Palette Colour LUTs
These are only used when the
Photometric_Interpretation is PALETTE
COLOR. They can be 8 or 16 bit, and 3 copies exist, one each for red, blue and
green.
Main DICOM LUTs
Modality LUT
The Modality LUT transformation transforms the manufacturer dependent pixel
values into pixel values which are meaningful for the modality and which are
manufacturer independent.
In the case of a linear transformation, the Modality LUT is described by the
Rescale Slope (0028, 1053) and Rescale Intercept (0028, 1052). In the case of a
non-linear transformation, the Modality LUT is described by the Modality LUT
Sequence (0028, 3000).
As Modality LUT is a pre-windowing transformation, Image's Window Center and
Width can still be changed after Modality LUT is applied.
Values of Interest (VOI) LUT
The Value Of Interest(VOI) LUT transformation transforms the modality pixel
values into pixel values which are meaningful for the user or the
application.
In the case of a linear transformation, the VOI LUT is described by the
Window Center (0028, 1050) and Window Width (0028, 1051). In the case of a
non-linear transformation, the VOI LUT is described by the VOI LUT Sequence
(0028, 3010).
In general, VOI LUT is the best supported. It serves as a Replacement for
Window Center and Width therefor it is NOT technically allowed to window an
image with a VOI LUT applied.
Presentation LUT
The Presentation LUT transformation transforms the pixel values into
P-Values, a device indenpendent perceptually linear space. It may be an identity
function if the output of the VOI LUT transformation is in P-Values.
In the case of a linear transformation, the Presentation LUT is described by
teh Presentation LUT Shape (2050, 0020). In the case of a non-linear
trnsformation, the Presentation LUT is described by the Presentation LUT
Sequence (2050,0010).
Please note,
NOT every Viewer supports all the LUTs. VOI LUT is best
supported, as we mentioned above, then comes the Modality LUT and finally the
Presentation LUT (This is from our experience). Even if all are individually
supported, some viewer may not "chain" them correctly. For those reasons,
sometimes it is better to apply any LUTs that your images need into the
Pixel
Data (i.e. replace the pixel data by a post-LUT equivalent).
DicomObjects ColourTable
This 2D-Array property allows a false-colour lookup table to be applied to a
monochrome image. This property is used as a Final LUT when the image is being
rendered for any purposes. The first dimension of the array must have lower
bound of 1 and upper bound of 3. The second dimension of the array may be any
size and may have any maximum value (up to 64K), as both input and output are
sclaed to filt the required ranges.
From:http://www.medicalconnections.co.uk/kb/Lookup_Tables
