VS6663CD datasheet(56/64 Pages) STMICROELECTRONICS

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On-chip image optimization

VS6663CD

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Doc ID027033 Rev 2

On-chip image optimization

9.1

Mapped couplet correction (Bruce filter)

The mapped couplet defect correction filter is designed to intelligently correct the first defect

in a couplet thereby changing a couplet into a single pixel defect. Single pixel correction is

achieved either by the median filter or by the host (coprocessor, MMP or baseband). The

mapped couplet correction filter operates in both full resolution, and in binned mode.

The mapped couplet correction filter requires exact coordinate information for each of the

couplets to be repaired. The couplet coordinates are stored in non-volatile-memory (NVM)

during production test.

The mapped couplet correction is controlled by register 0x0B05:

0 - Disable

1 - Enable

9.2

Median filter

This is a simple 1-D median filter defect correction which replaces every pixel value by the

median of itself, its predecessor and its successor (respecting the color pattern). The

median filter operates in both full resolution, and in binned mode. It is suggested that this

filter is only used for viewfinder images or other non stored images. (Note that the median

filter will not correct any defective pixels which occur in either the first two or the last two

columns).

The selection of the median filter is controlled using register (0x0B06)

0 - Disable

1 - Enable

9.3

Lens shading correction

The VS6663CD has an adaptive (four color temperature) lens shading correction function

which can be used to reduce the effect of roll off in the optical system. Correction is carried

out individually for all four color planes, each gain is calculated based on the distance from

the image centre to the pixel in question using a two factor polynomial (R2 and R4). The lens

shading filter operates in both full resolution, and in binned mode. The correction applied is

75%.

In order to optimize the AV algorithm, the coefficients for each device are calculated under

D65 (Fluorescent Philips Graphica Pro 965) lighting conditions and programmed in the NVM

memory at production test. (The coefficients from the NVM can be overwritten).

Settings for three other color temperatures (Cool White, U30, and Horizon) are calculated

from characterization data and these are stored in the NVM memory.

The calculation of the color temperature is performed by the sensor using the white balance

gains. The white balance gains can either be calculated internally by the sensor or they can

be calculated by the host and written back to the sensor.

Figure 21 provides an example of lens shading correction.

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