I was trying to scan some of my sketches in order to post them on some community sites, but the effects are quite bad. An example could be seen here:
Basically, the contrast is terribly off. All soft shading done with a hard pencil is gone, the white is too bright and too "aggressive" and bleeding all over. All the shading had been "flattened down" in the process of scanning.
So, my question is, are there some techniques or procedures I should follow, some typical settings for the scanner I should use in order to get good quality scans without the brightness/contrast distorion?
(upgraded comment to answer)
Scott, brendan and tim human all provide good advice regarding scanners.
I actually do a lot of work with paintings and drawings, and photographing them is almost always a better option than scanning. I have a low-end professional flatbed scanner on my desk, but I almost never use it anymore because I get better results in less time using a DSLR (even for the rare times I need to scan office documents). Then again, I have a dedicated station, with alignment marks on the floor and table, so the photo equipment is pretty much set up and ready to go.
I use 2 photo lights, polarizing filters to reduce glare, and a Digital SLR using RAW format. I use a low ISO setting to minimize noise, which usually requires longer exposures and therefore a tripod. Additionally, I set the aperture small to increase the depth of field as a way to compensate for the auto-focus and ensure that larger items are in focus across the entire surface (it is not always easy to get an old painting perfectly parallel). Usually this means 15-25 second exposures.
The polarizers are really only needed for items with glass or high reflectance--drawings are probably not going to exhibit glare. They do alter the color and/or saturation and they can mess with auto focus settings in some cameras.
If you only have a consumer pocket camera, consider a tripod at least. The key is decent consistent lighting across the composition, and as "straight-on" a shot as you can get. You want the plane of the camera's CCD to be parallel to the plane of the drawing to avoid having to distort or fix the perspective. Not so bad for a one-off, but if you need to fix 30 at a time, you are better off taking the time working on your set up first.
For consumer cameras, and non-RAW format, if you don't like the results, check to see if there is a "custom white balance" setting in the camera menus: you take a shot of a white piece of paper in the light setting you are using, and then set the custom white balance to that photo. This will help reduce the color cast of any lights you are using (regular lights usually cast yellow-red, fluorescents usually cast blue)
If you look at the levels of your scan, you can see that it is scanned too bright. Ideally the range of color information goes from almost black to almost white.
Try to change brightness settings on your scanner and avoid "helpers" like sharpening oder presets for text scans