Grayscale Display Function (GSDF)
Why DICOM ?
In medical imaging, it is important that there be a visual consistency in how a given digital image appears, whether viewed, for example, on the display monitor of a workstation or as a film on a lightbox.
In the absence of any standard which regulates how these images are to be visually presented on any device, a digital image which has good diagnostic value when viewed on one device could look very different and have greatly reduced diagnostic value when viewed on another device.
What is GSDF?
PS 3.14 specifies a standardized Display Function for display of Grayscale images, and is based on the human contrast sensitivity (CS). Human CS is distinctly non-linear within the luminance range of the GSDF, making it easier to see small relative changes in luminance in the bright areas of the image than in the dark areas.
The second objective of PS 3.14 is to select a Display Function which provides some level of similarity in Grayscale perception or basic appearance for a given image between Display Systems of different Luminance and which facilitates good use of the available Digital Driving Levels of a Display System.
The Luminance difference of a given target under given viewing conditions that the average human observer can just perceive is known as a Just Noticeable Difference (JND). The JND Index is the input value to the GSDF, such that one step in JND Index results in a luminance difference that is a JND.
For medical diagnostic purposes, a gamma correction is required that makes the Display perceptually linear to conform with the DICOM 3.14 GSDF.
For NEC MD and MDview Display Systems, after calibration to DICOM GSDF, the values for adjustment are loaded into the Look Up Table (LUT) of the display.
Simply put, displays that conform to the DICOM Part 14 standard
- maximise the number of grey tones that can be perceived on the display
- provide a consistently high level of image quality that aids the speed and accuracy of diagnosis
- can be recalibrated to ensure on-going life time conformance
- provides consistency of image display across all displays
DICOM Part 14 Complete Specification – please click here
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