JP2868633B2 - Video encoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture coding apparatus for transmitting a high quality picture by applying it to a television signal.

[0002]

2. Description of the Related Art In a moving picture coding apparatus which places importance on the statistical properties of an input picture and transmits picture information at a variable rate for efficient coding, the input picture is divided into frequency bands. After performing independent coding in each frequency band, cells are divided into frequency bands and cells are multiplexed over the entire band for output to a transmission path, and output to the transmission path.

FIG. 1 shows an example of such a conventional moving picture coding apparatus. The band dividing circuit 1 divides an input image signal into N frequency components, and the band dividing circuit 1 First to N-th band encoding circuits 21 to 2n for respectively encoding the first to N-th band image signals,
First to N-th band cell configuration circuits 31 to 3n for receiving the outputs coded by the respective coding circuits 21 to 2n and performing cellization;
A multiplexing circuit 5 is provided for multiplexing the cells configured for each frequency band by each of the band cell configuration circuits 31 to 3n so as to output them to one transmission line 7.

[0004] After dividing into frequency components of N bands, coding is performed in an independent manner while paying attention to the statistical properties of the image signals in each band, thereby reducing the amount of information generated by coding. The image quality reproduced on the receiving side was improved.

[0005] However, when congestion occurs in the transmission network using the variable-rate video encoding device, cells output from the video encoding device are discarded on the transmission network side, and the number of transmitted cells and the number of received cells are reduced. Unmatched phenomena occur. Therefore, it is possible to prioritize the transmission of each cell in order to prevent the cells from being discarded randomly.

Image information is concentrated on low frequency components,
If this important low-frequency component is discarded, the image quality is significantly degraded on the receiving side.

Therefore, when the first band is set to the lowest frequency band and the N-th band is set to the highest frequency band, the first band cell configuration circuit 31 gives the highest transmission priority to prevent significant deterioration in image quality. Make a cell with a degree,
The N-th band cell configuration circuit 3n performs cell formation with the lowest transmission priority so as not to be discarded even if the cell is discarded. Cell disposal measures were taken to prevent image quality degradation.

[0008]

However, in such a conventional moving picture coding apparatus, when the ratio of cells having the highest transmission priority is set to a large value so as not to cause deterioration of the picture quality, the maximum is set. Unless there is a guarantee that cells with the transmission priority will not be discarded, the phenomenon of discarding the cell with the highest transmission priority frequently occurs due to congestion, and serious image quality degradation occurs on the receiving side. Also, when a large number of video encoding devices are connected to a transmission path, the total number of transmission cells per transmission path increases and the absolute number of cells having the highest transmission priority also increases.

Normally, the relationship between the connected moving picture coding apparatus and the total number of transmission cells is not uniquely determined, but the relationship between the two is represented by a monotonically increasing function.

Here, an example in which the priority is divided into two of H and L will be described. As shown in FIGS. 7 and 8, a moving picture encoding apparatus connected to one transmission line When the number increases, cell discarding starts at the threshold th. As shown in FIG. 8, when the ratio of the number of cells having the highest transmission priority (H) to the total number of transmission cells increases, the priority becomes higher even with a smaller number of connected video encoding devices H2 (H1> H2). High cell discards occur.

Further, even if the total number of transmission cells per moving picture coding apparatus increases, the slopes of the curves shown in FIGS. Disposal occurs.

The present invention solves such a conventional problem. An excellent moving picture code capable of suppressing deterioration of image quality on the receiving side by voluntarily limiting the number of transmission cells on the transmitting side. It is an object to provide a chemical conversion device.

[0013]

According to the present invention, in order to solve the above-mentioned problems, an input image signal is filtered and separated into frequency bands, and coding and cell allocation are performed independently for each of the separated frequency bands. A moving image encoding apparatus that performs the configuration, multiplexes the obtained cells over the entire band, and performs image transmission at a variable rate, and when the total number of transmission cells generated by encoding in the past fixed period is equal to or more than a threshold value , The transmission of cells other than the lowest frequency band is restricted, and the threshold value is set so as to change according to the static state of the encoded image.

[0014]

FIG. 1 is a block diagram showing an embodiment of a moving picture encoding apparatus according to the present invention. As shown in FIG. 1, a band dividing circuit 1 for dividing an input image signal into N frequency components, A first to N-th band encoding circuit 21 for respectively encoding the first to N-th band image signals divided by the circuit 1
To 2n, and first to Nth band cell configuration circuits for performing cellization by receiving outputs coded by the coding circuits 21 to 2n.
31-3n, a transmission cell control circuit 4 for selecting a cell to be transmitted among the cells configured for each frequency band by each of the band cell configuration circuits 31-3n, and a selection by the transmission cell control circuit 4. And a multiplexing circuit 5 for multiplexing the output cells for each frequency band to one transmission path 7.

