[imsc] [WR/ARIB] Mixture of text and image (#543)

himorin has just created a new issue for https://github.com/w3c/imsc:

== [WR/ARIB] Mixture of text and image ==
Per: https://github.com/w3c/ttwg/issues/116
Comment 1

ARIB Data WG understands that the draft text of IMSC-1.2 employs Glyph Substitution (GSUB) of OpenType font to add the capability to handle some images in text-only mode. ARIB Data WG thinks that GSUB is originally intended to provide different representation of glyphs (variation) when needed, such as in case of vertical writing or combined forms. ARIB Data WG is afraid that use of GSUB to embed inline graphics in text-only mode may require complicated operation. It may require some additional rules for practical use such as use or not use of Private Use Area (PUA) for a code point of inline graphics. ARIB Data WG would like to point out that vertical writing and Ideographic Variation Selector (IVS) are already in use in ARIB STD-B62 compliant environment. As described in clause 3.2 below, ARIB STD-B62 supports Web Open Font Format (WOFF) thus ARIB STD-B62 compliant environment potentially supports GSUB. ARIB Data WG also understands that use of GUSB assumes the delivery of additional font file(s) with a TTML document. Then it is considered that difference between use of GSUB and simple Gaiji scheme is only manipulation of those glyph images in a TTML processor. Contextual substitution in GSUB is a complicated method, if a target string contains IVS in particular. ARIB Data WG thinks that use of additional fonts with PUA assigned code like Gaiji should be considered as a simpler alternative method for inline graphics. And ARIB Data WG also would like to point out that clear description on use of GSUB for inline graphics in the text of IMSC Recommendation will be helpful for the readers to understand how inline graphics is handled in IMSC-1.2.

Please view or discuss this issue at https://github.com/w3c/imsc/issues/543 using your GitHub account

Received on Friday, 8 May 2020 09:58:00 UTC