[CREATE] ORA spec: adding additional layer effects

Andrew Chadwick a.t.chadwick at gmail.com
Sat Feb 25 13:03:32 PST 2012


On 25 February 2012 17:02, Alexandre Prokoudine
<alexandre.prokoudine at gmail.com> wrote:
> On Sat, Feb 25, 2012 at 2:19 AM, Andrew Chadwick wrote:
>> The OpenRaster spec currently states (working from memory here) that
>> ORA files may use uses the SVG compositing ops[1]. These do not
>> provide colorize layer modes, nor modes for luminosity-setting,
>> hue-setting or saturation-setting.
>
> I've just asked in w3s svg mailing list, and Rik Cabanier replied:
>
> "I'm working on a new CSS composting spec that will add those missing
> blend modes.
> There will be a new CSS keyword 'blending' that will let you specify a
> blend mode on an HTML or SVG element."

Interesting, thank you. I'll keep an eye on that[1].

Looking at the fact that other open source image editors don't seem to
have implemented what appears to me to be a fairly conceptually
obvious transformation (take a perceptually-relevant luma of one pixel
in the target combined layer and the hue and value of the
corresponding pixel in the layer above it and combine them to make a
new pixel RGB value) but instead seem to just use simpler and less
perceptually-relevant H¹ + S²V² combinations in ordinary HSV space,
I'm wondering if there's some patent-related reason for not doing so.
Case in point from my recent minitrawl for PDF patents: US patent
6421460[2] seems especially dangerous (though TBH that seems to forbid
almost all possible ways of combining layers using alpha and some
combining function in a graphics program, and *many* implementations
surely exist). I don't want to make a system which cannot be sold and
used in the US. Entertainingly we could use the PDF method directly if
MyPaint also wrote PDF files thanks to a general but highly limited
patent grant of Adobe's[3].

Is there any reason why GIMP and Krita aren't (by quick
experimentation and/or code analysis) using this?


[1] http://lists.w3.org/Archives/Public/www-svg/2012Feb/0092.html
[2] http://www.google.com/patents/US6421460 - "Blending colors in the
presence of transparency"
[3] http://partners.adobe.com/public/developer/support/topic_legal_notices.html
- making PDFs only

-- 
Andrew Chadwick


More information about the CREATE mailing list