
I have had the problem of making illustrations that was bigger then my scanner. My scanner is the normal size A4, and it is a Canon CanoScan 1240 U. It is a normal scanner for photos and illustrations. My problem with it was that my drawings can often be bigger, say A3 or like for MistgriM as long as two sideways A4 in one drawing. If your scanning a picture using the scanner as it is, you will get the fade out with both color, shadow and focus on the drawing. And it is a big job to fix all the areas and reconstruct the image.
So I found that in order to get the scanner to work better, the edges of this scanner (and I guess a lot of others) is a plastic edge, so that you can put a A4-paper into the scanner easy. If this is removed from the scanner (a warning, doing things with your scanner can harm it, and you will probably not get your money back for things you have done with your scanner.) I also had to cut of some plastic parts to get everything flat, but the glass on this printer goes all the way out to the edge of the scanner. To avoid getting dust and other things into where the scanner parts is, I used some Scotch Magic tape along the edge. I don`t know if this is something you can do with every scanner so be careful, but it works for this scanner from Canon.
After removing the plastic that goes along the edges I have to be more carful when scanning The edges is there to avoid getting light into the scanner, so now it have to cover up the scanner glass plate on the long side edges of the scanner.
Also a nice thing to do is to use a big book to put upon you water color illustrations when scanning, or you will get areas that can be out of focus or is lighter than others. I use a book about trees from around the world (I can recommend the book both to hold paper flat on the scanner and to read and get information. It is a very good book about trees!) SO there you have it, you can go ahead and make that grand scanner.