Camera

Details Camera Camera

1999-06-30

2001-04-17

Perkey, W.B. (Department: 2851)

Photography

Attitude sensing

C396S121000

Reexamination Certificate

active

06219492

ABSTRACT:

This application is based on application No. H10-188369 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distance-measuring device, and to a camera provided with a distance-measuring device.
2. Description of the Prior Art
A distance-measuring device measures a distance on the principle of triangulation or the like, and is used, for example, in an automatic focusing (AF) mechanism of a camera. One known method adopted in a distance-measuring device is the passive-type correlation method, which exploits the image of an object intact without emitting light for distance measurement. The principle of this distance measurement method will be described below.
FIG. 6A
shows an example of a distance-measuring device adopting the passive-type correlation method, and
FIG. 6B
shows an example of the signal obtained from the image sensor, realized by the use of a CCD, provided in this distance-measuring device. The light emanating from an object
24
and transmitted through two lenses
20
provided on the right and on the left is focused onto the light-sensing surface of a one-dimensional CCD
23
to form two images thereon along a straight line by means of mirrors
21
and a prism
22
. The CCD
23
outputs an image signal as shown in
FIG. 6B
, where the position on the CCD
23
is taken along the vertical axis and the level of the image signal is taken along the horizontal axis. The distance between the two images varies according to the distance to the object. Accordingly, by subjecting the image signal to correlation calculation, it is possible to determine the distance between the two images and, on the basis of this distance, determine the distance to the object. This is the principle of the passive-type correlation method.
Conventionally, the majority of distance-measuring devices adopting the passive-type correlation method for use in cameras achieve distance measurement by the use of an image sensor having a row of pixels that extends only in the horizontal direction of the screen. For this reason, for example when a portrait is shot, the photographer first locks the focus with the person to be photographed caught within the distance measurement area shown in the viewfinder so as to determine the composition, and then releases the shutter.
To eliminate the need to lock the focus, a distance-measuring device is proposed that employs an area sensor having an array of pixels that extends in both the horizontal and vertical directions so as to sense part or the whole of the shooting field on an area-by-area basis. In a distance-measuring device of this type, distance calculation is performed by the use of signals obtained from specific regions (calculation regions) corresponding to each other on a pair of area sensors.
FIGS. 7 and 8
show examples of the relationship between the area sensor and a calculation region in a distance-measuring device of this type.
FIG. 7
shows the above-mentioned relationship as observed when the camera is held in such a posture that the direction of the shorter sides of the shooting screen coincides with the vertical direction of the object (hereafter, this posture of a camera will be referred to as the “horizontal posture”).
FIG. 8
shows the same relationship as observed when the camera is held in such a posture that the direction of the longer sides of the shooting screen coincides with the vertical direction of the object (hereafter, this posture of a camera will be referred to as the “vertical posture”).
The sensor unit
10
has left-hand and right-hand area sensors
11
L′ and
11
R′ and a sensor controller
12
for controlling those area sensors
11
L′ and
11
R′. The smaller areas L′(n) and R′(n) (where n represents a natural number from 1 to 9) within the area sensors
11
L′ and
11
R′ are calculation regions demarcated by the sensor controller
12
. Note that any two calculation regions bearing the same number n correspond to each other, and distance measurement data is calculated by the use of image signals obtained from mutually corresponding calculation regions.
With a camera provided with such an area-sensor-based distance-measuring device, distance measurement can be performed in varying areas, and accordingly the photographer can release the shutter without locking the focus. In achieving automatic focusing, different cameras adopt different methods of selecting the calculation regions from which to obtain distance measurement data to be used to perform focusing. For example, there is a method that places the calculation regions in the order of priority so that, from among the calculation regions from which distance measurement data can be obtained, the data obtained from those given the highest priority is selected.
However, in a conventional area-sensor-based distance-measuring device adopting the passive-type correlation method, all the calculation regions are of the same size irrespective of their positions. Therefore, in some cases, the object can be inappropriately large or small relative to the calculation regions, and this is a major cause of low distance measurement accuracy. Examples of such cases will be described below with reference to
FIGS. 9
to
11
. In these examples, it is assumed that the object (i.e. the main object) of which the distance needs to be measured is a person. In these figures, reference numeral
13
represents the area of the shooting screen, reference numeral
14
represents a calculation region, and reference numeral
15
represents the main object.
FIG. 9
shows a case in which the main object
15
is inappropriately small relative to the calculation region
14
. In such a case, the main object (a person) coexists with the objects (trees) in the background within the calculation region
14
, making it impossible to measure the distance to the main object
15
accurately. Such a situation is called foreground/background interference.
FIG. 10
shows a case in which the main object
15
is inappropriately large relative to the calculation region
14
. In such a case, the main object
15
shows low contrast within the calculation region
14
, reducing the reliability of distance measurement. Such a situation is called low contrast.
FIG. 11
shows a case in which the main object
15
is appropriately large relative to the calculation region
14
. In such a case, there is little influence of the background within the calculation region
14
, and the main object
15
shows contrast above an appropriate level. Thus, it is possible to measure the distance appropriately.
Note that, in
FIGS. 9
to
11
, how the relationship between the size of the calculation region
14
and the size of the object
15
varies is illustrated by varying the size of the calculation region
14
while keeping the size of the object
15
constant within the shooting screen
13
. However, in reality, as long as the same object is shot with the same camera, as the distance to the object varies, the size of the object varies while the size of the calculation region
14
remains constant, and as a result the relationship between the size of the calculation region
14
and the size of the object
15
varies. This is because, on the shooting screen, the same object appears small when it is far away and appears large when it is close.
As described above, conventionally, the size of the object can sometimes be inappropriately large or small relative to the calculation regions, causing foreground/background interference or low contrast. This often leads to low distance measurement accuracy, or to improper selection of calculation regions in automatic focusing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a distance-measuring device that is less prone to low contrast and foreground/background interference and that offers high distant measurement accuracy, and to provide a camera provided with such a distance-measuring device.
To achieve the above obj

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