Are blend-mode formulas identical in W3C Compositing 1, PDF and OpenRaster, and in what colour encoding are they evaluated?
W3C Compositing 1 defines blend modes as a mixing function applied in place (weighted by backdrop alpha) followed by a Porter-Duff composite, with exact formulas (soft-light uses a polynomial below Cb 0.25 and sqrt above); OpenRaster adopts these by reference. Neither text says whether blending happens on encoded or linear values; PDF 1.7 makes the blending colour space explicit (producer reading).
W3C Compositing 1 defines blend modes as a mixing function applied in place (weighted by backdrop alpha) followed by a Porter-Duff composite, with exact formulas (soft-light uses a polynomial below Cb 0.25 and sqrt above); OpenRaster adopts these by reference. Neither text says whether blending happens on encoded or linear values; PDF 1.7 makes the blending colour space explicit (producer reading).
Curator qualifications: Specifications read 2026-10-22; no images composited. PDF 32000-1 blending colour space and SoftLight row from producer reading (not re-read).
Limitations: Specifications read 2026-10-22; no images composited.
Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.
Structured fields
{
"citations": [
{
"url": "https://www.w3.org/TR/png-3/",
"note": "W3C Compositing and Blending 1 (TR) 5.x general formula; 10.1.10 soft-light; OpenRaster layer-stack spec (live) composite-op attribute"
},
{
"url": "https://www.w3.org/TR/compositing-1/",
"note": "W3C Compositing and Blending 1 (TR) 5.x general formula; 10.1.10 soft-light; OpenRaster layer-stack spec (live) composite-op attribute"
},
{
"url": "https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/PDF32000_2008.pdf",
"note": "W3C Compositing and Blending 1 (TR) 5.x general formula; 10.1.10 soft-light; OpenRaster layer-stack spec (live) composite-op attribute"
},
{
"url": "https://www.openraster.org/baseline/layer-stack-spec.html",
"note": "W3C Compositing and Blending 1 (TR) 5.x general formula; 10.1.10 soft-light; OpenRaster layer-stack spec (live) composite-op attribute"
}
]
}Evidence claims
- [sourced_fact] W3C Compositing 1 defines blend modes as a mixing function applied in place (weighted by backdrop alpha) followed by a Porter-Duff composite, with exact formulas (soft-light uses a polynomial below Cb 0.25 and sqrt above); OpenRaster adopts these by reference. Neither text says whether blending happens on encoded or linear values; PDF 1.7 makes the blending colour space explicit (producer reading). · locator: W3C Compositing and Blending 1 (TR) 5.x general formula; 10.1.10 soft-light; OpenRaster layer-stack spec (live) composite-op attribute source
Rights
| component | license | hosting | redistribution | modification | training | Evidence and notes |
|---|---|---|---|---|---|---|
| documentation | unknown | permitted | permitted | unknown | unknown | Applies to this original summary only, not to the cited sources. |