Digital Image Characteristics


Outline and Learning Guide


  • Introduction and Overview

  • Image Types
    Analog Images
    For human viewing
    Shades of gray
    Digital Images
    For computer system processing, distribution, and storage

  • Digital Image Structure
    Pixel values
    Pixel Bit Depth
    Number of bits
    Dynamic range
    Numerical Size
    Number of pixels
    Pixel bit depth


  • Digital Image Detail
    Pixel Size
    Matrix size
    Image size (Field of view)
    The imaging modalities

  • Digital Image Contrast
    Acquisition Dynamic Range
    Displayed Image Range
    Image Processing
    Window level
    Window width

  • Image Compression
    Why Compress

    Image storage
    Image transmission and distribution
    Levels of Compression
    Compression Methods

  • Summary



Learning Objectives

  1. Give examples of typical analog images and describe their general characteristics.

  2. Explain why analog images are useful.

  3. Describe the general structure of a digital image in terms of pixels and bits.

  4. Briefly describe as many functions as possible that can be performed with digital medical images that are not possible with analog images.

  5. Explain the structural characteristic of a digital image that introduces blurring and limits visibility of detail.

  6. Explain and illustrate how pixel size is affected by the size of the image matrix.

  7. Explain and illustrate how pixel size is affected by the size of the imaged area (field of view).

  8. Explain and illustrate how computers write numbers and the concept of bits.

  9. Illustrate how the range of values that can be written is related to the number of bits being used.

  10. Briefly compare the methods used by both humans and computers to write numbers and some general advantages and disadvantages of each.

  11. Describe and illustrate the concept of bit depth of a pixel.

  12. Identify and describe the characteristic of an image that is affected by the bit depth.

  13. Illustrate and describe how bit depth is represented by both bits and bytes.

  14. Identify the factors that determine the numerical size of a digital image.

  15. When you are given the appropriate factor values, calculate the numerical size of an image in: bits, bytes, kilobytes, and megabytes.

  16. Explain how the numerical size of a digital image relates to image quality.

  17. Explain why the numerical size of a digital image is a limiting factor in some applications.

  18. Briefly describe the concept of digital image compression.

  19. Explain what is meant by "lossless" compression.

  20. Explain what is meant by "lossy" compression and what must be considered in clinical applications.



Text Reference

Physical Principles of Medical Imaging, 2nd Ed
Chapter 22.

Medical Physics Publishing,



Mind Map