Home > Image Processing > 3a. Types of Digital Images

3a. Types of Digital Images

Image representation is one technique of (1) effectively depicting the expression of a picture; and (2) efficiently laying out the image for later processing or numerical manipulation.

Following are the basic types of digital images:

    Binary (Black and White) images are composed of pixels containing values of either 0 or 1, which can also be manipulated through thresholding.
    Image files can be sought for their types using the Scilab function, imfinfo() – a capability under the SIVP Toolbox.

    Filename  |  cat111.jpg
    FileSize  |  18092
    Width     |  302
    Height    |  298
    BitDepth  |  8
    ColorType |  grayscale
    Figure 1. A binary image of a cat. Courtesy of Mathworks.

    Grayscale images are made up of pixels holding the gray level of the image. These gray levels range from black to white in fine steps.

    Filename  |  SigmaDP1-053.jpg
    FileSize  |  1205981
    Width     |  2640
    Height    |  1760
    BitDepth  |  8
    ColorType |  truecolor
    Figure 2. An example of a grayscale image. Courtesy of Sigma.

    Indexed images are represented by colors within an 8-bit palette (256 colors).

    Filename  |  8_bit.png
    FileSize  |  38455
    Width     |  300
    Height    |  225
    BitDepth  |  8
    ColorType |  truecolor
    Figure 3. An indexed image of a leaf. Courtesy of Wikimedia.

    True color images are made up of pixel arrays containing values for red, green and blue (RGB) that define the specific color in that particular area.

    Filename  |  SigmaDP1-053.jpg
    FileSize  |  1579216
    Width     |  2640
    Height    |  1760
    BitDepth  |  8
    ColorType |  truecolor
    Figure 4. An example of a truecolor image. Courtesy of Sigma.

On the advent of more sophisticated computing and techniques, more advanced formats were also developed:

    HDR (High Dynamic Range) images are produced by either computer rendering or tone mapping.  Colors are more accurately represented by a wider range of luminances.

    Figure 5. An HDR image of two streets. Courtesy of Richard Lackey.

    Multi- and hyperspectral images are processed across the electromagnetic spectrum.  Other than visible light, it allows viewing other frequencies such as infrared and ultraviolet.

    Figure 6. A hyperspectral image of the South Moloka‘i reef tract. Courtesy of the U.S. Geological Survey.

    3D images involve representation of three-dimensional geometric data. Its calculations can later for rendering 2D images.
    Temporal images involve animations, slide shows and videos. They contain a fast sequences of images that create an illusion of movement.

    Figure 7. A 3D animation of a human. Courtesy of ThinkQuest.

With the knowledge of the basic types of images, one can achieve the artistic effects of a photographer and accurately reproduce the original image in a better representation.

[1] Mathworks, 2010. Image Types in the Toolbox (Accessed 26 June 2010).
[2] Soriano, M., 2010. Image types and formats. Applied Physics 186.
[3] Wikipedia, 2010. Color depth (Accessed 27 June 2010).

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