- From: Glenn Adams <glenn@skynav.com>
- Date: Wed, 25 Feb 2015 00:11:15 -0700
- To: Philip Jägenstedt <philipj@opera.com>
- Cc: Michael Borthwick <mb@michaelborthwick.com.au>, Silvia Pfeiffer <silviapfeiffer1@gmail.com>, David Singer <singer@apple.com>, "public-texttracks@w3.org" <public-texttracks@w3.org>
- Message-ID: <CACQ=j+dAmztPAqOS59urbOY4z+Yo1pS4RG-WOWkO5cCDzYfwDQ@mail.gmail.com>
FYI, attached is a simple spreadsheet for computing analog Y'PbPr and 8 bit Y'CbCr from RGB888. On Wed, Feb 25, 2015 at 12:05 AM, Glenn Adams <glenn@skynav.com> wrote: > > On Tue, Feb 24, 2015 at 10:24 PM, Philip Jägenstedt <philipj@opera.com> > wrote: > >> On Wed, Feb 25, 2015 at 12:16 PM, Glenn Adams <glenn@skynav.com> wrote: >> > >> > On Tue, Feb 24, 2015 at 9:36 PM, Philip Jägenstedt <philipj@opera.com> >> > wrote: >> >> >> >> On Sat, Feb 21, 2015 at 7:10 AM, Michael Borthwick >> >> <mb@michaelborthwick.com.au> wrote: >> >> > On 08/04/2014, at 1:08 PM, Silvia Pfeiffer wrote: >> >> > >> >> >> Note: I've made the change to "lime" and updated the related text, >> see >> >> >> https://dvcs.w3.org/hg/text-tracks/rev/07a843b7f31d >> >> >> >> >> >> Please let me know if there are more changes necessary. >> >> >> >> >> >> Regards, >> >> >> Silvia. >> >> > >> >> > >> >> > Dear list members, >> >> > >> >> > For those who are interested I have made the 22 minute video of my >> SMPTE >> >> > Australia 2013 talk regarding this issue available online with >> >> > appropriate >> >> > amendments to reflect the changes kindly made by Silvia last year to >> the >> >> > mapping of green into CSS lime. >> >> > >> >> > >> >> > >> http://michaelborthwick.com.au/closed_captioning_online_streaming_video_dfxp_webvtt.html >> >> >> >> Thanks Michael, this was a great talk! I'm not sure why, but I found >> >> the trouble with green and conflicting standards very amusing, a very >> >> familiar kind of problem. >> >> >> >> Since WebVTT doesn't have any dedicated syntax for colors it really >> >> comes down to the CSS that goes along with the captions, and of course >> >> any mapping specs. Unfortunately, I suspect you will not be the last >> >> to spend time looking for a suitable green color. >> > >> > >> > Haven't had a chance to watch yet, but from TTML: >> > >> > <named-color> >> > : ... >> > | "green" // #008000ff >> > | "lime" // #00ff00ff >> > | "olive" // #808000ff >> > >> > >> >> >> >> >> >> Did you ever hear back from the BBC about which the ultimate colors >> >> are? I doubt that #00FF00 is actually used on the Web, it's so bright! >> > >> > >> > Y = 0.299R + 0.587G + 0.114B >> >> Is this BBC green? Multiplying with 255 and rounding, that is rgb(76, >> 150, 29), assuming it's the same RGB colorspace of course... >> > > Y (or more accurately Y') is the luminance component of Y'UV or Y'PbPr > [1]. My point was that the G component of Y contributes ~60% of brightness. > So an #00FF00 mapping to Y would be bright indeed. > > [1] http://en.wikipedia.org/wiki/YUV > > >> >> In any case, it's a lot nicer than #00FF00, and a bit brighter than >> #008000. >> > > In 8-bit Y'CbCr (ITU-R BT.601) [2], which is a typical digital video > sample representation, the 8 bit value of Y' for #008000 would be 81 and > for #00FF00 would be 145 (in a range of [16,235], i.e., Y'(black) = 16, > Y'(white) = 235). > > [2] http://en.wikipedia.org/wiki/YCbCr > > The brightness (Y') of #00FF00 would be 149, and for #008000 would be 75, > when viewed relative to Y' > > >> >> Philip >> > >
Attachments
- application/vnd.openxmlformats-officedocument.spreadsheetml.sheet attachment: RGBtoYCbCr.xlsx
Received on Wednesday, 25 February 2015 07:12:04 UTC