DATA STORAGE AND REDUCTION METHOD FOR DIGITAL IMAGES, AND A SURVEILLANCE SYSTEM USING SAID METHOD

• US 20030133593A1
• Filed: 02/03/1999
• Published: 07/17/2003
• Est. Priority Date: 01/29/1999
• Status: Active Grant

• Current Assignee: Axis AB (Canon Inc.)
• Original Assignee: Axis AB (Canon Inc.)
• Inventors: TULLBERG, JOACIM, PETTERSSON, CARL-AXEL ALM
• Granted Patent: US 6,813,312 B2
• Time in Patent Office: Days
• US Class Current: 382/103
• CPC Class Codes: G08B 13/19667 Details realated to data compression, encryption or encoding, e.g. resolution modes for reducing data volume to lower transmission bandwidth or memory requirements
• CPC Class Codes: G08B 13/19669 Event triggers storage or change of storage policy
• CPC Class Codes: G08B 13/19697 Arrangements wherein non-video detectors generate an alarm themselves
• CPC Class Codes: H04N 19/587 involving temporal sub-sampling or interpolation, e.g. decimation or subsequent interpolation of pictures in a video sequence
• CPC Class Codes: H04N 7/188 Capturing isolated or intermittent images triggered by the occurrence of a predetermined event, e.g. an object reaching a predetermined position signal generation from motion picture films H04N5/253

Abstract

A data storage and reduction method for digital images having a chronological order involves storing a first and chronologically new image or group of images at a first image quality requiring a first amount of storage space, and processing a second image or group of images, chronologically older than said first image or group of images, by reducing the image quality thereof to a second image quality requiring a second amount of storage space, which is less than said first amount of storage space. Advantageously, the method is used for a surveillance system, comprising a camera, a digital storage device and an image storage controller, wherein image quality is reduced for old or otherwise less important images or groups of images, thereby obtaining additional storage space for allowing more important images (such as images relating to an alarm event) to be stored at higher image quality, while retaining an extended total recording time span.

Claims

1. A data storage and reduction method for digital images having a chronological order, characterized by

storing a first and chronologically new image or group of images at a first image quality requiring a first amount of storage space, and

processing a second image or group of images, chronologically older than said first image or group of images, by reducing the image quality thereof to a second image quality requiring a second amount of storage space, which is less than said first amount of storage space.

2. A method according to claim 1, wherein the processing involves deleting chronologically non-adjacent images within said second group of images, preferably for reducing a fps (frame per second) value of said second group of images.

3. A method according to claim 1, wherein the processing involves applying a data compression algorithm known per se to said second image or group of images.

4. A method according to claim 3, wherein said data compression algorithm is JPEG, MPEG, wavelet or fractal compression.

5. A method according to claim 1, wherein the processing involves discarding information relating to the color of individual pixels in said second image or group of images.

6. A method according to claim 1, wherein the processing involves discarding individual pixels in said second image or group of images.

7. A method according to any preceding claim, further characterized by

assigning said first image or group of images a factor of importance, which is set to a predetermined initial value,

considering said factor of importance when selecting said second image or group of images to be processed, and

increasing said factor of importance for images, which are chronologically adjacent to said second image or group of images.

8. A method according to claim 7, wherein said factor of importance is increased for images associated with an is alarm event.

9. A surveillance system, comprising:

a camera;

a digital storage device; and

an image storage controller operatively connected to the camera and the storage device for receiving a plurality of images from the camera and storing the images digitally in the storage device, the images having a chronological order reflecting the points of time, at which the images were produced;

characterized in that the image storage controller comprises;

first means for determining a qualitative value for individual images, or groups of images, stored in the storage device, the qualitative value being a function of a chronological position of the respective image or group of images;

second means for selecting, among the images stored in the storage device, a particular image or group of images in response to its qualitative value; and

third means for compressing or deleting said particular image or group of images.

10. A surveillance system according to claim 9, further comprising fourth means for determining an amount of storage space available in the storage device and for activating said first, second and third means, if the storage space is below a predetermined value.

11. A surveillance system according to claim 9 or 10, further comprising fifth means for maintaining a timezone table, in which the images stored in the storage device are divided into different timezones depending on the chronological positions of the images, the first means being operatively connected to the fifth means and being arranged to determine the qualitative value of each image in response to its timezone.

12. A surveillance system according to any of claims 9-11, further comprising sixth means, operatively connected to the fifth means, for allowing a user to define or redefine the timezone table.

13. A surveillance system according to any of claims 9-12, further comprising seventh means responsive to an external alarm signal and arranged to supply an alarm event to the first means in response to the alarm signal, the first means being arranged to consider the alarm event when determining the qualitative values, preferably by locally increasing the qualitative values for images within a time interval chronologically close to the alarm event.

14. A surveillance system according to any of claims 9-13, wherein the first, second and third means are arranged to select and delete chronologically non-adjacent images at regular intervals within a subset of the images in the storage device, preferably so that a frame per second (fps) value is reduced for said subset.