Calibration of Diagnostic Displays

As described previously in Diagnostic Display Basics and Human Visual System, different display devices have different characteristic response curves and the human visual system does not respond linearly to incident light intensity. These two properties of the display system and the human visual system can be corrected by creating a perceptual linearity across the grayscale values. Perceptual linearity can be achieved by setting display luminance values such that each change in pixel gray value corresponds to the same quantity of just noticeable difference (JND).

The Digital imaging and Communications in Medicine (DICOM) Grayscale Standard Display Function (GSDF) defines a way to take the existing display response characteristic curve of a display system (i.e. the relationship between the luminance output for each digital driving level or pixel value) and modify it to the grayscale standard display function. The practical result of using the GSDF is that different displays can be set to have the same grayscale response. Digital images will have the same visual presentation when displayed on different display systems in the dental practice that have also been calibrated to the GSDF. This can improve the perceptual linearity of a display and better match the capabilities of the human visual system, resulting in better diagnostic performance.

Calibration software such as the PerfectLum Dental used in conjunction with the X-rite i1Display PRO colorimeter can calibrate almost any commercial grade color monitor to the Grayscale Standard Display Function. The software can also measure the accuracy with which the calibration matches the GSDF.

PerfectLum Dental also provides display quality assurance by measuring maximum and minimum luminance, contrast and luminance ratios, luminance uniformity, ambient light levels, and response characteristic. PerfectLum Dental is a complete display quality assurance solution.

For more in-depth explanation of the gray-scale standard display function read the following reference.

Fetterly, KA, Blume, HR, Flynn, MJ, Samei, E. Introduction to Grayscale Calibration and Related Aspects of Medical Imaging Grade Liquid Crystal Display. Jounal of Digital Imaging, 2008; 21(2):193-207.