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Scanning

A quality scan is essential for proper reproduction, yet many artists use cheap, "do it yourself" scans, with disappointing results.

Always work as close to the source as possible. Scanning a photographic print loses at least 1/3rd of the detail you can get by scanning the original negative or slide.

Using a dedicated "film scanner," I can harvest details from slides and negatives that a cheap "flatbed" scanner cannot see. This is the preferred method of scanning 35mm slides for reproduction up to 16"x20" or so.

For the most exacting work, my "drum scanner" can see details that the finest film or flatbed scanner is blind to.

Reproduction-quality scans may require the utmost from a scanner. On the other hand, website or brochure scans can often get by with a cheaper scanner.

The best time to scan is immediately after processing film, before it has a chance to collect dust and fingerprints. I strongly encourage photography clients to order economical film scans with the photography.

Definitions

Scans can be characterized by light source, resolution (or dimensions) and dynamic range.

* Most cheap flatbed scanners employ a reflective light source, for scanning opaque artwork, and even those with transparency adaptors do only a mediocre job with their transmissive light source.

Film scanners use only a transmissive light source, for slides or negatives.

Drum scanners can use either reflective or transmissive lighting, for slides, negatives, or opaque artwork.

* Resolution is the number of samples per unit of distance that the scanner performs when converting a two-dimensional artifact into a digital image. For example, a scanner with a resolution of 10 samples per inch (often mis-called "dots per inch") would "look" at your artwork every tenth of an inch to produce a digital image.

A cheap flatbed scanner may harvest only 600 to 1200 samples per inch, whereas a film scanner will sample 2400 samples per inch or more. A drum scanner will typically sample 4000 samples per inch or more.

More resolution is not always better. With sensitive, high-speed film, more resolution only results in more "film grain" being sampled. Many films of ASA 100 or less can support 4000 samples per inch or more, whereas many films of ASA 800 or greater cannot support even 1200 samples per inch without showing excessive film grain.

The dimensions of a digital image are often confused with its resolution, but it is actually a count of pixels (width by height) that is independent of any unit of measure. A highest-quality, 35mm film scan will have dimensions of about 5400x3600 pixels.

* Dynamic range is a measure of the difference in brightness levels that can be detected by a scanner. A scanner with a large dynamic range will have more detail in shadows and highlights than will a scanner with small dynamic range.

Dynamic range is typically measured on a logarithmic scale, but there is little industry agreement on how to measure it accurately, so specifications, especially on cheap scanners, are often wildly optimistic. Cheap scanners often express dynamic range in "bits" of output data, but this is generally an extremely optimistic representation of the overall system dynamic range -- a $149 scanner with 16 bits of output data is NOT better than a $30,000 drum scanner with 8 bits of output data!

A flatbed scanner of even moderate expense will have a dynamic range no better than 3.0 or so; the best film scanners go to 3.8 or so; most drum scanners will have a dynamic range of 4.0 or better.

Dynamic range is generally measured on a global level, comparing the lightest and darkest points in an entire image. However, local dynamic range is also crucial to scan quality.

Due to the limitations of the charge-coupled-device (CCD) technology used in flatbed and film scanners, adjacent pixel dynamic range cannot exceed about 1.0 in such scanners, whereas a good drum scan will have adjacent pixel dynamic range approaching its full dynamic range of 4.0. This means drum scanners can preserve sharp, high-contrast edges that will look soft and fuzzy on a CCD scanner.

Dynamic range is often more important than resolution, especially when comparing cheap flatbed scanners to film scanners. Some cheap flatbed scanners claim as much as 2400 samples per inch of resolution -- nearly that of film scanners costing ten times as much -- but the resulting scans will have blocked-up shadows and blown-out highlights.

Capabilities

  • Flatbed: Epson Expression 636: 600 samples per inch over an 8.5"x11" area with a dynamic range of 3.0.
  • 35mm Film: Nikon 4000 ED: 4,000 samples per inch with a dynamic range of 3.8.
  • Drum: Optronics ColorGetter Falcon: 5,400 samples per inch over a 10"x12" area (flexible media only) with a dynamic range of 4.0.
  • Output and delivery:
    • CD-ROM: (Mac or Windows) up to 680 megabytes, 5 highest-quality 35mm film scans or one medium format drum scan.
    • DVD-ROM: (Mac or Windows) up to 4 gigabytes, two highest-quality 4"x5" drum scans, or 33 highest-quality 35mm film scans.

See prices for more details.

last modified on Monday, 12-Nov-2007 14:30:05 PST

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