Ok, so I feel like I've had to explain this alot recently. The process of taking inked bluelines and scanning it in so the lines don't show up seems to elude lots of folks. Recently having seen alot of people decide to use blue pencils and then only to have them show up in a messy grayscale scan.
So here's a simple tutorial laying out steps along the way of how to scan in B&W/LINEART mode and convert it to GRAYSCALE later. Also some explanation of threshold/tolerance settings... and the like.
Hope this helps some of you out there.
p.s. - as a side note... I like to use Staedtler brand Non-Photo blue pencils. Order them by the box at my local office supply store for cheap. Art stores around here seem to only carry Prismacolor brand Non-photo pencils... maybe because they're more "arty" brand or something... but I HATE Prismacolor pencils (pens are nice / pencils SUCK). They are all greasy and my brushed ink doesn't adhere to them well. Staedtler pencils seem to have a good mix of being easy to draw with and not all hard... but still inkable in a clean fashion.
Check it ---> [link]