JP2001111839A - Image decoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image decoder that can execute decoding processing of existing data with high quality even when JPEG data are missing on the way. SOLUTION: The image decoder consists of a marker detection section 101 that detects marker information included in the JPEG data, a 1st counter section 102 that counts number of the JPEG data read by the marker detection section 101, a delay section 103 that temporarily stores the JPEG data outputted from the marker detection section 101, a stripe decoding section 104 that reads the JPEG data outputted from the delay section 103 and applies decoding processing to the compressed image data on a line buffer in the unit of stripes, an image print control section 106 that outputs the decoded image data, a 2nd counter section 105 that counts number of the JPEG data read by the stripe decoding section 104, and a comparison section 107 that compares a count Ca of the 1st counter section 102 with a count Cb of the 2nd counter section 105. The image decoder stops decode processing in the case that a relation of Ca<Cb holds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image decoding apparatus, such as a color facsimile, for decoding JPEG data encoded by the JPEG method.

[0002]

2. Description of the Related Art The JPEG encoding method is widely used as compression of continuous tone color still images in digital image equipment such as the Internet, personal computers, digital cameras, etc., and is also adopted as a standard compression method in color facsimile.

[0003] There are several modes in the JPEG encoding system. In general, the baseline mode is the mainstream, and the baseline encoding system is also used in color facsimile. Another mode is progressive JPE
The G mode is the degree that can be seen on the Internet WWW (World Wide Web).

[0004] Hereinafter, the JPEG baseline mode will be described as an example. In the JPEG system, a certain file format is defined in order to maintain compatibility.

FIG. 3 is a schematic configuration diagram of a file format in the JPEG baseline mode. This file format includes a header section, compressed data, EOI
(EndOf Image) marker, the header portion includes parameter data describing the width X and the number of lines Y of the image,
The compressed data is obtained by compressing the image data by the JPEG method, and the EOI marker indicates the end of the image.

FIG. 4 is a configuration diagram showing details of the header section of FIG. The header part is a SOI (Start Of Image) marker, DHT (Define Huffman Table) marker, DQ
T (Define Quantization Table) marker, SOF0
(Start Of Frame No.0) marker, SOS (Start Of Frame
Scan) Consists of marker segments such as markers. The SOI marker indicates the start of the image, the DHT marker defines the Huffman code table, the DQT marker defines the quantization table, the SOF0 marker indicates the start of the frame, the SOS marker indicates the start of the scan, and these markers Is a marker essential for the JPEG system. Especially DHT marker, DQT marker, SOF
As long as the 0 marker is between the SOI marker and the SOS marker, the order of the markers does not matter, and the width X and the number of lines Y of the image are described in the segment of the SOF0 marker.

FIG. 5 is a configuration diagram showing details of a marker segment. The marker segment includes a marker, a segment length parameter, and other parameters. The marker consists of 2 bytes, the first byte is always 0x
ff (“0x” means hexadecimal notation; the same applies hereinafter)
Indicates the presence of the marker, the second byte is 0 and 0xf
The type of marker is specified by a number other than f. The segment length parameter also has a 2-byte configuration, and the total value of its own 2 bytes and the number of bytes of subsequent parameters is set. Therefore, the segment length parameter always has a value of 2 or more. The parameters have an arbitrary byte length, and necessary numerical values are set according to the type of the marker. For example, in the SOF0 marker, the width X and the number of lines Y of the image are described at the positions of the parameters.

[0008] Since the compressed data included in the file format is entropy-coded by the Huffman code, it can appear from 0 to 0xff with equal probability when viewed in byte units. Therefore, 0xff data indicating the presence of the marker appears in the compressed data. As a countermeasure, when 0xff data appears in the compressed data, 0 can be distinguished from 0xff indicating the presence of the marker by inserting 0 after the 0xff data.

