Hello Offis team,
I recently noticed that VOI LUT sequences (0028,3010) will be deleted from the dicom header if compressed with dcmcjpeg even if used with default (lossless sv1) option.
What is the reason for this behaviour? It is kind of problematic that there will be no information left about default window values when the LUT sequence is erased, because usually there will be no default window width/center values in the header that could be applied alternatively.
regards,
Andreas
VOI LUT Sequence missing after compression with dcmcjpeg
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AndreasKnopke
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Marco Eichelberg
- OFFIS DICOM Team
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AndreasKnopke
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dcmcjpeg version 3.5.3 for Windows.
I could read in the manual files that option --rescale-identity is set by default.
# This options prevents the creation of a modality transformation
# other than an identity transformation (which is required for
# many DICOM IODs). Window center/width settings encoded
# in the image are adapted, VOI LUTs are removed.
is this the reason for the VOI LUT deletion and if so why in case of CR?
regards,
Andreas
I could read in the manual files that option --rescale-identity is set by default.
# This options prevents the creation of a modality transformation
# other than an identity transformation (which is required for
# many DICOM IODs). Window center/width settings encoded
# in the image are adapted, VOI LUTs are removed.
is this the reason for the VOI LUT deletion and if so why in case of CR?
regards,
Andreas
-
Marco Eichelberg
- OFFIS DICOM Team
- Posts: 1446
- Joined: Tue, 2004-11-02, 17:22
- Location: Oldenburg, Germany
- Contact:
dcmcjpeg 3.5.4 will retain the VOI LUT when lossless compression is used (in general I would recommend dcmcjpeg 3.5.4 over 3.5.3 because this version of the tool contains a number of important improvements).
For lossy compression, there is usually no choice. The JPEG lossy algorithm only offers 8 bits/sample or 12 bits/sample, so in most cases the pixel data has to be scaled appropriately before being compressed. Of course the VOI LUT does not work with scaled pixel data. With the command line option --rescale-map, the Rescale Slope/Intercept is used to scale back the decompressed pixel data to the original range, and in that case VOI LUTs will still work and are retained in the image. This does not work with all SOP classes, though (XA uses the Modality LUT with different semantics and in MR many viewers will simply ignore Rescale Slope/Intercept), so this option is not the default. Default is to modify Window Center/Width settings to fit with the new pixel data range, and to remove VOI LUTs.
For lossy compression, there is usually no choice. The JPEG lossy algorithm only offers 8 bits/sample or 12 bits/sample, so in most cases the pixel data has to be scaled appropriately before being compressed. Of course the VOI LUT does not work with scaled pixel data. With the command line option --rescale-map, the Rescale Slope/Intercept is used to scale back the decompressed pixel data to the original range, and in that case VOI LUTs will still work and are retained in the image. This does not work with all SOP classes, though (XA uses the Modality LUT with different semantics and in MR many viewers will simply ignore Rescale Slope/Intercept), so this option is not the default. Default is to modify Window Center/Width settings to fit with the new pixel data range, and to remove VOI LUTs.
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AndreasKnopke
- Posts: 49
- Joined: Wed, 2005-02-16, 16:27
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