE4

OFFSET2

OFFSET3

OFFSET4

OFFSET1

(x2,y2)

(x1,y1)

(x3,y3)

Figure 13. 13-to-10 bit compander

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