[Matroska-devel] [Cellar] Colour Format proposal

Frank Galligan via Matroska-devel matroska-devel at lists.matroska.org
Tue Feb 16 20:01:33 CET 2016


On Fri, Feb 12, 2016 at 5:53 PM, Dave Rice <dave at dericed.com> wrote:

> Hi,
>
>
> Element Name: Colour
> Level:        4
> ID:           [55][B0]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         m
> Description:  Settings describing the colour format.
>
>
> Element Name: Matrix
>
>
> To align better with ISO/IEC 23001-8, could this be labelled as
> MatrixCoefficients?
>
Done


>
> Level:        5
> ID:           [55][B1]
> Mandatory:    -
> Multiple:     -
> Default:      2
> Type:         u
> Description:  ColourMatrix of the video. See ISO/IEC 23001-8 for more
>              information on enumerations. (0: IEC 61966-2-1 (sRGB), 1:
> BT709,
>              2: Unspecified, 3: Reserved, 4: FCC, 5: BT470BG, 6: SMPTE
> 170M,
>              7: SMPTE 240M, 8: YCOCG, 9: BT2020 Non-constant Luminance,
>              10: BT2020 Constant Luminance)
>
>
> Suggested description edit:
> The Matrix Coefficients of the video used to derive luma and chroma values
> from reg, green, and blue color primaries. For clarity, the value and
> meanings for MatrixCoefficients are adopted from Table 4 of ISO/IEC
> 23001-8:2013/DCOR1. (0: IEC 61966-2-1 (sRGB), 1: BT709, 2: Unspecified, 3:
> Reserved, 4: FCC, 5: BT470BG, 6: SMPTE 170M, 7: SMPTE 240M, 8: YCOCG, 9:
> BT2020 Non-constant Luminance, 10: BT2020 Constant Luminance)
>
Done

>
> Question:
> Value 0 is listed as "IEC 61966-2-1 (sRGB)" but the table for matrix
> coefficients in ISO/IEC 23001-8 says "GBR / Typically referred to as RGB".
> Should value 0 = RGB?
>
I changed it to GBR to match 23001-8.


> Add footnote:
> [IEC23001-8] ISO/IEC 23001-8:2013/DCOR1, "Coding independent media
> description code points", 2013, <
> http://standards.iso.org/ittf/PubliclyAvailableStandards/c062088_ISO_IEC_23001-8_2013.zip
> >.
>
> Element Name: BitsPerChannel
> Level:        5
> ID:           [55][B2]
> Mandatory:    -
> Multiple:     -
> Default:      0
> Type:         u
> Description:  Number of decoded bits per channel. This number may be less
> for
>              specific channels depending on the Matrix and
> ChromaSubsampling. A
>              value of 0 is unspecified.
>
>
> It may be fine, but I don't understand "This number may be less for
> specific channels depending on the Matrix and ChromaSubsampling." Is the
> value is less for specific channels, then it seems as if the value would
> different among channels, but only one BitsPerChannel is stored for a
> multi-channel video.
>
So we could have separate bits per channel, but then we would have to
define rgb and yuv. Most people know what this is. Basically the
information needed is, will the decoded video be 8 bits, 10 bits, 12 bits,
16 bits, ... Maybe I was just trying to be a little too pedantic. I'm fine
with removing this sentence. if any of the ChromaSubsampling elements are
set then that implies that one or more channels will have a different value.

So how about we just remove this sentence?


> I suggest changing the last line to: A value of 0 indicates that the
> BitsPerChannel is unspecified.
>
Done

>
> Element Name: ChromaSubsamplingHorz
> Level:        5
> ID:           [55][B3]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         u
> Description:  The amount of chrominance pixels to remove for every
> chrominance
>              pixel not removed horizontally.
>
>
> For these subsampling elements, we may need a statement to say when they
> should be used. For instance in QuickTime's TN2162
> https://developer.apple.com/library/mac/technotes/tn2162/_index.html it
> mandates the use of many values to better describe uncompressed video. When
> would these chroma subsampling elements be suggested?
>
I'm not really sure I follow. If any of the Cb or Cr channels are down
sized before encoding, then these elements should be set accordingly.


