Материал: part03

else if (x > c + w/2), then y = ymax​

else y = ((x - c) / w + 0.5) * (ymax- ymin) + ymin​

Window Width (0028,1051) shall always be greater than 0.​

Note​

1.​For example, given stored unsigned pixel values from 0 to 65535, a Rescale Intercept of 0 and a Rescale Slope of​ 1.0/65535, a Window Width of 1.0 and a Window Center of 0.5 would specify the entire range of values (the identity​ transformation for those rescale values).​

2.​Window Width (0028,1051) is required to be greater than zero to prevent division by zero (quite apart from being​ meaningless).​

C.11.3 LUT Identification Module​

This section has been retired. See PS3.3-2006.​

C.11.4 Presentation LUT Module​

Table C.11-4 specifies the Attributes that describe the Presentation LUT.​

Table C.11-4. Presentation LUT Module Attributes​

IDENTITY​ input to the Presentation LUT is in P-Values, no further​ translation is necessary​

LIN OD​ input to Presentation LUT is in linear optical density over the​ rangeofMinDensity(2010,0120)andMaxDensity(2010,1030)​

Note​

LIN OD is only defined for hardcopy devices and is not applicable​ to softcopy devices.​

C.11.4.1 LUT Descriptor​

The three values of LUT Descriptor (0028,3002) describe the format of the data in LUT Data (0028,3006).​

The first value is the number of entries in the lookup table. When the number of table entries is equal to 216 then this value shall be​ 0. The number of entries shall be equal to the number of possible values in the input. (For 8 bit input will be 256 entries, for 12 bit input​ it will be 4096 entries)​

The second value is the first input value mapped, and shall always be 0. The Value Representation of the second value is always​ US. This input value is mapped to the first entry in the LUT. Subsequent input values are mapped to the subsequent entries in the​

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LUT Data up to an input value equal to number of entries + first value mapped - 1 that is mapped to the last entry in the LUT Data.​ There are no input values greater than number of entries - 1.​

The third value specifies the number of bits for each entry in the LUT Data. It shall be between 10 and 16 inclusive. The LUT Data​ shall be stored in a format equivalent to 16 bits allocated where the high bit is equal to bits stored - 1, where bits stored is the third​ value.​

Note​

Since LUT Descriptor (0028,3002) is multi-valued, in an Explicit VR Transfer Syntax, only one value representation (US or​ SS) may be specified. Since all three values are always by definition interpreted as unsigned, the explicit VR actually used​ will always be US.​

LUT Data (0028,3006) contains the LUT entry values, which are P-Values.​

The output range is from 0 to 2n-1 where n is the third value of LUT Descriptor. This range is always unsigned.​

This range specifies the output range of the P-Values.​

C.11.5 Image Histogram Module​

Table C.11.5-1. Image Histogram Module Attributes​

C.11.5.1 Image Histogram Attribute Descriptions​

The Image Histogram is a Sequence with multiple Items representing a sequential count of binned stored image pixel values in as-​ cending order.​

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Note​

One reason to include a histogram with an image is as an aid to image processing applications. For applications that use​ them,computationsofhistogramsforverylargeimagescanbeasignificantburdenoncomputerresourcesandcanseriously​ degrade the response time to the user.​

The Image Histogram has multiple Items to support multiple histograms per image. One or more regions of interest or value ranges​ may be separately computed. A description of the region(s) of interest and value range may be included in Histogram Explanation​ (0060,3010). The Image Histogram may be related to parts or all of a specific image.​

The Attributes describing the parameters of the histogram are in image pixel value space, as stored in Pixel Data (7FE0,0010), before​ the application of any transformation such as Rescale Slope and Intercept or Modality LUT.​

The range of stored image pixel value instances is described by the Histogram First Bin Value (0060,3004) and Histogram Last Bin​ Value (0060,3006). All values outside of this range shall be ignored. The number of histogram bins shall be large enough to contain​ allofthepixelsintherangefromthesmallesttothelargeststoredimagepixelvalueinthatregionoftheimagefromwhichthehistogram​ has been derived (which may or may not be the whole image).​

The Histogram Bin Width (0060,3008) describes how many consecutive stored image pixel values are counted as one. All bins shall​ be of equal width.​

Note​

For example, a Histogram Bin Width (0060,3008) of 8 means that counts of pixel values in ascending groups of 8 are added​ together. If Histogram First Bin Value (0060,3004) were 0, then the first bin would contain the count of pixel values in the​ range of 0-7, the second bin the count of pixel values in the range of 8-15, etc. If Histogram Number of Bins (0060,3002)​ were 32, then the last bin would contain the count of pixel values in the range of 248-255 and Histogram Last Bin Value​ (0060,3006) would be 255 (not 248).​

This example is illustrated in Figure C.11.5-1, in which the vertical axis represents the count within each bin and the horizontal axis​ represents each bin in ascending order.​

Histogram Number of Bins (0060,3002) defines 32 bins

Figure C.11.5-1. Image Histogram Example​

C.11.6 Softcopy Presentation LUT Module​

Table C.11.6-1 specifies the Attributes that describe the Softcopy Presentation LUT.​

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Page 1304​ DICOM PS3.3 2020a - Information Object Definitions​

Table C.11.6-1. Softcopy Presentation LUT Module Attributes​

Enumerated Values:​

IDENTITY​ no further translation necessary, input values are​

P-Values​

INVERSE​ output values after inversion are P-Values​

See Section C.11.6.1.2.​

Note​

This Module differs from the Presentation LUT Module used in the hardcopy (print) related SOP Classes in that Optical​ Density is not supported for Presentation LUT Shape (since Optical Density has no meaning for softcopy display devices).​

