JP2002315000A - Data transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a highly efficient compression data transmission by suppressing the difference between a compression capacity being predicted from a specified compression rate and the actual compression capacity. SOLUTION: The data transmitter 1 comprises a section 11 for compressing image data using wavelet conversion, a temporary memory 13 for buffering compression data CD1 -CDn outputted from the data compressing section 11, a transmission schedule control section 14 for determining the transmission order of the compression data CD1 -CDn based on the compression capacity of each compression data, and a section 15 for transmitting the compression data CD1 -CDn on a communication line NW1 according to the transmission order. Since wavelet conversion is employed, difference between a compression capacity being predicted from a specified compression rate and the actual compression capacity can be suppressed. Consequently, the transmission order can be optimized easily to conform to the communication rate or communication conditions of the communication line NW1 and the compression data can be transmitted efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission apparatus for compressing and encoding image data and transmitting the data through a communication line.

[0002]

2. Description of the Related Art In networks and wireless communication networks, data such as moving images, still images, and voices are usually compressed and transmitted in order to reduce transmission time and avoid pressure on communication bands. Image data compression and encoding methods include ISO (International Organization for Standardi).
zation) standardized by JPEG (Joint Photographic
Coding Experts Group), Motion JPEG, MPE
G (Moving Picture Experts Group) and the like are known. In JPEG and MPEG, subband coding or DCT (Discrete Cosine Transform) for subdividing and coding a plurality of frequency bands is used, but the DCT does not converge at both ends of a transform base used. This causes a problem of so-called "block distortion" in which block-like noise occurs in the decoded image and a so-called "block noise" in which noise appears mainly in the outline portion of the decoded image due to quantization of high-band components. It is known that there is a problem of "mosquito noise".

[0003] Further, the compression capacity by DCT varies according to the amount of information contained in the original image, and is therefore difficult to predict. For example, even if an attempt is made to compress the original image at a compression rate of 1/10, the compression capacity may vary by several percent from that expected from the specified compression rate of 1/10. Due to this variation, it is difficult to estimate the transmission time required to transmit the compressed image and to set the transmission time, and it is difficult to perform efficient data transmission.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention is intended to solve the above problem by suppressing the difference between the compression capacity predicted from the designated compression ratio and the actual compression capacity, and improving the efficiency. Another object of the present invention is to provide a data transmission device which enables good compressed data transmission.

[0005]

According to a first aspect of the present invention, there is provided a data transmission apparatus for transmitting compressed data obtained by compressing and encoding image data through a communication line. Wavelet transform means for performing wavelet transform, quantizing means for quantizing the transform coefficients output from the wavelet transform means, and entropy encoding means for entropy encoding the quantized coefficients output from the quantizing means. An image compression unit that generates and outputs the compressed data in accordance with the specified compression ratio; a temporary storage unit that temporarily stores the plurality of pieces of compressed data output from the image compression unit; and a temporary storage unit that stores the compressed data. A transmission schedule control unit that determines a transmission order of the plurality of compressed data based on a compression capacity of each compressed data; In which and a transmission processing unit for transmitting said compressed data to said communication line in accordance with.

According to a second aspect of the present invention, in the data transmission apparatus according to the first aspect, the transmission schedule control unit includes transmission rate control means for determining the transmission order according to a fixed transmission rate. It is.

[0007] The invention according to claim 3 is the invention according to claim 1 or 2.
In the data transmission device described above, the transmission schedule control unit includes a transmission capacity control unit that determines the transmission order so that a predetermined transmission capacity can be transmitted within a predetermined time.

According to a fourth aspect of the present invention, there is provided the data transmission apparatus according to the third aspect, further comprising a control unit that controls switching between the transmission rate control unit and the transmission capacity control unit.

[0009]

FIG. 1 is a block diagram showing a schematic configuration of a data transmission device 1 according to an embodiment of the present invention. The data transmission apparatus 1 includes an A / D converter 10 that digitizes two-dimensional image data input from an imaging device 2 having an imaging device such as a CCD or a CMOS, and converts the digitized image data at a predetermined compression rate. A data compression unit 11 for high-efficiency encoding, a large-capacity image storage unit 12 for storing compressed data encoded by the data compression unit 11, and a small-capacity temporary memory 13 are provided. While the temporary memory 13 has only a capacity to temporarily store a plurality of compressed data, the image storage unit 12 has a storage area several hundred times to several thousand times or more the storage area of the temporary memory 13.

