- From: Rik Cabanier <cabanier@gmail.com>
- Date: Thu, 1 Sep 2011 21:53:22 -0700
- To: Dean Jackson <dino@apple.com>
- Cc: public-fx@w3.org, www-svg <www-svg@w3.org>
- Message-ID: <CAGN7qDAUQgk-J-x33LtTJ57xEtEryygFju1HKvdDiSVtcucZWg@mail.gmail.com>
Hi Dean, 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? 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. Rik 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 Friday, 2 September 2011 04:53:50 UTC