- From: Rik Cabanier <cabanier@gmail.com>
- Date: Tue, 13 Sep 2011 18:18:04 -0700
- To: Dean Jackson <dino@apple.com>
- Cc: public-fx@w3.org, www-svg <www-svg@w3.org>
- Message-ID: <CAGN7qDD_FiVHk_wRLCJJwRm56jkC9Y1cTG+vVOKjbKhYYiGWmQ@mail.gmail.com>
On Fri, Sep 2, 2011 at 10:44 AM, Dean Jackson <dino@apple.com> wrote: > Hi Rik, > > On 02/09/2011, at 2:53 PM, Rik Cabanier wrote: > > PDF (and all Adobe apps that create luminosity masks) use 0.03 Red, 0.59 > Green, 0.11 Blue which is close to ITU-R BT.601 > > Where did you get the values for Flash? > > > Good catch! It turns out that I thought I was reading the Flash docs, but I > was instead reading the docs for a Flash library. My mistake. > > Also, while admitting that error, I found another since sending that email. > The OpenGL values come from informative notes on the OpenGL site - not an > official value. > > Flash content generated from our applications (such as InDesign and > Acrobat.com) also use these values. > I can ask internally where these numbers came from. > > > Maybe the question to ask is if the BT.709 values are acceptable? Given > that they've been in the spec for a long time (although with a minor > difference/error) I think we'd need a good reason to change them > dramatically. I wonder what the Adobe SVG Viewer used - the Adobe values or > the SVG values? > Sorry, it took me a while to find the sources of the Adobe SVG viewer. It uses the same values as PDF to calculate luminosity so 0.3 Red, 0.59 Green, 0.11 Blue Rik > > Dean > > > > On Thu, Sep 1, 2011 at 6:10 PM, Dean Jackson <dino@apple.com> wrote: > >> Get your acronym hats on. >> >> A colleague has questioned the values used for luminanceToAlpha in >> FEColorMatrix. The specification (since SVG 1.0) has used: >> >> 0.2125 red, 0.7154 green, 0.0721 blue >> >> But where do these numbers come from? It turns out there are a few >> different specifications for this. The closest to what is specified is in >> Rec. ITU-R BT.709-5 [1], but it is slightly different: >> >> 0.2126 red, 0.7152 green, 0.0722 blue >> >> Yes, a minor difference, but it would be nice to reference an external >> specification. sRGB is based on Rec 709, so I guess this might be the >> definitive source. According to [2], sRGB uses the latter values. >> >> Even then, I'm told that it is more common to use other luminance to alpha >> values. For example, ITU-R BT.601 (YIQ? NTSC? JPEG?) [3] uses: >> >> 0.299 red, 0.587 green, 0.114 blue >> >> And Flash + OpenGL use: >> >> 0.3086 red, 0.6094 green, 0.0820 blue >> >> Since sRGB is used throughout the SVG specification, and sRGB takes its >> values from Rec 709, and Rec 709 seems modern (it's designed for HDTV), and >> the values are really close to what is already specified, I suggest we >> formally link to Rec 709 and use its values (a very slight change to current >> implementations). >> >> Note that these values are also used in other parts of FEColorMatrix, as >> well as other parts of the SVG specification (although it seems the spec >> doesn't always reference explicitly). For example: >> >> - FEColorMatrix type="saturate" and type="huerotate" >> - 'mask' property >> >> Dean >> >> [1] >> http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-5-200204-I!!PDF-E.pdf >> [2] http://en.wikipedia.org/wiki/SRGB >> [3] http://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.601_conversion >> >> > >
Received on Wednesday, 14 September 2011 01:18:42 UTC