refacto(primaries_inset): better README, add demo video

src/primaries_inset/README.md

@@ -5,42 +5,24 @@ a 3x3 matrix. It is possible to visuallize the gamut transformation in a
 CIE xy graph plot.
 
 The reshape transformation is called an "inset" as we are creating a smaller
-gamut than the original.
+gamut than the original (but note we actually apply the inverse conversion making
+the source gamut smaller than the new gamut).
 
-This is the main concept behind [the AgX DRT](https://github.com/MrLixm/AgXc) which
+This is the main concept behind [the AgX DRT](https://github.com/sobotka/AgX) ([ personal fork](https://github.com/MrLixm/AgXc)) which
 was also [ported to darktable](https://github.com/darktable-org/darktable/pull/15104).
 
-![nuke screenshot with PrimariesInset enable](doc/img/demo-inset-on.png)
+![demo recording of the node utilisation in Nuke](doc/img/demo.mp4)
 
-And disabled :
+| enabled                                                                  | disabled                                                                    |
+|--------------------------------------------------------------------------|-----------------------------------------------------------------------------|
+| ![nuke screenshot with PrimariesInset enable](doc/img/demo-inset-on.png) | ![nuke screenshot with PrimariesInset disabled](doc/img/demo-inset-off.png) |
 
-![nuke screenshot with PrimariesInset disabled](doc/img/demo-inset-off.png)
-
-The above example is in the context of a traditional ACES workflow (note the
+> The above example is in the context of a traditional ACES workflow (note the
 ACES view-transform in the viewer) but could be used with any other "tonemapping".
 
-The PrimaryInset operation works closely with the application of a 1D tonescale curve
-(usually reffered as tonemapping) after itself.
-
-If you find the effect of the Inset too strong and just woudl like to fix those
-very saturated camera artefact it's possible to apply an outset after the inset :
-
-![nuke screenshot of the outset workflow](doc/img/demo-outset.png)
-
-Unfortunately the workflow require to bake the view transform in the chain
-(OCIO Display node) :
-1. apply ACES view-transform
-2. revert the sRGB EOTF conversion to get back ACEScg value 
-3. duplicate the first `PrimaryInset` node but check the `Invert` option
-4. reapply the sRGB EOTF conversion
-
-## plotting
-
-It is possible to preview the new inset colorspace as a plot in the CIE1931 xy space.
-
-Just check the `show` checkbox next to the `Plot` title.
-
-![nuke gif of the plot being edited interactively](doc/img/demo-plot.gif)
+The PrimaryInset operation works bests with the application of a 1D tonescale curve
+(usually reffered as tonemapping) after itself thanks to the increase of complimentary
+in the RGB values, which help achieve crosstalk during per-channel (produced by the tonescale).
 
 # Instructions
 
@@ -50,14 +32,17 @@ Just check the `show` checkbox next to the `Plot` title.
 scene.
 - That's it
 
-System :
-- PrimariesInset uses:
-  - python code for `Presets` but works on non-commercial versions.
-  - blink script but works on non-commercial versions >= 14.0
-- The python code _should_ be python 2 compatible but has only been tested on latest
+## Requirements
+
+The tool use the following features :
+
+- python code for `Presets` but works on non-commercial versions.
+  - The python code _should_ be python 2 compatible but has only been tested on latest
 python3 versions of Nuke.
+- blink script but works on non-commercial versions >= 14.0
+
 
-## Usage
+## Basic-Usage
 
 - Expect an image to be transformed as input.
 - Select the preset corresponding to the input image's colorspace encoding.
@@ -68,10 +53,55 @@ in the _Plot_ section : your image disapear to leave a dark squared canvas with
 only a gamut visible.
 - Keep playing with the _Options_ to see how it works.
 
+### default values
+
+Here is some default values that are recommended when using `BT.2020` as source
+gamut. They are based on the [darktable implementation](https://github.com/darktable-org/darktable/pull/15104)
+and Troy Sobotka work.
+
+- inset: `0.15 - 0.25`
+- inset R: `0.06` : additional decrease of purity for red that can be still quite srong
+- inset B: `0.15` : additional decrease of purity for blue that tend to look deeper
+- rotate R: `5` : shift reds in favor of yellowness which work better for fire and sunsets.
+- rotate B: `-6` : sift blues to compensate for Abney effect
+
+## Outset-workflow
+
+If you find the effect of the inset too strong you can apply an outset after the
+tonescale has been applied to restore purity but preserve the "whiteness" in highlights:
+
+![nuke screenshot of the outset workflow](doc/img/demo-outset.png)
+
+Unfortunately the workflow is complicated because you need to apply the tonescale
+before applying the outset. And the tonescale is usually part of the output-transform.
+
+In the case of an ACES workflow :
+
+1. apply `PrimaryInset` node as usual
+2. apply ACES view-transform (OCIO Display node)
+3. revert the sRGB EOTF conversion to get back ACEScg value
+4. duplicate the first `PrimaryInset` node from step 1. but check the `Invert` option
+5. reapply the sRGB EOTF conversion for display.
+6. make sure the viewer view-transform is set to raw or similar.
+
+## Plotting
+
+It is possible to preview the new inset colorspace as a plot in the CIE1931 xy space
+(note this is not a perceptual space).
+
+Just check the `show` checkbox next to the `Plot` title.
+
+![nuke gif of the plot being edited interactively](doc/img/demo-plot.gif)
+
+While plotting you can check `Invert Inset` to see the actual destination colorspace
+being used for the math conversion (kind of unintuitive yes).
+
 # Developer
 
-See the [./src/](./src) folder for the original files that create the final node.
+See the [./src/](./src) folder for development instructions.
 
 ## TODO
 
-- [ ] fix NO_HANDLE flag issue that doesn't seems to work
+- [ ] fix NO_HANDLE flag that is not preserved between sessions (woudl require `onCreate` callback)
+- [ ] add grid to plot
+- [ ] draw gamuts boundaries with lines