Материал: part05

Note​

1.​Therequirementsonrowsandcolumnsaretomaximizeinteroperabilitybetweensoftwareenvironmentsandcommonly​ available hardware MPEG2 encoder/decoder implementations. Should the source picture have a lower value, it should​ be re-formatted accordingly by scaling and/or pixel padding prior to MPEG2 encoding.​

2.​The frame rate of the acquiring camera for '30 Hz HD' MPEG2 may be either 30 or 30/1.001 (approximately 29.97)​ frames/sec.Similarly,theframerateinthecaseof60Hzmaybeeither60or60/1.001(approximately59.94)frames/sec​ This may lead to small inconsistencies between the video timebase and real time.​

3.​The Frame Time (0018,1063) may be calculated from the frame rate of the acquiring camera. A frame time of 33.367​ ms corresponds to 29.97 frames per second.​

4.​The value of chroma_format for this profile and level is defined by MPEG as 4:2:0.​

5.​Examples of screen resolutions supported by MPEG2 Main Profile / High Level are shown in Table 8-y. Frame rates of​ 50 Hz and 60 Hz (progressive) at the maximum resolution of 1080 by 1920 are not supported by Main Profile / High​ Level. Interlace at the maximum resolution is supported at a field rate of 50 Hz or 60 Hz, which corresponds to a frame​ rate of 25 Hz or 30 Hz respectively as described in Table 8-y.​

6.​An MPEG2 Main Profile / High Level decoder is able to decode bit streams conforming to lower levels. These include​ the 1080 by 1440 bit streams of MP@H-14, and the Main Level bit streams used in the existing MPEG2 Main Profile /​ Main Level Transfer Syntax in the Visible Light IOD.​

7.​MP@H-14 is not supported by this Transfer Syntax.​

8.​TherestrictionofDARto16:9isrequiredtoensureinteroperabilitybecauseoflimitationsincommonlyavailablehardware​ chip set implementations for MPEG2 Main Profile / High Level.​

Table 8-3. Examples of MPEG2 Main Profile / High Level Screen Resolution​

One fragment shall contain the whole MPEG2 bit stream.​

Note​

1.​If a video stream exceeds the maximum length of one fragment (approximately 4 GB), 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 Refer-​ enced Image Sequence may be used.​

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

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The Basic Offset Table in the Pixel Data (7FE0,0010) 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 MPEG2 Main Profile / High Level bit stream shall comply with the restrictions as for MPEG2​ Main Profile / Main Level as stated in Section 8.2.5.​

8.2.7 MPEG-4 AVC/H.264 High Profile / Level 4.1 Video Compression​

MPEG-4 AVC/H.264 High Profile / Level 4.1 corresponds to what is commonly known as HDTV ('High Definition Television'). DICOM​ provides a mechanism for supporting the use of MPEG-4 AVC/H.264 Image Compression through the Encapsulated Format (see​ PS3.3). Annex A defines a Transfer Syntax that references the MPEG-4 AVC/H.264 Standard.​

Note​

MPEG-4 AVC/H.264 compression / High Profile compression is inherently lossy. The context where the usage of lossy​ compressionofmedicalimagesisclinicallyacceptableisbeyondthescopeoftheDICOMStandard.Thepoliciesassociated​ with the selection of appropriate compression parameters (e.g., compression ratio) for MPEG-4 AVC/H.264 High Profile /​ Level 4.1 are also beyond the scope of this Standard.​

The use of the DICOM Encapsulated Format to support MPEG-4 AVC/H.264 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 MPEG-4​ AVC/H.264 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​

IfMPEG-4CompressedPixelDataisdecompressedandre-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​

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

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

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

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•​Bits Stored (0028,0101) shall be 8​

•​High Bit (0028,0102) shall be 7​

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

•​The value of MPEG-4 AVC/H.264 sample aspect_ratio_idc shall be 1 in the encapsulated MPEG-4 AVC/H.264 bit stream if as-​ pect_ratio_info_present_flag is 1.​

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

•​The possible values for Rows (0028,0010), Columns (0028,0011), Cine Rate (0018,0040), and Frame Time (0018,1063) or Frame​ Time Vector (0018,1065) depend on the used Transfer Syntax.​

•​For MPEG-4 AVC/H.264 High Profile / Level 4.1 Transfer Syntax, the values for these data elements shall be compliant with the​ High Profile / Level 4.1 of the MPEG-4 AVC/H.264 standard ([ISO/IEC 14496-10]) and restricted to a square pixel aspect ratio.​

•​For MPEG-4 AVC/H.264 BD-compatible High Profile / Level 4.1 Transfer Syntax, the values for these data elements shall be as​ specified in Table 8-4.​

Table 8-4. Values Permitted for MPEG-4 AVC/H.264 BD-compatible High Profile / Level 4.1​

Note​

1.​The value of Planar Configuration (0028,0006) is irrelevant since the manner of encoding components is specified in​ the MPEG-4 AVC/H.264 standard, hence it is set to 0.​

2.​The limitation on rows and columns are to maximize interoperability between software environments and commonly​ available hardware MPEG-4 AVC/H.264 encoder/decoder implementations. Source pictures that have a lower value​ should be re-formatted by scaling and/or pixel padding prior to MPEG-4 AVC/H.264 encoding.​

3.​The frame rate of the acquiring camera for '30 Hz HD' MPEG-4 AVC/H.264 may be either 30 or 30/1.001 (approximately​ 29.97) frames/sec. Similarly, the frame rate in the case of 60 Hz may be either 60 or 60/1.001 (approximately 59.94)​ frames/sec.Thismayleadtosmallinconsistenciesbetweenthevideotimebaseandrealtime.Therelationshipbetween​ frame rate and frame time is shown in Table 8-5.​