The data transmission apparatus 1 further includes a plurality of compressed data CD1 to C1 temporarily stored in the temporary memory 13.
Transmission schedule control unit 1 for determining the transmission order of Dn
4. A transmission processing unit 15 for sending each of the compressed data CD1 to CDn to a server (hereinafter, referred to as an SVR) on the communication network NW1 according to the transmission order, a data compression unit 11, and a transmission schedule control unit 14. Is provided. Further, the data transmission device 1 includes a user interface 17 having an input device such as a pointing device and a key input button. The user operates the user interface 17 to control the control unit 16 with control information such as a compression ratio. Can be indicated. The data compression unit 11, the transmission schedule control unit 14, and the control unit 16 may have either a hardware configuration or a software configuration.

Each part of the data transmission apparatus 1 having the above configuration will be described below in detail with reference to the flowchart of FIG.

First, in step S1, the data compression unit 11
The original image data output from the A / D conversion unit 10 is compression-encoded at a compression ratio specified by the control unit 16 using a discrete wavelet transform using a discrete wavelet function family as a conversion base. The discrete wavelet transform uses a band-pass filter (two-divided filter) that divides the frequency band of the original image data into a high band and a low band. This is achieved by assembling the subbands that have passed through in a recursive manner. Such discrete wavelet transform is based on JPEG2000 which is a successor to JPEG.
It is adopted in. The discrete wavelet transform is
Since image data can be compression-coded with an accuracy of 1/10 or less as compared with DCT, there is an advantage that a transmission schedule in a transmission schedule control unit 14 described later is simplified. FIG. 3 is a functional block diagram illustrating a schematic configuration of the data compression unit 11 that compresses a still image. As shown in FIG. 1, the data compression unit 11 includes a preprocessing unit 20, a wavelet transform unit 21, a quantization unit 22, an entropy coding unit 23, and a coding block of a multiplexing unit 24.

The preprocessing means 20 performs a color space conversion process or the like on the input original image data. In the color space conversion process, when the input original image data is composed of RGB components of three primary colors of R (red component), G (green component), and B (blue component), the RGB components are converted into a luminance signal Y and two color differences. The signal is converted into a YCbCr component composed of the signals Cb and Cr. Instead of the YCbCr component, NTSC
(National Television System Commitee) or the like, a YUV component or a YIQ component may be employed.

The wavelet transform means 21 arranges the above-mentioned two-divided filter group in a tree-like manner and adds a down-sampler for thinning out each of the two-divided filters at a sampling rate of 1/2 to a known filter bank. To perform discrete wavelet transform by dividing input original image data into a plurality of band components. Note that a reversible or irreversible filter bank can be used. The discrete wavelet transform may be executed on a line basis in which input original image data is individually processed by vertical lines and horizontal lines, or the input original image data is divided into a plurality of tiles, and May be performed on a tile basis. When performing wavelet transform on a tile basis under low bit rate conditions, in order to prevent distortion from appearing near the boundary between adjacent tiles, transform the data near the tile boundary after overlapping, or It is desirable to perform conversion using a target cycle extension method that extends the tile image while maintaining continuity at the tile boundary.

Next, the quantizing means 22 quantizes each wavelet transform coefficient calculated by the wavelet transform means 21 and then encodes it in bit plane units (bit plane encoding). Thereafter, the entropy coding unit 23 performs entropy coding on the coded value output from the quantization unit 22 using Huffman coding or the like. Then, the multiplexing means 24 generates image information such as the image size and the number of quantization bits of the original image, and compressed information such as a color space conversion table, a type of discrete wavelet transform, and a Huffman table used in Huffman encoding. Is added to the encoded data output from the entropy encoding means 23 to generate and output compressed encoded data. In this embodiment, the data compression unit 11 compresses and encodes a still image (frame).
The above-described encoding processing may be applied to compression encoding of a moving image. For example, the above-described coding processing may be applied to compression based on spatial correlation in each frame, and well-known motion compensation prediction coding may be applied to compression based on temporal correlation between frames.

