How to Recognize Whether a Photograph Is 2D or 3D?

Author:

Prof. Kali Chandrakant

M.Sc., M.Ed., D.C.S.

50+ Years of experience in Physics teaching

 1. Introduction:

    Photography is an integral part of modern life. With the widespread use of smart phones, most people’s memories are filled with images, especially selfies. Digital platforms like Google provide a vast repository of visual information. Since the invention of the laser in 1960, methods for storing and representing visual information have advanced significantly.

    Today, we commonly encounter two types of photographic representations: two-dimensional (2D) and three-dimensional (3D) images. This article explains how to distinguish between a 2D photograph and a 3D photograph using principles of optics and human vision.

 2. Human Vision and Depth Perception:

  Fig. A                Fig. B

Fig. A: Light reflecting off an object toward the eye

   To understand photography, we must first understand the human eye. The process of “seeing” is a complex biological sequence: (Fig. B)

1. Light Entry: Light reflects off an object and enters the eye through the cornea and pupil.
2. Focusing: The eye’s lens refracts the light, focusing it onto the retina at the back of the eye.
3. Signal Conversion: Photoreceptor cells on the retina convert light into electrical signals.
4. Processing: The optic nerve carries these signals to the brain, which interprets them as the images we see.

    Although the images formed on the retina are fundamentally two-dimensional, the brain interprets them as three-dimensional by integrating information from both eyes and using depth cues such as stereopsis and perspective.

  Stereopsis refers to the brain’s ability to fuse slightly different views from the left and right eyes into a perception of depth and distance—a key aspect of 3D vision.

 3. Two-Dimensional (2D) Photography:

  3.1. Conventional Photography:

    Traditional photography—the kind we use every day—is limited. It only captures a fraction of the information available in light waves.

    A two-dimensional image exists only in length and width; it lacks depth. If a flat image is viewed edge-on, it appears as a line.(Fig. C)

Fig.C

Fig. C: Example of a two-dimensional representation

 Photography, in its conventional form, captures 2D images of three-dimensional objects by recording the intensity of light.(Fig. D)  Light from a scene strikes an image sensor or photographic film, which then records the brightness distribution.

Fig.D

Fig. D: Formation of a photographic image on film or sensor

    In conventional photography, the phase information of light waves (which encodes depth) is lost. As a result, features at different distances from the camera (such as the nose and eyes in a portrait) appear to lie on the same plane.

  3.2. Key Features of 2D Photography:

1. Only the intensity of light is recorded, without phase information.
2. Normal light sources such as sunlight or artificial lighting suffice.
3. A lens is required to focus the image onto a recording medium.
4. Damage to the negative or digital image can irreversibly lose information.
5. A single photograph cannot simultaneously record multiple distinct views.
6. The information storage capacity is limited.
7. Superimposing many images together is not feasible in a single exposure.
8. Traditional photography produces a negative on film.

 4. Three-Dimensional (3D) Photography: Holography:

  4.1. Holography:

    A true three-dimensional image contains depth (the Z dimension) in addition to height and width. This allows visualization from different angles.

Fig.E

Fig. E  A commercial hologram on product packaging

   One method to create a 3D image is to capture multiple views of an object from slightly different angles and combine them so that each eye sees a distinct perspective. This principle underlies stereoscopic photography and 3D movies.

  Fig. F           

Fig. F: A three-dimensional holographic image

 4.2. Dennis Gabor:

Fig.G

Fig. G: Dennis Gabor, pioneer of holography

     In 1948, Dennis Gabor developed a technique to record both the amplitude and phase of light waves reflected from an object, enabling true 3D imaging. This process is known as holography. A hologram captures the full optical information of the object via interference and diffraction patterns formed by coherent light, such as from a laser.

  4.3. Key Features of 3D Photography (Holography):

1. Both intensity and phase information of light are recorded.
2. A coherent, monochromatic light source (usually a laser) is required.
3. Light scattered directly from the object reaches the recording medium.
4. Even a fragment of a hologram can reconstruct the entire 3D image.
5. Multiple images can be recorded on a single hologram.
6. The information storage capacity is high.
7. Multilayered and superimposed images are possible.
8. Holograms typically produce a positive reconstructed pattern.

 5. Recognizing Whether a Photograph Is 2D or 3D:

    Consider three photographs of a building taken from different directions:

 

Fig. H: Front view of the building	Fig. I: Left-side view of the building	Fig. J: Right-side view of the building

  Each photograph captures different details depending on the angle from which it was taken. However, once a 2D photograph is taken, changing the observer’s viewing position does not reveal additional information—the recorded scene remains unchanged.

   In contrast, a true 3D representation (such as a hologram) changes perceptually with the angle of view, revealing additional spatial information about the object as the observer’s perspective changes.

 6. Practical Identification Rule:

    2D Photograph:

   The recorded view does not change with a shift in viewing angle.

    3D Image (Hologram):

    The observed image changes or reveals additional spatial information when viewed from different angles.

   Thus, a simple method to determine whether an image is 2D or 3D is to observe the scene from varying angles: unchanging information indicates a 2D photograph, whereas changing information indicates a 3D image.

Feature	2D Photograph (Figs C, D, )	3D Hologram (Figs E, F, )
Recorded Data	Intensity only	Intensity + Phase
Light Source	Ambient/Flash	Coherent Laser
Perspective	Static / Flat	Changes with viewing angle
Visual Depth	Optical Illusion	Physical Information
Technology	Standard Camera	Laser / Holography

  7. Conclusion:

     The transition from 2D to 3D is the transition from a “partial record” to a “total record” of light. Conventional photography captures two-dimensional images by recording only the intensity of light, resulting in flat representations of three-dimensional scenes.

     Holography, on the other hand, records both intensity and phase, enabling the reconstruction of full 3D images that reveal depth and parallax. Changing the viewing angle provides a straightforward way to distinguish between 2D photographs and 3D holographic images.

8. Video Support:

Please observe the 3d video by 360° video recording