> I also suggest including an example; such as "Example: For video with
> 4:1:1 chroma subsampling the ChromaSubsamplingHorz should be set to 3.
>
I added "Example: For video with 4:2:0 chroma subsampling the
ChromaSubsamplingHorz should be set to 1." As pretty much most video is
4:4:4 or 4:2:0 nowadays.


> Element Name: ChromaSubsamplingVert
> Level:        5
> ID:           [55][B4]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         u
> Description:  The amount of chrominance pixels to remove for every
> chrominance
>              pixel not removed vertically.
>
> Element Name: CbSubsamplingHorz
> Level:        5
> ID:           [55][B5]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         u
> Description:  The amount of Cb chrominance pixels to remove for every Cb
>              chrominance pixel not removed horizontally. This is additive
> with
>              ChromaSubsamplingHorz.
>
>
> I'm confused about the relationship between CbSubsamplingHorz
> and ChromaSubsamplingHorz.
>
These elements are only defined because I was trying to handle 4:2:1.
Basically this is an old format where the Cr channel is half the size of
the Y channel, and the Cb channel is half the size of the Cr channel. The
Cb channel is a quarter the size of the Y channel.

The CbSubsampling* elements were a late edition, right before I sent my
previous email. At first I didn't have these elements and had text that
4:2:1 was not supported.

How about I change the CbSubsamplingHorz element text too: "The amount of
pixels to remove in the Cr and Cb channels for every pixel not removed
horizontally." And the CbSubsamplingHorz too: "The amount of pixels to
remove in the Cb channel for every pixel not removed horizontally. This is
additive with ChromaSubsamplingHorz. Example: For video with 4:2:1 chroma
subsampling the ChromaSubsamplingHorz should be set to 1 and
CbSubsamplingHorz should be set to 1." Does this help the confusion?


> Element Name: CbSubsamplingVert
> Level:        5
> ID:           [55][B6]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         u
> Description:  The amount of Cb chrominance pixels to remove for every Cb
>              chrominance pixel not removed vertically. This is additive
> with
>              ChromaSubsamplingVert.
>
>
> Element Name: ChromaSitingHorz
> Level:        5
> ID:           [55][B7]
> Mandatory:    -
> Multiple:     -
> Default:      0
> Type:         u
> Description:  How Chroma is subsampled horizontally. (0: Unspecified, 1:
> Left
>              collocated , 2: Half)
>
> Element Name: ChromaSitingVert
> Level:        5
> ID:           [55][B8]
> Mandatory:    -
> Multiple:     -
> Default:      0
> Type:         u
> Description:  How Chroma is subsampled vertically. (0: Unspecified, 1: Top
>              collocated , 2: Half)
>
>
> Element Name: Range
> Level:        5
> ID:           [55][B9]
> Mandatory:    -
> Multiple:     -
> Default:      0
> Type:         u
> Description:  Clipping of the color ranges. (0: Unspecified, 1: Broadcast
> range,
>              2: Full range (no clipping), 3: Defined by
>              Matrix/TransferFunction)
>
>
> Element Name: TransferFunction
>
>
> To align with ISO/IEC 23001-8, could we use TransferCharacteristics?
>
Done.

>
> Level:        5
> ID:           [55][BA]
> Mandatory:    -
> Multiple:     -
> Default:      2
> Type:         u
> Description:  Transfer Function. See ISO/IEC 23001-8 for more information
> on
>              enumerations. (0: Reserved, 1: ITU-R BT.709, 2: Unspecified,
>              3: Reserved, 4: Gamma 2.2 curve, 5: Gamma 2.8 curve,
>              6: SMPTE 170M, 7: SMPTE 240M, 8: Linear, 9: Log, 10: Log Sqrt,
>              11: IEC 61966-2-4, 12: ITU-R BT.1361 Extended Colour Gamut,
>              13: IEC 61966-2-1, 14: ITU-R BT.2020 10 bit,
>              15: ITU-R BT.2020 12 bit, 16: SMPTE ST 2084,
>              17: SMPTE ST 428-1 18: ARIB STD-B67 (HLG))
>
>
> Comment:
> The table in ISO/IEC 23001-8 for transfer characteristics does not include
> values or meaning for 16, 17 and 18 as above. Are these values from
> ffmpeg's list?
>
16 and 17 is an artifact form the FFmpeg list, but also form looking at
FFmpeg CL's I think they are defined in an h265 spec. 18 is a proposed
value for HLG.


