High speed digital framing camera

United States Patent m

Bellan

llllllllllllllllllllllllllll

US005387926A

[ii] Patent Number: 5,387,926

[45] Date of Patent: Feb. 7, 1995

[54] HIGH SPEED DIGITAL FRAMING CAMERA [75] Inventor: Paul M. Bellan, Pasadena, Calif.

[73] Assignee: California Institute of Technology,

Pasadena, Calif.

[21] Appl. No.: 906,898

[22] Filed: Jun. 30, 1992

[51] Int. CI." H04N 5/225

[52] U.S. CI 348/61; 348/231;

348/203

[58] Field of Search 358/209, 206, 332, 108,

358/105, 213.11, 199; 348/61, 203, 231

[56] References Cited

U.S. PATENT DOCUMENTS

3.809,806 5/1974 Walker et al 178/7.6

3,885.090 5/1975 Rosenbaum 358/105

3,956.586 5/1976 Ullstig 178/7.6

4,008,371 2/1977 Barron 358/206

4,054,752 10/1977 Dennis, Jr. et al 358/108

4,176,907 12/1979 Matsumoto 358/199

4,274,703 6/1981 Fisli 358/199

4.281,354 7/1981 Conte 358/108

4,393,408 7/1983 Beck et al 358/205

4,574,197 3/1986 Kliever 358/206

4,589.030 5/1986 Kley 358/225

4,811,037 3/1989 Avai 346/108

5,055,935 10/1991 Ohno 358/296

FOREIGN PATENT DOCUMENTS

2219330 4/1992 Germany 358/108

Primary Examiner—Joseph Mancuso

Assistant Examiner—Wendy R. Greening

Attorney, Agent, or Firm—Robbins, Berliner & Carson

[57] ABSTRACT

The present invention provides a system for recording images occurring both before and after a triggering event. Temporarily stored images are continually refreshed, the most recent images replacing the oldest images, providing a continuously updated history of recent events in a memory configured as an endless loop. Upon receipt of an external trigger, a predetermined further quantity of temporary images are stored until the capacity of the temporary storage medium is reached and then all temporarily stored images are then permanently stored. The system includes a rotating polygon mirror which produces a sequence of image scan lines. A lens system focuses the scan lines onto a linear array of photodetectors. Transient digitizers or a CCD linear storage array temporarily stores image data received from the photodetectors. Upon receipt of a trigger, the temporarily stored images are transferred to permanent digital memory after a predetermined further quantity of images have been stored.

20 Claims, 2 Drawing Sheets

10

HIGH SPEED DIGITAL FRAMING CAMERA

BACKGROUND OF THE INVENTION

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of work under a National Science Foundation Grant.

FIELD OF THE INVENTION

The present invention relates generally to the field of high speed motion camera systems and in particular to a system for permanently recording monitored images upon receipt of an external trigger. 15

DESCRIPTION OF THE PRIOR ART

High speed motion camera systems including film, video tape and digital systems are presently known. Some high speed film cameras use a rotating mirror to 20 make a sequence of images on film. High speed video cameras record directly on magnetic tape. Digital cameras normally utilize 2-dimensional pixel detector arrays and a magnetic recording medium to capture high speed events. 25

A problem associated with such camera systems is the amount of recording medium expended in order to capture a high speed random event. Presently a field of view must be continually recorded in order to capture the desired event and any associated preceding data, ^° such as the cause of the event. Continuous high speed recording requires significant quantities of the recording medium and is therefore a relatively expensive way to capture random events. Digital camera systems are also often limited by the relatively long time required to read the recorded data out of the 2-dimensional array as well as the practical limitations of available memory.

What is needed is a recording system which is able to record and store high speed random events without 4Q requiring the utilization of large amounts of recording medium or, in the case of digital camera systems, a lengthy process to read the detected data out of the 2-dimensional array.

SUMMARY OF THE INVENTION

35

45

The present invention provides a high speed electronic camera utilizing an array of solid state detectors. A plurality of scan lines of images are superimposed on the array by a rotating optical element, such as a polyg- 50 onal mirror. The output of the detectors are digitized and temporarily stored in a fixed capacity memory. CCD detectors may be used as transient digitizers for temporary storage and speed of digitization. The temporary storage is arranged in an endless loop fashion, 55 that is, when the memory capacity is filled, the next data to be stored is written over the earliest data stored. Upon receipt of an external trigger, a predetermined number of subsequent detector outputs are stored and then all the temporarily stored data are transferred to a go permanent storage device.

In a first aspect, the present invention provides a digital framing camera including means for converting images into sequences of scan lines, means for detecting the scan lines, means having a fixed capacity for tempo- 65 rarily storing a quantity of the detected scan lines, trigger means for temporarily storing a predetermined further quantity of the detected scan lines, and means re

sponsive to the trigger means for permanently storing the quantity of temporarily stored detected scan lines.

In another aspect, the present invention provides an optoelectronic scanning system for recording images including an optical element driven in rotation to produce a sequence of image scan lines, a detection system having an array of optical detectors, an optical element for focusing the image scan lines on the detection system, a digital system in communication with the detection system for temporary storage of a sequence of image scan lines, and a memory system in communication with the detection system and responsive to a trigger for temporarily storing a predetermined further quantity of image scan lines.

In another aspect, the present invention provides a method of detecting and storing random high speed events by converting images into sequences of scan lines, detecting the scan lines, temporarily storing a quantity of the detected scan lines, detecting a trigger signal for temporarily storing a predetermined further quantity of the detected scan lines, and then permanently storing the quantity of temporarily stored detected scan lines. The images may conveniently be converted into sequences of scan lines by reflecting the images with a rotating polygon mirror to form scan lines and focussing the scan lines into an image plane detected with a linear array of photodetectors placed in the image plane.

These and other features and advantages of this invention will become further apparent from the detailed description that follows, which is accompanied by several drawing figures. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic view of a digital framing camera embodying principles of the current invention.

FIG. 2 is a pictorial representation of how images are stored in digital memory.

DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENT

The present invention provides a high speed digital framing camera system for making motion pictures at very high framing rates, such as 20,000 frames per second. Images within a field of view of the camera are digitized and temporarily stored on an ongoing basis in a fixed capacity memory arranged in an endless loop fashion. That is, the temporarily stored images are continually refreshed, with the most recent images replacing the oldest images, providing a continuously updated history of recent images within the field of view. In other words, when the fixed capacity of the temporary memory storage is filled, the old data is overwritten by the next data to be stored.

Upon receipt of an external trigger, the data storage is continued for a predetermined number of data bytes and then all the temporarily stored images are transferred to a permanent storage medium. The predetermined number of data bytes may, for example, be one half of the total data that may be stored in the temporary storage so that half the permanently recorded data occurred before and half after the trigger.

In such an arrangement, upon receipt of a trigger, recording or storage would continue until one half of the temporary storage was filled with additional data