Television – Camera – system and detail – Optics
Reexamination Certificate
1998-06-25
2002-09-03
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Optics
Reexamination Certificate
active
06445415
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention comprises a method to increase the depth of focus (or field) for photography, and means for the method. The method constitutes an improvement of the depth of focus in use of traditional T / S —technology, “Tilt and Shift”, and an increased possibility for improved depth of field with other cameras. The method is mainly aimed for digital cameras, where the image is created from a sensor in the camera, instead of on a photographic film. By use of present scanning technology however, it is easy to transfer a film photo to an electronic image. The method can be used also for those cases. In the following the method is mainly presented for the cases, when the picture is created electronically directly in the camera.
2. Description of the Related Art
In T / S cameras one or both of the lens and the “image plane” are movable. The image plane is that plane, where the film or the sensor is positioned. A plane in the scene is sharply focused in a “focused plane”, which might be localized in front of, back of or cutting the image plane. Proportional to the distance between the image plane and the focused plane, the blurring grows larger in the image. In T / S cameras the photographer often views the image on a focusing screen positioned in the image plane. He controls the camera settings for a focused image on the focusing screen. Then he places the film or sensor in this position and shoots.
Photographers use many different ways of working. The profession is often creative, sometimes artistic. In practice the photographer puts the camera in position directed to the subject, arranges the image plane in the desired perspective, usually vertical, as we are used to view the world from a vertical perspective. Tilting an ordinary camera upwards, e g for placing a church tower inside the seeker, the camera will produce an image of the tower with a tilting perspective, showing a tower tilting or falling in. Parallel vertical lines are no more parallel in the image.
Then the photographer focuses and positions the subject for the image. Here difficulties might arise, which the invention can solve. The focal aperture is not only used for control of the light strength, but also for increasing the depth of field, e g at product photography. Increased exposure can compensate smaller apertures. However long time of exposure implies risks for mechanical disturbances blurring the sharpness.
T / S cameras are used for product photography, and when there is a desire to increase the depth of field from what an ordinary camera can offer. A close picture on a product with large extension in distance, might be given focus both on the front and back parts, by tilting the focal plane, cutting the front as well as the back part of the product image. The tilting might be arranged in two ways. One by positioning the film or sensor in the tilting image plane. The other by tilting the lens instead, turning the focal plane into the desired angle. Usually a vertical image plane is desired, obtaining a vertical perspective, and then there is just the method of tilting the lens, until the focal plane is positioned vertically in the desired image plane.
As subjects generally are not extended just in a plane of two dimensions, but are three-dimensional bodies with varying extensions, also focal aperture reductions are used to decrease the angle of refraction from the lens. Thus the image plane can be farther from the real focus, without too large blurring errors. However the subject or the light conditions might reduce the possibilities.
Examples on Prior Art
In the field of television the image experienced by the human beings has always been created by the use of many “subimages” integrated together. By showing several frames (50 to 60) per second, the subimages are integrated in time, in order to show smooth movements, increase the resolution and the signal to noise ratio. A study of only one subimage reveals a poor image quality. An ordinary still camera, in contrast gives a single shot image of excellent quality, including much higher resolution and very low noise content.
In the field of research for high definition television, there has been an increased awareness of second order effects of the increase of image resolution. The one that will be discussed here is the aspect of depth of focus.
For a television image with low resolution, there is a large span of subject distances that can be “focused” to a single image plane, because the blurring of the optics is anyhow less than the resolution of the sensor detectors. However increasing the sensor pixel resolution e. g. with a factor 4 means a decrease of the depth of focus with a factor 2.
For television it is an obvious method to increase the depth of focus, by using the natural stream of new video images integrating those together, while changing the focus setting.
There are several similar patents in the field of television using this method of increasing the depth of focus. Most of those patents use transfer of the ordinary X,Y -based image to a space frequency based image description. They are using power comparisons in the space frequency or frequency filtered band pass domain, between subimages to define which subimage is in focus. They are differing in the method details of performing this object.
One method according to Mimura et. al. (U.S. pat. No. 5, 282,045) uses changing of the focus distance between frames, and then utilizing the integration of subimages in the mind of human viewers. The result is said to increase the experienced depth of focus in the mind of humans.
The method also includes a “contour corrector”, which function is not described, but is implicitly an ordinary artificial “contour sharpener”, said to add higher frequencies to the contour, which after integration in the mind of humans, is experienced as a higher resolution image.
There are many different problems involved in those television applications, e g.
There are time restrictions. Only a short time is available for calculations and mechanical focusing, due to the high image frequency.
By the selection process of focused frames, the number of integrations decreases and the noise increases, decreasing the image quality.
In television there are generally movements, by subjects in the scene, or the camera panning or zooming the scene. In fact the movements are inherent in the television approach, and necessary for the human expectations on the television media. Then there are small possibilities for methods utilizing exact matching of successive subimages with different focus, as the subimages contains other changes due to movements. In the patent of Mimura et al, the depth of focus function is simply put off, when there are movements.
On the other hand the television is in many ways “forgiving” image deficiencies. A poor image is immediately followed by new ones in the continuous video-stream of images. The short time involved means that many imperfections pass the viewer unnoticed. Then a process of selecting focused image parts and combining those together can be allowed to involve some inaccuracies and non-perfect matches, without disturbing the viewer's total integrated experience of the television video-image quality. This is opposite to the application of a still camera. The still photo is viewed for much longer time periods, and all imperfections and small details are also time integrated to noticeable and disturbing image quality problems. In the professional business, e. g. in case of a new company product photo, there is no forgiveness to be expected for even small image quality deficiencies.
BRIEF SUMMARY OF THE INVENTION
Invention Functions
The present invention concerns a method to achieve sharpness and depth of field for a still photo by use of multi-shots, where different camera settings can be used including aperture reduction technique. The method utilizes possibilities for digital image transfer after the shot, and the involved processes might be performed using automatic methods to various ext
Connolly Bove & Lodge & Hutz LLP
Ho Tuan
LandOfFree
Increased depth of field for photography does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Increased depth of field for photography, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Increased depth of field for photography will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2839857