The FDA, ICC, DICOM, and AAPM held a two day summit on issues related to color and color management in medical imaging. These are my initial conclusions about the present situation. There will be further discussions and conversations about what should be done.
sRGB and consumer grade equipment presents important issues
- Use of sRGB and consumer grade equipment is inevitable. It has nearly 100% penetration for patients and providers. It is cheap, and they know how to use it.
- sRGB and consumer grade equipment is inadequate. Examples:
- The sRGB color gamut does not include the colors found in fresh blood. This is not important to consumers, but it matters in surgery and some other medical uses.
- Typical human vision has the ability to discriminate color and contrast with 10-12 bit resolution. Consumer equipment is only 8 bit resolution.
- Mobile equipment lacks calibration capability and lacks manufacturer claimed specifications. PC class equipment has some calibration and claimed specifications, but most is limited to 8 bit data paths.
- Measurements of consumer equipment indicates huge quality problems for acquisition (e.g., camera variability) and modest problems for displays. The typical errors for consumer cameras were 20-40 delta E. A typical person says that two colors do not match when the delta E exceeds 3-5.
- Huge variability is also introduced by other acquisition variations: lighting, positioning, preparation, etc. all matter and introduce significant effects.
- Displays used to be a big problem. Now they are a modest problem, and with calibration become a small problem. Calibrated color monitors had measured delta E around 3.
- Clinical trials and anecdotal evidence indicate that:
- Diagnostic efficacy is not affected by the variability of monitors, nor by some of the acquisition issues. Skill, experience, and the eye-brain complex compensate for the variations.
- Diagnostic speed is significantly affected. (This is statistical significance.) The measured diagnostic tasks were performed 50% faster on calibrated monitors. This is likely significant in the context of medical workflow, capacity, etc.
- User fatigue is reduced on calibrated monitors. This was not quantitatively assessed, but was consistently reported by the subjects.
- The goals and requirements of various medical activities are substantially different and not well enunciated. There are needs like "consistency", "looking natural", matching memories of color, etc. The needs vary significantly in different disciplines. Pathology slide staining, dermascopic exams, endoscopic exams, and laproscopic surgery all have different needs.
- Issues like focus, depth of field, lighting, etc. are similarly important and poorly controlled sources of variability. Color is not easily separated from these issues.
- The relationship with multi-spectral imaging is unresolved. E.g., a slide stain is a series of spectral spikes that correspond to the stain, yet it is being represented by a tri-stimulus value. This is combined with other stains and the inherent broadband spectrum of the underlying tissue. This kind of mapping of spikes onto tri-stimulus is problematic due to numerical stability issues.