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Parallax


Two adjacent images, like many of those that Hugin’s users may want to stitch to a bigger picture. Unfortunately, these two won’t stitch well.

Bad Parallax

Looking at the detail below the relative position of the finger and the library’s vertical support beam has shifted when moving the camera.

parallax detail

This shift is called parallax and it is the most common problem for stitching pictures.

wrong NPP turn

Feel it yourself: Stretch an arm in front of you, like the above picture. Raise a finger and note its position relative to an object in the background. Turn your head left and right and notice how the position of the finger relative to the background changes. Two images taken like that won’t stitch.

Now try a variation on the above experiment: Don’t move your head. Close one eye and move the other eye left to right. Unless wearing glasses or contacts, you will notice that the relative position has not shifted. The nodal point of the rotation is better aligned with the no parallax point (NPP) of your eye.

right npp turn

Your eye focuses all rays of light into one point before expanding them on the retina. Most lenses do the same before expanding the image on the sensor. The NPP is this one theoretical point inside the lens where all the rays of light focus.

Turning a camera around the lens’ NPP is the single most important precaution to achieve a perfect stitch.

To do this, we need to identify the NPP of the camera and constrain its rotation to that point. How to identify the NPP will be topic of a future tutorial.

10 Responses

  1. It is important to mention that parallax reducing when the objects become farther. So, when you making photos of landscape and mountains, you can forgot about parallax, and think about another problem of stitching: moving objects (clouds, cars, weaves, people,…).

    In fact, even when rotaiting your eye you have a small parallax. You can check it by the following experiment (view from the top):

    * | ^ ^
    light wall eyes

    Look forward and move you head until you the light will apear from behind the wall at the left of your sight. Then rotate you eyes leftmost (do not move your head!) and the light will disappear behinfd the wall!

  2. A pano head like the Nodal Ninja helps rotating the camera around the No-Parallax Point.

  3. Hi, I dont exactly know how can i count where is focus crossing inside of lens. I dont know how can i describe it better, my english is rather poor… If anyone knows what im talking about and know the answer, please shorten my suffering :)

    thx in advance

  4. For stitched panoramas we try to keep the no-parallax-point (NPP) constant, while for stereo photometrology the NPP’s position should be controlled so that there is a known distance between each pair of images to allow for the triangulation from 2D to 3D.

  5. Rolling the camera has no influence on the NPP.

  6. I may express a desire for one of these from my spouse however in the time between actually getting a professional one, I was thinking of some ideas. A few site detail simple arms as poor mans anti-parallax arms yet I just realized the cheapest and simplest to make would not even be an arm. The premise is simple for flat level shots.

    If your camera sits alone flat, and all you wish to snap is a level panorama, all one would need to do is screw a platform to the top of the tripod. This platform could be made of any thin stiff rectangular material with a screw hole in one corner. Sit the camera on it so the lens edge is over the pin. This platform would be good for multiple cameras too. Perfect enough for a DSC-H5 or the likes. If the camera doesn’t sit so well, use duct tape.

  7. by one of these, I mean the Ninja as I was thinking to post this as a comment on a different article…

  8. @TJ: If you can’t afford the Ninja, try a Panosaurus.

  9. There are plans and ideas for homemade rigs in many places on the web. It’s true you can build a serviceable rig yourself, although flexibility and portability are harder. Remember to pivot on the nodal point of the lens (not the front of the glass. One of the neatest “homemade” rigs uses a weight on a string hanging from your lens. A carpenter’s weight with a pointed tip is perfect. Keep this point in the same place as you pivot around. Add a cheap bubble level – there are some that go in the flash shoe – and you have a functional “non-parallax” rig without a tripod! Sorry misplaced link, but should be easy to google or design from this (I improvised considerably!).

  10. Hi, I´m just getting into panoramic Photography. I think is amazing what you can do with pano-photos, I would like to get a lot of info. Best regards from Venezuela.

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