Avoiding Chromaticity Creep with PseudoGrey

Abstract

We examine the calibration of Commodity, Off-The-Shelf (COTS) monitors to the DICOM GreyScale Display Function (GSDF) standard (as used for medical imaging). We note that uncalibrated and calibrated (using commercial and non-commercial tools) monitors exhibit Chromaticity creep along the black body locus in CIE 1931 colourspace; this is at odds with high-end medical monitors which do not introduce colour-but cost significantly more than COTS colour monitors. Alternative algorithms are investigated to produce a DICOM GSDF compliant calibration, where we take into account both luminance and chromaticity. Using PseudoGrey we generate thousands of shades of grey on a colour monitor to produce a high dynamic range, albeit in greyscale, improving on the standard 256 shades of grey. In this work, we now restrict our introduction of colour to minimise chromaticity deviation from a given white point. We have found various chromatic anomalies with COTS monitors, and discuss our findings along with algorithmic variations to cope with such issues. We believe this work contributes to the availability of a robust method to calibrate COTS colour monitors to the GSDF and hence any required intensity curve whilst retaining a pure colour, enabling greyscale images with over 256 shades to be accurately displayed. This may have significant cost, and potentially improved diagnostic implications, in the reporting of medical radiological images, and could be used to display high dynamic range greyscale imagery (such as multiple exposure black and white photography).