Материал: part05

compresseddatastream.ThePixelDatacharacteristicsincludedintheJPEG2000bitstreamshallbeusedtodecodethecompressed​ data stream.​

The requirements when using a Standard Photometric Interpretation (i.e., a Defined Term from PS.3. C.7.6.3.1.2) are specified in​ Table 8.2.4-1. No other Standard Photometric Interpretation values shall be used.​

Table 8.2.4-1. Valid Values of Pixel Data Related Attributes for JPEG 2000 Transfer Syntaxes using​ Standard Photometric Interpretations​

Note​

Theserequirementsarespecifiedintermsofconsistencywithwhatisencapsulated,ratherthanintermsoftheuncompressed​ pixel data from which the compressed data stream may have been derived.​

Whendecompressing,shouldthecharacteristicsexplicitlyspecifiedinthecompresseddatastreambeinconsistentwiththosespecified​ in the DICOM Data Elements, those explicitly specified in the compressed data stream should be used to control the decompression.​ The DICOM data elements, if inconsistent, can be regarded as suggestions as to the form in which an uncompressed Data Set might​ be encoded, subject to the general and IOD-specific rules for uncompressed Photometric Interpretation and Planar Configuration,​ which may require that decompressed data be converted to one of the permitted forms.​

The JPEG 2000 bit stream specifies whether or not a reversible or irreversible multi-component (color) transformation [ISO 15444-1​ Annex G], if any, has been applied. If no multi-component transformation has been applied, then the components shall correspond​ tothosespecifiedbytheDICOMAttributePhotometricInterpretation(0028,0004).IftheJPEG2000Part1reversiblemulti-component​ transformation has been applied then the DICOM Attribute Photometric Interpretation (0028,0004) shall be YBR_RCT. If the JPEG​ 2000 Part 1 irreversible multi-component transformation has been applied then the DICOM Attribute Photometric Interpretation​ (0028,0004) shall be YBR_ICT.​

Note​

1.​For example, single component may be present, and the Photometric Interpretation (0028,0004) may be MONO-​ CHROME2.​

2.​The application of a JPEG 2000 Part 1 reversible multi-component transformation is signaled in the JPEG 2000 bit​ stream by a value of 1 rather than 0 in the SGcod Multiple component transformation type of the COD marker segment​ [ISO 15444-1 Table A.17]. No other value of Photometric Interpretation than YBR_RCT or YBR_ICT is permitted when​ SGcod Multiple component transformation type is 1.​

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3.​Though it would be unusual, would not take advantage of correlation between the red, green and blue components, and​ would not achieve effective compression, a Photometric Interpretation of RGB could be specified as long as no multi-​ component transformation [ISO 15444-1 Annex G] was specified by the JPEG 2000 bit stream. For some applications​ the use of RGB is permitted, e.g., Whole Slide Microscopy Images, to allow conversion to DICOM from proprietary​ formats without loss due to color space transformation. Alternative methods of decorrelation of the color components​ than those specified in [ISO 15444-1 Annex G] are permitted as defined in PS3.3, such as a Photometric Interpretation​ of YBR_FULL; this may be useful when converting existing YBR_FULL Pixel Data (e.g., in a different Transfer Syntax)​ without further loss.​

Ineithercase(PhotometricInterpretationofRGBorYBR_FULL),thevalueofSGcodMultiplecomponenttransformation​ type would be 0.​

PS3.3 may constrain the values of Photometric Interpretation for specific IODs.​

4.​Despite the application of a multi-component color transformation and its reflection in the Photometric Interpretation at-​ tribute, the "color space" remains undefined. There is currently no means of conveying "standard color spaces" either​ by fixed values (such as sRGB) or by ICC profiles. Note in particular that the JP2 file header is not sent in the JPEG​ 2000 bit stream that is encapsulated in DICOM.​

5.​If JPEG 2000 Compressed Pixel Data is decompressed and re-encoded in Native (uncompressed) form, then the Data​ Elements that are related to the Pixel Data encoding are updated accordingly. If color components are converted from​ YBR_ICT or YBR_RCT to RGB during decompression and Native re-encoding, the Photometric Interpretation will be​ changed to RGB in the Data Set with the Native encoding.​

