Gamma Correction
In this article:
The Linear Gamma Correction feature allows EventIDE to compensate for the non-linear luminance characteristics of display devices. By applying an inverse correction profile, EventIDE ensures that stimulus intensity values correspond more closely to actual physical luminance. This improves stimulus consistency and accuracy, making gamma correction an essential tool for experiments that rely on precise visual presentation.
Introduction
Modern displays do not produce luminance in a perfectly linear relationship to the digital RGB values sent to them. When a stimulus is displayed with an RGB value of 50%, the physical brightness emitted by the monitor is typically not 50% of the maximum brightness. Instead, most monitors follow a non-linear response curve known as a gamma curve.
For experiments involving visual perception, psychophysics, neuroscience, or any task where precise control of stimulus luminance is important, this non-linearity can introduce unintended variations in stimulus intensity. EventIDE provides a Linear Gamma Correction feature that compensates for the monitor’s gamma characteristics and creates a linear relationship between requested stimulus intensity and actual luminance output.
Why Gamma Correction is Important
Without gamma correction:
Equal numerical steps in RGB values do not produce equal changes in brightness.
Visual stimuli may appear brighter or darker than intended.
Contrast levels may not correspond to experimental specifications.
Luminance-dependent measurements can become inaccurate.
With gamma correction enabled:
Requested stimulus intensities are transformed before being sent to the display.
Physical luminance changes proportionally with the specified stimulus intensity.
Visual stimuli can be presented with greater precision and reproducibility.
This is particularly important for:
Psychophysical experiments
Visual neuroscience studies
Contrast sensitivity measurements
Brightness discrimination tasks
Calibration-sensitive visual paradigms
Enabling Gamma Correction
To configure gamma correction open the Application Menu and navigate to the Gamma section.
The Gamma Correction window contains three main panels:
Monitor's Gamma Profile. The profile can be defined in two ways: by entering measured calibration values or by generating an approximate profile using a gamma power function. A typical monitor profile shows a curved relationship rather than a straight line.
Correction Profile. This profile displays the inverse transformation calculated from the monitor profile. This correction profile determines how EventIDE modifies RGB values before sending them to the display.
Resulting Profile. This profile shows the expected luminance response after correction. An ideal gamma-corrected display produces a straight diagonal line, indicating linear luminance output, predictable brightness increments, and accurate intensity control.
The Linear Gamma Correction switch at the top of the window enables or disables gamma correction. When enabled, EventIDE automatically applies the correction profile to all visual stimuli during experiments running in full-screen mode. When disabled, stimuli are presented using their original RGB values without modification.
Creating a Monitor Gamma Profile
Method 1: Using Measured Calibration Data
For the highest accuracy, measure the monitor using a photometer, colorimeter, or luminance meter.
For each color channel:
Display a series of intensity levels.
Measure the corresponding luminance values.
Normalize the measurements to a range between 0 and 1.
Enter the values into the Profile Values table.
Once the profile is entered, EventIDE automatically calculates the correction profile.
This method is recommended for experiments requiring precise luminance control.
Method 2: Using the Power Function Generator
If calibration hardware is not available, an approximate profile can be generated using the Power Function Generator. The generator uses the equation:
where:
X = input intensity
Y = normalized luminance
γ = monitor gamma value
min = minimum luminance level (in most cases, 0.0)
max = maximum luminance level (typically, 1.0)
Separate parameters can be specified for red, green, and blue channel.
Gamma Power defines the shape of the monitor response curve. Typical values:
Display Type | Gamma |
Standard PC monitor | 2.2 |
Mac displays (historical) | 1.8 |
Calibrated displays | Varies |
To create an approximate monitor profile:
Enter gamma values for each color channel.
Specify minimum and maximum intensity values.
Click Generate Gamma Profile.
EventIDE then automatically computes the correction profile table.
Best Practices
Create separate gamma profiles for different monitors.
Recalibrate when changing displays or display settings.
Disable automatic monitor brightness adjustments.
Use fixed contrast and brightness settings during calibration and experiments.
Recalibrate periodically, especially in long-term research setups.
Use measured luminance values whenever experimental accuracy is critical.