Digital image

Dr Daniel J Bell and Andrew Murphy et al.

A digital image is a numerical representation of an image via a set of picture elements known as pixels. This simplified article lists three parameters of a digital image that moderate spatial and contrast resolution.

The image matrix is comprised of columns (M) and rows (N) that define the elements or pixels within an image.
The size of an image is:

  • matrix = M x N x k bits

The field of view (FOV) is the size of the displayed image. However, if you maintain the same FOV and increase the matrix size the pixels will be smaller and hence spatial resolution is improved.

The pixel is the element that makes up the image matrix, each pixel is a respective value that will represent a brightness level. The size is determined via: pixel size = FOV/matrix

A decreased FOV means that the pixel is smaller and results in an improvement in spatial resolution.

The voxel is a pixel that represents information that is contained in a volume.

The k bit is the number of bits per pixel, the grey scale of an image is equal to 2k-bit, for example:

  • k bit of 2 = 4 shades of grey
  • k bit of 8 = 256 shades of grey

The higher the bit depth, the more grey scale and therefore the higher the contrast resolution.

Imaging technology

Article information

rID: 53396
Section: Radiography
Synonyms or Alternate Spellings:
  • Digital images
  • Image matrix (general)

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Cases and figures

  • Figure 1: image matrix
    Drag here to reorder.
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