GB2332321A

GB2332321A - Surveillance image transmission system

Info

Publication number: GB2332321A
Application number: GB9725741A
Authority: GB
Inventors: Baruh Hason; Moshe Holzer; Reuven Livneh
Original assignee: Motorola Israel Ltd
Current assignee: Motorola Solutions Israel Ltd
Priority date: 1997-12-05
Filing date: 1997-12-05
Publication date: 1999-06-16
Anticipated expiration: 2017-12-05
Also published as: GB2332321B; GB9725741D0

Abstract

An image capturing device 2, 3 transmits image information to a receiving station 4 where images of a scene 26 are displayed. The devices 2,3 respond to a request for a specific image from the receiving station 4 by transmitting a specific differential image from a stored 12 set of differential images. The differential image is then merged with a reference image 8 in the device to provide a new reference image for future use in deriving new differential images. The previously held set of differential images is discarded. At the receiving station 4 the differential image is combined with the locally stored (and displayed) image to produce a new image for display and storage.

Description

b 2332321 IMAGE TRANSMISSION APPARATUS AND A METHOD OF TRANSMITTING IMAGES

Field of the Invention

This invention relates to an image transmission apparatus and a method for transmitting an image. The invention is particularly applicable to, but not limited to, transmitting images on a narrow band communication link such as a radio communication link.

Background of the Invention

Image transmission apparatus is becoming increasingly used in surveillance operations. Typically, the apparatus will include a number of remotely positioned cameras transmitting via a radio link to a receiving station. There the images captured by the camera are displayed to an operator.

Radio links have a low bandwidth and it is therefore necessary in such apparatus to use an image compression method to compress the data to be transmitted. The compression of the images is necessary in order to provide a smaller image file and to increase the image transmission rate. One of the methods which is in use to transmit images is an International Organisation for Standardisation (ISO) standard for compressing images which is named as differential Joint Photographic Expert Group (JPEG).

The operation of the difFerential JPEG method will be described briefly. Typically, image transmission apparatus will include a receiving station and at least one transmitting station. The receiving station requests an image from the transmitting station and in response the transmitting station transmits a compressed differential image which is the difference between a current image, which has been recently captured by the transmitting station, to an earlier image which is displayed at the receiving station. The disadvantage of this method is that only one update of the image at the receiving station can be done per transmission and there is a waste of processing resources at the 2 transmitter station. To overcome these disadvantages, a background routine is utilised in which a sequence of capturing, comparing and compressing images at the transmitting station is applied. Furthermore, the background routine stores compressed differential images in a buffer whereby each differential image is the difference between a previous image and a present image. On request from the receiving station, the transmitting station transmits the set of differential images which are stored in the buffer. Since the information of each differential image of the set of differential images is based on the previous differential image, the complete set of differential images has to be transferred to the receiving station in order to reconstruct an up dated image. Thus, if a fault occurs a complete set of differential images has to be transmitted if the receiving station needs to reconstruct an image.

Disadvantageously, the buffer has a predefined length and when the buffer is full information will be lost because there will be no room for storing 'new comer" differential images. Furthermore, because of the limitations of available bandwidth restricting the image transmission rate the filling of the buffer is quicker than the empting of the buffer. Thus, if at the receiving station a new differential image does not match with the previous deferential image (because some information, that is to say an earlier image, was lost due to lack of buffer capacity) the reconstruction of an updated image at the receiving station cannot be done.

This invention seeks to provide an image transmission apparatus and a method for transmitting images which mitigates at least some of the above mentioned disadvantages.

Summal:y of the Invention According to the invention there is provided an apparatus having at least one image transmitting station for capturing and transmitting images on a communication link to a receiving station, and wherein the image transmitting station comprises; an image capture device for capturing images of a scene in sequences; a memory for storing a reference image, a memory for storing an image; a processing device C) 3 operably coupled to the image capture device and the memory for comparing between the reference image and the image to provide a differential image; a memory operably coupled to the processing device for storing a set of differential images; and a transmitting device operably coupled to the memory for transmitting a differential image of the set of differential images to the receiving station.

According to the invention there is provided a method of capturing and transmitting images comprising the steps of. storing a reference image a first memory; capturing an image and storing the image in a second memory; comparing the image and the reference image to provide a differential image; storing the differential image as one of a set of differential images; transmitting a differential image of the set of differential images to an image displaying device; and removing the set of differential images from the third memory.

