Additive Light in linearized Rec.709

With Nuke, Pixelmator, Affinity Photo and FCPX

Years back (2013) I was reading and hearing about that FCPX is prepared for modern workflows. At the time I didn’t know how FCPX is actually handling pixel data. The working colorspace is linearized Rec.709. So then it must work the same as Nuke with the Default ColorManagement.

To start out I created a little preparation setup in Nuke (Non-Commercial edition).


The result looks like this:


This image is created in Nuke. “Nuke_constant_dark_grey.jpg”

Next I added some circles. On the left side taking the same grey and added it overlapping twice. On the right side add three circles in red, green and blue and overlap them as well. The grey values add up to 0.16 (112/112/112 in sRGB) and 0.24 (134/134/134 in sRGB). The color values are adding up to the expected numbers.


This image is created in Nuke. The file is called “Nuke_constant_dark_grey_light_cirlces.jpg”.
The setup can be downloaded here. Nuke_constant_dark_grey_v01.nknc

Next I take both jpg file into Pixelmator and Affinity Photo. The empty one to recreate the light circles in each program and the finished one to compare the results.

This is Pixelmator. Of course Pixelmator doesn’t work in linear light so the grey circles add up from the background value of 80 to 160 and 240 in the overlapping area. The RGB circles adding up properly. In the info bar you can read all the color values. The file is called “NK_dark_grey_pixelmator_add_light.pxm”.

Next is Affinity Photo.


The results are the same. And they should. The file is called “NK_dark_grey_afphoto_add_circles.afphoto”.

Now lets check how the files behave in FCPX. To Import layered images they need to be in the Photoshop format.Sadly at the moment (16th of August 2015) the exported PSD from Affinity Photo does not show up in FCPX as a layered document.
Anyway now it gets interesting.


The selected track on he left is coming from Pixelmator. It has layers and it gets “color managed”. The color values are still the same, the grey value suddenly add up from 80 to 151 and 216 instead of 160 and 240. The values of the Affinity Photo PSD, which is like baked now for the moment show the expected values of 80, 160 and 240 for the grey values.

The Pixelmator PSD can be opened and now change the transfer mode to add of all the layers or at least all of the circle layers.


After changing all the layers to “ADD”, suddenly the result changes…. and now it looks like we working in Nuke again.
The add mode actually works in linear light and not in a gamma corrected color space.

Here again a screenshot from the Nuke Viewer.


All the image files can be found here. PSD_ADD_in_FCPX