CHARACTERISTICS OF A DIGITAL IMAGE

Image Characteristics

  • Contrast Resolution
  • Spatial Resolution
  • Detector Latitude
  • Detector Sensitivity
  • Signal to noise ratio

CONTRAST RESOLUTION

  • Contrast resolution is the ability to distinguish different densities in the radiographic image. 
  • Current digital detectors capture data at 8-, 10-, 12-, or 16-bit depths. 
  • The bit depth is a power of 2. 

Spatial Resolution

  • Spatial resolution is the capacity for distinguishing fine detail. 
  • The theoretical limit of resolution is a function of picture element (pixel) size for digital imaging systems.

DSCN6702

Film based IOPA – 20 lp / mm.

Digital receptors 7 lp / mm.

Film  >  CCD  >  PSP 

Detector Latitude

It is the ability of the image receptor to capture a range of x-ray exposures as different densities.

  • The latitude ofCCD and CMOS detectors is similar to film

Photostimulable phosphor receptors have larger latitudes and have a linear response to five orders of magnitude of x-ray exposure.

Detector  Sensitivity

  • Sensitivity of a detector is its ability to respond to small amounts of radiation. Intraoral film sensitivity is classified according to speed.
  • High resolution CCD and CMOS systems achieve less dose reduction than lower resolution PSP systems. CCD and PSP systems or extraoral imaging require exposures similar to those needed for 200-speed screen-film systems.

REFERENCE-WHITE AND PHAROAH 5TH EDITION

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