Sheet feed scanners are ideal for large format documents because only width and thickness are limited.

The main difference to flat bed scanners is that the image sensor does not move but the document itself is pulled past the mounted image sensor. The  precision of the paper transport (beside the maximum resolution of 400 - 600 dpi) is the reason for an amazing scan result. That is why mostly all rollers are used for the paper feed rate.

The reading unit is normally a linear CCD. Current CCDs have four lines (RGB + gray) with each 7.500 pixels like the Toshiba TCD2704D as used in VIDAR large format scanners. Scanners with only three line CCD's with each 5.300 pixels could not convince in quality.

Usually there are three CCDs plus cameras in 36"/40" scanners. 25"  scanners have two CCDs and cameras - 54" though need four! Some providers do experiments in the low-cost/low-quality area and use only two or even one CCD for scanners up to 36" - these have a very poor quality, though.