Ulf Welander

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A color scale was designed with an approach that combined both human visual response to color and physical properties of color. The design was initiated with a subjective evaluation of a 16 step color scale running from dark blue via magenta, orange to light yellow. The CIELUV chromaticity diagram was employed to verify the subjectively generated scale and(More)
OBJECTIVE A colour scale has been developed as a complement to the grey scale in radiographs. The aim of the present study was to compare colour-coded with conventional black-and-white radiographs in terms of the perceptibility curve test. MATERIALS AND METHODS Twelve digital radiographs were exposed on a test object from low to high exposures and(More)
The perceptibility curve test is a method for evaluating the psychophysical properties of radiographic systems. The concept of the perceptibility curve is based on the minimum perceptible exposure differences that are recorded by a particular imaging system. The perceptibility curve test was applied to a Charge-Coupled Device (CCD)-based digital intraoral(More)
OBJECTIVES Two digital image processing algorithms, one aimed at correction for exponential attenuation and one at correction for visual response, have been developed. The aims of the present study were to test whether digital radiographs processed with these algorithms improve determination of the length of endodontic files and whether such processed(More)
OBJECTIVES To derive and test a method to linearize the visual response of the display of digital radiographs so that equal steps in gray levels will be perceived as equal steps in brightness. METHOD A mathematical analysis was performed and expressions for visual linearization were derived. Twenty-four test images were computer generated to confirm that(More)
OBJECTIVES To assess intra- and interobserver agreement on marginal changes in periodontal bone from color-coded compared with subtraction radiographs. METHODS Sequential radiographs from patients undergoing periodontal treatment were acquired using direct digital intra-oral radiography. Fifty-one pairs of color-coded and subtraction radiographs were(More)
A 3-D photographic technique was developed for the registration of bite conditions. This technique may replace plaster models for archiving purposes. To achieve this, photographic equipment and computer programs should be user friendly, not too expensive, and allow measurements that satisfy scientific demands. This purpose was fulfilled by combining the(More)
The Zonarc (Palomex Oy, Helsinki, Finland) uses the principles of rotational panoramic radiography to image various structures of the head and neck. System parameters obtained from the manufacturer have been used to derive data on the imaging characteristics of the Zonarc when using each of the following programmes: MT, DENT, TMJ, EAR, CV and LAT. The beam(More)
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