[Insight-developers] Coordinate system semantics of ImageIOBase?

[Steve M. Robbins]

On Tue, Dec 30, 2008 at 11:48:19AM -0500, Luis Ibanez wrote:

>> The intensity transformation in point 2 does include LUTs and DICOM's
>> Palette Colour transformations (meaning that the output would be RGB)?
>> What do you do when there are two LUTs for the image?
>>
>
>
>        I'm not sure how you arrived to this conclusion.

DICOM provides several ways to map Stored Values (pixel values) to
Ouput Units (real-world values).  The most common is using a slope and
intercept pair.  But there can be, instead, a scalar-to-scalar
Look-Up-Table (Modality LUT), or a scalar-to-RGB mapping (Palette
Colour Lookup Table Data).  Only one of these can be present in a
given image, AFAIK.


>        You seem to be assuming that it would be possible to
>        receive DICOM images that have simultaneouly set a
>        photometric interpretation to palette colour, *and*
>        also set the Slope an Intercept to non-trivial values.

No, but I was mixed up on another point.  I thought you could
have multiple Modality LUTs.  You cannot.  

I was mixing the Modality LUT up with another kind of LUT that DICOM
allows: the Values-of-Interest LUT (VOI LUT).  The VOI LUT provides a
mapping *for presentation* (display) only, akin to the window centre /
window width pair.  You *can* have multiple VOI LUTs or multiple
window centre/width pairs.  But these are not relevant to image
processing.

The Modality LUT is the one relevant for image processing so it is the
only one that ImageIO needs to be concerned with and, happily, there
is only one such.  So ignore my musings about two LUTs.


Cheers,
-Steve
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