4.​The Frame Time (0018,1063) may be calculated from the frame rate of the acquiring camera. A frame rate of 29.97​ frames per second corresponds to a frame time of 33.367 ms.​

5.​The value of chroma_format for this profile and level is defined by MPEG as 4:2:0.​

6.​Example screen resolutions supported by MPEG-4 AVC/H.264 High Profile / Level 4.1 can be taken from Table 8-4.​ Frame rates of 50 Hz and 60 Hz (progressive) at the maximum resolution of 1080 by 1920 are not supported by MPEG-​ 4 AVC/H.264 High Profile / Level 4.1. Interlace at the maximum resolution is supported at a field rate of 50 Hz or 60 Hz,​ which corresponds to a frame rate of 25 Hz or 30 Hz respectively. Smaller resolutions may be used as long as they​ comply with the square pixel aspect ratio. An example is XGA resolution with an image resolution of 768 by 1024 pixels.​ For smaller resolutions there are higher frame rates possible. For example it may be up to 80 Hz for XGA.​

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7.​The display aspect ratio is defined implicitly by the pixel resolution of the video picture. Only square pixel aspect ratio​ is allowed. MPEG-4 AVC/H.264 BD-compatible High Profile / Level 4.1 will only support resolutions that result in a 16:9​ display aspect ratio​

8.​The permitted screen resolutions for the MPEG-4 AVC/H.264 BD-compatible High Profile / Level 4.1 are listed in Table​ 8-4. Only HD resolutions and no progressive frame rates for 25 or 29.97 frames per seconds are supported. Frame​ rates of 50 Hz and 60 Hz (progressive) at the maximum resolution of 1080 by 1920 are not supported.​

Table 8-5. MPEG-4 AVC/H.264 High Profile / Level 4.1 Image Transfer Syntax Frame Rate Attributes​

One fragment shall contain the whole MPEG-4 AVC/H.264 bit stream.​

Note​

If a video stream exceeds the maximum length of one fragment (approximately 4 GB), it may be sent as multiple SOP In-​ stances, 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 Sequence may be used.​

ThecontainerformatforthevideobitstreamshallbeMPEG-2TransportStream,a.k.a.MPEG-TS(see[ISO/IEC13818-1])orMPEG-​ 4, a.k.a. MP4 container (see [ISO/IEC 14496-12] and [ISO/IEC 14496-14]). The PTS/DTS of the transport stream shall be used in​ the MPEG coding.​

Any audio components included in the data container shall follow the constraints detailed in Section 8.2.12 Constraints for Audio Data​

Integration in AVC and HEVC Compressed Bit Streams.​

8.2.8 MPEG-4 AVC/H.264 High Profile / Level 4.2 Video Compression​

DICOM provides a mechanism for supporting the use of MPEG-4 AVC/H.264 Image Compression through the Encapsulated Format​ (see PS3.3). Annex A defines Transfer Syntaxes that reference the MPEG-4 AVC/H.264 Standard.​

Note​

MPEG-4 AVC/H.264 compression / High Profile compression is inherently lossy. The context where the usage of lossy​ compressionofmedicalimagesisclinicallyacceptableisbeyondthescopeoftheDICOMStandard.Thepoliciesassociated​ with the selection of appropriate compression parameters (e.g., compression ratio) for MPEG-4 AVC/H.264 High Profile /​ Level 4.2 are also beyond the scope of this Standard.​

The use of the DICOM Encapsulated Format to support MPEG-4 AVC/H.264 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 MPEG-4​ AVC/H.264 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​

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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​

IfMPEG-4CompressedPixelDataisdecompressedandre-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​

•​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​

•​The value of MPEG-4 AVC/H.264 sample aspect_ratio_idc shall be 1 in the encapsulated MPEG-4 AVC/H.264 bit stream if as-​ pect_ratio_info_present_flag is 1.​

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

•​The values for Rows (0028,0010), Columns (0028,0011), Cine Rate (0018,0040), and Frame Time (0018,1063) or Frame Time​ Vector (0018,1065) shall be compliant with the High Profile / Level 4.2 of the MPEG-4 AVC/H.264 standard ([ISO/IEC 14496-10])​ and restricted to a square pixel aspect ratio.​

Note​

1.​The value of Planar Configuration (0028,0006) is irrelevant since the manner of encoding components is specified in​ the MPEG-4 AVC/H.264 standard, hence it is set to 0.​

2.​The frame rate of the acquiring camera for '30 Hz HD' MPEG-4 AVC/H.264 may be either 30 or 30/1.001 (approximately​ 29.97) frames/sec. Similarly, the frame rate in the case of 60 Hz may be either 60 or 60/1.001 (approximately 59.94)​ frames/sec.Thismayleadtosmallinconsistenciesbetweenthevideotimebaseandrealtime.Therelationshipbetween​ frame rate and frame time is shown in Table 8-7.​

3.​The Frame Time (0018,1063) may be calculated from the frame rate of the acquiring camera. A frame rate of 29.97​ frames per second corresponds to a frame time of 33.367 ms.​

4.​The value of chroma_format for this profile and level is defined by MPEG as 4:2:0.​

Table 8-7. MPEG-4 AVC/H.264 High Profile / Level 4.2 Image Transfer Syntax Frame Rate Attributes​

Stereo Pairs Present (0022,0028) shall be YES if stereoscopic pairs are present, otherwise shall be NO or absent.​

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