EP0545874A1
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EP
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A method and a device for image coding
Assignee: Telia Co AB
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Filing: 1992-11-12
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Granted: —
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Expires: 2012-11-12
Abstract
Abstract The invention relates to a method and a device for image coding having a particular, but not necessarily an exclusive, application in the transmission of video signals. The video signal is converted to a bit stream by coding and quantising and stored in a buffer store before it is transmitted on a transmission line at a constant bit rate. Problems experienced with the known technology have been the prevention of overflow in the buffer store and the buffer store being emptied prematurely. Both of these problems give rise to a deterioration in image quality. At the same time, the content of the buffer store should be as small as possible. According to the invention, not all the frames are coded and transmitted, but a certain number (k) of frames are skipped between each coded frame. The number k is based on the transmission rate R, the frame rate fo of the video signal and minimum value (bR/fo) set for the content of the buffer store. The number of skipped frames is selected so that the buffer store is not emptied below the set lower limit before the next frame is coded. The buffer store content is also regulated by skipping or setting to zero certain components in the bit stream from the coder core. The actual and ideal buffer store contents are determined and selected components of the bit stream are set to zero in dependence on the difference between the actual and the ideal content values. The invention also relates to a device for carrying out the method. The device is preferably constructed as a VLSI circuit.
Inventors
- 👤 Harald Brusewitz
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-10 02:35
CPC Classifications
H; H04; H04N; H04N19/00; H04N19/50; H04N19/587; H04N19/10; H04N19/102; H04N19/124; H04N19/132; H04N19/134; H04N19/146; H04N19/152; H04N19/169; H04N19/17; H04N19/172; H04N19/18; H04N19/60; H04N19/61
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
183 words
A method for image coding a video signal having a known frame rate wherein the video signal is coded and quantised to effect digitisation and compression of the signal to form a bit stream having a bit rate determined by the transmission line on which the bit stream is to be transmitted and wherein the bit stream is stored in a buffer store before transmission, characterised in that the method includes the steps of monitoring the buffer store content (B), sensing the rate (R) of the bit stream at the output of the buffer store, calculating the ideal buffer store content (Bideal), and setting to zero selected components of the bit stream at the output of the quantiser (Q) in dependence on the difference (B-Bideal) between the values of the monitored (B) and ideal (Bideal) buffer store contents and/or skipping a number (k) of frames between each coded frame, the number (k) of skipped frames being selected so that the content of the buffer store is not reduced to a level below a selected lower limit (bR/fo) before the next frame is coded.
Claim 2
Independent Claim
183 words
A method for image coding a video signal having a known frame rate wherein the video signal is coded and quantised to effect digitisation and compression of the signal to form a bit stream having a bit rate determined by the transmission line on which the bit stream is to be transmitted and wherein the bit stream is stored in a buffer store before transmission, characterised in that the method includes the steps of monitoring the buffer store content (B), sensing the rate (R) of the bit stream at the output of the buffer store, calculating the ideal buffer store content (Bideal), and setting to zero selected components of the bit stream at the output of the quantiser (Q) in dependence on the difference (B-Bideal) between the values of the monitored (B) and ideal (Bideal) buffer store contents and/or skipping a number (k) of frames between each coded frame, the number (k) of skipped frames being selected so that the content of the buffer store is not reduced to a level below a selected lower limit (bR/fo) before the next frame is coded.
Claim 3
Dependent Claim
40 words
A method as claimed in claim 1, characterised in that the number (k) of skipped frames is set, at least, to a value (k0) which is determined by the decoder of the receiver to which the bit stream is transmitted.
Claim 4
Dependent Claim
113 words
A method as claimed in claim 1 or claim 2, characterised in that the determination of the number (k) of skipped frames is effected in accordance with the following formula at a time when a frame has been coded and the content (Be) of the buffer store at that time has not been reduced to a level below the selected lower limit (bR/fo): where k is the number of skipped frames, k0 is the number of skipped frames, Be is the buffer store content, R is the bit stream rate, fo is the frame rate of the video input signal, and g takes into account when the coding of a frame is terminated,
Claim 5
Dependent Claim
143 words
A method as claimed in claim 1 or claim 2, characterised in that the number (k) of skip frames is determined at the beginning of each frame interval and in that the buffer store is emptied and the following frame is skipped if the content (Bs) of the buffer store at the beginning of a frame interval is of such a value that the buffer store will not be emptied below the selected lower limit (bR/fo), that is to say If k < k0 : skip next frame, set k = k+1; or else If Bs > (1 + b + g) R/fo; skip next frame, set k = k+1; or else code next frame, set k=0 where Bs is the buffer store content at the beginning of a frame, and g takes into account when the coding of a frame is terminated.
Claim 6
Independent Claim
47 words
A method as claimed in any one of the preceding claims, characterised in that the selected lower limit (bR/fo) is less than the value of the buffer store content that can be emptied from the store in three frame intervals and greater than or equal to zero.
Claim 7
Dependent Claim
32 words
A method as claimed in claim 1, characterised in that the selected components of the bit stream that are set to zero are those which represent frequencies higher than a predetermined value.
Claim 8
Independent Claim
38 words
A method as claimed in any one of the preceding claims, characterised in that a certain number of non-zero components in a block are transmitted and in that the remaining components in the block are set to zero.
