1. Copy the .3dl file into the following directory:
/Applications/Hiero1.6v1/Hiero1.6v1.app/Contents/Plugins/OCIO/nuke-default/luts
2. Edit the following file in your favorite text editor:
/Applications/Hiero1.6v1/Hiero1.6v1.app/Contents/Plugins/OCIO/nuke-default/config.ocio
3. Look for the section in the file that specifies the display luts. It looks like this:
displays:
default:
- !<View> {name: None, colorspace: raw}
- !<View> {name: sRGB, colorspace: sRGB}
- !<View> {name: rec709, colorspace: rec709}
4. Add another view definition for your custom LUT:
- !<View> {name: LogCRec709, colorspace: LogCRec709}
5. Go to the very end of the file, and add a colorspace definition:
- !<ColorSpace>
name: LogCRec709
family: ""
equalitygroup: ""
bitdepth: 32f
description: |
Conversion from Alexa LogC to Rec. 709
isdata: false
allocation: uniform
allocationvars: [-0.125, 1.125]
from_reference: !<FileTransform> {src: LogC_to_Rec709.3dl, interpolation: linear}
6. Restart Hiero
And that should do it.