By the above-described compression coding using the wavelet transform, the difference between the compression capacity predicted from the specified compression ratio and the actual compression capacity becomes extremely small. For example, 256
When K bytes of image data are compressed with a compression target value of 20 Kbytes (compression ratio: about 78%), the compression capacity of the conventional JPEG varies in a range of about 18 Kbytes to 22 Kbytes. With compression encoding, the compression capacity varies only in the range of about 19.99 Kbytes to 20.00 Kbytes.

In the next step S2, the data compression unit 1
, CD compressed data CD1, CD2,.
n is transferred to the temporary memory 13 and temporarily stored (buffered). In step S3, when a predetermined number of compressed data (compressed image files) CD1 to CDn are accumulated from the temporary memory 13, the transmission schedule control unit 14 determines the transmission order of the compressed data CD1 to CDn. Then, the transmission schedule control unit 14 sends the compressed data CD1 to the transmission processing unit 15 in accordance with the transmission order.
To CDn, and also outputs to the transmission processing unit 15 table information in which the correspondence between the transmission order and the compressed data is recorded. The transmission schedule control unit 14 has two types of control means 14A and 14B as means for determining the transmission order. One is a transmission rate control means 14 for determining the transmission order according to a fixed transmission rate (bit rate).
A. Another is a transmission capacity control means 1 for determining the transmission order so that a predetermined transmission capacity can be transmitted within a predetermined time.
4B. The control unit 16 includes a transmission rate control unit 14A.
And transmission capacity control means 14B. In the next step S4, the transmission processing unit 15
Converts the compressed data output from the transmission schedule control unit 14 into communication data based on the communication protocol of the communication line NW1, and transmits the communication data to the SVR. At this time, table information including the transmission order is also transmitted to the SVR so that the compressed data received by the SVR can be rearranged to the original order.

An example of the processing in the transmission rate control means 14A will be described with reference to FIG. 40K bytes /
A case where transmission is performed at a transmission rate of seconds will be exemplified. As shown in the figure, the compressed data 30A is stored in the temporary memory 13.
(15K bytes), 30B (30K bytes), 30C
When (10 Kbytes) and 30D (25 Kbytes) are buffered, the transmission rate control unit 14A determines the transmission order in the order of the compressed data 30A, 30D, 30B, and 30C. First transmitted compressed data 30A, 30
Since the total capacity of D is 40 Kbytes and the total capacity of the compressed data 30B and 30D to be transmitted next is also 40 Kbytes, it is easy to maximize the data transmission amount per unit time at a constant transmission rate (40 Kbyte / sec). It can be seen that the real-time property of data transmission is improved.

An example of the processing in the transmission capacity control means 14B will be described with reference to FIG. An example of transmitting 400 Kbytes of data in the first minute and 480 Kbytes of data in the next minute will be described. 10 of the first minute
The second is the time required for the data transmission device 1 to establish a connection with the SVR. As shown in FIG. 5, image data 31A (175 Kbytes), 31
B (165K bytes), 31C (150K bytes), 3
1D (125K bytes), 31E (100K bytes),
When 31F (85K bytes) and 31G (80K bytes) are buffered, the transmission capacity control means 14B
The transmission order is set to the compressed data 31A, 31D, 31E, 31
B, 31C, 31F, and 31G are determined in this order. The total capacity of the compressed data 31A, 31D, and 31E transmitted first is 400 Kbytes, and the image data 31B,
Since the total capacity of 31C, 31F, and 31G is 480 Kbytes, it can be seen that compressed data of a fixed transmission capacity can be efficiently transmitted within a predetermined time. For example, the communication line N
If the transmission rate of W1 is 8 Kbytes / sec, the telephone charge is calculated in units of one minute, and it takes 10 seconds to establish the first connection.
0 seconds × 8 Kbytes = 400 Kbytes, and the capacity that can be transmitted in the next minute is 60 seconds × 8 Kbytes = 480 Kbytes. Since the transmission time is shortened by such a transmission schedule, the communication cost can be reduced.

