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Prepping Onset Lighting Stills Photography

Here we will look at how we go about prepping our onset lighting stills photography into ACEScg.

Test Data

If you are looking for some test data, you can pick up a series of photographed Macbeth charts here:


At CAVE, we are rendering in ACEScg, and for all lighting references, we are also prepping them in ACEScg. This includes HDRIs and lightmaps.

We are using RawTherapee to convert the images from RAW cr2 to 32bit TIF. The reason we are going with 32bit TIF is to ensure no data is clamped. However, , if you are merging and stitching your HDRIs in PTGui, then we find you can work directly in the app with cr2 images and export to ACES, as demonstrated here:

But… if you do need to go through RawTherapee, the workflow looks something like so:

Once you’ve prepped your data, you can then use Nuke for grading and balancing your exposure values.

Prepping your Data in RawTharepee

In RawTherapee, navigate to the directory containing your RAW (in our case, CR2) images and load them into RawTherapee. For this example, we are using the following images:

  • D:\shop\cave_greyChromeMacbeth_reference_1001\cave_referenceKit_test\raw\

This set of images is of the Macbeth chart along with a grey and chrome sphere. Along with a evenly exposed shot, we have a bracketed set of images (7 brackets, 2 stops apart), which is what I’ll be working with.


Once you’ve loaded your images, select the mid-exposed shot, jump to the Exposure tab and set the following:

  • clip-out-of-gamut colours: Disable
  • Highlight reconstruction: Luminance Recovery
  • Tone curve 1: Linear, Standard
  • Tone curve 2: Linear, Standard

White Balance

This step is not necessary (as we’ll be doing a proper grade in Nuke) but we like to do it as a kind-of pre-grade.

On the Colour tab, go to White Balance and click on the ‘Pick’ button, and then click on a grey swatch (mid grey).

Colour Management

This is where we will define our Working Profile and Output Profile. For lighting reference, as mentioned previously, we’ll be maintaining an ACES colour pipeline. So, set the Working Profile to ACESp1.

Next, set the Abstract Profile to Custom and the Gamma value to 1 (Slope should automatically be at 1).

Lastly, set the Output Profile to: RTv4_ACES_AP1


Jump to the Raw tab now and set the Demosaicing Method to: RCD+VNG4

Copy/Paste your Modifications to all the Images

As we are dealing with a bracketed set of images, we’ll want to apply our tweaks to all the images. To do this, select your image and hit the right-mouse-button. Then go Processing profile operations > Copy.

…Then hit Ctrl+A to select all the images, and go Processing profile operations > Paste.

Export your Images

If all looks good and once you’ve applied all the tweaks to all the images, select them, hit the right-mouse-button and go ‘Put to queue‘:

Jump to the Queue tab and set the following:

  • File format: TIFF (32-bit float)
  • Uncompressed TIFF: Enabled
  • Save processing parameters with image: Enabled

Once all looks good, kick off the processing of the images.

You should now see something like so:

Assessing your Image in Nuke

Just a quick note that we’ll not be covering a full grading workflow in this doc. We’ll just be running through the basics in order that you can check your data, and so you get an idea of how to continue pushing your data through the pipeline.

If you now launch Nuke, hit the S key to bring up the Settings and go to the Color tab. Then, set the following:

  • color management: OCIO
  • OCIO config: aces 1.1 or aces 1.2

Then read in your mid-exposed image and make sure the Colorspace is set to default (scene_linear)


You can now grade your reference using your standard tools, or in our case, we are using the mmColorTarget tool. For lighting and as we are looking to maintain an ACES workfow, set the colorspace to ACEScg for the target.

You should end up with something like so:

You can now apply the colour transform to all the other images.

For writing out images, we are using the following settings:

  • colorspace: ACES – ACEScg
  • File type: EXR
  • datatype: 32 bit float
  • compression: none (our preference)

That’s it. Your lighting images should be good to go and ready to merge and stitch together to generate your 360 HDRIs or lightmaps.


  • RawTherapee – RawTherapee is a free, cross-platform raw image processing program.
  • Jedypod blog – Excellent info on working with RawTherapee for VFX.

Onset Data Acquisition and Creating Look Dev Environments Course

If you are looking for a more detailed step-by-step breakdown, you can check out our courses on capturing and working with light maps here:

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