Speaking Notes from a Tech Talks Presentation by Mark Phillips, March 30, 2005

Things Covered in This Month's Presentation

What is a scanner?

"A device that converts visual information into digital data." -- cjs.cadmus.com/da/glossary.asp

  • Flatbed Scanner
  • Transmissive Flatbed Scanner
  • Roller Scanner
  • Negative Scanner
  • Planetary Scanner
  • High Speed Duplex Scanner
  • Large Format Scan Back

What is a CCD?

"(Charge-Controlled-Device). A semiconductor element commonly used for electronic light detection or imaging. Converts the photon energy of light to electrical charge for electronic processing."

What is a pixel?

"Picture element. The smallest element in a visual display."

What is DPI?  PPI?

DPI stands for Dots Per Inch
PPI stands for Pixels Per Inch

DPI and PPI have become interchangeable in the digital imaging world over the past few years. DPI is for the most part a holdover from the print industry and is used in the computer world to describe the number of "pixels per inch" and has nothing to do with a dot.

Don't worry if you use one or the other, or switch back and forth, it happens all the time to all of us.

What is resolution?

"The number of pixels (in both height and width) making up an image. The more pixels in an image, the higher the resolution, and the higher the resolution of an image, the greater its clarity and definition (and the larger the file size). Image file resolution is often expressed as a ratio (such as 640x480 pixels), as is monitor resolution; however, resolution is also expressed in terms of dots per inch (dpi).

What is bit depth?

  • 1 Bit Bitonal (binary/bitmap) - Black and White
    • Binary images are images whose pixels have only two possible values. They are displayed as black and white. Numerically, the two values are often 0 for black, and either 1 or 255 for white.
  • 8 Bit Grayscale - 256 shades of gray
    • Grayscale images treat all colors in an image as a shade of gray. If the levels are evenly spaced then the difference between successive graylevels is significantly better than the graylevel resolving power of the human eye.
  • 24 Bit Color -- 224 = 16,777,216 colors
    • 24 Bit (RGB) color is made up of three color components for each and every pixel (a red, green and blue setting).

Scanning Standards

Minimum Standards for the UNT Libraries' Digital Projects Department

Things Covered in Next Month's Presentation

[Editor's Note:  See Photo Editing 101.]

  • What format do I use to save files?
  • How do I rotate (deskew) the image?
  • How do I resize the image?
  • How do I crop the image?
  • How do I save the image for the Web?


What is a scanner?

A scanner is anything that transforms visual information into digital data...

What is a CCD?

For the most part, a CCD is the thing that makes the whole thing tick... It is where all of the magic happens...

What is a pixel?

The smallest piece.. one of the pieces in a mosaic, a single tile on a tile floor

What is DPI?  PPI?

One of the ways that we measure quality of a digital image

What is resolution?

The other way we measure quality of a digital image

What are 3 types of bit depth?

1 bit bitonal
8 bit Grayscale
24 bit color

About the Author:  Librarian Mark Phillips is head of the UNT Libraries' Digital Projects Unit.


Wednesday, March 30, 2005 - 12:00pm