Dear DCMTK-forum,
I have a question about changes which are applied to DICOM image attributes upon (lossy) on-the-fly compression. We can handle the DCMTK good enough to change the behaviour if needed, but we would like to understand the decisions made in development.
1. Image Type (0008,0008)
Originally the Image Type of our image (in this case: Computed Radiography) was set to "ORIGINAL\PRIMARY". After compression, it is set to "DERIVED". In our understanding, the Image Type shall have at least 2 values, so I would have expected that only the first component would be updated, resulting in an Image Type of DERIVED\PRIMARY.
(appears to be contradictory by itself, but as I understand PS3.3, C.7.6.1.1.2, this would be the correct value if the image is lossily compressed right after acquisition)
2. Derivation Code Sequence (0008,9215)
The sequence contains one item with the following code:
Code: Select all
(0008,0100) SH [121327] # 6, 1 CodeValue
(0008,0102) SH [DCM] # 4, 1 CodingSchemeDesignator
(0008,0104) LO [Full fidelity image] # 20, 1 CodeMeaning
Code: Select all
(0008,0100) SH [121325] # 6, 1 CodeValue
(0008,0102) SH [DCM] # 4, 1 CodingSchemeDesignator
(0008,0104) LO [Lossy compressed image] # 20, 1 CodeMeaning
Since PS3.3, C.12.4.1.1 Derivation Description says that:
I would think that code 121325 would describe "the way of derivation" more accurately. I suspect there are good reasons behind the behaviour that we are observing, but I would like to understand them.[...] Derivation Code Sequence (0008,9215) describe the way in which the image was derived [...]
Thoughts very welcome! Thank you!