How to's....
In order to produce a good, quality scan we need to understand tones and resolutions. First a good photograph always has a full range of tones, from black to white. Many older photographs will not need to be scanned at high resolutions because they lack that detail, but you can determine this by scanning a small section at different resolutions and compare the scans. Considerations need to involve how to scan particular types of photographs:
· How to scan a faded Black and White print: For allowing less gaps in the histogram you need to do all the scanning in 16-bit mode, which will capture enough gray levels to produce a full histogram. You also need to adjust levels to optimize your scans by adjusting RGB levels to the majority of value ranges in each level of the scanner channels.
· How to scan a dark black and white print: These prints have significant fading and staining that limit the range of tones. Keep the scan values of 10 and 20 and the lightest pixels around 240.
· How to improve color with a good scan: adjust the levels or Curves in the scanner software and also adjust the midtone sliders in each channel’s levels until the average color looks good.
· How to scan halftones: Halftones are made up of a pattern of black or colored dots on white paper. Use a high resolution scan, which shows the size and shapes of the dots clearly. Never scan less than 600 ppi.
· How to scan black and white film and glass plates: Silver emulsion or glass causes light to scatter our of the optical path and back into it, which makes scanning these difficult. You need to scan black and white film and glass plates with 16-bit mode using whatever scanner setting will let you capture the maximum density.
· How to scan color negatives: Scan at 16-bit mode because a negative’s contrast is naturally low this gets boosted when its printed, especially when the negative is faded. If the scans are clipping either the highlight or shadow detail scan the negative as a slide.
· How to enhance almost-black photos: Use a 16-bit scan and set the levels controls in the scanner software to maximum in the range of values in the file. If you are using Photoshop you can use the multiply blend mode, which duplicates the layers to increase contrast and density.
· How to fix shadows on faces: There should be a shadow/highlight adjustment to lighten shadows and reduce harshness.
· How to scan a tarnished photos: Correct the color and adjust the RGB channel to darken the tarnish until it is no different in brightness from the unaffected parts of the photograph.
Other photo improvements, such as color negatives, skin tones, saturation and tinting can be adjusted using computer software tools like multiple layers, air brush, and picture window that they provide in Photoshop. Other tips on how to scan particular photographs or understanding software tools check out Ctein’s book Digital Restoration from Start to Finish
Commonly used color systems
There are three common color systems or models that represent color in digitization.
1. RGB: Most scanners and display devices use RGB. RGB combines red, green and blue to form other colors. This provides the greatest flexibility for capture of color information in a digital image.
2. CMYK: Printing systems commonly use CMYK. This is a subtractive color system using cyan, magenta, yellow and clack.
3. CIE L*A*B: The Commission Internationale L’Eclairage develops device independent color space that contain a wide color gamut that RGB or CMYK.
Peterson, K. A. (2005). Introduction to basic measures of a digital image for pictorial
collections. Prints and Photographs Division, Library of Congress, Washington, D. C. Retrieved from http://www.loc.gov/rr/print/tp/IntroDgtlImage.pdf
