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Quintiles Intelligent Imaging Clear Vision for the Healthcare Industry

I 2. Quintiles Intelligent Imaging Clear Vision for the Healthcare Industry. DICOM Grayscale Standard Display Function David Clunie. Outline. Inconsistent appearance of images Why is it a problem ? What are the causes ? Grayscale Standard Display Function The DICOM solution to the problem

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Quintiles Intelligent Imaging Clear Vision for the Healthcare Industry

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  1. I2 Quintiles Intelligent ImagingClear Vision for the Healthcare Industry DICOM Grayscale Standard Display Function David Clunie

  2. Outline • Inconsistent appearance of images • Why is it a problem ? • What are the causes ? • Grayscale Standard Display Function • The DICOM solution to the problem • How it works • How to implement it

  3. Workstation Workstation Digital Modality Laser Printer Distributed Image Consistency Identical perceived contrast

  4. Workstation Workstation Digital Modality Laser Printer Distributed Image Consistency Identical perceived contrast

  5. Workstation Workstation Digital Modality Laser Printer Distributed Image Consistency Identical perceived contrast

  6. Workstation Workstation Digital Modality Laser Printer Distributed Image Consistency Identical perceived contrast and color !!

  7. What about color ? • Consistency is less of an issue: • US/NM/PET pseudo-color; VL true color ?? • Consistency is harder to achieve • Not just colorimetry (i.e. not just CIELAB) • Scene color vs. input color vs. output color • Gamut of devices much more variable • Greater influence of psychovisual effects • Extensive standards efforts e.g. ICC

  8. Problems of Inconsistency • VOI (window center/width) chosen on one device but appears different on another device • Not all gray levels are rendered or are perceivable • Displayed images look different from printed images • …

  9. Problems of Inconsistency • VOI chosen on one display device • Rendered on another with different display • Mass expected to be seen is no longer seen mass visible mass invisible

  10. Problems of Inconsistency 0.5 1.0 • Not all display levelsare perceivable on alldevices 1.5 3.0

  11. Problems of Inconsistency 0.5 1.0 • Not all display levelsare perceivable on alldevices 1.5 3.0

  12. Digital Modality Laser Printer Problems of Inconsistency • Printed images don’t looklike displayed images

  13. Causes of Inconsistency • Gamut of device • Minimum/maximum luminance/density • Characteristic curve • Mapping digital input to luminance/density • Shape • Linearity • Ambient light or illumination

  14. Causes of Inconsistency • Display devicesvary in the maximumluminance they canproduce • Display CRT vs. film on a light box is an extreme example 1.0 .66

  15. Monitor Characteristic Curve 100 10 1 0.1 0 50 100 150 200 250 300 Digital Driving Level Monitor Characteristic Curves Maximum Luminance Gamma Ambient Light

  16. Towards a Standard Display • Can’t use absolute luminance since display capabilities different • Can’t use relative luminance since shape of characteristic curves vary • Solution: exploit known characteristics of the contrast sensitivity of human visual system - contrast perception is different at different levels of luminance

  17. Human Visual System • Model contrast sensitivity • assume a target similar to image features • confirm model with measurements • Barten’s model • Grayscale Standard Display Function: • Input: Just Noticeable Differences (JNDs) • Output: absolute luminance

  18. Grayscale Standard Display Function 4500 4000 3500 3000 2500 2000 1500 1000 500 0 0 200 400 600 800 1000 1200 JND Index Standard Display Function

  19. Standard Display Function Grayscale Standard Display Function 4500 4000 3500 Film Monitors 3000 2500 2000 1500 1000 500 0 0 200 400 600 800 1000 1200 JND Index

  20. Grayscale Standard Display Function 1000 100 10 1 0 200 400 600 800 1000 .1 .01 JND Index Standard Display Function

  21. Standard Display Function Grayscale Standard Display Function 1000 Film 100 10 Monitors 1 0 200 400 600 800 1000 .1 .01 JND Index

  22. Perceptual Linearization • JND index is “perceptually linearized”: • same change in input is perceived by the human observer as the same change in contrast • Is only a means to achieve device independence • Does not magically produce a “better” image

  23. Grayscale Standard Display Function 1000 100 10 1 0 200 400 600 800 1000 .1 .01 JND Index Perceptual Linearization Despite different change in absolute luminance Same number of Just Noticeable Difference == Same perceived contrast

  24. Display Display Modality Perceptual Linearization Ambient Light Perception of Contrast By Human Visual System

  25. Using the Standard Function • Maps JNDs to absolute luminance • Determine range of display • minimum to maximum luminance • minimum to maximum JND • Linearly map: • minimum input value to minimum JND • maximum input value to maximum JND • input values are then called “P-Values”

  26. Monitor Characteristic Curve 100 10 0 0.1 0 50 100 150 200 250 300 Digital Driving Level Monitor Characteristic Curve Ambient Light

  27. Grayscale Standard Display Function 1000 100 10 1 0 200 400 600 800 1000 .1 .01 JND Index Standard Display Function Maximum Luminance + Ambient Light Monitor’s Capability Minimum Luminance + Ambient Light Jmax == P-Value of 2n-1 Jmin == P-Value of 0

  28. 100 Standard 10 1 0 50 100 150 200 250 Characteristic Curve 0.1 DDL or P-Values Standardizing a Display

  29. Mapping P-Values to Input of Characteristic Curve (DDL’s) 300 250 200 DDL 150 100 50 0 0 50 100 150 200 250 300 P-Values Standardizing a Display

  30. Standardizing a Display Standard Display Function Standardized Display P-Values: 0 to 2n-1

  31. Device Independent Contrast Standard Display Function Standard Display Function Standardized Display B Standardized Display A P-Values: 0 to 2n-1

  32. So what ? • Device independent presentation of contrast can be achieved using the DICOM Grayscale Standard Display Function to standardize display and print systems • Therefore images can be made to appear the same (or very similar) on different devices

  33. So what ? • Images can be made to appear not only similar, but the way they were intended to appear, if images and VOI are targeted to a P-value output space • New DICOM objects defined in P-values • Old DICOM objects and print use new services (Presentation State and LUT)

  34. Not so hard … • If you calibrate displays or printers at all, you can include the standard function • If you use any LUT at all, you can make it model the display function • If you ignore calibration and LUTs totally (e.g. use window system defaults) the results will be inconsistent, mediocre and won’t use the full display range

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