Illuminant Direction
Definition
The 3-D vector pointing from the scene toward the dominant light source. In a single-exposure photograph from a single scene, the illuminant direction should be consistent across all objects. Inconsistency between regions indicates compositing.
- Definition
- 3-D vector from scene toward dominant light source
- Expected property
- Consistent across all objects in a genuine single exposure
- Forgery indicator
- Inconsistency between regions signals compositing
- Analysis category
- Lighting-based image forensics
Common questions
How does an examiner actually estimate illuminant direction from a photograph?+
Analysts typically use the shape and orientation of shadows, highlights, and specular reflections on curved surfaces such as eyes to model the direction light would need to come from to produce those patterns. Software tools automate this by mapping surface normals and comparing predicted versus observed shading.
Can natural scene features create a false illuminant inconsistency without forgery?+
Yes. Multiple light sources, such as sunlight plus an indoor lamp, or complex reflective surfaces like water and glass, can legitimately produce different apparent light directions in one genuine photograph. Examiners have to consider the scene's actual lighting setup before concluding compositing occurred.
Related terms
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- Photometric Stereo
- A technique that recovers surface normals and illuminant direction from shading patterns. When applied to a single image, it uses local shading...
- Shot Noise
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- Specular Highlight
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