Presentation Information for DICOM Printing - DICOM

This is a discussion on Presentation Information for DICOM Printing - DICOM ; As per my current understanding of specifying presentation information to SCP, the SCU can either transmit pre-formatted image in p-value or send pre-formatted bitmap with a LUT so that print server can convert bitmap to p-values. I have the following ...

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Thread: Presentation Information for DICOM Printing

  1. Presentation Information for DICOM Printing


    As per my current understanding of specifying presentation information
    to SCP, the SCU can either transmit pre-formatted image in p-value or
    send pre-formatted bitmap with a LUT so that print server can convert
    bitmap to p-values.

    I have the following queries:

    1. Are the LUTs standardised and if so where can we get information
    about
    which LUT to use. Does the type of LUT to be used change with the
    image
    type?
    2. If image grayscale or color values (RGB) values are mapped to LUT
    values, how is the p-value derived from this mapping?
    3. Finally, how does the SCU convert p-values to Optical density
    values for
    printing?
    4. If Presentation LUT is not supported, as it is an optional SOP
    class, how
    will the p-values be sent by the SCU?

  2. Re: Presentation Information for DICOM Printing

    > As per my current understanding of specifying presentation information
    > to SCP, the SCU can either transmit pre-formatted image in p-value or
    > send pre-formatted bitmap with a LUT so that print server can convert
    > bitmap to p-values.
    >
    > 1. Are the LUTs standardised and if so where can we get information
    > about which LUT to use. Does the type of LUT to be used change with the
    > image type?


    The syntax of the LUT is standardised (i.e. possible numbers of entries,
    bits per entry etc. are defined in the N-CREATE-RQ primitive for the
    Presentation LUT SOP Class). The LUT content is not standardized - an
    SCU may send whatever may seem appropriate.

    > 2. If image grayscale or color values (RGB) values are mapped to LUT
    > values, how is the p-value derived from this mapping?


    Presentation LUTs can only be used with monochrome images (Basic Grayscale
    Print Management). The result of mapping the Basic Grayscale Image Box
    pre-formatted pixel values through the Presentation LUT produces p-values
    by definition - i.e. whatever the result of the LUT is, the printer will
    interpret that as p-values.

    > 3. Finally, how does the SCU convert p-values to Optical density
    > values for printing?


    That is defined in great detail in part 14 of the DICOM standard.
    The transformation is based on the DICOM Grayscale Standard Display Function.

    > 4. If Presentation LUT is not supported, as it is an optional SOP
    > class, how will the p-values be sent by the SCU?


    If presentation LUT is not supported, then the precise interpretation
    of the Image Box pixel values by the printer is simply undefined.
    The printer may apply a LUT defined in the printer configuration,
    or may select a LUT based on the Configuration Information attribute
    in the Basic Film Box (many printers do support that). The printer
    may interpret the raw pixel values as p-values or a linear optical density.
    Unless the SCU knows exactly which printer it is talking to, and how this
    printer is configured, the result is somewhat unpredictable, which is
    exactly the reason why the Presentation LUT SOP class was defined as
    an add-on to solve that problem.

    Regards,
    Marco Eichelberg
    OFFIS

  3. Re: Presentation Information for DICOM Printing

    On Jan 24, 2:02*pm, Marco Eichelberg
    wrote:
    > > As per my current understanding of specifying presentation information
    > > to SCP, the SCU can either transmit pre-formatted image in p-value or
    > > send pre-formatted bitmap with a LUT so that print server can convert
    > > bitmap to p-values.

    >
    > > 1. Are the LUTs standardised and if so where can we get information
    > > about which LUT to use. Does the type of LUT to be used change with the
    > > image type?

    >
    > The syntax of the LUT is standardised (i.e. possible numbers of entries,
    > bits per entry etc. are defined in the N-CREATE-RQ primitive for the
    > Presentation LUT SOP Class). The LUT content is not standardized - an
    > SCU may send whatever may seem appropriate.
    >
    > > 2. If image grayscale or color values (RGB) values are mapped to LUT
    > > * * values, how is the p-value derived from this mapping?

    >
    > Presentation LUTs can only be used with monochrome images (Basic Grayscale
    > Print Management). The result of mapping the Basic Grayscale Image Box
    > pre-formatted pixel values through the Presentation LUT produces p-values
    > by definition - i.e. whatever the result of the LUT is, the printer will
    > interpret that as p-values.
    >
    > > 3. Finally, how does the SCU convert p-values to Optical density
    > > values for printing?