Further, the same 0xff data can be continuously added after 0xff data in the compressed data. In this case, the second and subsequent 0xff data have no meaning as image data, but can be used as padding for adjusting the data length.

When JPEG data is decoded by executing image processing software on a personal computer, a sufficiently large memory area for image expansion can be secured. Therefore, decoding processing can be performed on an image basis, and JPEG data can be decoded at a time by referring to parameters of the image width X and the number of lines Y in the SOF0 marker.

On the other hand, most home color facsimile machines use a sheet feeder system which reads and prints line by line, and cannot mount a sufficient memory due to cost and other restrictions. Therefore, when reading the original image, while scanning with the scanner, it encodes and transmits only the amount of reading, while receiving the facsimile, while receiving the data,
Only the received data is decrypted and printed.

Similarly, when a home color facsimile employs the JPEG encoding method, the original image is read by a scanner while the read image is encoded in stripe units required for encoding and transmitted. During facsimile reception, while receiving data, the received data is decoded and printed in stripe units. Therefore, when the transmitting facsimile starts JPEG encoding, the number of lines of the document image cannot be determined in advance.

As a countermeasure, since the line number parameter Y of the header portion is set to 0 indicating indefinite at the start of encoding, the number of lines of the image is determined when encoding of all stripes is completed. As shown in FIG. 6, in the file format, after the compressed data and before the EOI marker, a DNL (DefineNu) defining the number of lines NL is defined.
mber of Lines) Marker segments can be inserted.

When the facsimile receives the JPEG data in the file format with the DNL marker, the decoding process is started immediately while the data is being received, and when the DNL marker segment is received, the number of lines NL can be determined, and the line after the decoding is completed. When the number matches NL, all decoding processes have been completed.

As a related prior art, Japanese Patent Laid-Open No.
No. 99579, decoding on a page basis is terminated by recognizing the DNL marker.

[0016]

When JPEG data is transmitted via a communication line, communication may be interrupted on the way due to an abnormality in the transmission side device or the line. Particularly, as shown in FIG. 7, if the data is interrupted in the middle of JPEG data compressed data, the DNL located at the rear of the format
Since the marker cannot be received, the decoding process cannot be terminated.

When received data is stored halfway in the line buffer for performing decoding processing in stripe units, dust data remains in the remaining area of the line buffer. The part becomes an image like noise, and the quality of the received image is greatly deteriorated.

Further, when receiving JPEG data in a file format without a DNL marker, even if the communication is interrupted in the middle of the compressed data, the number of lines Y of the image is determined by the reception of the SOF0 marker. , An image like noise appears after the received data.

An object of the present invention is to provide an image decoding apparatus capable of executing decoding processing of existing data with high quality even when JPEG data is lost from the middle.

[0020]

According to the present invention, there is provided an image decoding apparatus for decoding JPEG data encoded by a JPEG system and including a marker and compressed image data.
A marker detector for detecting marker information included in the JPEG data, and a JP read by the marker detector.
A first counter unit for counting the number of EG data, a delay unit for temporarily storing JPEG data output by the marker detection unit, and a JPEG data output by the delay unit are read and based on the marker information. A stripe decoding unit for performing initialization processing and performing decoding processing in stripe units on the line buffer based on the compressed image data, an output unit for outputting image data decoded by the stripe decoding unit, and a stripe decoding unit. A second counter unit for counting the number of the read JPEG data, a comparison between the count value Ca of the first counter unit and the count value Cb of the second counter unit, and notification of the comparison result to the stripe decoding unit. Wherein the stripe decoding unit stops the decoding process when Ca <Cb holds. A decoding device.

According to the present invention, the first counter counts the number of JPEG data input to the marker detector, and the second counter counts the number of JPEG data input to the stripe decoder. Then, the count value Cb of the second counter unit is calculated from the count value Ca of the first counter unit.
Is larger, it can be determined that the portion below the count value Ca is normal data and the portion exceeding the count value Ca is abnormal data. As a result, only normal data can be decrypted and abnormal data can be prohibited from being decrypted.
The appearance of an image such as noise can be reliably prevented.

