MITSUBISHI ELECTRIC DV1248ST - Manual (Page 49)

Threshold button
Threshold function is very useful when you scan line art images or
scan documents for OCR (optical character recognition) use. You may
use this function to adjust the quality of line art images or eliminate
unwanted dots in the document to improve the accuracy of
recognition.
Note: this function is only applicable when you select Line Art as the
Image Type.
Select the Threshold button, and the Threshold dialog box will appear:
The x-axis in the histogram represents the
brightness level of the pixels in the image (from
0 to 255, from left to right). The y-axis
represents the quantity of pixels.
To adjust the threshold value, drag the triangle
below the histogram or enter the threshold
value in the Threshold entry box directly. For
example:
Image 1 Image 2