Brief Description of the Drawings

FIG. 1 is a block diagram of an image transmission system according to the preferred embodiment of the invention; FIG. 2 is a block diagram of an image transmission device according to a preferred embodiment of the invention; FIG. 3 is an explanatory diagram of images arranged in the memories of the apparatus of FIGs. 1 and 2; and FIG. 4 is a flow chart of a method for transmitting an image in accordance with the preferred embodiment of the invention.

4 Detailed Description of the Drawings

Referring firstly to FIG. 1, an image transmission apparatus for capturing and transmitting images via a radio frequency (RF) communication link is shown. The image transmission apparatus 1 includes a number of image transmitting devices two of which, devices 2 and 3, are shown, for capturing and transmitting images to a receiving station 4. The image transmission devices are nominally identical and their form will be explained by referring to device 2.

Device 2 includes an image capture device 6, for example a video camera, a first memory 8, a second memory 10, a third memory 12, a processing device 14 and a transmitting device 16.

The receiving station 4 includes a receiving device 18, a decompressor 22, a computer 20 and a display unit 24. In the preferred embodiment of the present invention the transmitting device 16 is a first radio transceiver and the receiving device 18 is a second radio transceiver to allow two-way comirnuni cation.

In operation, the video camera 6 captures an image of scene 26 and stores the image in the second memory 10. (For convenience, the image will be referred to as image A.) The first memory 8 contains a reference image (not shown). The reference image is a composition of a previous reference image with a previously transmitted differential image. The processing device 14 which is operably coupled to the video camera 6, the first memory 8 and the second memory 10, compares the reference image and the image A. The result of the comparison is a differential image which the processing device 14 stores in the third memory 12. The above described operation is done in sequence and the processing device 14 provides a set of differential images (not shown) which are stored in the third memory 12.

When the receiving station 4 requests a specific image from the image transmitting devices 2, for example, the image that was captured at 9:45 AM, the transmitting device 16 which is operably coupled to the third memory 12 under the instruction of the processor 14, loads the differential image (not shown) from the set of differential images held in C) memory 12 and transmits it to the receiving station 4. The processing device 14 then updates the reference image which is stored in the first memory 8. The processing device 14 merges the reference image with the transmitted differential image to provide an updated reference image. Furthermore, the processing device 14 removes the set of differential images from the third memory 12 thus freeing memory space.

The receiving device 14 receives the differential image and transfers the differential image to the decompressor 22. The decompressor 22 decompresses the differential image and merges the decompressed differential image with a currently displayed image to provide an updated image 28. The computer 24 displays the updated image 28 on the display unit 24.

The receiving station 4 may request the image transmitting device 2 to transfer any specified image of the set of the differential images which are stored in the third memory 12.

Referring now to FIG. 2, a block diagram of an image transmitting device according to a preferred embodiment of the invention is shown. The image transmitting device 30 includes a first memory 32, a second memory 34, a third memory 36, a transmitting device 38, a video camera 39 and a processing device 40. The processing device 40 further includes a compressor 42, a decompressor 44 and a control unit 46.

Having introduced the parts of the image transmitting device 30 a detailed description of the operation of the image transmitting device 30 will now be given with reference to FIG. 3.

In operation, a reference image 50 is stored in the first memory 32. The reference image 50 is a composition of a previous reference image with the transmitted ditTerential image. The processing device 40 initiates a background routine. The background routine is performed in sequence. In each sequence, the video camera 39 captures an image 52 of a scene 48. The image 52 or 52a or 52b or 52c are stored in the second memory 34. The control unit 46 of the processing device 40 compares the image 52 and the reference image 50. The comparison result is compressed by the compressor 44 to provide a differential image 54a, 54b, C) 6 54c and 54d. The differential images are compressed images which are the difference of the image 52 with respect to the reference image 50.

The differential images 54a, 54b, 54c and 54d are stored at the third memory 36 to provide a set of differential images 54. The processing device 40 receives from the transmitting device 38 a command for transfer a specific differential image, for example 54d issued by the receiving station 4. The tran iver 38 which is operably coupled to the third memory via the processing device 40, transmits the specific differential image 54d of the set of differential images 54. On completion of the transmission of the differential image 54d, the processing device updates the reference image 50 by merging the reference image 50 with the transmitted differential image 54d and removes the set of differential images 54 from the third memory 36.

