ITK/Release 5/DICOM/Color

Multiple Components in DICOM

ITK 5.0

DICOM standard allow storing of image with more than one components. As of today, only 1 or 3 components are considered valid DICOM SOP Class instances (for all IODs).

By design the itk::GDCMImageIO was designed and implemented so that an input YBR_FULL image would be loaded as such (no implicit conversion to RGB was done). The main reason for that is that ITK is a processing toolkit, so quantitative analysis is supposed to be done on the best possible pixel representation. Since conversion from integer YBR_FULL to integer RGB colorspace is a lossy operation (truncation in floating point representation), the conversion has never been implemented.

As side note MONOCHROME1 color space is not converted to MONOCHROME2 (itk::GDCMImageIO / ITK 5.0)

Issue

This behavior was considered ok, as long as the image was not directly loaded in viz application such as Slicer, where suddenly the image would appears with a weird color scheme. (original bug report from Mihail Isakov)

Notation

1. JPEG refers to the subset of ITU-T T.81, ISO/IEC IS 10918-1 (lossy 8bits)
2. JPEG 2000 refers to ITU-T T.800, ISO/IEC IS 15444-1

ITK 5.x

The behavior for YBR_FULL vs RGB color model has been discussed and it seems consensus would be to convert to RGB always. Since DICOM, JPEG and TIFF can be somewhat relates for this matter, we should strive to keep the behavior consistent.

Current behavior of ITK 5.0:

Photometric Interpretation	JPEG	TIFF	GDCM	DCMTK
MONOCHROME1	X	MONOCHROME2 (aka min-is-black)	MONOCHROME1	?MONOCHROME1?
MONOCHROME2	MONOCHROME2	MONOCHROME2 (aka min-is-black)	MONOCHROME2	MONOCHROME2
PALETTE_COLOR	X	RGB (??)	Converted to RGB	?Converted to RGB? (need to check compressed LUT)
RGB	RGB	RGB	RGB	?RGB?
HSV
ARGB
CMYK
YBR_FULL	ITU 81 enforce sub-sampling	??	YBR_FULL	??
YBR_FULL_422	RGB	RGB	YBR_FULL	??Maybe RGB?
YBR_PARTIAL_422
YBR_PARTIAL_420
YBR_ICT	ITU 81 does not support this colorspace	??	RGB	no J2K plugin
YBR_RCT	ITU 81 does not support this colorspace	??	RGB	no J2K plugin

Desired behavior of ITK 5.0:

Photometric Interpretation	JPEG	TIFF	GDCM	DCMTK
MONOCHROME1	X	MONOCHROME2 (aka min-is-black)	MONOCHROME1	?MONOCHROME1?
MONOCHROME2	MONOCHROME2	MONOCHROME2 (aka min-is-black)	MONOCHROME2	MONOCHROME2
PALETTE_COLOR	X	RGB	Converted to RGB	??
RGB	RGB	RGB	RGB	?RGB?
HSV
ARGB
CMYK
YBR_FULL	ITU 81 enforce sub-sampling	??	RGB	??
YBR_FULL_422	RGB	RGB	RGB	??Maybe RGB?
YBR_PARTIAL_422
YBR_PARTIAL_420
YBR_ICT			RGB	no J2K plugin
YBR_RCT			RGB	no J2K plugin

Discussion

For visualization people it is important that:

1. MONOCHROME1 (min-is-white) is converted to MONOCHROME2 (min-is-black)
2. YBR_FULL / YBR_FULL_422 are converted to RGB

The requirements for quantitative analysis may be different, please list reqs here:

1. ? Extract Luminance out of YBR ?
2. ? Need MONOCHROME1 native support, because <fill reason ??>
3. ? Is there a need to manipulated native palette data ? I doubt so

References

• http://gdcm.sourceforge.net/wiki/index.php/Color_Space_Transformations