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A light field camera can be used to make shots which can be truly refocused after the shot, however if I understand the technology correctly it would be just as easy to process the "image data" in such a way that you can get a shot which is entirely in focus, which seems even more interesting than after the fact focusing. However, as far as I know with the current light-field camera(s) this is not possible, so is this technically impossible or is there another reason this has not yet been done? (Such as it being possible somehow with traditional cameras?)

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Relevant - petapixel.com/2014/04/22/… - note that in the preview thing there, the perspective shift actually does just this. –  AJ Henderson Apr 22 at 17:31
    
@AJHenderson: WOW! I had seen those previews before, but didn't notice the drag functionality until now. Got to say I also don't get why there is that 3d effect and I only noticed now that often the background layers (as the viewer at least I also noticed now works in layers) isn't in focus no matter what... oh well, looking forward to the results when it gets on the market. –  David Mulder Apr 22 at 18:04

2 Answers 2

up vote 2 down vote accepted

No. They cannot be entirely in focus. That is why there is a focus control.

You see, the lightfield is captured by micro-lenses splitting light. This effectively creates a stack of images at different focus-distances. Software interpolates between these to generate an image which is in focus at any range from the nearest to the furthest focus-plane which is captured.

This lets you have a great depth-of-field but not an infinite one. If you want to cover a much wider range of focus, you will have to resort to manually focus-stacking because you can move and set the lens at a greater number of distances and with greater depth. The difference in focus between micro-lenses is just not that big.

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It is certainly possible through a similar principal to focus stacking. If that feature actually isn't available, it's entirely opinion as to why it hasn't been added unless they have some disclosure of that, but the same focus stacking technique that works for traditional images would work for individual slices taken from a light-field shot.

As for why this is necessary with a light-field camera, think about determining what part of the image is in focus. The camera may capture the image at an infinite number of focal depths, but in order to piece together an image that is more in focus than the optical system would have produced for a given selection of focal plane, parts of the image have to be taken from different focal distances and this means that each pixel has to be selected for the most in focus distance and blend them with the sharpest parts from other parts. This is the same if your source is either a light-field camera or a still camera, the only difference is the simplicity in capturing the depth information.

If I had to guess, I'd say it is because the entire point of a light field camera is that it gives depth of field blur but still allows shifting. If someone want's an image entirely in focus, there's not much reason to use a light-field camera since you don't gain anything by its use, but you give up a whole lot of resolution.

That said, I can also see the argument that you might want to simultaneously have an image that could have different things in focus and a copy of the image with everything in focus, so I don't necessarily think that is good reasoning.

Update: It appears that the software is actually capable of doing this already. On this review of the new Lytro, if you do the perspective shift, everything comes in to focus.

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Focus stacking is taking multiple images after eachother which is quite far from taking a 'single' 'shot' which would be entirely in focus which should in theory be possible with light field camera's if my understanding is correct. –  David Mulder Apr 22 at 13:31
    
@DavidMulder - but the technique is the same. My understanding of the lytro is basically that it captures information about various focus depths simultaneously. Focus stacking would still have to be used in order to piece together the overall image because you effectively have a bunch of different focal depths that need the sharpest parts chosen from each. This is the same process whether the source is one light field or multiple still images with different focal lengths. You still have to figure out the sharpest part of each layer. –  AJ Henderson Apr 22 at 13:33
    
Just for the record, the downvote isn't mine, either way, if my understanding is correct you actually get post-processing a spatial space map including depth using light field shots. –  David Mulder Apr 22 at 13:57
    
@DavidMulder - it should certainly be possible to compute a depth map with a light-field shot, though you could do the same with a focus stack, though not at the same level of detail and only if you know where the focus plane was set. If they are computing one, it makes even less sense that they wouldn't offer this feature built in to the software as they have to find what parts of the image are in focus at each focal distance in order to generate the depth map. –  AJ Henderson Apr 22 at 14:33
    
This is not how light fields work. This answer sounds plausible (hence the upvotes, I guess), but it's fundamentally not right at all. –  mattdm Apr 22 at 17:51

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