VX6953CB datasheet(78/107 Pages) STMICROELECTRONICS

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Image optimization

VX6953CB

78/107

8209023 Rev 5

9.1

Defect categorization

9.1.1

Pixel defects

Illuminated defects are tested with a flat field illumination and a pass-fail criteria that is a

percentage deviation from a local mean. In order to effectively test the sensor in a

reasonable test time, it is necessary to put the limits of gain error above the normal noise

distribution of photon shot noise and sensor noise otherwise false single pixel fails are

detected. A typical defect criteria for single-pixel gain errors is ± 9%. In fact, any element in

the array outside ±9% is a “minor” fail, and outside of ± 25% is a “major” fail.

Note:

The defect detection method is applied to raw Bayer images.

9.1.2

Sensor array area definition

For specific aspects of pixel defect testing the image sensor array is subdivided into two

regions as illustrated in Figure 33.

Figure 33. VX6953CB pixel defect test area

The inner array in Figure 33 is centre justified, in the x and y axis, with respect to the outer

array. The inner array is 50% of the full width and 50% of the full height of the larger outer

array, therefore the inner array is one quarter of the area of the outer array.

Note:

The border pixels (outer eight rows and columns) affect the image quality of the

reconstructed picture to a lesser degree than the actual image pixels (2592 x 1944), due to

their lower contribution within the reconstruction algorithm, but for simplicity we test them as

the image pixels, hence the test image size for defects will be 2608 x 1960.

Outer Area

Inner Area

1304 pixels

2608 pixels

1960

pixels

980

pixels

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