Scanning large prints

From Silvergrain Labs

Scanning Negatives v. Prints

Scanning negative is a better approach if you like to pull out the maximum information registered on the negative and edit the scanned data on a computer. However, if you do all manipulation in darkroom and consider print to be the final form of work, scanning print is more natural way to go. For example, effects of burning, dodging, paper flashing, toning, split toning, bleaching, etc. can only be shown if print is scanned.

Print Scanning Issues

For best scan results, it is best to use RC in glossy surface. However, for display purpose, RC semimatte or fiber based glossy may be preferred, and it is possible to make acceptable scan images from these materials, especially if the print is sufficiently large.

One problem of scanning print, especially RC paper and some fiber paper with very bright white base, is that the color is shifted to blue, particularly in highlight area. Although it is not easy to match the color exactly to the original, it is relatively simple to correct for this in Photoshop or Gimp.

Another problem is that, many prefer to print in 11x14 or larger for display purpose, but most scanner can handle up to legal (or A4) original size. This can be solved by scanning piecewise, save each piece in an 8bit/ch TIFF, and use File -> Automation -> Photomerge function of Photoshop CS or CS2. This will automatically align and adjust the image pieces and stich them. Photomerge can currently handle only 8bit/ch, even if the original is 16bit/ch.

As with any flatbed scanning, it is best to scan at 2x the resolution you need, and scale down after stiching. For best results, I suggest the following steps:

1. Scan print piecewise using VueScan, using at least 2x the resolution necessary. Save each piece in a TIFF file.
2. Use Photoshop's Photomerge function to merge the TIFF pieces.
3. Change the image mode to 16bit/channel.
4. Change the image size/resolution to desired values.
5. Do all necessary editing, such as color correction, dust removal, sharpening, etc.
6. Save a master copy of the edited image in 16bit/ch TIFF, PNG or PSD.
7. Convert the image mode to 8bit/channel.
8. Print, or save print-quality file.

If you are scanning 11x14, you can cover the entire image with sufficient overlap by 2 pieces. When scanning each piece, slide the print left-right to get two scans. Do not rotate, as this doesn't work well with Photomerge. When scanning larger pieces, you'll need 4 pieces and so rotating is inevitable. Use Vuescan's rorating function to make them all in the same direction (top-bottom) so that Photomerge works nicely.

Cleaning the scanner

Scanning prints will bring a lot of dusts and stains to the scanner's glass table. Clean it frequently with optical cleaning solution, lint-free wipes, and air blower.