How To ‘Trace’ a LUT’s Contrast Curve By Hand

May 26, 2022

Learn how to use Layer Mixer nodes to recreate a LUT's contrast curve for further creative manipulation in Part 6 of the Visual Math series.


Series

Visual Math Part 6 – Rebuilding (rather than extracting) contrast for more creative control

Throughout this series, we’ve explored different methods for isolating, extracting, and modifying the individual behaviors of a LUT. These exercises encourage us to think more deeply about what we find appealing or problematic in our grades. These techniques also equip us with the ability to exert greater control over the final image.

One of the signatures of any creative LUT is its contrast curve. If you learn to rebuild, tweak, and use a LUT’s contrast curve independently of its other transforms, then this opens up a whole new dimension of creative possibilities.

In today’s Insight, we’ll explore my technique for doing this in a precise yet intuitive fashion through blending modes.

About This Insight

Today, we’re trying a bit of a twist on our previous LUT-centric installments in the series: rather than extracting a particular component, we’re going to rebuild it from scratch, but with the benefit of objective feedback from our scopes that tells us how well we’re doing. It’s a great example of using math and image science in service of a more intuitive process: essentially, we’re “tracing” the original curve like you might have done in art class as a kid.

We will also use the fruits of my previous Insight in this series about split-tone extraction to further ‘trace’ a LUT’s individual RGB channel contrast curves.

Learning Goals

In this Insight, you learn how to:

  • Deploy the Grayscale Ramp DCTL as a quick way of analyzing the net 1D effects of a particular LUT or other process
  • Creatively apply blend modes to give ourselves an easier, more intuitive development/viewing context
  • Understand the difference between modeling precise details versus capturing the essence of a curve or transform
  • Recombine our decoupled LUT elements and exert modular control over each element

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Comments

Homepage Forums How To ‘Trace’ a LUT’s Contrast Curve By Hand

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    • Stephen A
      Participant

      No comment, just a thanks to you Cullen. This series is full of neat tricks. And recorded at 6AM no less!


      • Cullen Kelly
        Participant

        Thanks Stephen! Lol, you found my secret superpower — operate like I’m three time zones east of California😂


    • Jim Robinson
      Participant

      Hey Cullen,
      I like the idea of splitting the contrast out. Without seeing this video, I think that to get the curve of the contrast that my thoughts would have been to put a grey scale in, but a stepped version of it and add the LUT and desat and take a still, then to construct the contrast, I would do an image wipe of the still on a virgin node of the greyscale with a horizontal reference and then move the contrast to match the still on the curves.
      Not sure how close it would be to your demo here, but I have done this in the past to put film look  power grades to no contrast in the past and used them with my own contrast and curves.
      I’ll have to give this a shot and see how they compare. The process that I did was really easy, so there might be something that I am missing. But I find it easy to click on the source monitor and set the curve points to be an easier process than just eyeballing it.
      Thanks again for all your information that you have provided. I really enjoy them because they get me thinking about things that on a day to day process, I tend to neglect.

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