Polaroid SprintScan SS35, Repair Manual

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Slide Scanner Repair Manual Diagnostics and Troubleshooting
150
Part two of this test checks for the min or max variation from the dark set point. Any single
pixel which deviates a large amount from the calibrated dark is expected to produce a
streak. The Min or Max Fixed Dark - Dark Set Point is checked against the Min Or Max
Fixed Dark - Dark Set Point target in the constants file.
Dark Uniformity Response (Noise)
In addition to the column average of each pixel of each color, the test calculates a standard
deviation over the 64 line sample for each pixel. In the stand-alone version, this single
pixel standard deviation or column standard deviation response is plotted vs. pixel
number as shown in Figure 5-16. Similar to the test of the column means against the dark
set point, the standard deviations are recorded in terms of the A/D converter’s LSB’s so
that the SS35 Plus numbers are four times as sensitive as those from the SS35ES.
Figure 5-16. Single pixel standard deviation vs. pixel number
The SS35 Plus DMT units indicate that we can expect single pixel standard deviations from
the average pixel around 2 to 3 LSB’s. Higher responses occur when:
• Light levels or CCD signal levels are low and must be gained up
• When there is problem with grounding or shielding
• When the sensor and/or its electronics are defective
The test checks that the Mean Single Pixel Std Dev, and the worst response in the
sampled pixels, or the Max Single Pixel Std Dev are less than the constraints in the
constants file.