The present invention also relates to a JPEG encoding method which includes a marker and compressed image data.
An image decoding device that decodes data detects a marker information included in the JPEG data, and outputs a JPEG data, a marker detection unit for continuously outputting the specific data, and temporarily outputs the JPEG data output by the marker detection unit. Delay section for saving and JPE output by the delay section
A stripe decoding unit for reading the G data, performing an initialization process based on the marker information, and performing a decoding process in stripe units on a line buffer based on the compressed image data, and image data decoded by the stripe decoding unit And a decoding unit that stops the decoding process when the number of consecutive specific data is greater than a predetermined value.

According to the present invention, the marker detecting unit is a JPE
By continuously outputting the specific data after the output of the G data, when the number of continuous specific data becomes larger than a predetermined value, the part before this point is normal data and the part after this point is abnormal. It can be determined that it is data. as a result,
Since decoding processing can be performed only for normal data and decoding processing for abnormal data can be prohibited, the appearance of an image such as noise can be reliably prevented. Note that 0xff data which is not affected by continuous input can be used as the specific data.

The present invention also relates to a JPEG encoding method which includes a marker and compressed image data.
In an image decoding device for decoding data, a marker detecting section for detecting marker information included in JPEG data and continuously outputting specific data after outputting the JPEG data, and data of the JPEG data read by the marker detecting section. A first counter for counting the number, a delay for temporarily storing the JPEG data output from the marker detector, and a read of the JPEG data output from the delay, and performing an initialization process based on the marker information. A stripe decoding unit for performing a decoding process in stripe units on a line buffer based on the compressed image data, an output unit for outputting image data decoded by the stripe decoding unit, and JPEG data read by the stripe decoding unit. A second counter unit for counting the number of data of the Values Ca and count C of the second counter portion
b, and a comparison unit for notifying the comparison result to the stripe decoding unit.
An image decoding apparatus characterized in that the decoding process is stopped when b is satisfied or when the number of consecutive specific data is greater than a predetermined value.

According to the present invention, the first counter counts the number of JPEG data input to the marker detector, and the second counter counts the number of JPEG data input to the stripe decoder. Then, the count value Cb of the second counter unit is calculated from the count value Ca of the first counter unit.
Is larger, it can be determined that the portion below the count value Ca is normal data and the portion exceeding the count value Ca is abnormal data.

Further, the marker detector continuously outputs the specific data after outputting the JPEG data,
If the number of consecutive specific data exceeds the specified value,
It can be determined that the part before this point is normal data and the part after this point is abnormal data. Note that 0xff data which is not affected by continuous input can be used as the specific data.

As a result, decoding processing can be performed only for normal data and decoding processing for abnormal data can be prohibited, so that the appearance of an image such as noise can be reliably prevented.

Further, the invention is characterized in that the output unit prints the decoded image data on a recording medium.

According to the present invention, a facsimile receiving function capable of recording JPEG data can be realized by printing the decoded image data on a recording medium.

[0030]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. The image decoding apparatus includes a marker detection unit 101, a delay unit 103, a stripe decoding unit 104, an image print control unit 106, a first counter unit 1
02, a second counter unit 105, a comparison unit 107, and the like. These can be realized by hardware such as a CPU, a ROM, and a RAM and software corresponding to each block, or may be entirely or partially configured as a JPEG decoding LSI.

The marker detection unit 101 writes JPEG data input from an external image transmission device via a communication line, a network, or the like into a marker detection line buffer, and detects various markers as shown in FIG. Analyzes marker-specific parameter information. The analyzed marker information is output to the stripe decoding unit 104. For example, when the DNL marker is detected as shown in FIG. 6, the number of lines NL is notified to the stripe decoding unit 104.