> Suggested description edit:
> The transfer characteristics of the video. For clarity, the value and
> meanings for TransferCharacteristics are adopted from Table 3 of ISO/IEC
> 23001-8:2013/DCOR1. (0: Reserved, 1: ITU-R BT.709, 2: Unspecified, 3:
> Reserved, 4: Gamma 2.2 curve, 5: Gamma 2.8 curve, 6: SMPTE 170M, 7: SMPTE
> 240M, 8: Linear, 9: Log, 10: Log Sqrt, 11: IEC 61966-2-4, 12: ITU-R BT.1361
> Extended Colour Gamut, 13: IEC 61966-2-1, 14: ITU-R BT.2020 10 bit, 15:
> ITU-R BT.2020 12 bit)
>
Done.


>
> Element Name: Primaries
> Level:        5
> Mandatory:    -
> Multiple:     -
> ID:           [55][BB]
> Default:      2
> Type:         u
> Description:  Values that can be represented in the CIE 1931 colour space.
> See
>              ISO/IEC 23001-8 for more information on enumerations.
>              (0: Reserved, 1: ITU-R BT.709, 2: Unspecified, 3: Reserved,
>              4: ITU-R BT.470M, 5: ITU-R BT.470BG, 6: SMPTE 170M, 7: SMPTE
> 240M,
>              8: FILM, 9: ITU-R BT.2020, 10: SMPTE ST 428-1)
>
>
> Suggested description edit:
> The colour primaries of the video. For clarity, the value and meanings for
> TransferCharacteristics are adopted from Table 2 of ISO/IEC
> 23001-8:2013/DCOR1. (0: Reserved, 1: ITU-R BT.709, 2: Unspecified, 3:
> Reserved, 4: ITU-R BT.470M, 5: ITU-R BT.470BG, 6: SMPTE 170M, 7: SMPTE
> 240M, 8: FILM, 9: ITU-R BT.2020, 10: SMPTE ST 428-1)
>
Done.

>
> Note that ISO/IEC 23001-8 also includes a value for 22 for JEDEC P22
> phosphors. Any reason to exclude this?
>
Added.


>
> Element Name: MaxCLL
> Level:        5
> ID:           [55][BC]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         u
> Description:  Maximum brightness of a single pixel in candelas per square
>              meter (cd/m²).
>
>
> Suggested:
> Maximum brightness of a single pixel (Maximum Content Light Level) in
> candelas per square meter (cd/m²).
>
Done


>
> Element Name: MaxFALL
> Level:        5
> ID:           [55][BD]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         u
> Description:  Maximum brightness of a single full frame in candelas per
> square
>              meter (cd/m²).
>
>
> Suggested:
> Maximum brightness of a single full frame (Maximum Frame-Average Light
> Level) in candelas per square meter (cd/m²).
>
Done


>
> Element Name: MasteringMetadata
> Level:        5
> ID:           [55][D0]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         m
> Description:  SMPTE 2086 mastering data.
>
>
> Element Name: PrimaryRChromaticityX
> Level:        6
> ID:           [55][D1]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
>
>
> I think "0.0-1.0" is preferred for float range expressions.
>
Done


