In computer graphics and human–computer interaction, which of the following is considered a graphical input device for direct interaction with on-screen graphics?

Introduction / Context:
Graphical input devices allow users to specify positions, select objects, or draw directly within a graphical display environment. This question asks which device is specifically designed for direct graphical interaction with the display surface.

Given Data / Assumptions:

• Interaction takes place with a raster display.
• Devices may be direct (on-screen) or indirect (on a surface separate from the screen).
• We focus on classic categorization used in HCI and graphics texts.

Concept / Approach:

A light pen is a pen-like device used to point to or draw directly on a CRT display by detecting light emitted from the screen. It is historically labeled a 'graphical input device' because it captures coordinates from the display itself rather than a separate surface.

Step-by-Step Reasoning:

Verification / Alternative Check:

Historical graphics systems categorized light pens with tablets and digitizers as graphical input devices, distinct from text keyboards and general pointing devices.

Why Other Options Are Wrong:

Keyboard is for text entry. Mouse and trackball are indirect pointing devices; while used in GUIs, they do not directly acquire graphical coordinates from the screen surface.

Common Pitfalls:

Equating any pointing device with 'graphical input'; many curricula reserve the term for devices that capture on-screen or tablet coordinates directly.

Final Answer:

Light pen