Digital image

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 resolution.

The image matrix 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 as a respective value that will represent a brightness level. The size is determined via: pixel size = FOV/matrix

A decreased FOV means the pixel is smaller and hence 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.

Physics and imaging technology: x-ray
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Article information

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

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Cases and figures

  • Figure 1: image matrix
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