JPE input to marker detection section 101
The G data is output to the delay unit 103 as it is. When the marker detection unit 101 finishes outputting the JPEG data, it continuously outputs 0xff data.

The delay section 103 has a buffer function for temporarily storing JPEG data output from the marker detection section 101 and adjusting the processing timing on the input side and output side.

The stripe decoding unit 104 performs an initialization process based on the marker information detected by the marker detection unit 101, reads the JPEG data output from the delay unit 103, and converts the compressed image data included in the JPEG data into an image. Then, the data is written in the line buffer for decoding, and the decoding process is performed on the image line buffer in stripe units. The initialization processing includes creation of a quantization table based on DQT marker information, creation of a Huffman code table based on DHT marker information, determination of an image size and a subsampling ratio based on SOF0 marker information, and the like, and sets data necessary for decoding processing. In the case of a file format with a DNL marker, the DNL following the compressed image data
The number of lines NL is determined by the marker information.

The image printing control unit 106 includes the printing unit 10
8 has a function of controlling the operation of the stripe decoding unit 10
4 supplies the image data decrypted to the printing unit 108, and the printing unit 108 prints the image data on a recording medium.

The first counter unit 102 counts the number of JPEG data read by the marker detection unit 101, for example, in byte units.

The second counter unit 105 counts the number of JPEG data read by the stripe decoding unit 104, for example, in byte units.

The comparing section 107 compares the count value Ca of the first counter section 102 with the count value Cb of the second counter section 105, and notifies the stripe decoding section 104 of the comparison result.

Next, the operation will be described. When JPEG data is input to the marker detection unit 101, the stripe decoding unit 104 is initialized based on various types of marker information. The JPEG data is passed through the marker detection unit 101 and the delay unit 103 to the stripe decoding unit 104 as it is.
Handed over to At this time, the first counter unit 102 counts the number of data that has passed through the marker detection unit 101.

After the initialization process, the stripe decoding unit 104 decodes the compressed image data written in the image line buffer in stripe units, and outputs the decoded image data to the image print control unit 106. Regarding the number of stripe lines, when the subsampling ratio is 4: 1: 1, one stripe is composed of 16 lines, and at other subsampling ratios, one stripe is composed of 8 lines.

In the decoding process, 0x is included in the compressed image data.
If 0 data exists after the ff data, the 0 data is removed. If a plurality of 0xff data are consecutive, the second and subsequent 0xff data are ignored. However, 0xf
If the f data continues forever, the process will not end, so 0x
If the number of consecutive ff data is larger than the predetermined value N, a decoding error is determined. If data other than 0 and 0xff exists after the 0xff data in the compressed image data, it means that a marker is present, and thus a decoding error is generated. When a decoding error occurs, the decoding process is stopped at that point, and the output to the image print control unit 106 is also stopped.

When the line number parameter Y defined in the header of the JPEG data satisfies Y> 0, the line number Ya of the image to be decoded can be specified. Therefore, the number Ya of lines to be decoded is set to Y, and the stripe decoding unit 10
4 counts the number of lines Yc for which decoding processing has been completed, and Yc = Y
The decoding process ends at the point of time a.

On the other hand, when the line number parameter Y in the header portion is Y = 0, it can be estimated that the file format is a file format with a DNL marker, and the line number Ya to be decoded is set to JPE.
It is set to 0xffff which is the maximum number of lines in the G image. The stripe decoding unit 104 counts the number of lines Yc for which decoding processing has been completed. When the number of lines NL is notified from the marker detection unit 101 during the decoding processing, the number Ya of lines to be decoded is reset to NL. The decoding process ends when Yc = Ya.

The conditions under which the decoding process of the stripe decoding unit 104 ends normally are as follows: (1) When the number of lines Yc after the decoding process matches or exceeds the number of lines parameter Y in the header part, 2) When the number of lines Yc after the decoding process matches or exceeds the number of lines NL by the DNL marker, either one of the conditions is satisfied.