Of the first to N-th band encoding circuits 21 to 2n,
First band coding circuit 21 for coding the lowest frequency component
Performs block coding of the image signal divided as the first band, determines whether the coding block is a static region or a moving region, and uses the determination result as a static / moving information signal via the signal line 6 It has a function of applying the voltage to the control circuit 4.

As shown in detail in FIG. 2, the transmission cell control circuit 4 includes first to Nth band cells for counting the number of cells formed by the first to Nth band cell configuration circuits 31 to 3n. An adder 40 for adding the outputs of the counters 11 to 1n and all the band cell counters 11 to 1n to calculate the total number of generated cells per unit time in the past, and a unit time output from the adder 40 Total number of cells per hit and threshold set from outside
a determination circuit 41 for determining, for each band, a cell to be transmitted among the generated cells based on th and a static information signal applied from the first band coding circuit 21 via the signal line 6; It comprises second to N-th band cell selection circuits 42 to 4n for selecting transmission cells of the second to N-th bands according to the determination result at 41.

Next, the operation of the moving picture coding apparatus of the present invention configured as described above will be described.

As shown in the time chart of FIG. 3 in which the horizontal axis indicates time and the vertical axis indicates the number of cells generated in each unit time, that is, the output of the adder 40, When the number of generated cells changes, a threshold (t
h-1), the unit time t2 to t3 indicates that the Nth
And the (N−1) th band cell selection circuit 4n, 4n−1,
The transmission of the entire band and a part of the cells in the (N-1) th band is restricted, and in the unit time t3 to t4, the Nth band cell selection circuit
By 4n, transmission of some cells in the N-th band is restricted, and as a result, transmission of high frequency band components is restricted as shown in FIG.

When the threshold value (th-2) is set in the decision circuit 41, the unit cells are switched to the N-th to (N-2) -th band cell selection circuits 4n to 4n-2 in the unit time t2 to t3. And transmission of a part of the cells in the entire (N-1) th band and the (N-2) th band is restricted, and in the unit time t3 to t4, by the Nth and the (N-1) th band cell selection circuits 4n and 4n-1, Transmission of all cells in the Nth band and a part of cells in the (N-1) th band is restricted, and as a result, transmission of high frequency band components is restricted as shown in FIG. By limiting the cell transmission in this way, the total number of transmitted cells can be reduced as shown by the dotted line in FIG.

Since the resolution of visual perception deteriorates for an image having a lot of movement, transmission of a cell having a high frequency component may be restricted, so that a static information signal transmitted through the signal line 6 is not transmitted. In response, the threshold for limiting cell transmission is changed. For example, as shown in FIG. 3, the threshold value set in the determination circuit 41 is set to th-1 for a stationary block and th-2 for a moving block, so that the number of transmission cells can be statically changed. Can be restricted according to the state.

[0021]

As described above, according to the present invention, if the total number of cells generated by coding during a certain period in the past is equal to or greater than a certain threshold, cell transmission outside the lowest frequency band is restricted. Further, since the threshold value is changed in accordance with the static state of the image block, the transmission side can voluntarily select a cell to be transmitted and transmit the cell, and the transmission cell number can be reduced. Can be reduced, and as a result, frequent congestion can be reduced, so that it is possible to reduce the number of times of unidirectional cell discarding in the transmission network and the number of times of deterioration of reproduced images on the receiving side based on cell discarding. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a moving picture coding apparatus according to the present invention.

FIG. 2 is a block diagram of a transmission cell control circuit that is a main part of the device shown in FIG.

FIG. 3 is a time chart showing the distribution of the number of generated cells per unit time.
It is a chart.

FIG. 4 is a time chart showing transmission cells per unit time when a certain threshold is set.

FIG. 5 is a time chart showing transmission cells per unit time when different thresholds are set.

FIG. 6 is a block diagram illustrating an example of a conventional video encoding device.

FIG. 7 is a curve diagram showing the relationship between the total number of transmission cells per transmission path and the number of video encoding devices that can be connected.

FIG. 8 is a curve diagram showing the relationship between the total number of transmission cells per transmission path and the number of connectable video encoding devices under different conditions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Band division circuit 4 Transmission cell control circuit 5 Multiplexing circuit 7 Transmission line 11-1n Band cell counter 21-2n Band encoding circuit 31-3n N band cell configuration circuit 40 Adder 41 Judgment circuit 42-4n Band cell selection circuit

Claims (2)

(57) [Claims] 1. An input image signal is filtered to separate a frequency band, and data obtained by subjecting the separated image signal to independent encoding for each frequency band is divided into a fixed length to divide cells. In the moving image encoding apparatus configured to multiplex cells configured for each frequency band and perform image transmission at a variable rate, when the total number of cells generated by encoding in a past fixed period is equal to or greater than a set threshold, A moving picture coding apparatus comprising means for restricting cell transmission in a frequency band other than the lowest frequency band. 2. The moving picture coding apparatus according to claim 1, wherein a threshold value for limiting cell transmission is changed according to a still or moving state of the coded picture.