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proper FileTransform usage

Paul Miller <pa...@...>
 

I need advice on the correct way to use a LUT file transform in an OCIO processor. My results when using a FileTransform look different than in Nuke, with whites appearing more subdued using the test LUT I have. Am I doing this right?

My normal OCIO processor looks like this:

DisplayTransformRcPtr transform = DisplayTransform::Create();
transform->setInputColorSpaceName(colorSpaceName);
transform->setDisplay(displayName);
transform->setView(lookName);
transform->setLinearCC(gainTransform);
transform->setChannelView(swizzle);
transform->setDisplayCC(exposureTransform);

processor = config->getProcessor(transform);

However, I also allow bringing in an external LUT file, and I use it like this in lieu of the DisplayTransform:

FileTransformRcPtr fileTransform = FileTransform::Create();
fileTransform->setSrc(path);
fileTransform->setInterpolation(OCIO::INTERP_LINEAR);

GroupTransformRcPtr group = GroupTransform::Create();
group->push_back(gainTransform);
group->push_back(fileTransform);
group->push_back(exposureTransform);

processor = config->getProcessor(group);

I'm using the same display shader for both.

Mark Boorer <mark...@...>
 

Hi Paul,

When you say your FileTransform results differ from Nuke's, is this from using a Vectorfield node, or an OCIO FileTransform node, or perhaps an OCIO Display node entirely? Also what format of LUT are you using?

(I'd also recommend using INTERP_TETRAHEDRAL where possible)

Cheers,
Mark

On Tue, Mar 8, 2016 at 5:52 PM, Paul Miller <pa...@...> wrote:
I need advice on the correct way to use a LUT file transform in an OCIO processor. My results when using a FileTransform look different than in Nuke, with whites appearing more subdued using the test LUT I have. Am I doing this right?

My normal OCIO processor looks like this:

  DisplayTransformRcPtr transform = DisplayTransform::Create();
  transform->setInputColorSpaceName(colorSpaceName);
  transform->setDisplay(displayName);
  transform->setView(lookName);
  transform->setLinearCC(gainTransform);
  transform->setChannelView(swizzle);
  transform->setDisplayCC(exposureTransform);

  processor = config->getProcessor(transform);

However, I also allow bringing in an external LUT file, and I use it like this in lieu of the DisplayTransform:

  FileTransformRcPtr fileTransform = FileTransform::Create();
  fileTransform->setSrc(path);
  fileTransform->setInterpolation(OCIO::INTERP_LINEAR);

  GroupTransformRcPtr group = GroupTransform::Create();
  group->push_back(gainTransform);
  group->push_back(fileTransform);
  group->push_back(exposureTransform);

  processor = config->getProcessor(group);

I'm using the same display shader for both.

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Paul Miller <pa...@...>
 

On 3/8/2016 7:01 PM, Mark Boorer wrote:
Hi Paul,

When you say your FileTransform results differ from Nuke's, is this from
using a Vectorfield node, or an OCIO FileTransform node, or perhaps an
OCIO Display node entirely? Also what format of LUT are you using?

(I'd also recommend using INTERP_TETRAHEDRAL where possible)
Actually, what we found was creating an actual OCIO config out of the LUT file transform produced the proper results. Not entirely sure what the actual difference is under the cover.

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