ACES synthetic chart

Discussions - Using ACES
1

Hi all

I would like to understand a bit more about the ACES synthetic chart.

Does it represent all possible values of ACES? Or is ACES bigger/smaller then the chart?

When playing about with very extreme colour adjustments in grading software I can bring what appears to be white/black into what my grading software, monitor and brain understands as saturated colour. How can I visualise where these values sit within the visible light spectrum, and also with respect to Rec709, Rec2020, P3, PQ D65, etc?

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2

Hi @jamesv,

Here is some text I had previously prepared explaining this chart. It was created because we needed “a test chart”. In hindsight, some of the things are of questionable use and we could most likely add or modify for ACES 2.0 if there are other items that would be judged useful. But it has been serving its purpose for now…

About the “SytheticChart.01.exr” image

General

Overall target size is 2K (2048x1080)
The background value is [0, 0, 0]

Columnar gradients

  • 190 columnar gradients, 10 pixels wide each, 1900 pixels wide total
  • generated from spectra of the “190 Patches” (used for IDT training set of spectral reflectances - from US Patent 5582961)
  • nominal ACES RGBs were calculated using RICD spectral sensitivities and a D60 illuminant
  • then scaled across a (-7/+7) exposure range

Horizontal gradient ramps

  • 14 horizontal gradients
  • Left half consists of logarithmically spaced values between -65504 and -2^{-14}
  • Right half consists of logarithmically spaced values between 2^{-14} and +65504
  • Ramp is then a joining of the left half and right half (i.e. negative and positive ramps)
  • Ramp is replicated vertically and ordered neutral, red, green, blue, cyan, magenta, yellow
    • e.g gradients are generated as [ramp, zeros, zeros], [zeros, ramp, zeros], [zeros, zeros, ramp], …
  • top 7 gradients are pure ACES ramps
  • lower 7 ramps have had a P3D60-to-ACES matrix applied (i.e. they are supposed to be P3-D60 values re-expressed in AP0 colorimetry)

ColorChecker SG

  • 5 ColorChecker charts at various exposures, interior colored patches only
    • i.e. not including the surrounding Black/White/Gray chips
  • From left to right the charts are -3, -1.5, normal, +1.5, +3 stops

Noise

  • 5 patches of Gaussian noise with mean of 0 and varying variances
  • NOTE - this section in particular is of questionable intent and could use revision

ColorChecker 24

  • 18%, 100% and 24 Macbeth ColorChecker patches arranged in vertical series
  • generated from spectra of the ColorChecker chart (ISO 17321-1 Tables C.2 and C.3)
  • nominal ACES RGBs were calculated using RICD spectral sensitivities and a D60 illuminant
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