Scanning in Pieces

[Think Tank Bob]

Okay. I seem to have trouble scanning things and making them look right...My scanner is a 9x12 Canon LIDE 30, and when I scan work I need to do it in two passes. That's fine, but when I piece 'em together, it just looks bad, cause one part'll look different than the other, contrast wise and such. No matter what I do, I can never get it to look right; after they're pieced toghether, there's a big ol' shadow across the image, and the bottom half (second scan) looks darker. Any one have any ideas on what I need to do?
-b-

[Chris Piers]

Change the image to greyscale if it's black and white. Then adjust the levels (ctrl+L) and slide the white bar in until the whites are even, then slide the black bar in to darken up the linework.

[Baloodoo Bill]

Scanning in Grayscale, scan one half, slide the work across the scanner and scan the second half. You may need to attach a registration bar of your own making. Make sure the two halves overlap. NEVER turn the work to scan the other half. Your chances of turning it exactly 180 degrees are close to nil.

Increase the canvas size of part one so it's large enough for the assembled image. Copy and paste part two. Go to Layers Palette and change mode from Normal to Difference. The overlap area will go negative. Black is where the images match, white is where the images don't match. Adjust the Floating Selection until the negative area is solid black (or as close to it as possible). Revert to Normal in the Layers Palette and Deselect. If at all possible, place the seam in a gutter.

Once assembled, use Levels to gradually bring the image towards bitmap, with an eye towards minimizing damage. Follow with Threshold, which will catch any stray pixels you missed, leaving you with a pure Black and White image. Now you're safe to switch to Bitmap.

[Think Tank Bob]

Thanks for the info guys. One question though, What's a Registration bar?
-b-

[Baloodoo Bill]

That would be a "bar," fixed to the scanner, to which you abut the page. It keeps the work "square," assuring each half of your page scans at precisely the same angle.

It needn't be an actual bar, it could be: a thin plastic ruler, a strip of card stock, stacked pieces of masking tape ... just something that will stop the page from moving past an assigned position.

Tape some art to the scanner, scan and check to see if it's square. If not, untape one end, readjust the art and scan again. Rinse, lather, repeat until the scan is square. Now affix your "bar" or other registration device. I use 3 strips of masking tape (each strip being 3 strips stacked on top of each other for triple thickness) that are placed against the side of the art at the 1/4, 1/2, 3/4 positions. Remove, and then replace art using your bar or tabs for placement and check the scan to see if it's square. You may also wish to place a tab or bar at top and bottom to prevent you from cutting off the tops or bottoms of your scan.