title: Evaluating noise in digitized radiographic images by means of histogram.
abstract: To evaluate the performance of three digital devices regarding the noise added to digital radiographic images containing different optical densities.
  
  
  METHODS
  A radiographic image was digitized repeatedly ten times using two scanners (HP 4c/T and HP 5370C) and a digital camera (Nikon 990). A histogram tool measured a mean pixel value and the standard deviation of the region of interest in each image. Both values were used to calculate the image noise at the different optical densities.
  
  
  RESULTS
  The noise values found were different for all devices and optical densities. There was a statistically significant difference (p<0.05) between the scanner HP 4c/T and the digital camera regarding the noise values. There was a significant correlation (p<0.05) between the noise values found for the HP 4c/T scanner and the digital camera and between both scanners (p<0.01).
  
  
  CONCLUSIONS
  The noise added to the image was higher for scanner HP 4c/T and less for the digital camera. The noise was higher at the lower optical densities for the scanners. It seems that depending on the equipment and the optical density, a variable amount of noise can be incorporated to the images.
authors.affiliation: Department of Stomatology, Bauru School of Dentistry, University of São Paulo, Bauru, Brazil. izrubira2000@yahoo.com.br
authors.forename: Izabel Regina Fischer
authors.initials: IR
authors.lastname: Rubira-Bullen
authors.forename: Maurício Cunha
authors.initials: MC
authors.lastname: Escarpinati
authors.forename: Homero
authors.initials: H
authors.lastname: Schiabel
authors.forename: Marcelo Andrade da Costa
authors.initials: MA
authors.lastname: Vieira
authors.forename: Cássia Maria Fischer
authors.initials: CM
authors.lastname: Rubira
authors.forename: José Roberto Pereira
authors.initials: JR
authors.lastname: Lauris