image aspect ratio tag - DICOM

This is a discussion on image aspect ratio tag - DICOM ; Hi everyone, We are making a DICOM version of image format for a new optical imaging modality and this modality has a parameter which is difficult to find an appropriate tag among existing ones. The vertical scale should be normalized ...

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Thread: image aspect ratio tag

  1. image aspect ratio tag

    Hi everyone,

    We are making a DICOM version of image format for a new optical imaging
    modality and this modality has a parameter which is difficult to find an
    appropriate tag among existing ones. The vertical scale should be
    normalized to a media refraction index, which is a float number in the
    range of 1 to 2. The only "relevant" tag I was able to find is 0028.0034
    (pixel aspect ratio), but it is integer and evidently cannot serve for
    the purpose of vertical scale normalization and appropriate adjustment
    of the image aspect ratio.
    Any ideas how to handle this issue are appreciated. I understand that
    new tags can be suggested to be introduced, but it will take a while
    before it will be recognized by existing DICOM viewers (unless they are
    open system with ability to write and supply plugins, including
    recognition of new, non-standard tags). Therefore, if nothing else,
    information about DICOM viewers/editors with such a possibility will be
    appreciated as well.
    Advices can be posted in the newsgroup or directly E-mailed to
    felixfel00@yahoo.com

    Thanks, Felix

  2. Re: image aspect ratio tag

    Hi Felix

    In the DICOM Data Dictionary (Part 6) you'll notice Pixel aspect ratio
    has a VM=2. This means there are always two values specified for the
    attribute. These are interpreted, not as an integer but as a ratio of
    two integers to provide either vertical or horizontal scaling of the
    pixel values when they are rendered.

    --Eric Goodall


  3. Re: image aspect ratio tag

    Actually I should clarify the above, from the dicom standard the pixel
    aspect ratio is defined as:
    "The pixel aspect ratio is the ratio of the vertical size and
    horizontal size of the pixels in the image specified by a pair of
    integer values where the first value is the vertical pixel size, and
    the second value is the horizontal pixel size."
    A graphic gives and example and further explanatory text:
    "Pixel Aspect Ratio = *Vertical Size \ Horizontal Size = 0.30 mm
    \0.25 mm. Thus the Pixel Aspect Ratio could be represented as the
    multivalued integer string "6\5", "60\50", or any equivalent integer
    ratio."
    In practice found manufactures ignore the VR=IS of the aspect ratio
    attribute which indicates the actual pixel dimensions should be
    converted to some ratio of whole numbers. Instead they simply plug in
    the actual pixel dimensions. So, in the example given in the standard,
    these manufactures would provide values 0.30\0.25 in the pixel aspect
    ratio attribute. This is a violation of the standard seems to be one
    that the majority of implementors have learned to live with.


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