Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1999-02-19
2003-12-02
Tran, Thai (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000
Reexamination Certificate
active
06658203
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image recording method of an image recording system comprising an electronic camera for control of illumination uniformity of a recorded image of illuminated objects and an image recording system utilizing this method.
BACKGROUND OF THE INVENTION
Replacement of conventional cameras for photographing and recording still images by use of the photosensitivity of photographic films by electronic cameras has gained increasing attention in recent years.
An electronic camera uses a solid state imaging device, typically a charge coupled device (CCD), for recording of an image. The CCD is an array of a large number of light sensitive elements connected to each other as an analog shift register. In each element of the CCD a charge is formed that is proportional to the light energy incident on the element during an integration period. The analog charge of each element is shifted serially out of the CCD and are typically converted to digital values whereby a digital representation of the recorded image is formed. The digitized image is either transferred to an external computer through a computer interface or is stored on a memory card or on a rotating magnetic recording medium in the camera.
It is well known to use linear CCDs in electronic cameras, in which the light-sensing elements are arranged in a single line. Typically, the array is moved across the image, scanning it one line at a time. For color images, filters can be placed in front of the array, which then makes three passes across the image during image recording.
Offering a good compromise of image resolution (high pixel count) and cost in electronic cameras, is the trilinear CCD array, which comprises three linear CCDs positioned side by side. Each line is covered by its own color filter, typically in the form of dye that is painted over the elements. The array makes a single pass across the image, and each linear CCD records a line at a time. Typically, an image is recorded in this way in 1 to 10 minutes.
At a higher cost, a rectangular CCD array can capture the entire image in a very short time. Three separate exposures with three color filters are needed to make a color photo. One way to do this is to place the filters in a rotating color wheel that sequentially inserts each color filter in the optical path between the image forming optics of the electronic camera and the rectangular CCD array.
It is known to mount the circuitry of a digital camera in a camera back (sometimes denoted a digital camera back) that attaches like a film holder to a conventional camera.
SUMMARY OF THE INVENTION
Lighting is a crucial element in any form of photography and lighting is one of the key points of differentiation among digital cameras, and because lights are among the costliest tools of the trade, the differences are significant.
The long time needed to record an image with an electronic camera is a major disadvantage of presently known cameras of the above-mentioned type. Highly stabilized and expensive light sources are needed to ensure a temporal uniform illumination of the objects to be recorded by the camera during the recording period. A fluctuating light source may cause different areas Or the recorded image to be recorded at different intensity levels of the illuminating light, for example in an image recorded line by line, the lines may show up. For a photographer who already has an investment in one kind of lighting, the cost of new lights is a significant factor to consider when purchasing a new camera.
It is an object of the present invention to provide a new image recording system comprising an electronic camera and an image recording method by which influence of temporal fluctuations in intensity of light illuminating the objects is significantly reduced compared to known systems and methods thereby enabling the use of inexpensive light sources for illumination of objects to be recorded with an electronic camera.
According to the invention the above-mentioned object is fulfilled by providing
an image recording method for recording of an image of objects illuminated by light incident upon them by an image recording system comprising an electronic camera, the method comprising synchronizing the recording of the image with intensity fluctuations of the illuminating light whereby the image is recorded as if the objects were illuminated with light of a temporally substantially constant light intensity, and
an image recording system comprising an electronic camera and synchronizing means for synchronizing recording of an image of illuminated objects with intensity fluctuations of light that illuminates the objects to be recorded so that the image is recorded as if the objects were illuminated with light of a temporally substantially constant light intensity.
It is a main aspect of the present invention that recording of an image is synchronized with temporal fluctuations in light intensity in such a way that influence of temporal objects is significantly reduced compared to known systems and methods.
This reduction is obtained by controlling the recording of the image in such a way that each part of the objects to be recorded is illuminated by substantially the same quantity of light energy as other parts of the objects during exposure of the corresponding parts of the image.
The image may be recorded using a solid state imaging device, such as a CCD. Each light sensitive element of the CCD integrates the intensity of the light incident upon it during an integration period and accumulates a charge in it that is proportional to the integrated light intensity. Until start of the integration of light intensity, the element is short-circuited so that the charge is zero at the start of the integration period.
The illuminating light may be generated by any artificial or natural light source, such as lamps of the light bulb type, such as tungsten lamps, etc., arc lamps, such as metal-vapour lamps, etc., fluorescent tubes, such as high-frequency fluorescent tubes, household fluorescent tubes, etc., strobe lamps, flash lights, sun light, etc.
In the present context, the term exposure is to be understood in a broad sense as the time period during which a light sensor is actually sensing the light. For example, a photographic film is exposed to light whenever light is incident upon it, while a CCD is exposed to light when the elements of the CCD are allowed to integrate light incident upon them. The CCD is not exposed when the light sensing elements are short-circuited although light may be incident upon them.
Synchronization of image recording with fluctuations of illumination of the objects to be recorded may be performed by synchronizing the integration periods of the CCD elements with these fluctuations.
The synchronization may be performed by starting and/or stopping the integration period at specific predetermined intensity levels of the illuminating light.
For example, when image recording is done with an electronic camera having a rectangular CCD array and a flash for illumination of the objects to be recorded, the synchronization of the three exposures needed to make a color photo may be performed by starting the integration period of the rectangular CCD array at a specific predetermined intensity level of the illuminating flash light.
If the fluctuations are periodical, the integration may take place over a large number of periods, such as from 1 to 10 periods, preferably 2 to 10 periods, most preferred 2 to 5 periods, such as 2 to 3 periods, e.g. 2 periods. When the light intensity is integrated over an integer number of periods of the light fluctuations, the integrated light intensity will be constant and, thus, independent of the position of the integration period in relation to the fluctuation period.
For both periodically and non-periodically varying light intensity of the illuminating light, synchronization may be performed by determination of light energy incident upon the objects during exposure of a part of the image, e.g. by integration of the monitored light
Knudsen Niels V.
Oster Jan
Onuaku Christopher
Phase One A/S
Tran Thai
Volentine & Francos, PLLC
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