ID 353295 - F_Regrain node that uses a grain image source directly from a AlexaV3LogC-based Read node can create a 'not enough detail' error message in the viewer

Problem summary
When using the 'F_Regrain' node, if you use a source image as the grain source that is of an 'AlexaV3LogC' colorspace, in some instances the grain will not calculate correctly and create the following error:
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This only occurs when the colorspace of the 'Read' node is set to 'AlexaV3LogC', and the 'Read' node is connected directly to the 'F_Regrain' 'Grain' input.

Customer reported version
nuke.11.1v3

Customer reported platform
centos7

Steps to reproduce

Open the attached script and change the analysis region to view the issue.

or

1) Read in your 'AlexaV3LogC' footage

2) Create a 'F_Regrain' node and connect the 'Read' node directly into the 'F_Regrain' 'Grain' input

3) Create a 'Constant' node and set the value to '0.18'

4) Connect the 'Constant' node to the 'F_Regrain' 'Src' input

5) Ensure that the 'Grain Type' in the F_Regrain node is set to 'From Grain Clip'

6) Drag the analysis region selector in the Viewer to select the grain from the grain to apply to the Constant node.
Result: You will receive an error letting you know that you have not provided enough information for the grain to use (see image above)

7) Alter the Read nodes colorspace to another colorspace e.g. sRGB
Result: Regrain process works correctly.

Workaround
There are two workarounds for this:

- Break the direct connection between the 'Read' node and the 'F_Regrain' node with a processing node such as a 'Grade' node. This node does not need to have any values changed, it just needs to break the direct connection.

- Change the 'Read' node's 'colorspace' to an alternative 'colorspace', such as 'sRGB' or 'Cineon'.

Reproduced by support
This bug has been reproduced in:
Nuke 11.1v4 - Windows 7 - MacOS 10.13.4 - CentOS 6.9
Nuke 11.1v1 - Windows 7
Nuke 11.0v4 - Windows 7
Nuke 11.0v1 - Windows 7
Nuke 10.5v7 - Windows 7
Nuke 10.5v1 - Windows 7
Nuke 10.0v6 - Windows 7
Nuke 10.0v1 - Windows 7
Nuke 9.0v9 - Windows 7
Nuke 9.0v1 - Windows 7
Nuke 8.0v7 - Windows 7
Nuke 8.0v1 - Windows 7
Nuke 7.0v10 - Windows 7 - MacOS 10.13.4 - CentOS 6.9

Earliest version tested
Nuke 7.0v10
- This issue appears to be in all versions of the product

Expected behaviour
The F_Regrain node should not be producing an error when using 'AlexaV3LogC' is used as the source

Actual behaviour
The F_Regrain node is producing an error when using 'AlexaV3LogC' is used as the source