6.​The upper limit of 40 on Bits Allocated (0028,0100) and 38 on Bits Stored (0028,0101) reflects the maximum JPEG​ 2000 sample precision of 38 and the DICOM requirement to describe Bits Allocated (0028,0100) as multiples of bytes​ (octets).​

The JPEG 2000 bit stream is capable of encoding both signed and unsigned pixel values, hence the value of Pixel Representation​ (0028,0103) may be either 0 or 1 for monochrome Photometric Interpretations depending on what has been encoded (as specified​ in the SIZ marker segment in the precision and sign of component parameter).​

The value of Planar Configuration (0028,0006) is irrelevant since the manner of encoding components is specified in the JPEG 2000​ standard, hence it shall be set to 0.​

8.2.5 MPEG2 Main Profile / Main Level Video Compression​

DICOMprovidesamechanismforsupportingtheuseofMPEG2MainProfile/MainLevelVideoCompressionthroughtheEncapsulated​ Format (see PS3.3). Annex A defines a Transfer Syntax that references the MPEG2 Main Profile / Main Level Standard.​

Note​

MPEG2 compression is inherently lossy. The context where the usage of lossy compression of medical images is clinically​ acceptableisbeyondthescopeoftheDICOMStandard.Thepoliciesassociatedwiththeselectionofappropriatecompression​ parameters (e.g., compression ratio) for MPEG2 Main Profile / Main Level are also beyond the scope of this Standard.​

The use of the DICOM Encapsulated Format to support MPEG2 Main Profile / Main Level compressed pixel data requires that the​ Data Elements that are related to the Pixel Data encoding (e.g., Photometric Interpretation, Samples per Pixel, Planar Configuration,​ Bits Allocated, Bits Stored, High Bit, Pixel Representation, Rows, Columns, etc.) shall contain values that are consistent with the​ characteristics of the compressed data stream, with some specific exceptions noted here. The Pixel Data characteristics included in​ the MPEG2 Main Profile / Main Level bit stream shall be used to decode the compressed data stream.​

Note​

Theserequirementsarespecifiedintermsofconsistencywithwhatisencapsulated,ratherthanintermsoftheuncompressed​ pixel data from which the compressed data stream may have been derived.​

Whendecompressing,shouldthecharacteristicsexplicitlyspecifiedinthecompresseddatastreambeinconsistentwiththosespecified​ in the DICOM Data Elements, those explicitly specified in the compressed data stream should be used to control the decompression.​ The DICOM data elements, if inconsistent, can be regarded as suggestions as to the form in which an uncompressed Data Set might​ be encoded, subject to the general and IOD-specific rules for uncompressed Photometric Interpretation and Planar Configuration,​ which may require that decompressed data be converted to one of the permitted forms.​

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The MPEG2 Main Profile / Main Level bit stream specifies whether or not a reversible or irreversible multi-component (color) trans-​ formation, if any, has been applied. If no multi-component transformation has been applied, then the components shall correspond​ to those specified by the DICOM Attribute Photometric Interpretation (0028,0004). MPEG2 Main Profile / Main Level applies an irre-​ versible multi-component transformation, so DICOM Attribute Photometric Interpretation (0028,0004) shall be YBR_PARTIAL_420 in​ the case of multi-component data, and MONOCHROME2 in the case of single component data (even though the MPEG2 bit stream​ itself is always encoded as three components, one luminance and two chrominance).​

Note​

1.​If MPEG2 Compressed Pixel Data is decompressed and re-encoded in Native (uncompressed) form, then the Data​ Elements that are related to the Pixel Data encoding are updated accordingly. If color components are converted from​ YBR_PARTIAL_420 to RGB during decompression and Native re-encoding, the Photometric Interpretation will be​ changed to RGB in the Data Set with the Native encoding.​

2.​MPEG2 proposes some video formats. Each of the standards specified is used in a different market, including: ITU-R​ BT.470-2 System M for SD NTSC and ITU-R BT.470-2 System B/G for SD PAL/SECAM. A PAL based system should​ therefore be based on ITU-BT.470 System B for each of Color Primaries, Transfer Characteristic (gamma) and matrix​ coefficients and should take a value of 5 as defined in [ISO/IEC 13818-2].​