Since the storage capacity of the temporary memory 13 is limited, the compressed data is temporarily output from the data compression unit 11 to the large-capacity image storage unit 12 without being directly output to the temporary memory 13. You may keep it.
The compressed data stored in the image storage unit 12 is transmitted to the control unit 16
After being read out and buffered in the temporary memory 13 in a predetermined time zone determined by the above, the data is transmitted from the transmission processing unit 15 in accordance with the transmission order determined by the transmission schedule control unit 14. Thereby, for example, the communication line NW
1 during the time period when the traffic of the image storage unit 12 is reduced.
Since the compressed data stored in the storage device can be transmitted, the transmission time can be reduced, and the communication cost can be reduced.

[0021]

As described above, according to the data transmission apparatus according to the first aspect of the present invention, the compression capacity of the image data predicted from the designated compression ratio and the actual capacity are reduced by the compression encoding using the wavelet transform. The compression capacity can be kept low. For this reason, based on the compression capacity of each compressed data, the transmission order of the compressed data can be easily optimized according to the communication cost and communication conditions of the communication line, and efficient data transmission can be performed.

According to the second aspect, since a plurality of compressed data can be rearranged and transmitted according to a fixed transmission rate,
It is easy to maximize the amount of data transmission per unit time, and real-time data transmission is enhanced.

According to the third aspect, it is possible to easily maximize the amount of data transmission within the predetermined time, thereby reducing the transmission time and the communication cost.

According to the fourth aspect, the transmission rate control means and the transmission capacity control means are selectively used according to the communication cost and the communication conditions, and the transmission schedule of the compressed data can be further optimized. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a data transmission device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation example of the data transmission device according to the embodiment.

FIG. 3 is a block diagram illustrating a schematic configuration of a data compression unit of the data transmission device according to the embodiment.

FIG. 4 is an explanatory diagram showing a processing example in a transmission rate control unit of the data transmission device according to the embodiment.

FIG. 5 is an explanatory diagram showing a processing example in a transmission capacity control unit of the data transmission device according to the embodiment.

[Explanation of symbols]

 Reference Signs List 1 data transmission device 2 imaging device 10 A / D conversion unit 11 data compression unit 12 image storage unit 13 temporary memory 14 transmission schedule control unit 15 transmission processing unit 16 control unit 17 user interface

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C059 MA24 MC11 ME02 PP01 PP04 RB02 RE06 SS06 TA74 TC18 TD11 UA02 UA38 5C075 CA10 CF90 5C078 AA04 BA53 CA01 DA07 DB19 5J064 AA02 BA09 BA16 BB01 BB03 BC01 BC02 BC06 BD02

Claims (4)

[Claims] 1. A data transmission apparatus for transmitting compressed data obtained by compression-encoding image data through a communication line, comprising: a wavelet transform unit for performing a wavelet transform on the image data; and a transform coefficient output from the wavelet transform unit. An image compression unit having quantization means for quantizing, and entropy encoding means for entropy encoding the quantized coefficient output from the quantization means, for generating and outputting the compressed data according to a specified compression ratio; A temporary storage unit that temporarily stores the plurality of pieces of compressed data output from the image compression unit; and a transmission order of the plurality of pieces of compressed data stored in the temporary storage unit based on a compression capacity of each piece of compressed data. A transmission schedule control unit for determining the compressed data, and a transmission processing unit for transmitting the compressed data to the communication line according to the transmission order. The data transmission apparatus comprising: a. 2. The data transmission device according to claim 1, wherein the transmission schedule control unit includes a transmission rate control unit that determines the transmission order according to a fixed transmission rate. 3. The data transmission device according to claim 1, wherein said transmission schedule control unit includes a transmission capacity control unit that determines said transmission order so that a predetermined transmission capacity can be transmitted within a predetermined time. A data transmission device. 4. The data transmission device according to claim 3, further comprising: a control unit that controls switching between the transmission rate control unit and the transmission capacity control unit.