Dynamic Web TWAIN: What are the differences between BlankImageThreshold and BlankImageMaxStdDev

BlankImageThreshold and BlankImageMaxStdDev are two useful properties when you detect whether a page is blank or not.


Blank Image Threshold Property is the dividing line between black & white.
In this context, a pixel is considered a shade of grey with a value between 0 & 255.
A pixel that is 0 is black.  A pixel that is 255 is white.  The Image Threshold Property lets algorithms know at what place to consider a pixel black.  The default value is 1/2 way between black & white - 128.
This property might be important on colored sheets of paper where the background is not completely white.  Then the user would want to set it to a high value.  When the paper is known to be white, you may set it to a low value - like 64 or so.


This property is to divide black & white by comparing the pixels of the image with white and then to set it to how close the result is, if it is within the set range we will take it as a blank image.

The allowed values are from 0 to 100. 0 means it is a totally white image. The default value is 1. It means when the standard deviation of the pixels is within 1% compared to blank, the control will take the image as blank.

For example, a blank image with only a few words in black, the standard deviation of the pixels compared to white may be set around 10. An image full of words and colors with some blank board, the value may be around 80~90.

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