Digitization | Lantern Slides Project

After looking through several of the boxes of slides, some of the particularly interesting ones (generally, color-tinted slides and images of well-known landmarks) were selected to digitize. The slides were gently cleaned using lint-free cloths and a streak-free lens/screen cleaner, with care being taken to avoid coming into contact with the tape holding the slides together. Any slides with cracked glass were gently cleaned with only a dry cloth.

The slides were scanned on an Epson 1640XL flat-bed scanner with a film-scanner back in transmissive mode (the light source shines through the slide) attached at 4800 dpi, using the Espon Scan Utility version 2.77A on Mac OS X (10.3.9). This actually surpasses the optical resolution of the scanner but makes sure that the greatest amount of data can be extracted from each slide. Since the slides were placed directly on the glass and no film holder was used (due to the shape and thickness of the glass slides), the "focal position" of the scanner's imaging sensor had to be adjusted to compensate for the fact that an extra layer of glass lay between the scanning bed and the film emulsion. After experimentation, I determined that a "focal position" of about 1.0 was optimal (the default is 2.5). The images were saved as 8 bit/channel color TIFF files, averaging around 500 MB a piece.

The images (as TIFF files) then were imported into Adobe Photoshop CS2, where they were cropped/rotated/mirrored to the correct orientation. The contrast and color (for tinted slides) were adjusted to match as closely as possible the original slide, since the scanner has an auto-iris feature which, depending on the selection of the area to be scanned, may under- or over-compensate for the black borders of the slides. Black and white images had the color information removed (partly to make the files more managable in size, also to maintain the image as it should be seen--in black and white). The adjustment in the contrast/black levels was done using the "Levels" adjustment, setting the darkest bit of the slide image (not the border) as the baseline black). In addition, since the scanner used a cold-cathode light source (not an LED source) the correct color of the slides could not be ensured by default (as cold-cathode light sources' color temperature shifts over time). The screen (an 15 inch MacBook Pro) was color-calibrated prior to adjusting the images, with a white point of D65 and a gamma of 2.2 (the common PC and graphics standard, not the Macintosh standard gamma of 1.8) using an Eye-One colorimeter.

The images were saved four times: once as a TIFF for archival (in case something needed to done with the full-res, uncompressed files later), once as a full-resolution JPEG, once as a 600 pixel wide JPEG, and again as a 200 pixel wide JPEG (all of the JPEGs were saved as "Maximum Qualiity").

The large-sized, color- and contrast-corrected JPEGs were then "Zoomified," to allow web users to quickly zoom in on portions of the images of interest without having to download the entire file. The full-resolution JPEGs were also uploaded and linked via their thumbnail images, in case they were needed as downloadable files (e.g., for use in a Powerpoint presentation).