Psychtoolbox release “Tag games” released

Psychtoolbox 3.0.19 Beta update “Tag games” was released at 16th March 2024.
As usual, the complete development history can be found in our GitHub repository.
The release tag is “”, with the full tree and commit logs under the URL:

This release adds some experimental April tag marker tracking support via the
PsychCV file on Linux. The outcome of a little vacation hobby coding project,
a revival of marker tracking, using the modern apriltags library as successor of
good old ARToolkit, whose support was phased out quite a while ago. Backwards
incompatible changes are in principle possible for this new functionality, as I learn
from practical dabbling with April tag marker tracking.

Compatibility changes wrt. Psychtoolbox



Experimental Apriltags fiducial marker tracking support on Linux.


  • New helper function PsychCamIntrinsicsToGLProjectionMatrix().
    Given camera intrinsic parameters from some camera calibration software,
    and the desired zNear and zFar clipping planes of the view frustum,
    compute and return a projection matrix for use as GL_PROJECTION_MATRIX
    for OpenGL rendering with a virtual pinhole camera that approximates the
    properties of the real camera.


  • Psychtoolbox was built and lightly tested against Matlab R2023b.

    (Re-)add PsychCV() mex file for Octave and Matlab, with support for
    vision based tracking of AprilTag fiducial markers (aka tags) by use
    of the apriltag library. This PsychCV mex file will only work on
    Ubuntu 22.04-LTS and later, not on Ubuntu 20.04-LTS anymore.


  • Psychtoolbox was built and lightly tested against Matlab R2023b.


  • Psychtoolbox was built and lightly tested against Matlab R2023b and
    Octave 8.4 from HomeBrew.