Category:Panoramic images

From The Brighton Toy and Model Index

A panorama, or panoramic image is a special type of photograph with an extremely wide field of view.

Uses

Panoramic images projected onto a curved screen can produce a more immersive affect for the viewer, making it easier for them to feel that they are inside the view, which is visible in a range of directions.

A panoramic background printed onto a curved piece of card can be used as the backdrop for a diorama, where it lets the model be viewed from a range of angles and still have an appropriate background. The lack of an obvious flat plane for the backdrop or distracting joints between rear an side backdrops makes it easier for the onlooker to suspend disbelief and imagine the scene to be real.

Implementations

"Fisheye" lenses

Very wide-angle lenses are available that take images with typically up to 180 degrees field of view. These have a tendency to make vertical lines at either extremity of the image appear bowed.

"slit" cameras

Rather than use expensive custom glass optics, some early wide-angle photographic-still "rigs" used a standard lens with a "vertical slit" mask that only allowed a single vertical line of the image to be exposed. A clockwork motor then made the camera sweep horizontally across the view, while simultaneously smoothly winding the strip of film through the camera to produce a rectangular image with a wide range of viewing angles

Due to the time needed for the camera to slowly sweep across the subject, this method was normally only suitable for photographing landscapes and other stationary views. An exception was the taking of school group photographs, where an entire school year would be arranged in a wide group, and would have to stay very still as the camera swept across the group. A common joke was for a child to be at one end of the group to wait until the camera had moved on, then to run around the back of the group and stand at the other end and wait for the camera to scan them a second time – they'd then end up in the same school photograph twice.

Slit cameras produce "cylindrical" distortion: vertical lines remain perfectly vertical across the whole image.

Anamorphic lenses

Anamorphic lenses combine a wide-angle lens with further optics to compact the view horizontally, so the a "wide" image can be recorded on a conventional-format film negative, with the image using the full height, but also squeezing in the full width. Similar optics are then used to expand the image width on playback.

This method was used with the Cinemascope system in the 1950s as a way of allowing studios to distribute "wide-angle" films that could be played on a standard cinema film projector, as long as the projector was fitted with a fitted with a corresponding optical "stretcher".

Digital recomposition

Arbitrarily wide-angle images can be created by software. A range of photographs are taken form the same point in space, with the camera pointing in different directions, the software identifies common features that appear in multiple photos, identifies them as being the same features, and uses these to calculate how the different images need to be distorted in order to get them to fit together to produce a cylindrical projection (or another form of projection). The software then distorts and composites all the images together to produce the final image.

"Panorama mode"

Some modern mobile phones have sufficient processing power to support a panorama mode, in which the user pans their cameraphone across a view and the camera composites the different live images together, real-time, to produce a panorama sweep image. This can be thought of as the modern equivalent of the old "slit camera" technique. However, the resolution of the resulting image is usually lower than the normal resolution of the camera, in order to allow the camera's processor to cope with the data bandwidth real-time, and also to minimise the results of image mismatches and a parallax errors.

Panoramic rigs

Serious panorama photographers will invest in a special panoramic photography camera mount that allows the camera to be tiled on both axes. these mounts (after calibration) allow the camera to be rotated around its precise optical centre, to make sure that the contents of all the images have the exact same relative alignment in every picture. Without this sort of exact positioning, objects in the foreground will seem to move horizontally or vertically wrt these in the background when the camera is moved to take a new picture (parallax error). The idea of a panoramic rig is to allow the photographer to find the "sweet spot" in a camera's optics and rotate the whole camera body around this special point to take the images.

Robotic panoramic rigs

At the upper and of the range, "robotic" panoramic rigs have stepping motors fitted on the x-y and x-z tilt axes, and a mechanism to automatically fire the camera's shutter release. These rigs allow the photographer o place the camera, press start, and have the rig then automatically reposition the camera and take a picture at every preprogrammed angle without further intervention.

360×360 methods

Double-fisheye cameras

An "effective" 360-degree digital camera can be made by attaching a pair of fisheye camera elements with sensors back-to-back, and then using custom software to blur over the inevitable "seam" between the images. "Double-fisheyes" are used where there is a need for 360×360 video, or for large numbers of 360^2 images to be taken in sequence with a small device, quickly and (comparatively) cheaply. Google Streetview's optical hardware can be thought of as "a double-fisheye on a pole".

Multi-camera pods

A more extreme version of the double-fisheye idea involves having a larger number of small lightweight "GoPro"-style cameras with wide-angle lenses, attached together to produce a "camera ball" that can be triggered to produce a simultaneous set of overlapping wide-angle images that can then reconstruct a 360^2 view. The ball can be mounted on a pole, or (in some versions) can be thrown into the air, with onboard sensors detecting when the ball has reached the highest part of its trajectory and triggering the cameras. A camera ball can have a thin protective protective skeletal mesh above the surface to allow it to be handled without touching the lenses, as long as the elements don't obscure the same parts of the background image for different cameras. The frame elements can be removed automatically by software based on their known geometry, or can be rejected by the software during the composition process as "outlier" data that conflicts with views from other cameras.

External links

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Subcategories

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Media in category ‘Panoramic images’

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