AR0331 datasheet(21/52 Pages) ONSEMI

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AR0331

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Table 9.

COMPANDING TABLE

Segment 1

Segment 2

Segment 3

Segment 4

Input Code Range

0 to 1023

1024 to 4095

4096 to 32767

32768 to 65535

Output Code

Range

0 to 1023

1024 to 2559

2560 to 3455

3456 to 3967

Companding

Formula

Pout = Pin

Pout = (Pin − 1024)/2 + 1024

Pout = (Pin − 4096)/32 + 2560

Pout = (Pin − 32768)/64 + 3456

Decompanding

Formula

Pout = Pin

Pout = (Pin − 1024)*2 + 1024

Pout = (Pin − 2560)*32 + 4096

Pout = (Pin − 3456)*64 + 32768

Table 9 illustrates the input and output codes as well as

companding and decompanding formulas for each of the

four colored segments in Figure 19.

Table 10.

KNEE POINTS FOR COMPRESSION FROM 16 BITS TO 12 BITS

T1/T2

Exposure Ratio

(R1)

R0x3082[3:2]

POUT1

= P1

POUT2=

(P2 − P1)/2 + 1024

POUT3=

(P3 − P2)/32 + 2560

PMAX

POUTMAX =

(PMAX − P3)/64 + 3456

4x, 8x, 16x, 32x

210

1024

212

2560

215

3456

216

3968

As described in Table 10, the AR0331 companding block

operates on 16-bit input only. For the exposure ratios that do

not result in 16-bits, bit shifting occurs before the data enters

the companding block. As a result of the bit shift, data needs

to be unshifted after linearization in order to obtain the

proper image. Table 11 provides the bit operation that

should occur to the data after linearization.

Table 11.

BIT OPERATION AFTER LINEARIZATION

ratio_t1_t2 (R0x3082[3:2])/ratio_t1_t2_cb (R0x3084[3:2])

Bit Shift Operation after Linearization

Right Shift 2 Bits

Right Shift 1 Bit

16x

No Shift

32x

Left Shift 1 Bit

HDR-Specific Exposure Settings

In HDR mode, pixel values are stored in line buffers while

waiting for both exposures to be available for final pixel data

combination. There are 70 line buffers used to store

intermediate T1 data. Due to this limitation, the maximum

coarse integration time possible for a given exposure ratio is

equal to 70*T1/T2 lines.

For example, if R0x3082[3:2] = 2, the sensor is set to have

T1/T2 ratio = 16x. Therefore the maximum number of

integration lines is 70*16 = 1120 lines. If coarse integration

time is greater than this, the T2 integration time will stay at

70. The sensor will calculate the ratio internally, enabling the

linearization to be performed. If companding is being used,

then relinearization would still follow the programmed

ratio. For example if the T1/T2 ratio was programmed to 16x

but coarse integration was increased beyond 1120 then one

would still use the 16x relinearization formulas.

An additional limitation is the maximum number of

exposure lines in relation to the frame_length_lines register.

In linear mode, maximum coarse_integration_time =

frame_length_lines − 1. However in HDR mode, since the

coarse integration time register controls T1, the max coarse

integration time is frame_length_lines − 71.

Putting the two criteria listed above together, the formula

is as follows:

maximum coarse_integration_time + minimum(70

, frame_length_lines–71)

(eq. 2)

There is a limitation of the minimum number of exposure

lines, which is one row time for linear mode. In HDR mode,

the minimum number of rows required is half of the ratio

T1/T2.

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