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Re: March 20 - Day THREE: Improving Image Understanding by Improving Image Quality
jbswindle   3/20/2013 2:35:36 PM
What about correction for optical, mechanical, and pixel vignetting effects?  In analog days this kind of shading error was corrected with scaled parabola signals added to the baseband video at horizontal and vertical rates.  Gradient shading errors were corrected with scaled saw tooth signals added to the baseband video at horizontal and vertical rates.  Feature extraction such as that required for OCR might benefit from shading correction.  OCR binarization algorythms attempt to deal with adjacent pixel levels changed due desired feature brightness dealing with both noise and background brightness changes (perhaps due to background artwork).  I haven't seen anything about shading correction outside of telecine/live studio video camera enviornments.

What, if anything, is done either in the camera itself or in digital post processing to correct shading errors or, indeed, is shading correction even desirable in computer vision processing?

Thank you for a very informative presentation.

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