However, when JPEG data is transmitted via a communication line, communication may be interrupted on the way due to an abnormality in the transmitting device or the line, and the JPEG data may be lost from the middle. In particular, in the case of a file format with a DNL marker, if the DNL marker disappears, the decoding process cannot be completed until the number of lines Yc reaches the maximum number of lines 0xffff.

Therefore, a description will be given of a stop process capable of terminating normally so that a noise image does not appear even if JPEG data is lost halfway.

First, regarding the first stop processing, the comparison unit 107
Compares the count value Ca of the first counter unit 102 with the count value Cb of the second counter unit 105, and when Ca <Cb holds, the stripe decoding unit 104 stops the decoding process. That is, in the compressed image data written in the image line buffer, it can be determined that the portion below the count value Ca is normally transmitted data and the portion exceeding the count value Ca is abnormal data. As a result, decoding processing can be performed only for normal data and decoding processing for abnormal data can be prohibited, so that the appearance of an image such as noise can be reliably prevented.

Regarding the second stop processing, the marker detecting unit 1
01 outputs the 0xff data continuously following the output of the JPEG data, and the stripe decoding unit 104 outputs the 0xff data.
When the number of consecutive f data is larger than the predetermined value N, the decoding process is stopped as a decoding error. That is, of the compressed image data written in the image line buffer, the portion before the continuous 0xff data is normal data, and 0xff
It can be determined that the part after the f data is abnormal data. As a result, decoding processing can be performed only for normal data and decoding processing for abnormal data can be prohibited, so that the appearance of an image such as noise can be reliably prevented.

As described above, by executing one of the two stop processes, only the normal image portion is decoded, and the garbage data remaining in the memory is decoded even if the JPEG data has been lost halfway as shown in FIG. Can be prevented.

FIG. 8 is an explanatory diagram showing a configuration example of partially decoded image data. Upper white area is JPEG
The data is a partially decoded area, and the black area below is an undecoded area. The print unit 108 prints the image data of the white area and does not print the black area, thereby maintaining the image quality.

FIG. 2 is a block diagram showing the configuration of the second embodiment of the present invention. Here, a configuration in which the first counter unit 102, the second counter unit 105, and the comparison unit 107 in FIG. 1 are omitted and a second stop process is adopted is shown. The image decoding device includes a marker detection unit 101, a delay unit 103,
It is composed of a stripe decoding unit 104, an image printing control unit 106, and the like. The operation of each block is the same as that of FIG.

Regarding the second stop processing, the marker detecting unit 1
01 outputs the 0xff data continuously following the output of the JPEG data, and the stripe decoding unit 104 outputs the 0xff data.
When the number of consecutive f data is larger than the predetermined value N, the decoding process is stopped as a decoding error. That is, of the compressed image data written in the image line buffer, the portion before the continuous 0xff data is normal data, and 0xff
It can be determined that the part after the f data is abnormal data. As a result, decoding processing can be performed only for normal data and decoding processing for abnormal data can be prohibited, so that the appearance of an image such as noise can be reliably prevented.

[0053]

As described in detail above, according to the present invention, the first counter counts the number of JPEG data input to the marker detector, and the second counter inputs the JPEG data to the stripe decoder. When the number of JPEG data is counted and the count value Cb of the second counter section is larger than the count value Ca of the first counter section, the portion below the count value Ca is normal data and the count value Ca Can be determined to be abnormal data. As a result, decoding processing can be performed only for normal data and decoding processing for abnormal data can be prohibited, so that the appearance of an image such as noise can be reliably prevented.

Further, according to the present invention, the marker detecting section can
By continuously outputting the specific data after the output of the PEG data, if the continuous number of the specific data exceeds a predetermined value, the part before this point is normal data and the part after this point is abnormal. It can be determined that it is data. As a result, decoding processing can be performed only for normal data and decoding processing for abnormal data can be prohibited, so that the appearance of an image such as noise can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a second exemplary embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a file format in a JPEG baseline mode.

