Knowledge Base

Calibrate FaceReader

Aim

To correct for person-specific biases in facial expressions, for example if someone looks angry or sad by nature. Instead of calibration you can also use a Stimulus to score an episode in which your test participants have a neutral expression and carry out relative analysis. See Select absolute or relative values for your parameters.

Prerequisites

• You have the regular version of FaceReader. Calibration is not available in Baby FaceReader.
• You notice a person-specific bias in facial expressions. If there is no such bias, we recommend not to use calibration since it may then decrease analysis accuracy.
• You first checked whether changing the camera, or lighting conditions removes the bias.

Two Calibration Methods

FaceReader has two calibration methods:

• Participant calibration — Use this method if you analyze videos or images. Also use this method if you do camera analysis and the experimental setup allows capturing a neutral phase before the experiment starts. See Participant calibration
• Continuous calibration — Use this method if you carry out camera analysis and the experimental setup does not allow capturing a neutral phase before the experiment starts. This is for example the case if you start FaceReader automatically with another program. See Continuous calibration

Participant Calibration

Aim

To correct for person-specific biases in facial expressions.

Prerequisite

You have a video fragment, or images in which the expression of the test participant was neutral. Alternatively, if you carry out camera analysis, you are able to record a scene during which the test participant looks neutral. Please note that you need at least 100 images for the calibration.

See also How participant calibration works

Procedure

1. Create a participant calibration
2. Select a participant calibration

Create A Participant Calibration

1. Make sure all analyses of the participant are closed. To close an open analysis, click the button next to it.
2. Do one of the following:
   • Choose Participant > Calibrate Participant.
   • Right-click the participant and choose Calibrate Participant.
3. Select the Face Model. See Active Face Model
4. Choose the calibration source:
   • Images – Select the files in which the participant looks neutral.
   • Video – Select the video file and scroll to the part where the test participant looks neutral.
   • Camera – Ask the test participant to look neutral.
5. Click the Start analysis button. When the calibration is created, the Calibration Effect field shows the facial expressions before and after calibration.
6. When you are satisfied with the calibration, give it a name and click OK. FaceReader asks whether you want to use this calibration for all future analyses of this participant. Choose Yes if you want this.

   If you are not satisfied with the calibration, click the Retry with same source button and repeat step 5.

Notes

• If you chose to use the calibration for all new analyses of this participant in step 6, the calibration is selected automatically in all new analyses of that participant. For the already created analyses you must select the calibration manually and redo the analysis.
• To change a calibration for a participant, select the new one, choose Participant > Set calibration as default.
• To delete a participant calibration do one of the following:
  • Choose Participant > Delete calibration.
  • Unfold the participant item in the Project Explorer. Then right-click the calibration and choose Delete calibration.

Select A Participant Calibration

IMPORTANT Use the same Face model (see Active Face Model) in the analysis, as was used to create the calibration. To use another face model, first create a new calibration with this model. Then do one of the following:

• Select the calibration for a specific analysis
• Select the calibration automatically for all future analyses of a participant

Select the calibration for a specific analysis

1. Make sure that continuous calibration is set to No in the Analysis settings window on the bottom-left of the analysis part on your screen.
2. Click the pencil button next to Selected calibration and select the calibration from the list.

Select the calibration automatically for all future analyses of a participant

1. Open the Participant item and then the Calibrations item in the Project Explorer.
2. Right-click the calibration and select Set Calibration as Default.

Source: FaceReader 10 Reference Manual (Help), Noldus Information Technology