Real-world objects appear three-dimensional when viewed as a two-dimensional image through a camera lens due to a combination of several factors:
Perspective: When we observe objects in the real world, our eyes perceive depth and perspective cues. These cues include the relative size of objects, their position in the visual field, and the convergence of parallel lines. When a camera captures an image, it records these cues, which can help create the illusion of depth in a two-dimensional representation.
Binocular disparity: Our eyes are positioned slightly apart, providing two slightly different views of the same scene. This disparity allows our brains to perceive depth and create a three-dimensional mental representation. While a camera captures only a single view, the perspective cues can still provide a sense of depth.
Lighting and shading: Objects in the real world have complex lighting conditions that create variations in brightness, shadows, and highlights. These lighting cues provide additional depth information. A camera can capture these lighting and shading effects, enhancing the perception of three-dimensionality in the resulting image.
Texture and detail: Real-world objects often have intricate textures and fine details. When captured by a camera, these textures can contribute to the perception of depth. The variation in texture and detail across different parts of the image adds visual depth cues.
Although a camera captures a two-dimensional projection of a three-dimensional scene, the combination of perspective, binocular cues, lighting, shading, textures, and details in the captured image can create the illusion of depth, allowing us to perceive real-world objects as three-dimensional, even in a flat photograph.