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Proceedings Paper

Iso-precision scaling of digitized mammograms to facilitate image analysis
Author(s): Nico Karssemeijer; Leon J.Th.O. van Erning
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Paper Abstract

A 12 bit CCD camera equipped with a linear sensor of 4096 photodiodes is used to digitize conventional mammographic films. An iso-precision conversion of the pixel values is performed to transform the image data to a scale on which the image noise is equal at each level. For this purpose film noise and digitization noise have been determined as a function of optical density and pixel size. It appears that only at high optical densities digitization noise is comparable to or larger than film noise. The quantization error caused by compression of images recorded with 12 bits per pixel to 8 bit images by an iso-precision conversion has been calculated as a function of the number of quantization levels. For mammograms digitized in a 40962 matrix the additional error caused by such a scale transform is only about 1.5 percent. An iso-precision scale transform can be advantageous when automated procedures for quantitative image analysis are developed. Especially when detection of signals in noise is aimed at, a constant noise level over the whole pixel value range is very convenient. This is demonstrated by applying local thresholding to detect small microcalcifications. Results are compared to those obtained by using logarithmic or linearized scales.

Paper Details

Date Published: 1 June 1991
PDF: 12 pages
Proc. SPIE 1445, Medical Imaging V: Image Processing, (1 June 1991); doi: 10.1117/12.45214
Show Author Affiliations
Nico Karssemeijer, St. Radboud Univ. Hospital Nijmegen (Netherlands)
Leon J.Th.O. van Erning, St. Radboud Univ. Hospital Nijmegen (Netherlands)

Published in SPIE Proceedings Vol. 1445:
Medical Imaging V: Image Processing
Murray H. Loew, Editor(s)

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