On 23 Jun, Detlef Grittner wrote: >>For specific examples of how this can be used, see >>http://medical.nema.org/dicom/2001.html/01_14PU.PDF or Barten's book >>Contrast Sensitivity of the Human Eye and Its Effects on Image Quality >> >>Then follow the references to track down other major researchers on this >>topic. >> >>R Horn > > I found the correct link at http://medical.nema.org/dicom/2001/01_14PU.PDF > > Thank you for the information. As I'm working on medical viewers people often ask me >how many gray scales are needed. > Some people even doubt that more than 8 Bit (256) gray scales are necessary. > But typical radiological images often come with 10 Bit (1024) gray scales. > If you have a display and a video card that can display distinguishable 1024 grays >that would be invaluable.
Sorry about the typo. If you are working in medical you must also take a look at http://www.rsna.org/IHE/tf/ihe_tf_index.shtml In particular, it is becoming a market necessary to comply with the Consistent Presentation of Images (CPI) profile. At present it only applies to greyscale images. Calibrating color monitor presentation to comply with the greyscale standard makes a significant improvement to the quality of a color presentation. The further work on color space calibration remains in committee. This came up very briefly at last weeks DICOM WG-6 meeting, mostly as a question regarding when was the color standard going to be ready, with a response of "Don't know". One of the issues is the weakness of the scientific literature regarding the diagnostic requirement for color consistency. The minimum realistic requirement for medical work is a high quality monitor and a 10-bit DAC. This lets you adjust the output LUT so that you can comply with the display standard while using 8-bit data. Assuming that there is compliance with the CPI profile, you can degrade 10-bit to 8-bit image data with a minimum loss of utility. There are a number of vendors for medical quality displays. These are all quite expensive because they provide both 10-bit input and 12+bit DAC controls so that they can both calibrate the system to comply with the display standard and convey 10-bit image data. They also incorporate the very high luminance required to achieve 10-bit viewability. Unfortunately from an XFree perspective, most of the medical vendors will not disclose the programming information for the display controllers. The actual requirement for resolution depends on the imaging modality and the purpose of viewing. For many purposes, an 8-bit display that meets the display standard will be sufficient. For other purposes it will not. I would never consider doing general radiographic diagnosis of a chest with anything under 10-bit. I would never consider doing it in without controlled ambient lighting and the very high brightness of a radiology oriented monitor. These are the norm in any reading room. But for ultrasound an 8-bit display with calibration and proper lighting should suffice. There is also a big difference between diagnosis and other uses. Further, just a warning about safety regulations. The FDA regulates medical devices under the Safe Medical Device Act. You might be an unwitting manufacturer. The definitions of device and manufacturer are very broad. So check whether these safety laws apply to you. It is a very serious crime to ship a medical device without a serious effort to comply with the laws. It is a far less serious crime to make mistakes in compliance. The website at http://www.fda.gov/cdrh/overview.html is a good starting point. FDA regulations include efficacy rules, and questions about necessary display quality might be an efficacy question. R Horn _______________________________________________ Xpert mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/xpert
