Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1986-08-13
1988-01-05
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358105, H04N 713
Patent
active
047179570
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a video compression method which is employed in connection with the conditional replenishment transmission and receiving method. In the transmitter used in the method, those areas which are changed with respect to the previous image are detected and the respective picture information, together with the addresses of the respective areas, is transmitted into the transmission channel. In the receiver a new image is reconstructed on the basis of the previous image and the addresses of the changed picture areas as well as on the basis of the picture information representing the occurred changes.
A digitized video signal which contains the picture information and is transmitted by means of the pulse code modulation method, requires a transmission channel capacity, the magnitude whereof is defined on the basis of the amount of picture elements and grey scale levels as well as the number of images to be transmitted per second. The information to be transmitted can be decreased without deteriorating the quality of the image by transmitting only the video signal representing the change occurred in between successive images. Therefore it is necessary, in one way or another, to detect the areas in the image which are changed with respect to the previous image, and only these changed areas are then transmitted. The information concerning these transmitted changed picture areas must also be provided with addresses which denote the picture area in question. Thus it is possible to reconstruct every image in a true and accurate fashion.
In the transmitter applying the above explained method, two separate picture memories are needed, the first containing the new image and the second containing an image corresponding to that which was last reconstructed by the receiver. In the receiver, only one picture memory is needed, which is the display memory.
SUMMARY OF THE INVENTION
The object of the present invention is to improve the aforementioned video compression method so that the amount of transmitted information is further decreased.
The method of the invention is characterized in that in connection with the above described prior art method, the conditional replenishment method, there is employed a reference memory both in the transmitter and the receiver. A so-called reference image made according to the transmitted picture information is stored in this reference memory, and the reference memory is used so that whenever a picture area is detected to have changed in the transmitter, a check is made to see whether this changed picture information corresponds to the information located in the respective place in the reference memory. If the answer is positive, a code word is sent to inform the receiver that the necessary picture information must be picked from the respective location in the reference memory. If the answer is negative, the picture information representing the change that has occurred in the picture area is transmitted.
In the transmitter of the apparatus applying the method of the present invention, there are, in addition to the two previously mentioned picture memories, other additional picture memories, i.e. a so-called reference memories--in the simplest case, however, only one. The reference memories are also provided in the receiver.
The method of the invention is designed to be employed in particular, but not exclusively, in connection with the above described prior art method in such cases where the transmitted video signal is created while the camera does not move but remains stably on the same spot. Thus a solid background is seen in the image, and the changes are created while the objects move in front of the background. Consequently, the proceeding front edge of the moving object keeps covering the background, and respectively the back edge of the object keeps revealing the same background. The conditional replenishment method, which was described in the beginning of this specification, recognizes as changed areas both the movi
REFERENCES:
patent: 3956580 (1976-05-01), Murayama
patent: 4307420 (1981-12-01), Ninomiya
patent: 4410916 (1983-10-01), Pratt
patent: 4591907 (1986-05-01), Catrus
Haikonen Pontti
Korhonen Ilkka
Leppanen Juha
Santamaki Harry
Britton Howard W.
Valtion teknillinen tutkimuskeskus
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