Access Services for UHDTV: an Initial Investigation of W3C TTML2 Subtitles (Closed-Captions)

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Publisher: SMPTE — White Plains, NY, USA
Doc Type: Conference Paper
Content Type: Original Research
Volume: 2017, No. 10, pp. 1–15
Abstract: Ultra High Definition Television and High Dynamic Range has been a focus of research for the past few years, however only now is work starting on the provision of access services for such content. These services are used by a large minority of the audience (up to 25%) and legislation mandates their inclusion in many territories. — The authors present work undertaken to verify the transform for use with HLG high dynamic range video in Appendix P of the W3C Timed Text Markup Language version 2 working draft specification which is likely to be used for subtitling in traditional and IP-based video services. Further they present test results investigating whether there is a perceived brightness variability for subtitles using the TTML conversions when displayed over different HDR video content.
Publication Date: 2017-10-23
DOI: 10.5594/M001777
ISBN: Print: 978-1-61482-959-1
Link: https://doi.org/10.5594/M001777
Author(s): Simon ThompsonBritish Broadcasting Corporation, United Kingdom
Peter CherrimanBritish Broadcasting Corporation, United Kingdom
Keyword(s): HDR, HLG, Video, ITU-R BT.2100, Subtitles, Closed-captions, W3C TTML2, EBU-TT-D
Copyright: © 2017 Society of Motion Picture and Television Engineers, Inc.

Bibliographic Reference(s)

CIE.1931.1931 — Let (X,Y,Z) be pixels in the system colorimetry specified in the CIE 1931 XYZ colour space [XYZ] . EXTERNAL
Apply 10-bit narrow-range quantization: (Q(r),Q(g),Q(b)) → (r,g,b) where Q(x) = floor((940 − 64) • x + 64.5) EXTERNAL
Compute HDR absolute luminance using the tts:luminanceGain attribute and the sRGB illuminant: 80 ∙ tts:luminanceGain ∙ (r, g, b) → (r, g, b) EXTERNAL
Apply composition to yield (Rc, Gc, Bc): (clamp(r + R), clamp(g + G), clamp(b + B)) → (Rc, Gc, Bc) 1 + (1 - a) ∙ (A - 1) → Ac where clamp(x) = 0 for x < 0 and clamp(x) = x for 0 ≤ x ≤ 1023 and EXTERNAL
Apply inverse PQ EOTF specified in [ITU BT.2100-1]: (PQ(r), PQ(g), PQ(b)) → (r, g, b) with PQ(L) = [(c1 + c2 ∙ Lm1) / (1 + c3 ∙ Lm1)]m2 and m1 = 0.1593017578125, m2 = 78.84375, c1 = 0.8359375, c2 = 18.8515625, and c3 = 18.6875. EXTERNAL
Let (r, g, b) be a full-range 8-bit sRGB pixel with opacity of A between 0 and 255. EXTERNAL
Invert the 8-bit full-range quantization: (r, g, b)/255 → (r, g, b) A/255 → A EXTERNAL
Let (R,G,B) and (Rc,Gc,Bc) be narrow-range 10-bit pixels in the system colorimetry specified in [ITU BT.2100-1] using HLG EOTF and narrow-range quantization. Subscript c denoting the video signal post-compositing. EXTERNAL
Convert from sRGB color space to [ITU BT.2100-1] color space: [(0.62740389593470, 0.32928303837789, 0.04331306568741), (0.06909728935823, 0.91954039507545, 0.01136231556630), (0.01639143887515, 0.08801330787723, 0.89559525324763)] ∙ (r, g, b) → (r, g, b) EXTERNAL
Apply simplified inverse HLG OOTF: ((0.265r),(0.265g),(0.265b)) → (r,g,b) EXTERNAL
Composite foreground graphic (r,g,b) over background video (R,G,B) with opacity A to yield (Rc,Gc,Bc): ((A•r+(1−A)R),(A•g+(1−A)G),(A•b+(1−A)B)) → (Rc,Gc,Bc) EXTERNAL

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Simon Thompson and Peter Cherriman; Access Services for UHDTV: an Initial Investigation of W3C TTML2 Subtitles (Closed-Captions), SMPTE Meetings and Conferences ( October 2017); SMPTE, 2017, ISBN: 978-1-61482-959-1. Available at https://doi.org/10.5594/M001777

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Simon Thompson and Peter Cherriman; Access Services for UHDTV: an Initial Investigation of W3C TTML2 Subtitles (Closed-Captions), SMPTE Meetings and Conferences ( October 2017); SMPTE, 2017, ISBN: 978-1-61482-959-1. Available at https://doi.org/10.5594/M001777

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<span class="citation">Simon Thompson and Peter Cherriman; <cite>Access Services for UHDTV: an Initial Investigation of W3C TTML2 Subtitles (Closed-Captions)</cite>, SMPTE Meetings and Conferences ( October 2017); SMPTE, 2017, ISBN: 978-1-61482-959-1. Available at <a href="https://doi.org/10.5594/M001777" target="_blank" rel="noopener">https://doi.org/10.5594/M001777</a></span>

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Simon Thompson and Peter Cherriman; <cite id="bib-10-5594-m001777">Access Services for UHDTV: an Initial Investigation of W3C TTML2 Subtitles (Closed-Captions)</cite>, SMPTE Meetings and Conferences ( October 2017); SMPTE, 2017, ISBN: 978-1-61482-959-1
<span class="doi">10.5594/M001777</span>
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