C.11.6.1 Softcopy Presentation LUT Attributes​

When the Presentation LUT is specified as a Presentation LUT Sequence, then the input range of values is specified by the LUT​ Descriptor as the first value mapped and the number of entries (values mapped). However, there is an implicit linear scaling of the​ output range of the preceding transformation (such as the VOI LUT transformation) so that it is always mapped to the specified input​ range of the Presentation LUT.​

When the Presentation LUT is specified as Presentation LUT Shape, then the input range is implicitly specified to be the output range​ of the preceding transformation (VOI LUT, or if the VOI LUT is identity or absent, the Modality LUT, or if the Modality LUT and VOI​ LUT are identity or absent, the stored pixel values). In this case, the full range of the output of the preceding transformation will be​ mapped to the full input range of the display device that receives the output of the Presentation LUT.​

Note​

The output of the preceding transformation may be signed. This does not mean that signed P-Values actually need to be​ generated, only that the output of the preceding transformation is to be interpreted by the display device as perceptually​ linear over the range from the minimum to the maximum values output by the preceding step, and that the minimum value​ be mapped to the lowest JND Index (and hence luminance) that the display can generate, and the maximum value be​ mapped to the highest JND Index (and hence luminance) that the display can generate.​

In other words, in both cases, the Presentation LUT Module is always implicitly specified to apply over the full range of output of the​ preceding transformation, and it never selects a subset or superset of the that range (unlike the VOI LUT).​

The output bit precision of the VOI LUT Sequence is not required to match the input range of the Presentation LUT Sequence.​

Note​

1.​For example, if the VOI LUT is specified as a Window Center of 0 and a Window Width of 100, then the range from -50​ to +49 is selected to be mapped to the full range of the display or print device (the full range of P-Values) if the​ Presentation LUT Shape is specified as IDENTITY or INVERSE. This example demonstrates the conventional under-​

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standing of the meaning of Window Center and Width to select "values of interest" that are to be displayed across the​ full range of the output device, without explicitly having to map each choice to P-Values.​

2.​For example, if the VOI LUT is specified as a Window Center of 0 and a Window Width of 100, and the Presentation​ LUT Sequence is present with a LUT Descriptor first value of 256 and second value of 0, then the range from -50 to​ +49isimplicitlylinearlyscaledfrom0to255beforeselectingvaluesfromtheLUTDatainthePresentationLUTSequence.​ This example demonstrates that it is not necessary to send a different Presentation LUT for different Window Center​ and Width values.​

3.​For example, if the VOI LUT is specified as VOI LUT Sequence with a LUT Descriptor with a 3rd Value of 16, then the​ range from 0 to 216-1 is selected to be mapped to the full range of the display or print device (the full range of P-Values)​ if the Presentation LUT Shape is specified as IDENTITY or INVERSE. This example demonstrates that a VOI LUT may​ be specified with the desired precision, without having to explicitly send a Presentation LUT to rescale that precision to​ whatever range of P-Values is preferred by the display application.​

4.​For example, if the VOI LUT is specified as VOI LUT Sequence with a LUT Descriptor with a 3rd Value of 16, and the​ Presentation LUT Sequence is present with a LUT Descriptor first value of 4096 and second value of 0, then the range​ from 0 to 216-1 is implicitly linearly scaled to the range 0 to 4095 before selecting values from the LUT Data in the​ PresentationLUTSequence.Thisexampledemonstratesthecasewhere,tosavespace,thePresentationLUTisencoded​ in a compact form that a display application may choose to interpolate more precisely, yet the VOI LUT output may be​ encoded with 16 bit precision.​

C.11.6.1.1 LUT Descriptor​

The three values of LUT Descriptor (0028,3002) describe the format of the LUT Data in the corresponding LUT Data (0028,3006)​ Attribute.​

The first value is the number of entries in the lookup table. When the number of table entries is equal to 216 then this value shall be​ 0.​

The second value is the first implicitly scaled input value mapped, and shall always be 0. The Value Representation of the second​ value is always US. This implicitly scaled input value is mapped to the first entry in the LUT. There are no implicitly scaled input values​ less than the first value mapped. An implicitly scaled input value one greater than the first value mapped is mapped to the second​ entry in the LUT Data. Subsequent implicitly scaled input values are mapped to the subsequent entries in the LUT Data up to an im-​ plicitly scaled input value equal to number of entries + first value mapped - 1 that is mapped to the last entry in the LUT Data. There​ are no implicitly scaled input values greater than number of entries + first value mapped.​

The third value specifies the number of bits for each entry in the LUT Data. The third value of LUT Descriptor (0028,3002) shall be​ between 8 and 16 inclusive. The LUT Data shall be stored in a format equivalent to 8 bits allocated when the number of bits for each​ entry is 8, and 16 bits allocated when the number of bits for each entry is 16, where the high bit is equal to bits stored - 1, and where​ bits stored is the third value.​

Note​

1.​Since LUT Descriptor (0028,3002) is multi-valued, in an Explicit VR Transfer Syntax, only one value representation (US​ or SS) may be specified. Since all three values are always by definition interpreted as unsigned, the explicit VR actually​ used will always be US.​

2.​Some implementations have encoded 8 bit entries with 16 bits allocated, padding the high bits; this can be detected by​ comparing the number of entries specified in the LUT Descriptor with the actual value length of the LUT Data entry. The​ value length in bytes should equal the number of entries if bits allocated is 8, and be twice as long if bits allocated is​ 16.​

The LUT Data contains the LUT entry values, which are P-Values.​

The output range is from 0 to 2n-1 where n is the third value of LUT Descriptor. This range is always unsigned.​

This range specifies the output range of the P-Values.​

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