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Finding out what happens when compositing layers

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Finding out what happens when compositing layers Ofnuts 15 Sep 21:39
  Finding out what happens when compositing layers David Gowers (kampu) 16 Sep 00:20
   Finding out what happens when compositing layers Ofnuts 16 Sep 23:06
    Finding out what happens when compositing layers David Gowers (kampu) 17 Sep 03:43
Finding out what happens when compositing layers 丰 17 Sep 04:31
  Finding out what happens when compositing layers 丰 17 Sep 04:37
  Finding out what happens when compositing layers Patrick Horgan 17 Sep 16:18
Ofnuts
2011-09-15 21:39:29 UTC (over 12 years ago)

Finding out what happens when compositing layers

I'll trying to find out what happens when a layer is in subtract mode with a global opacity not one or zero (i.e. what computations are done with the pixels values of the composite image of the layers below, the pixel values of the layer, and the general opacity). I have a git extract of the Gimp source code (and of gegl & babl) but got lost... Can someone help?

David Gowers (kampu)
2011-09-16 00:20:56 UTC (over 12 years ago)

Finding out what happens when compositing layers

In GEGL, the layer mode code is autogenerated from formula strings -- see operations/generated/math.rb

The opacity behaviour is not documented there, but my understanding is that the alpha of the underlying composite is preserved, and opacity only effects how much of the layer's COLOR channels are applied (per the standard blending formula).

On Fri, Sep 16, 2011 at 7:09 AM, Ofnuts wrote:

I'll trying to find out what happens when a layer is in subtract mode with a global opacity not one or zero (i.e. what computations are done with the pixels values of the composite image of the layers below, the pixel values of the layer, and the general opacity). I have a git extract of the Gimp source code (and of gegl & babl) but got lost... Can someone help?
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Ofnuts
2011-09-16 23:06:37 UTC (over 12 years ago)

Finding out what happens when compositing layers

On 09/16/2011 02:20 AM, David Gowers (kampu) wrote:

In GEGL, the layer mode code is autogenerated from formula strings -- see operations/generated/math.rb

The opacity behaviour is not documented there, but my understanding is that the alpha of the underlying composite is preserved, and opacity only effects how much of the layer's COLOR channels are applied (per the standard blending formula).

On Fri, Sep 16, 2011 at 7:09 AM, Ofnuts > wrote:

I'll trying to find out what happens when a layer is in subtract mode with a global opacity not one or zero (i.e. what computations are done with the pixels values of the composite image of the layers below, the pixel values of the layer, and the general opacity). I have a git extract of the Gimp source code (and of gegl & babl) but got lost... Can
someone help?

Well, I know that in "Normal" mode, I have in each RGB channel:

Composite=Over*alpha+Under(1-alpha)

(assuming "Under" is fully opaque), but in Subtract mode, I would have several possibilities

Composite=Under(1-alpha)-Over*alpha or
Composite=Under(1-alpha)+(1-Over)*alpha or
Composite=Under(1-alpha)+(1-Over*alpha)

and $deity knows what else.

math.rb isn't taking the opacity in account (but is an interesting read...)

Thx.

David Gowers (kampu)
2011-09-17 03:43:22 UTC (over 12 years ago)

Finding out what happens when compositing layers

On Sat, Sep 17, 2011 at 8:36 AM, Ofnuts wrote:

**
On 09/16/2011 02:20 AM, David Gowers (kampu) wrote:

In GEGL, the layer mode code is autogenerated from formula strings -- see operations/generated/math.rb

The opacity behaviour is not documented there, but my understanding is that the alpha of the underlying composite is preserved, and opacity only effects how much of the layer's COLOR channels are applied (per the standard blending formula).

On Fri, Sep 16, 2011 at 7:09 AM, Ofnuts wrote:

I'll trying to find out what happens when a layer is in subtract mode with a global opacity not one or zero (i.e. what computations are done with the pixels values of the composite image of the layers below, the pixel values of the layer, and the general opacity). I have a git extract of the Gimp source code (and of gegl & babl) but got lost... Can someone help?

Well, I know that in "Normal" mode, I have in each RGB channel:

Composite=Over*alpha+Under(1-alpha)

(assuming "Under" is fully opaque), but in Subtract mode, I would have several possibilities

No, you just subtract Over from Under with no multiplication, then you

perform a RGB (not RGBA) Composite of the result and Under, to produce the final composite.

丰
2011-09-17 04:31:45 UTC (over 12 years ago)

Finding out what happens when compositing layers

I came across this quite some time ago: http://www.simpelfilter.de/en/basics/mixmods.html

丰
2011-09-17 04:37:21 UTC (over 12 years ago)

Finding out what happens when compositing layers

I came across this quite some time ago: http://www.simpelfilter.de/en/basics/mixmods.html

PS: I thought I had type in my word before I send the mail. I did not know what had happened. Sorry to everybody for the spam and wish this mail is all right.

Patrick Horgan
2011-09-17 16:18:27 UTC (over 12 years ago)

Finding out what happens when compositing layers

On 09/16/2011 09:31 PM, 丰 wrote:

I came across this quite some time ago: http://www.simpelfilter.de/en/basics/mixmods.html

That's wonderful! Even mentions GIMP a bit.

Patrick