Until the introduction of HDR, a video display’s color reproduction range was typically represented with a two-dimensional chromaticity diagram such as the 1931 or 1976 CIE chromaticity diagram. A triangle overlaid on the chromaticity diagram indicated the bounds of the color gamut reproduced by a given device or specified by a particular color standard.

However, a color gamut triangle on a 2D chromaticity diagram represents a display’s range of colors at only one luminance level, typically 75% of the display’s peak luminance. As the luminance of any color decreases toward black or increases toward white, the saturation of the color decreases. Thus, at lower and higher luminance levels, the range (gamut) of colors produced by a display decreases; the gamut triangle gets smaller.

Adding luminance levels to the 2D color gamut diagram results in a 3-dimensional color volume that represents the combined ranges of hue, saturation, and luminance that a display can produce.

The Calman Color Volume Analysis workflow provides two different metrics to analyze the volume of a display’s color reproduction range, CIE L*a*b* and ICtCp.
The CIE L*a*b* Color Volume metric measures 140 points and calculates the CIE L* a*b* volume as a percentage of BT.709, DCI-P3, and BT.2020. There is also a Relative or Absolute calculation selection in the workflow page.

The ICtCp Color Volume metric measures 393 points on the gamut shell and calculates how many Millions of Distinguishable Colors (MDC) the display can reproduce.

Setup

Hardware Connect page

Meter

1. Connect your color meter to the computer running Calman.
2. On the Meter Settings tab, click the Find Meter button to connect your meter.
3. On the Find Meters dialog, select your meter if it is listed, then click Search. If your meter is not listed on the Find Meters dialog, just click Search.
4. On the Meter Settings tab, under the Meter Mode drop-down, for a colorimeter select a meter mode appropriate for the display type you are calibrating. No special selection is required for a spectrophotometer.

Source

1. Connect your HDR10-compatible test pattern source to the computer and then connect Calman to the source. Enable HDR10 on the Source Settings tab and select a 1-second source delay.
2. Select the “Window 4-40” pattern window size, if it is available. Otherwise, select the default “Window 10%” pattern window size.

Pattern Insertion

Depending on the display technology you are measuring (LCD or OLED) and the test pattern you selected above, you will need to enable “Full Field Pattern Insertion” (FFPI). In the Calman Settings menu (gear wheel), under Application Measurement Options, configure FFPI as shown below.

• LCD
  • Window 10% pattern: FFPI Settings – Frequency: 1 , Duration: 2, Level: 0%
  • Window 4-40 pattern: FFPI Disabled
• OLED
  • Window 10% pattern: FFPI Settings – Frequency: 30 , Duration: 4, Level: 10%
  • Window 4-40 pattern: FFPI Settings – Frequency: 30 , Duration: 4, Level: 10%

L*a*b* Color Volume page

Setup

• For Peak Luminance Target, select 540, 1000, 1500, 2000, 4000, or 10,000 nits if you want to compare the display to a theoretical display of a certain peak luminance.
• Otherwise, select “Relative” to compare the display to a theoretical display with the same peak luminance of the display you are measuring.
• The number of total measurement points will be indicated.

Results

The results of the CIE L*a*b* Color Volume analysis are shown in terms of the percentage of the calculated color volume to the BT.709, DCI-P3, and BT.2020 color volumes.

Color Volume Visualizer

• When the CIE L*a*b* Color Volume measurement is complete, you can export the measurement data and view it in the Color Volume Visualizer application. Currently, the Color Volume Visualizer is compatible only with the “Relative” CIE L*a*b* measurement type. 

To view the measured color volume:

1. At the bottom of the CIE L*a*b* Color Volume page, click the Export Data button.
2. Edit the name of the file, if desired, and save the .csv file to a convenient directory location.
3. Click the Download App button to download the Color Volume Visualizer.exe file. Copy the executable file to a convenient location.
4. Run the Color Volume Visualizer.exe file.
5. On the Color Volume Visualizer screen (Figure 3), under File, click “Open” and navigate to the .csv data file that you previously saved.
6. When you open the .csv file, the CIE L*a*b* color volume of the display that you measured will be plotted as a 3D volume. You can grab the plot and rotate it to any desired orientation.

ICtCp Color Volume

This metric is based on the ICtCp color space, included in ITU-R BT.2100. ICtCp is an absolute color space that was designed specifically for high dynamic range (over 10,000 nits) and wide color gamut (BT.2020) images. It describes perceptually uniform JNDs over a wide range of luminance and colors. ICtCp can be used to determine the total number of distinguishable colors that can be rendered by a display throughout its entire color volume.

Setup

• The number of total measurement points will be indicated.

Results

• The results of the ICtCp Color Volume analysis is shown in terms of the millions of distinguishable colors (MDC) able to be rendered by the display.