Optical: systems and elements – Stereoscopic – Having record with lenticular surface
Reexamination Certificate
1998-11-09
2003-06-03
Chang, Audrey (Department: 2872)
Optical: systems and elements
Stereoscopic
Having record with lenticular surface
C359S462000, C359S464000, C348S059000
Reexamination Certificate
active
06574042
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to an autostereoscopic image-forming device comprising n viewpoints (or elementary images), said device including a lens array comprising elementary cylindrical lenses referred to as cylindrical “lenticles”, placed side by side parallel to a first direction.
It is known that such devices have been implemented to constitute autostereoscopic cameras, specifically the autostereoscopic picture-taking devices described in the Applicant's following patents: U.S. Pat. No. 5,099,320, and French patents FR-2 705 007 and 2 704 951.
Those picture-taking devices implement a lens array having a large number of cylindrical lenticles placed side by side, and in practice, the video image is obtained in interleaved manner in the form of columns of pixels, the first elementary image being constituted by the pixels of the first column of pixels together with the pixels in the other columns offset therefrom modulo n, the second elementary image being made up of the pixels of the second column and of columns that are offset modulo n therefrom, and so on, each lenticle being of a width that corresponds to n columns of pixels.
The term “row” and “column” respectively designate the horizontal lines and the vertical lines of pixels as seen by a standing or sitting observer, independently for example of the horizontal or vertical scanning direction of a display cathode ray tube (CRT). For example, for a CRT screen whose scan lines extend vertically, such “scan lines” are considered to be “columns” in the meaning of the present text.
The quality of those picture-taking devices depends on the quality with which the lens array is made, which array has N
lenticles, N designating the number of pixels in a video image line in the chosen standard.
As described in the above-specified French patents, an image transfer device makes it possible to use a lens array of dimensions that are about ten times greater than the dimensions of a sensor comprising a charged coupled device (CCD), thereby facilitating practical implementation.
Such a lens array thus has a large number of cylindrical lenticles, with the number of lenticles depending both on the chosen video standard (SECAM, PAL, NTSC, HDTV, etc.) and on the number of viewpoints. Unfortunately, the required accuracy of positioning is proportional to the number of lenticles.
In addition, video applications that require miniature cameras, e.g. endoscopes, require the dimensions of the lens array to be reduced very considerably, thereby making implementation much more complicated or even impossible.
SUMMARY OF THE INVENTION
An object of the present invention is thus to provide an autostereoscopic image-forming device and in particular a picture-taking device which is relatively simple to make and to adjust, and which in particular lends itself well to miniaturization, in particular for endoscopy.
The invention thus provides a device for forming an autostereoscopic image having n viewpoints (or elementary images), said device including a lens array comprising cylindrical lenticles disposed side by side and having longitudinal axes parallel to a first direction perpendicular to an optical axis of the device, the device being characterized in that it includes a cylindrical optical assembly comprising at least one cylindrical lens whose longitudinal axis is perpendicular to the first direction and to said optical axis, in that the lens array includes n cylindrical lenticles, in that the lens array and the cylindrical optical assembly share a common focusing plane corresponding to a focusing distance &Dgr;, and in that the absolute value of the focal length of the cylindrical optical assembly is substantially equal to n times the absolute value of the focal length of the lens array. For focusing at infinity (&Dgr;=∞), the common focusing plane is a focal plane common to the lens array and to the cylindrical optical assembly.
In the invention, the lens array now has only n cylindrical lenticles of pitch p, e.g. n=4, compared with the large number of lenticles implemented in the prior art picture-taking devices, i.e. N
, e.g. 144 cylindrical lenticles for N=576 and n=4.
In addition, in the device of the invention, the stereoscopic observation baseline can be equal to twice the pitch p of the cylindrical lenticles, i.e. for n=4, to half the width L of the array. In the autostereoscopic system of the invention, e.g. having a number of viewpoints lying in the range 3 to 6, the offset between two adjacent viewpoints (or elementary stereoscopic baseline) can be equal under optimized observation conditions to half the offset E between the eyes of an observer (E=65 mm). More generally, it can be equal to half the chosen stereoscopic baseline B.
At the nominal observation distance (which is the distance at which solid color should theoretically be seen), the observer sees (for n=4) a stereoscopic pair made up in the invention by the first and third viewpoints I
1
and I
3
, or else by the second and fourth viewpoints I
2
and I
4
. Choosing parameters in this way so that a stereoscopic pair is made up of not of two adjacent viewpoints but of two viewpoints having an intermediate viewpoint interposed therebetween (or indeed m, where m>1, intermediate viewpoints in which case the elementary stereoscopic baseline between two adjacent viewpoints is equal to the pitch p of the picture-taking lens array which is equal to B/(m+1)), thereby enabling an observer without special eyeglasses to have a viewing volume enabling the observer to move both parallel and perpendicularly to the display screen, which characterizes uniform autostereoscopy in the meaning of the present application.
As a result, and referring to the above example, an observer at the theoretical solid color distance can move towards the screen or away from it or can indeed move sideways without losing stereoscopic vision.
Once the image has been frozen on the screen, if the spectator moves towards the display screen from the nominal observation distance (or the theoretical solid color distance), the stereoscopic baseline actually seen grows while if the observer goes away from the screen, then the baseline shrinks, and the overall sensation is constant because this variation in the stereoscopic baseline compensates exactly for variation in the sensation of depth associated with modifications to the vergence force, i.e. the muscular force exerted to bring the two retinal images into correspondence so as to obtain the stereoscopic fusion that is required for relief to be perceived, which modification to vergence force necessarily accompanies displacement in the direction perpendicular to the screen.
Once the “solid color” has been adjusted so that the observer sees viewpoints [(I
1
) and (I
3
)] or [(I
2
) and (I
4
)] and the observer comes close enough to the display screen, then the observer will see viewpoints (I
1
) and (I
4
) and will no longer be free to move parallel to the screen, as happens in reality when looking from close up. When the observer goes away from the screen, then the perceived viewpoints will be [(I
1
) and (I
2
)] or [(I
2
) and (I
3
)] or [(I
3
) and (I
4
)] and the observer can make large movements, thus leaving the observer free to move in a volume.
The same applies, but with improved comfort, when m is chosen to be greater than 1.
For a miniature camera or for endoscopy, the picture-taking stereoscopic baseline B is much smaller than the distance between the pupils of an observer because of the desired large magnification. For n=4, the lenticle pitch p nevertheless remains equal to half the required picture-taking stereoscopic baseline B.
Naturally this remains true for an objective lens of long focal length, for which the stereoscopic baseline B is selected to be greater than the distance E between the pupils of the observer.
In the present invention, the total stereoscopic baseline B
T
, i.e. the ste
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