Camera projected viewfinder

Photography – With exposure objective focusing means – focusing aid – or... – Having auxiliary illumination

Reexamination Certificate

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Details

C396S431000, C396S050000

Reexamination Certificate

active

06516151

ABSTRACT:

The present invention relates to a camera that projects a pattern of visible light onto an object to be photographed to indicate to a photographer the area of the object within view of the camera.
TECHNICAL FIELD
In recent years, document scanners have become commonplace. Although these work well and are relatively inexpensive, a document scanner occupies a significant amount of scarce desk space.
BACKGROUND ART
The use of a camera to take a photograph of a document consisting of text and/or images offers one way of dealing with the problem of wasted desk space. In conventional film or electronic photography, a person may look through a viewfinder to aim the camera at an object. When the object is a document, for example a document lying on a desk, this means a person has to stand up, lean over the document, look through the viewfinder and then take the photograph. This is not very convenient. Furthermore, if the document is at the back of a desk, the person may have to move the document. In addition, the person's body may block ambient light, thereby requiring the use of a flash. The use of a flash in an office environment may be unacceptable.
Recently, some digital cameras have been provided with a liquid crystal display (LCD) viewfinder that may be viewed at some distance and that can be oriented by a user so that the LCD viewfinder may be viewed over a range of angles, for example at right angles to the optical axis of the camera. By pointing the lens downward while keeping the viewfinder at a convenient angle, it would then be possible to take a picture of a document on a desktop from a sitting position. Unfortunately, it is not intuitively obvious to most people which way a hand-held camera should be moved by looking at the LCD viewfinder.
SUMMARY
It is an object of the present invention to provide a camera that is more convenient to use when taking a photograph, for example a photograph of a document lying on a desk.
According to the invention, there is provided a camera comprising image capture means, a lens arranged to image an object in an object plane onto the image capture means, a light projector operable to project visible optical radiation onto the object plane to indicate to a user of the camera the field of view imaged onto the image capture means, and a camera attitude sensor system for sensing the attitude of the camera, wherein the image framing projector is operable in response to the attitude sensor system to project the optical radiation onto the object plane only when the attitude sensor system senses that the camera is oriented so that the optical radiation will be projected downwards.
The light projector may project just one area or pattern of light onto the object plane, for example a cross pattern centered in the camera field of view, or a box surrounding the field of view. Alternatively, more than one such area or pattern may be projected, for example four light beams which indicate the corners of the area in the object plane imaged by the camera.
Various light patterns, for example a cross, a framing box or four L-shaped framing indicators, may be formed in various ways. For example, the light source or sources may have corresponding shapes that are directed or focussed onto the image plane. Alternatively light from a point image source or sources can be shaped by passing the light through a transmissive optical diffractive element or reflecting the light off a reflective diffractive optical element.
In one embodiment of the invention, the light projector is an image framing projector operable to project visible optical radiation onto the object plane to indicate to a user of the camera the bounds of the object imaged onto the image capture means.
The camera can then be configured so that the optical radiation can projected either automatically or manually only when the optical radiation will be projected downwards.
Because the document will normally be below the level of the camera, for example lying on a desktop, the projected optical radiation can therefore be made available only when the camera is to be used to capture an image of such a document. This reduces the concern of such optical radiation being directed into a person's eyes, which makes the camera potentially safer, as well as less likely to annoy such persons.
The term “lens” as used herein is not restricted to a single lens element and includes lenses with compound optical elements.
The image capture means may be photographic film, or an electronic device, for example a detector array, in particular a two-dimensional CCD array or CMOS array.
The source of visible optical radiation is preferably a compact solid state device or devices, for example one or more light emitting diodes or laser diodes. There may be several such devices, for example, four devices each providing light projected onto one of the four corners of the object plane. Alternatively, one such device may be used with the light being split into discrete sources by a number of fibre optic light guides.
The attitude sensor system may comprise one or more tilt sensors or accelerometers, arranged to provide a signal indicative of the attitude of the camera.
So that the projected optical radiation is not projected when such radiation would be close to horizontal, it is preferred if the image framing projector is operable in response to the attitude sensor system to project the optical radiation onto the object plane only when the attitude sensor system senses that the camera is oriented so that the optical radiation will be projected downwards with a predetermined angle at least 30° below horizontal. Such as angle corresponds with that which may be appropriate when using a hand-held camera to image a document lying on a work surface such as a desktop. A further degree of safety can be achieved if the optical radiation is projected onto the object plane only when the attitude sensor system senses that the camera is oriented so that the optical radiation is projected downwards within 30° of vertical. This may be appropriate if the camera is mounted on a support nearly above a document to be imaged, such as a post attached to the side of a work surface or desktop.
Optionally, the camera may have means by which the angle at which the projected light becomes operable can be selected by a user of the camera.
In a preferred embodiment of the invention, the attitude sensor system senses the rate of change of the attitude of the camera, the image framing projector being operable in response to the attitude sensor system to project the optical radiation onto the object plane only when the attitude sensor system senses that the rate of change of camera attitude is below a predetermined threshold.
For the convenience of the user, the camera may have a timer that times a predetermined time delay in response to the camera attitude sensor when the camera has been oriented so that the optical radiation would be projected downwards. The optical radiation is then automatically projected downwards following the predetermined time delay.
It may be, however, that a person may wish to image a document that is not below the level of the camera. For example, if the document is posted on a notice board, then it may even be above the level of the camera. Therefore, the camera may have an override feature, such as a user-selectable switch, that disables the operation of the camera attitude sensor system.
Preferably, however, the camera has two or several automatically configurable modes of operation, for example in addition to a document-capture mode, the camera have a scene-capture mode, such as a still camera mode, or video camera mode. In this case, the camera is automatically configured in a document-capture mode when the attitude sensor system senses that the camera is oriented so that the optical radiation will be projected downwards. The camera may then be automatically configured in a different mode of operation when the attitude sensor system senses a different camera attitude in which the optical radiation would not be so projec

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