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A digital frame of reference for viewing digital images

Department of Medical Physics & Engineering, Leeds Teaching Hospitals NHS Trust, Lincoln Wing, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK

View larger version (33K): [in a new window]   Figure 1. Layout and dimensions for the digital frame of reference (DFOR). (a) The main features of the DFOR are the four quadrants of varying contrast covering the complete grey scale range. The ellipses intercept the outer diameter to produce a range of frequencies. They also introduce internal curvilinear features. (b) The cropping mask used to crop (a). This helps improve the aesthetic presentation of the DFOR by removing boundary processing artefacts.

View larger version (44K): [in a new window]   Figure 2. Effects of simple image processing. (a) The unprocessed digital frame of reference (DFOR) for comparison with (b) and (c); (b) the DFOR after it has been sharpened with a medium level convolution kernel; (c) the DFOR after it has been processed with an unsharp mask filter. Radius=30.

View larger version (80K): [in a new window]   Figure 3. Clinical example of use of the digital frame of reference (DFOR). (a) Digital chest radiograph before processing. (b) The chest radiograph has been processed with unsharp mask and sharpening algorithms. The image now has the appearance of increased lung markings. The DFOR is shown at 15% of the image size. (DFORs displaced for clarity.)