What is it?
"Large Areas Spatial Crosstalk" is the terminology used by the IEC standard for scanners, 61966-8. It refers to the effect of nearby colors shifting the scanned colors towards the neighboring colors.
What problems does it cause?
The effect can produce large differences in the colors of scanned photos which makes it sometimes impossible to scan a photo and get a colorimetrically accurate image file. These aren't often noticed in complex photos but some are quite susceptible. A scanned picture of a hot air balloon against a bright sky will tend to lighten the brighter sky more than the balloon.
Accurate reproduction is highly desired for, inter alia, precision duplication and retaining historical images.
Here's a scanned image from a moderately high end, V850 Epson Scanner. It's large, shifted L* values are labeled underneath each circle. The three, circular, patches on the left were printed the same as the three on the right. The lighter ones were RGB(240,240,240) while the darker ones were RGB(118,118,118). The circles surrounded by white have scanned L*s about 6 higher than the same ones on the right. This shift is from "Large Area Spatial Crosstalk."
This problem is caused by light reflecting off nearby parts of a document, getting scattered around and bouncing off the translucent, illuminating white rails on either side of a horizontal aperture through which the CCD scan is captured. It's as if the Lux levels on the right side white surround area were boosted over 20%, the increase in light needed to increase L* from 85.7 to 92.7.
Question: Are their any reflection desktop scanners that have addressed this issue in their design and/or is there any software that corrects or is looking to correct this defect?