In this article, you will learn,
- what gray axis correction is and how it works,
- what role the resulting selective color correction profile plays in the color policy,
- how the two correction axes affect the gray balance in print,
- what recommendations we can provide for configuring this option in a profiling project.
1. Introduction
Gray Axis Correction allows you to deliberately shift the gray axis of the calculated characterization profile along the a* axis (red-green) and b* axis (yellow-blue) of the Lab color model to compensate for a visible color cast in neutral and gray image areas in the print.
The intended color impression of the remaining color positions remains largely unchanged. The gray axis itself is shifted, while chromatic colors and spot colors remain largely unaffected by the correction. The background is that the calculated gray axis can show a visible color cast despite correct separation parameters if the substrate, printing ink, or measurement conditions deviate slightly from the reference state, for example, when gray tones appear slightly greenish or yellowish in the highlights.
Figure 1: Correction of the Gray Axis in the a*b* space (schematic)
2. Functioning
The calculated gray axis of a characterization profile ideally follows the neutral axis in the Lab color model, meaning with a* = 0 and b* = 0. If the gray axis deviates from this neutral axis, a visible color cast occurs in gray tones and neutral image areas.
The deviation from the neutral color position is corrected in two independent steps:
- The color position of the gray axis is shifted along the a* axis to compensate for a red or green cast.
- The color position of the gray axis is shifted along the b* axis to compensate for a yellow or blue cast.
The two correction values are used to calculate a selective color correction profile, which affects the achromatic area of the color space and is integrated into the color space transformation of the color policy. Saturated chromatic and spot colors that contain no or only a small achromatic component are not affected, or are affected only slightly, by the correction.
Figure 2: Gray axis before and after correction (schematic)
Using the Correction Axes Independently
Please note that the two correction axes operate independently of each other. The red-green and yellow-blue corrections can be applied individually or in combination, depending on the direction of the observed color cast.
2.1. Effect of the Correction Values
The magnitude of each correction value determines how strongly the color cast of the gray axis is compensated:
- Low correction values (up to approx. ±3 ΔE₀₀) – compensate for a slight, barely perceptible color cast without visibly affecting the rest of the color space.
- Higher correction values (from approx. ±5 ΔE₀₀) – compensate for a clearly visible color cast, for example resulting from a significantly deviating substrate white point.
- Excessively high correction values – cause the gray axis to be shifted beyond the neutral point, thereby introducing a color cast in the opposite direction.
Gray Axis Correction builds on the characterization profile that has already been calculated and does not change its separation; instead, it corrects the color position of the gray axis in the Lab color model. It should therefore be considered separately from the separation parameters described earlier – GCR, Black Start, Black Point Compensation (BPC), and White Point Compensation.
3. Use in a Profiling Project
You can find the Enable Gray Axis Correction option in a profiling project under the Gamut Adjustment tab of the Create Characterization Profile step.
Figure 3: The options in the Gamut Adjustment tab of the Create Characterization Profile step
The two sliders red-green correction and yellow-blue correction are only displayed once the Enable Gray Axis Correction option [1] has been enabled. Both sliders cover a range of −10 to +10 ΔE₀₀ and are set to 0 by default.
Shifting the color position of the gray axis by the configured ΔE₀₀ values generates a selective color correction profile, which is inserted into the color space transformation chain of the color policy. The remaining color positions of the characterization profile remain largely unaffected.
The following recommendations apply to the use of this option:
- Enable Gray Axis Correction [1] – the option is disabled by default. If the option is not enabled, the gray axis of the calculated characterization profile remains unchanged. Use this setting if the gray balance of the profile is already neutral.
Examples of a Red-Green Correction
- Greenish gray – a positive value for red-green correction neutralizes the greenish cast.
- Reddish gray – a negative red-green correction value neutralizes the red cast.
Examples of a Yellow-Blue Correction
- Yellowish gray – a negative yellow-blue correction value neutralizes the yellow cast.
- Bluish gray – a positive yellow-blue correction value neutralizes the blue cast.
Article Update: $PRODUCT_NAME_WORKFLOW 2.3.0 – 09/2026