The value of Planar Configuration (0028,0006) is irrelevant since the manner of encoding components is specified in the MPEG2​ Main Profile / Main Level standard, hence it shall be set to 0.​

In summary:​

•​Samples per Pixel (0028,0002) shall be 3​

•​Photometric Interpretation (0028,0004) shall be YBR_PARTIAL_420​

•​Bits Allocated (0028,0100) shall be 8​

•​Bits Stored (0028,0101) shall be 8​

•​High Bit (0028,0102) shall be 7​

•​Pixel Representation (0028,0103) shall be 0​

•​Planar Configuration (0028,0006) shall be 0​

•​Rows(0028,0010),Columns(0028,0011),CineRate(0018,0040)andFrameTime(0018,1063)orFrameTimeVector(0018,1065)​ shall be consistent with the limitations of Main Profile / Main Level, as specified in Table 8-1.​

Table 8-1. MPEG2 Main Profile / Main Level Image Transfer Syntax Rows and Columns Attributes​

Note​

1.​Although different combinations of values for Rows and Columns values are possible while respecting the maximum​ values listed above, it is recommended that the typical 4:3 ratio of image width to height be maintained in order to avoid​ image deformation by MPEG2 decoders. A common way to maintain the ratio of width to height is to pad the image with​ black areas on either side.​

2.​"Half" definition of pictures (240x352 and 288x352 for NTSC and PAL, respectively) are always supported by decoders.​

3.​Main Profile / Main Level allows for various different display and pixel aspect ratios, including the use of square pixels,​ and the use of non-square pixels with display aspect ratios of 4:3 and 16:9. DICOM specifies no additional restrictions​ beyond what is provided for in Main Profile / Main Level. All permutations allowed by Main Profile / Main Level are valid​ and are require to be supported by all DICOM decoders.​

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4.​The actual frame rate for NTSC MPEG2 is approximately 29.97 frames/sec.​

5.​The nominal Frame Time is supplied for the purpose of inclusion on the DICOM Cine Module Attributes, and should be​ calculated from the actual frame rate.​

One fragment shall contain the whole MPEG2 stream.​

Note​

1.​If a video stream exceeds the maximum length of one fragment, it may be sent as multiple SOP Instances, but each​ SOP Instance will contain an independent and playable bit stream, and not depend on the encoded bit stream in other​ (previous) instances. The manner in which such separate instances are related is not specified in the Standard, but​ mechanisms such as grouping into the same Series, and references to earlier instances using Referenced Image Se-​ quence may be used.​

2.​This constraint limits the length of the compressed bit stream to no longer than 232-2 bytes.​

The Basic Offset Table shall be empty (present but zero length).​

Note​

The Basic Offset Table is not used because MPEG2 contains its own mechanism for describing navigation of frames. To​ enable decoding of only a part of the sequence, MPEG2 manages a header in any group of pictures (GOP) containing a​ time_code - a 25-bit integer containing the following: drop_frame_flag, time_code_hours, time_code_minutes, marker_bit,​ time_code_seconds and time_code_pictures.​

The container format for the video bit stream is not constrained. For example, it may MPEG-2 Transport Stream (MPEG-TS), MPEG-​ 2 Program Stream (MPEG-PS), MPEG-2 Elementary Stream (MPEG-ES), MPEG-2 Packetized Elementary Stream (MPEG-PES)​ (see [ISO/IEC 13818-1]) or MPEG-4 (MP4) container (see [ISO/IEC 14496-12] and [ISO/IEC 14496-14]).​

Any audio components present within the MPEG bit stream shall comply with the following restrictions:​

•​CBR MPEG-1 LAYER III (MP3) Audio Standard​

•​up to 24 bits​

•​32 kHz, 44.1 kHz or 48 kHz for the main channel (the complementary channels can be sampled at the half rate, as defined in the​ Standard)​

•​one main mono or stereo channel, and optionally one or more complementary channel(s)​

Note​

1.​MPEG-1 Layer III is standardized in Part 3 of the MPEG-1 standard (see [ISO/IEC 11172-3]).​

