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An ideal camera captures the light rays passing through a pinhole. It generates a 2D image where each pixel corresponds to a ray, and the X and Y coords determi

An ideal camera captures the light rays passing through a pinhole. It generates a 2D image where each pixel corresponds to a ray, and the X and Y coords determine the direction of the ray. Because every ray passes through the same pinhole point, you can't do things like change the depth-of-field or move the camera once the image is created. (An ideal pinhole camera has everything in focus) A light-field camera captures the light rays passing through an entire area. This generates (in theory) a 4D image. Still 2 degrees of freedom for ray direction, but an extra 2 degrees for ray position. Because the rays pass through different points, you can re-project a light field image to create 2D images with different depth of field, or different virtual camera positions.

jiggawatts 4y ago
A surprising aspect is that the lightfield merely appears to be 4D. If you stop and think about it, all of the information can be captured in the 2D plane of the aperture. So effectively, it is just a 2D image! This is akin to a hologram, which looks truly 3D, with depth of field, refocusing, and the works, but is physically a 2D photographic plate. Literally just a sheet. The hologram captures the 2D slice through the EM field the same way that a lightfield captures a 2D slice through the aperture. The key thing is that the phase information must be captured also, which in the case of holograms requires a resolution finer than the wavelength of light. Lightfield imaging does it differently, but the same concepts apply.
- tragictrash 4y ago
  When you say hologram, are you referring to something like a holographic sticker, or a star trek hologram?
  - mlyle 4y ago
    He's referring to not the star trek hologram, and not really the holographic sticker. This is one holographic plate illuminated by a laser, viewed from different viewpoints: https://en.wikipedia.org/wiki/Holography#/media/File:Holomouse2.jpg https://en.wikipedia.org/wiki/Holography#/media/File:Holomou... And it's not like those things with the bumpy lenses, that show you an image from a few chosen viewpoints, either. You can look at that mouse from a wide range of angles and distances. Handwavy, short explanation: All the light arriving back from the mouse-- in different directions-- is encoded into the speckles on the plate. When a coherent source of light is used to illuminate the plate, again, the light exits with the same characteristics it had entering the plate.

jiggawatts 4y ago

A surprising aspect is that the lightfield merely appears to be 4D. If you stop and think about it, all of the information can be captured in the 2D plane of the aperture. So effectively, it is just a 2D image! This is akin to a hologram, which looks truly 3D, with depth of field, refocusing, and the works, but is physically a 2D photographic plate. Literally just a sheet. The hologram captures the 2D slice through the EM field the same way that a lightfield captures a 2D slice through the aperture. The key thing is that the phase information must be captured also, which in the case of holograms requires a resolution finer than the wavelength of light. Lightfield imaging does it differently, but the same concepts apply.

tragictrash 4y ago
When you say hologram, are you referring to something like a holographic sticker, or a star trek hologram?
- mlyle 4y ago
  He's referring to not the star trek hologram, and not really the holographic sticker. This is one holographic plate illuminated by a laser, viewed from different viewpoints: https://en.wikipedia.org/wiki/Holography#/media/File:Holomouse2.jpg https://en.wikipedia.org/wiki/Holography#/media/File:Holomou... And it's not like those things with the bumpy lenses, that show you an image from a few chosen viewpoints, either. You can look at that mouse from a wide range of angles and distances. Handwavy, short explanation: All the light arriving back from the mouse-- in different directions-- is encoded into the speckles on the plate. When a coherent source of light is used to illuminate the plate, again, the light exits with the same characteristics it had entering the plate.