FIG. 4 is a configuration diagram showing details of a header unit.

FIG. 5 is a configuration diagram showing details of a marker segment.

FIG. 6 is a schematic configuration diagram of a file format with a DNL marker.

FIG. 7 is an explanatory diagram illustrating a partially erased state of JPEG data.

FIG. 8 is an explanatory diagram showing a configuration example of partially decoded image data.

[Explanation of symbols]

 Reference Signs List 101 Marker detection unit 102 First counter unit 103 Delay unit 104 Stripe decoding unit 105 Second counter unit 106 Image print control unit 107 Comparison unit 108 Printing unit

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) H04N 11/04 H04N 7/133 Z F term (reference) 5C053 FA04 FA07 GA11 GB06 GB36 JA21 KA03 KA21 KA24 LA03 LA14 5C057 AA07 BA14 CB07 CC04 CE04 EL01 EM13 FB03 GE09 GF03 GF04 GF05 GH05 GJ01 5C059 KK34 MA00 MC23 ME02 PP01 RC28 SS06 SS08 SS15 TA49 TB04 TC20 TD06 TD11 UA05 5C078 BA21 BA23 CA41 DA00 DA02 DA03 DA06 5J064 BC01 BC05 BD06

Claims (4)

[Claims] 1. An image decoding apparatus for decoding JPEG data including a marker and compressed image data encoded by the JPEG method, comprising: a marker detection unit for detecting marker information included in the JPEG data; and a marker detection unit. Read JP
A first counter unit for counting the number of EG data, a delay unit for temporarily storing JPEG data output by the marker detection unit; and a JPEG data output by the delay unit. A stripe decoding unit for performing an initialization process and performing a decoding process in stripe units on a line buffer based on the compressed image data; an output unit for outputting image data decoded by the stripe decoding unit; and a stripe decoding unit. A second counter unit for counting the number of read JPEG data, a comparison between the count value Ca of the first counter unit and the count value Cb of the second counter unit, and notification of the comparison result to the stripe decoding unit. Wherein the stripe decoding unit stops the decoding process when Ca <Cb holds. The image decoding apparatus. 2. An image decoding apparatus for decoding JPEG data including a marker and compressed image data, which is encoded by the JPEG method, detects marker information included in the JPEG data,
A marker detection unit for continuously outputting specific data after the output of the EG data; a delay unit for temporarily storing JPEG data output by the marker detection unit; and a JPEG data output by the delay unit. A stripe decoding unit for performing an initialization process based on the information and performing a decoding process in stripe units on a line buffer based on the compressed image data; and an output unit for outputting the image data decoded by the stripe decoding unit. An image decoding apparatus comprising: a stripe decoding unit that stops a decoding process when a continuous number of specific data is greater than a predetermined value. 3. An image decoding apparatus which decodes JPEG data including a marker and compressed image data, which is encoded according to the JPEG system, detects marker information included in the JPEG data,
A marker detector for continuously outputting specific data after the output of EG data; a first counter for counting the number of JPEG data read by the marker detector; and a JPEG data output by the marker detector. And a delay unit for temporarily storing JPEG data output from the delay unit, perform initialization processing based on the marker information, and perform decoding processing in stripe units on the line buffer based on the compressed image data. A decoding unit for outputting image data decoded by the stripe decoding unit, a second counter unit for counting the number of JPEG data read by the stripe decoding unit, and a first counter unit. The numerical value Ca is compared with the count value Cb of the second counter unit, and the comparison result is notified to the stripe decoding unit. And a comparison of the eye, the stripe decoding unit, Ca <if when Cb is satisfied or continuous number of the specific data is more than the predetermined value, the image decoding apparatus characterized by stops the decoding process. 4. The image decoding apparatus according to claim 1, wherein the output unit prints the decoded image data on a recording medium.