2.​Although MPEG describes each channel as including up to 5 signals (e.g., for surround effects), it is recommended to​ limit each of the two channels to 2 signals each one (stereo).​

8.2.6 MPEG2 Main Profile / High Level Video Compression​

MPEG2 Main Profile / High Level corresponds to what is commonly known as HDTV ('High Definition Television'). DICOM provides​ a mechanism for supporting the use of MPEG2 Main Profile / High Level Video Compression through the Encapsulated Format (see​ PS3.3). Annex A defines a Transfer Syntax that references the MPEG2 Main Profile / High Level Standard.​

Note​

MPEG2 compression is inherently lossy. The context where the usage of lossy compression of medical images is clinically​ acceptableisbeyondthescopeoftheDICOMStandard.Thepoliciesassociatedwiththeselectionofappropriatecompression​ parameters (e.g., compression ratio) for MPEG2 Main Profile / High Level are also beyond the scope of this Standard.​

The use of the DICOM Encapsulated Format to support MPEG2 Main Profile / High Level compressed pixel data requires that the​ Data Elements that are related to the Pixel Data encoding (e.g., Photometric Interpretation, Samples per Pixel, Planar Configuration,​ Bits Allocated, Bits Stored, High Bit, Pixel Representation, Rows, Columns, etc.) shall contain values that are consistent with the​

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characteristics of the compressed data stream, with some specific exceptions noted here. The Pixel Data characteristics included in​ the MPEG2 Main Profile / High Level bit stream shall be used to decode the compressed data stream.​

Note​

Theserequirementsarespecifiedintermsofconsistencywithwhatisencapsulated,ratherthanintermsoftheuncompressed​ pixel data from which the compressed data stream may have been derived.​

Whendecompressing,shouldthecharacteristicsexplicitlyspecifiedinthecompresseddatastreambeinconsistentwiththosespecified​ in the DICOM Data Elements, those explicitly specified in the compressed data stream should be used to control the decompression.​ The DICOM data elements, if inconsistent, can be regarded as suggestions as to the form in which an uncompressed Data Set might​ be encoded, subject to the general and IOD-specific rules for uncompressed Photometric Interpretation and Planar Configuration,​ which may require that decompressed data be converted to one of the permitted forms.​

Note​

IfMPEG2CompressedPixelDataisdecompressedandre-encodedinNative(uncompressed)form,thentheDataElements​ that are related to the Pixel Data encoding are updated accordingly. If color components are converted from YBR_PAR-​ TIAL_420 to RGB during decompression and Native re-encoding, the Photometric Interpretation will be changed to RGB in​ the Data Set with the Native encoding.​

The requirements are:​

•​Planar Configuration (0028,0006) shall be 0​

Note​

The value of Planar Configuration (0028,0006) is irrelevant since the manner of encoding components is specified in the​ MPEG2 standard, hence it is set to 0.​

•​Samples per Pixel (0028,0002) shall be 3​

•​Photometric Interpretation (0028,0004) shall be YBR_PARTIAL_420 or MONOCHROME2​

•​Bits Allocated (0028,0100) shall be 8​

•​Bits Stored (0028,0101) shall be 8​

•​High Bit (0028,0102) shall be 7​

•​Pixel Representation (0028,0103) shall be 0​

•​Rows (0028,0010) shall be either 720 or 1080​

•​Columns (0028,0011) shall be 1280 if Rows is 720, or shall be 1920 if Rows is 1080.​

•​The value of MPEG2 aspect_ratio_information shall be 0011 in the encapsulated MPEG2 data stream corresponding to a 'Display​ Aspect Ratio' (DAR) of 16:9.​

•​The DICOM attribute Pixel Aspect Ratio (0028,0034) shall be absent. This corresponds to a 'Sampling Aspect Ratio' (SAR) of 1:1.​

•​Cine Rate (0018,0040) and Frame Time (0018,1063) or Frame Time Vector (0018,1065) shall be consistent with the limitations of​ Main Profile / High Level, as specified in Table 8-2.​

Table 8-2. MPEG2 Main Profile / High Level Image Transfer Syntax Frame Rate Attributes​

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