HP Scanjet -  Learning About the Bit Depth that is Used When a Scanner Converts an Image into Digital Form

Introduction
When a scanner converts an image into digital form, it looks at the image pixel by pixel and records what it sees. Different scanners record different amounts of information about each pixel. How much information a given scanner records is measured by its bit depth.
A black and white scanner can only express two values, on or off for each bit. In order to see the many tones in between black and white, a scanner needs to be at least 4-bit (for up to 16 tones) or 8-bit (for up to 256 tones). A 24-bit color scanner can collect 8-bits of information about each of the primary scanning colors: red, blue, and green The higher the scanner's bit depth, the more precisely it can describe what it sees when it looks at a given pixel.
A well-exposed 24-bit image is photographic quality, however, in creating a well-exposed 24-bit image, a scanner can make use of higher bit depth data, such as 30-bit, 36-bit, or 48-bit data. Once a high quality image is created, the extra data in a 30-bit or 48-bit image just makes the file larger. This larger file size will slow print time and limits the applications that can use the image. Extra bit depth is particularly important when creating a quality 24-bit image from slides or negatives.
The real merit of increasing the bit depth of a scanned image is better tonal transformations or the ability to create a better 24-bit image for later use or editing. Areas impacted in an image include:

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      Better exposure or improved brightness and contrast. Brightness is a measure of the overall intensity of the image. The lower the brightness value, the darker the image; the higher the value, the lighter the image will be. Contrast is the difference between the dark and light areas of an image.
    *
      Better gamma compensation. Gamma compensation assures an image will print or display properly on a computer display or printer.
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      High bit-depth tonal transformations are critical to the ability to scan negatives and slides.

Below are examples of slides scanned with and without extra bit depth information, and without tonal transformations applied to the image.


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HP Scanjet -  Product Specifications for the Scanjet 5200C series


Features

    *      Dual image scanning
    *      Unsurpassed quality for logos and drawings
    *      Page analysis
    *      Deskewing
    *      Preserving page integrity
    *      Smart Dialogs for resolution
    *      Right-click editing
    *      Enhancement
    *      9600-enhanced resolution
    *      Internet-ready file formats, plus many more file format options
    *      TWAIN and OLE compliance
    *      HP Customer Care:
          o            One-year HP limited hardware warranty
          o            HP Express Pickup and Delivery Service (U.S. and Canada)
          o            90-day free telephone support (installation and hardware issues only)
          o            Optional HP Supportpack for two years of additional Express Pickup and Delivery
          o            24-hour online support available free at www.hp.com/support/home_products

Performance information
Task speeds
The following speeds are achieved using a 233 MHz PC with 32 megabytes (MB) RAM, Microsoft(R) Windows 98, and a USB interface by pushing the HP Scanjet 5200C series scanner's front panel button and scanning directly to end-user programs through the HP Precisionscan 2.0 program.
Task                                            Speed
4 x 6 color photo into Microsoft Word           Less than 90 seconds
OCR a full page of text into Microsoft Word     Less than 90 seconds
Black and white drawing into Microsoft Word     Less than 90 seconds


Resolution

    *
      600 dpi optical resolution
    *
      600 x 1200 hardware resolution
    *
      1200 dpi hardware super sampling
    *
      9600 dpi enhanced resolution

Bit depth
36-bit color (internal hardware)
Scaling
12 to 1200% in 1% increments at 600 dpi (dots per inch) resolution (scaling range dependent upon resolution)