    >
    > That is defined in great detail in part 14 of the DICOM standard.
    > The transformation is based on the DICOM Grayscale Standard Display Function.
    >
    > > 4. If Presentation LUT is not supported, as it is an optional SOP
    > > class, how will the p-values be sent by the SCU?

    >
    > If presentation LUT is not supported, then the precise interpretation
    > of the Image Box pixel values by the printer is simply undefined.
    > The printer may apply a LUT defined in the printer configuration,
    > or may select a LUT based on the Configuration Information attribute
    > in the Basic Film Box (many printers do support that). The printer
    > may interpret the raw pixel values as p-values or a linear optical density..
    > Unless the SCU knows exactly which printer it is talking to, and how this
    > printer is configured, the result is somewhat unpredictable, which is
    > exactly the reason why the Presentation LUT SOP class was defined as
    > an add-on to solve that problem.
    >
    > Regards,
    > Marco Eichelberg
    > OFFIS




    Hi Marco,

    Thanks a lot for the inputs. I have a few questions based on your
    response.


    You have mentioned that the LUT content/ data generated by SCU is not
    standardized. Does this mean that there is no standard logic to
    generate p-values based on image gray level intensity received from
    application? Can you please describe any one of the methods used to
    generate p-values based on a 8 bit grayscale image? Even if you could
    point me to some good references it will be of great help.

    How will p-values be generated for color image or how will color
    images be standardised for printing if presentation LUT is only
    supported for gray scale images?

    Is there an option that SCU does not send p-values? SCU retains the
    image as a bitmap image and sends PLUT values separately for the SCP
    to do the conversion to p-values.

  4. Re: Presentation Information for DICOM Printing

    > You have mentioned that the LUT content/ data generated by SCU is not
    > standardized. Does this mean that there is no standard logic to
    > generate p-values based on image gray level intensity received from
    > application? Can you please describe any one of the methods used to
    > generate p-values based on a 8 bit grayscale image? Even if you could
    > point me to some good references it will be of great help.


    The point is that the precise meaning of "gray level intensity" is not
    standardized. If you have gray values from 0 to 255 (to simplify discussion),
    and 0 is black and 255 is white, what is 128? 50% of the physical luminance?
    50% of the perceived brightness according to the characteristics of the human eye?
    50% of the density of the film produced from the gray values in the printer?
    Actually vendors have interpreted this differently, which caused hardcopies
    to look "funny" if the printer interpreted gray values linear to density
    and the client sent gray values linear to human perception.

    When negotiating the Presentation LUT SOP Class, the SCU simply guarantees
    that the gray values it sends are always linear to human perception (which is
    the definition of p-values), and the printer guarantees to interpret the
    gray values as such.

    In most cases the "Presentation LUT" as such is never used. The client
    will in most cases I have ever seen install a "Presentation LUT Shape"
    of "IDENTITY" meaning that the pixel values are already p-values without
    further modification.

    The only reason when sending a LUT really makes sense is when the SCU
    can only send 8 bits/pixel bitmaps (as is the case for some older modalities)
    and one can send a LUT that maps original pixel data to p-values and
    uses 12 or 16 bit LUT entries. In that case, applying the LUT on SCU side
    would reduce the number of shades of gray (for any non-linar mapping function),
    whereas having the printer (which might be 12-bit capable) doing the job
    might not. But that's about the only case, in all other cases it is preferrable
    to have the SCU send pre-formatted p-values.

    > How will p-values be generated for color image or how will color
    > images be standardised for printing if presentation LUT is only
    > supported for gray scale images?


    DICOM Print Management, to my knowledge, does not yet support color calibration
    (but maybe that information is already outdated - if some reader has newer
    information, please correct me).
    For the softcopy "world", a so-called "Color Softcopy Presentation State" object
    has been defined that makes use of ICC profiles to describe the color space of
    color image data transmitted.

    > Is there an option that SCU does not send p-values? SCU retains the
    > image as a bitmap image and sends PLUT values separately for the SCP
    > to do the conversion to p-values.


    See above.

    Regards,
    Marco Eichelberg

  5. Re: Presentation Information for DICOM Printing

    Marco Eichelberg wrote:

    > DICOM Print Management, to my knowledge, does not yet support color
    > calibration
    > (but maybe that information is already outdated - if some reader has newer
    > information, please correct me).


    ftp://medical.nema.org/medical/dicom/final/cp705_ft.pdf

    David

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