>
> Default:      -
> Type:         f
> Description:  Red X chromaticity coordinate as defined by CIE 1931.
>
>
> Element Name: PrimaryRChromaticityY
> Level:        6
> ID:           [55][D2]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
> Default:      -
> Type:         f
> Description:  Red Y chromaticity coordinate as defined by CIE 1931.
>
>
> Element Name: PrimaryGChromaticityX
> Level:        6
> ID:           [55][D3]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
> Default:      -
> f
> Description:  Green X chromaticity coordinate as defined by CIE 1931.
>
>
> Element Name: PrimaryGChromaticityY
> Level:        6
> ID:           [55][D4]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
> Default:      -
> Type:         f
> Description:  Green Y chromaticity coordinate as defined by CIE 1931.
>
>
> Element Name: PrimaryBChromaticityX
> Level:        6
> ID:           [55][D5]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
> Default:      -
> f
> Description:  Blue X chromaticity coordinate as defined by CIE 1931.
>
>
> Element Name: PrimaryBChromaticityY
> Level:        6
> ID:           [55][D6]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
> Default:      -
> Type:         f
> Description:  Blue Y chromaticity coordinate as defined by CIE 1931.
>
>
> Element Name: WhitePointChromaticityX
> Level:        6
> ID:           [55][D7]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
> Default:      -
> Type:         f
> Description:  White point X chromaticity coordinate as defined by CIE
> 1931.
>
>
> Element Name: WhitePointChromaticityY
> Level:        6
> ID:           [55][D8]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 1
> Default:      -
> Type:         f
> Description:  White point Y chromaticity coordinate as defined by CIE
> 1931.
>
>
> Element Name: LuminanceMax
> Level:        6
> ID:           [55][D9]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 9999.99
> Default:      -
> Type:         f
> Description:  Maximum luminance. Shall be represented in candelas per
> square
>              meter (cd/m²).
>
>
> Element Name: LuminanceMin
> Level:        6
> ID:           [55][DA]
> Mandatory:    -
> Multiple:     -
> Range:        0 <= f <= 999.9999
> Default:      -
> Type:         f
> Description:  Minimum luminance. Shall be represented in candelas per
> square
>              meter (cd/m²).
>
>
>
>
> I removed ChromaSubsampling and added ChromaSubsamplingHorz,
> ChromaSubsamplingVert, CbSubsamplingHorz, and CbSubsamplingVert.
>
> This is how I think the elements should be written for the different
> subsampling types:
> 1: 4:4:4
>     - ChromaSubsamplingHorz and ChromaSubsamplingVert will not be set as
> there should be no chroma subsampling.
>
> 2: 4:4:0
>   - ChromaSubsamplingHorz :not set
>   - ChromaSubsamplingVert :1
>
> 3: 4:2:2
>   - ChromaSubsamplingHorz :1
>   - ChromaSubsamplingVert :not set
>
> 4: 4:2:1
>   - ChromaSubsamplingHorz :1
>   - ChromaSubsamplingVert :not set
>   - CbSubsamplingHorz :1
>   - CbSubsamplingVert :not set
>   - We could remove CbSubsamplingHorz and CbSubsamplingVert if we didn't
> care about handling formats where the Cr and Cb channels are different
> sizes.
>
>
> I forgot about 4:2:1. That answers my question about CbSubsmaplingHorz
> though perhaps we need a narrative section to expand on this with the
> examples you have here.
>
> 5: 4:2:0
>   - ChromaSubsamplingHorz :1
>   - ChromaSubsamplingVert :1
>
> 6: 4:1:1
>   - ChromaSubsamplingHorz :3
>   - ChromaSubsamplingVert :not set
>
> 7: 4:1:0
>   - ChromaSubsamplingHorz :3
>   - ChromaSubsamplingVert :1
>
> 8: 3:1:1
>   - ChromaSubsamplingHorz :2
>   - ChromaSubsamplingVert :not set
>   - I'm assuming the luma subsampling can be handled by PixelWidth, and
> DisaplyWidth.
>
> Jerome's vertical subsampling of 4
>   - ChromaSubsamplingHorz :not set
>   - ChromaSubsamplingVert :3
>
>
>
> The other issue I want to bring up is the value of "18: ARIB STD-B67 (HLG)"
> in TransferFunction. Unfortunately, in WebM we will need to use this value
> sooner than Matroska v4 will be finalized. Should I make this value much
> higher? Or leave at 18? I think "16: SMPTE ST 2084" and "17: SMPTE ST
> 428-1" will be standardized across most documents, like 1-15 are. Just
> not sure if 18 will be HLG.
>
>
> I see a few references to ARIB STD-B67 as 18, such as
> http://www.arib.or.jp/english/html/overview/doc/2-STD-B32v3_5.pdf.
> Perhaps we need a caveat that values 1-15 are defined based upon ISO/IEC
> 23001-8. Then for values 16, 17, and 18 we could add better descriptions
> and citations to define it better internally.
>
I'm fine with this. I'm just worried about the case where we diverge from
one of the lists. Would be nice to have one canonical list.


> If (hopefully) a revision to ISO/IEC 23001-8 adds those values (as
> expected) then we could update are description to say all values are
> defined by ISO/IEC 23001-8.
>
Sounds good to me.


> Thanks,
> Frank
>
>
> Thanks too,
> Dave Rice
>
>
>
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