# Common Image and Pattern Variations

The following table summarizes common image variations, the possible effect of these variations on PatMax, and recommended approaches for handling these variations.

Variation | Possible Effect | Possible Remedy
--- | --- | ---
Severe video noise | Reduced accuracy Failure to locate pattern | Increase granularity limits, especially the fine granularity limit. Reduce accept threshold. Use high sensitivity mode.
Feature polarity reversal | False matches Slightly slower speed | Ignore polarity
Extremely low image contrast | Reduced accuracy Failure to locate pattern | Increase granularity limits, especially fine granularity limit. Reduce accept threshold. Use high sensitivity mode.
Extremely high image contrast (camera saturation) | Reduced accuracy Failure to locate pattern | Reduce accept threshold. Adjust camera aperture or lighting to produce less saturated images.
Changes in shading | None |
Rotation or size changes | Reduced speed False matches | Enable appropriate degrees of freedom and specify appropriate nominal values or ranges.
Aspect ratio changes | Reduced speed False matches Reduced accuracy | Enable appropriate degrees of freedom and specify appropriate nominal values or ranges.
Shape changes (change in geometrical arrangement of pattern features) | False matches Reduced accuracy | Increase elasticity value. Reduce accept threshold.
Missing features | Failure to locate pattern | Reduce accept threshold
Extra features | Failure to locate pattern False matches | Reduce accept threshold. Score using coverage score only.