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Is Grey the New Black? Image Display Optimisation & Consistency for Softcopy Reporting Mark Barnfield St James’s University Hospital, Leeds. Softcopy Concerns…. Softcopy more often becoming last component in the ‘Imaging chain’ .
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Is Grey the New Black?Image Display Optimisation & Consistency for Softcopy ReportingMark BarnfieldSt James’s University Hospital, Leeds
Softcopy Concerns… • Softcopy more often becoming last component in the ‘Imaging chain’. • In NMed chain can cost in excess of £300K – undertake well developed QA protocols. • … however, workstation monitors relatively inexpensive ~£300 – possible weak link with little or no QA system employed.
Image Quality ApproachSt James’s NMed • Optimisation (currently qualitative) • To improve presentation of radiological images and ensure that important image information is not lost during visual inspection. • Consistency • Images should appear similar on different displays or on the same display at different times.
First step - Display Preparation • Monitor Cleanliness • Display quality is compromised by dust, fingerprints, ink, etc. • Reduction in luminance. • Possible misinterpretation. • Needs cleaning on regular basis and on as-needed basis. • Lint free cloth to reduce static. • Never spray directly onto monitor. • Manufacturer may recommend special cleaner for monitors coated with antireflective or antiglare coatings.
Picture Boarder Linearity & Geometric distortion Uniformity Mid-band streaking Brightness & Contrast Resolution response Focus The SMPTE Test Pattern Ref:Radiology 1985; 154: 519-527
An Optimal Contrast Range Brightness & Contrast Adjustment • Set to ~50% and back off • Bring up until black just turns grey and back off fraction • Set to give reasonably bright white level but avoid loss of image definition The brightness and contrast of yourmonitor are adequately set if the inner 5% squares at both ends of gray scale are visible.
Observations • 17” Iiyama – Vision Master 403 • Visual • Geometric (Aspect ratio) distortion – squares rectangles • Barrelling • Also observed pincushion on my PC! • Refreshverticalrate66Hz - <72Hz some observers can perceive flicker and greater eye stain is possible. • Known that nearly all parameters are dependent on position on screen - degrading from centre.
DICOM Part14: (GSDF) Grey-Scale Standard Display Function The Consistent image • Aims to mathematically define a display function for all image presentation systems. • Aims for similarity in grey-scale perception between different display systems. • Not a performance or image display standard. • It does not define luminance range.
Measuring Monitor Characteristic CurveAnnex D - DICOM pt14 pp27-36 Background (20% of max lum) Target (10% area of screen) Photometer (Light-O-Meter P10 Std) Step target through greyscale range
LUT set-up verification • 5% & 95% contrast equally perceptible. • Linear perception along the colour bar.
Effect of brightness & contrast setting on display characteristic curves - PCs
Reproducibility of monitor set-up using SMPTE test pattern NB. A – B done as consecutive measurements, C – D on separate occasions over a week.
Proposed Frequency of QC Tests • Weekly • Monitor preparation • Brightness & contrast adjustment • Monthly • Geometry • Spatial resolution • Quarterly • Spatial uniformity • Veiling glare
Acknowledgements I would like to thank, Sarah Jervis for allowing the use of her SMPTE and DICOM 14 Matlab programs; David Brettle for guidance and technical support.