Claim 9
Dependent Claim
69 words
A method as claimed in claim 7, characterised in that the bit stream is scanned after quantisation, in that the components of the scanned bit stream that are indicative of frequency values are arranged in ascending order of frequency values, in that the number of non-zeros of the components are calculated, and in that some of the non-zero components are transmitted and the remaining components are set to zero.
Claim 10
Independent Claim
105 words
A method as claimed in any one of the preceding claims, characterised in that the ideal buffer store content (Bideal) is calculated as follows: Bideal = (GOB - 1 + MB/33)/12 x (k1 + g) R/fo + bR/fo where GOB is the number of the block group, MB is the number of the macroblocks, k1 is the number of skipped frames which are determined by the coder, R is the bit stream rate, bR/fo is the minimum allowed content in the buffer store, fo is the frame rate of the video signal, and g takes into account when the coding of a frame is terminated.
Claim 11
Independent Claim
32 words
A method as claimed in any one of the claims 7 to 9, characterised in that the number of transmitted non-zeros is a function of the step height in the quantiser (Q).
Claim 12
Independent Claim
28 words
A device for image coding of a video signal having a known frame rate, in accordance with the method as claimed in any one of the preceding claims.
Claim 13
Dependent Claim
191 words
12 A device for image coding of a video signal having a known frame rate including an arrangement for coding and quantising the video signal to effect digitisation and compression of the signal to form a bit stream having a bit rate determined by the transmission line on which the image coded signal will be transmitted and a buffer store for storing the bit stream before transmission, characterised in that the device also includes control means (6) for monitoring the content (B) of the buffer store and the bit rate (R) of the signal at the output of the buffer store, and for calculating the ideal buffer store content (Bideal), and setting to zero selected components of the bit stream at the output of the quantiser (Q) in dependence on the difference (B-Bideal) between the values of the monitored (B) and ideal (Bideal) buffer store contents and/or skipping a number (k) of frames between each coded frame, the number (k) of skipped frames being selected so that the content of the buffer store is not reduced to a level below a selected lower limit (bR/fo) before the next frame is coded.
Claim 14
Dependent Claim
191 words
12 A device for image coding of a video signal having a known frame rate including an arrangement for coding and quantising the video signal to effect digitisation and compression of the signal to form a bit stream having a bit rate determined by the transmission line on which the image coded signal will be transmitted and a buffer store for storing the bit stream before transmission, characterised in that the device also includes control means (6) for monitoring the content (B) of the buffer store and the bit rate (R) of the signal at the output of the buffer store, and for calculating the ideal buffer store content (Bideal), and setting to zero selected components of the bit stream at the output of the quantiser (Q) in dependence on the difference (B-Bideal) between the values of the monitored (B) and ideal (Bideal) buffer store contents and/or skipping a number (k) of frames between each coded frame, the number (k) of skipped frames being selected so that the content of the buffer store is not reduced to a level below a selected lower limit (bR/fo) before the next frame is coded.
Claim 15
Dependent Claim
89 words
A device as claimed in claim 12, characterised in that the device includes a first zero setting arrangement (SKIP 1), the input of which is connected to the output of the quantiser (Q) and the output of which is connected to the input of a zig-zag scanning arrangement (ZIG) and in that the components of the bit stream that are indicative of frequency values which are higher than a predetermined value are set to zero by the first arrangement (SKIP 1) under the control of the control means (6).
Claim 16
Dependent Claim
102 words
A device as claimed in claim 12 or 13, characterised in that the device includes a second zero setting arrangement (SKIP 2), the input of which is connected to the output of a zig-zag scanning arrangement (ZIG) and the output of which is connected to a coding arrangement (RL) and in that a number of the non-zero components of the scanned bit stream at the output of the scanning arrangement (ZIG) are transmitted to the coding arrangement (RL) whilst the remaining components are set to zero by the second zero setting arrangement (SKIP 2) under the control of the control means (6).
Claim 17
Dependent Claim
64 words
15 A device as claimed in claims 13 or claim 14, characterised in that the device includes a first switch (S1) interposed between the quantiser (Q) and the first zero setting arrangement (SKIP 1) and in that the first switch (S1) is adapted to effect the removal of a number of frames from the bit stream under the control of the control means (6).
Claim 18
Dependent Claim
63 words
A device as claimed in claim 14 or claim 15, characterised in that the device includes a second switch (S2) the operation of which is under the control of the control means (6) and in that the second switch (S2) is adapted to connect the output of the first zero setting arrangement (SKIP 1) to the output of the second zero setting arrangement.
Claim 19
Independent Claim
31 words
A device as claimed in any one of the claims 11 to 16, characterised in that the device is in the form of an integrated circuit, for example, a VLSI circuit.
Claim 20
Dependent Claim
41 words
18 A device as claimed in any one of the claims 11 to 17, characterised in that the device also includes a BOOT-PROM for storing the data from which the required parameters for effecting frame skipping and/or zero setting are derived.
Claim 21
Dependent Claim
43 words
19 A video system characterised in that the system includes a device as claimed in any one of the preceding claims 11 to 18 and/or operates in accordance with the method as claimed in any one of the preceding claims 1 to 10.
Claim 22
Dependent Claim
19 words
20 A video system as claimed in claim 19 characterised in that the system is a video telephone system.
References Cited (Backward Citations)
US4833535A
Cited
EP0444839A2
Cited
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