How to Choose a High Res Scanner for Slides, Film Negatives and Glass Plates
You start by making a choice: 1) do the work in-house; purchase equipment for scanning slides, roll film, negatives and glass plates, 2) use the services of an outside Service Bureau. In business parlance, "make it" or "buy it."
The decision will rest with how large a collection has to be scanned, do you have reoccurring work, what is the cost of equipment, and what is the cost of knowledgeable labor to operate it?
Assuming an answer of buy it (outsourcing), you want to consider that source's prices, experience, equipment and technology, customer service, and understanding of your unique needs.
Assuming an answer of make it, you need to consider the following variables in choosing a scanning system:
Primary Economic Considerations
- Price
- Required expertise level of labor
- Throughput/Productivity
Image Quality Considerations
- 35mm Slides or 2.25
- Type of mounts and condition of mounts
- Clean?
- Handling (will originals have to be removed and replaced after scanning from carousels, sleeves or stackers
- Negatives
- Clean?
- Scanned to positive (RGB or Grayscale) or converted after post- processing
- Large Format Sheet Film 4" X 5" or 8" X 10"
- Clean?
- Lies flat or requires special prep and scanning techniques
- Glass Plates
- Scanned to positive (RGB or Grayscale) or converted after post-processing
- Any pin holes or scratches
The Following Has to be Taken Into Account for All Originals
Required Resolution
Resolution determines detail captured in the scan, and is quantified as dots per inch (dpi) for printers (output) and pixels per inch (ppi) for scanners. A scanner's basic resolution, "native," is the actual number of active sensors on the CCD array, or the actual number of active sensors for each color channel multiplied by the number of lines scanned on a line scanner.
Pragmatically, how much resolution is needed should be determined by what the scans will be used for. Archiving requires highest resolution and electronic dissemination, Web, the lowest. Or put another way, how large do you want a reproduction of a scan to be? As always, smaller derivatives can be made from hi-res scans, however, sampling up requires interpolation and is subject to a loss of image quality.
Color
The Bit Depth of a Scanner
Bit depth is a measure of the potential number of color tones available on an individual pixel. Obviously the greater the number of tones the greater nuance or tonal range of color of the overall image. The standard for professional work is currently 16 bits, which produces billions of colors.
The Dynamic Range
The dynamic range is a measure of the scanner's ability to record the range of tonal values in the original between shadow and highlight. Dynamic range is expressed as a number on a scale between 0 to 4. And, while it makes sense to say that the higher the number the better the image quality of a scanner will be, that is not the case, because dynamic range is determined by an interaction between the sensors (read that quality thereof), pixel size, the electronics utilized, signal to noise ration, and the A/D converter. Dynamic range can also be expressed in f stops. In general, acceptable dynamic range should be 2.8 > with 11+ stops an indication of superior performance.
Light Source
Light sources on flatbed scanners are not discussed here as they are uncontrollable and assumed adequate for those machines. Since AIA is concerned primarily with oversized and high resolution/high image quality scanning using photographic techniques, we will briefly discuss the need for so-called illuminators or light boxes.
These devices come in various sizes, and are used to "back light" transparent film for capture by scanning backs or single capture back digital cameras. Variables to keep in mind:
- Light source cannot produce heat which will damage originals
- Light should be evenly diffused
- The denser the originals to be scanned, the brighter the lights should be
- Masks should be light tight
Taking all these variables and issues into account, you may find that using the needs assessment button at the top of this page will help you in your planning.
As always, AIA turnkey systems are presented by relative "ball park" budget levels, and equipment and technology can also be searched via an A La Carte menu. All systems are modular and can be recombined in multiple ways.