‘Drop Out Red’ is a feature found on many desktop scanners and may be called differently (such as ‘Filter Out Red’ or ‘Ignore Red’…). It is usually an ‘advanced’ setting.
It filters our all red color from the scanned image.
Here is a sample screen shot of this setting on an Epson DS-510 scanner:
Here is a sample scan. First a full color scan at 200 dpi so you can see what we put into the scanner:
The same page scanned at black/white, 200 dpi. The scanner automatically converts the red into black. This DOES NOT WORK with BubbleScan.
And here is the same page scanned at b/w, 200 dpi with DROP OUT RED enabled. Notice that all red printing has been dropped out. The BubbleScan OMR software can easily differentiate between a mark made by the user and pre-printed text.