Referring now to FIG. 4 a flow chart of a method of capturing and transmitting images is shown. The method starts with the step of:

applying a reference image 50 as is shown in step 100. If there is a request to update the reference image, as in step 102, the step of updating the reference image 32, step 118 is performed. If there is no request for updating the reference image 32, the reference image 32 is stored at the first memory 32. In the next step, step 106, the image transmitting device 2 waits for a request for transferring a specific image to the receiving station 4. While waiting, the processing device 14 starts a background routine. The background routine includes the steps of capturing an image 52, step 108, storing the image 52 in the second memory 34 as is shown in step 110, comparing between the image 52 and the reference image 50 to provide a differential image 54a, as is shown in step 112 and storing the differential image 54a at a third memory 12 for providing a set of differential images 54, as is shown in step 114. The background routine stops when a request for transfer a specific image arrives, as is shown in step 106. The processing device 14 transfers the specific differential image 54d to the transmitting device 16, as in step 120. The next step, step 122, the processing device 14 removes the set of differential images 54 from the third memory 12. The last step is updating the reference image. In step 118, the reference image 52 is 7 merged with the last transmitted differential image 54d to provide an updated reference image.

Whilst in the preferred embodiment the information is transmitted by radio communication. Other forms of communication may be used, for example, the communication may be provided by an optical fibre link.

8

Claims

1. Image transmission apparatus having at least one image transmitting station for capturing and transferring images on a communication link to a receiving station, and wherein the image transmitting station comprises:

an image capture device for capturing images of a scene in sequence; memory for storing a reference image; a memory for storing an image; processing device operably coupled to the image capture device and the memory for comparing between the reference image and the image to provide a differential image; a memory operably coupled to the processing device for storing a set of differential images; and a transmitting device operably coupled to the memory for transferring a differential image of the set of differential images to the receiving station.

2. Apparatus as claimed in claim 1, wherein the reference image is a composition of a previous reference image with the transferred differential image.

3. Apparatus as claimed in claims 1 or 2, wherein the processing device updates the reference image on a completion of transferring of the differential image; and removes of the set of differential images from the memory.

4. Apparatus as claimed in claims 1,2 or 3, wherein the image capture device is a video camera.

5. Apparatus as claimed in claims 1 to 4, wherein the processing device comprises:

9 a compressor for compressing the differential images; and a controlling unit for controlling the operation of the image transmission device.

6. Apparatus as claimed in claims 1 to 5 wherein the set of differential images which are stored in the third memory are a set of compressed images.

7. Apparatus as claimed in claims 1 to 6 wherein the transferring device is a first radio transceiver.

8. An image receiving station for use in apparatus as claimed in any one of the preceding claims, wherein the receiving station comprises:

a receiving device for receiving the differential image a decompressor operably coupled to the receiving device for decompressing the said differential image to provide a decompressed differential image; and a processor operably coupled to the decompressor for merging the decompressed differential image with a previous image to provide an updated image.

9. An image transmitting station for transferring images comprising:

memory for storing a reference image; memory for storing an image; processing device operably coupled to the image capture device, and the memory for comparing between the reference image and the image for providing a differential image; a memory operably coupled to the processing device for storing a set of differential images; and a transmitting device operably coupled to the memory for transferring a differential image of the set of differential images.

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10. An image transmitting station as claimed in claim 9, wherein the reference image is a composition of a previous reference image with a last transmitted differential image.

11. An image transmitting station as claimed in claims 9 or 10, wherein the differential image is a compressed image which is the difference of the image with respect to the reference image.

12. An image transmitting station as claimed in claims 9,10 or 11, wherein the processing device updates the reference image on a completion of transmission of differential image; and removes the set of differential images ftom the memory.

13. A method of capturing and transmitting images comprising the steps of: storing a reference image at a first memory; capturing an image and storing the image at a second memory; comparing the image and the reference image to provide a differential image; storing the differential image as one of a set of differential images; transmitting a differential image of the set of differential images to an image displaying device; and removing the set of differential images from the third memory.

14. A method of capturing and transmitting images as claimed in claim 13, wherein the step of transmitting further comprises the step of: merging a previous reference image with a last transferred differential image to provide an updated image; and storing the updated image at the first memory.