JP2001313943A - Image encoder, its method and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deviation of picture image quality of an image of one region for encoding with higher definition than the periphery part and the image of other regions by controlling code quantity of the region for encoding with the higher definition rather than the periphery part. SOLUTION: The image encoder which performs encoding to the image including the region for encoding with the high definition rather than the periphery part is provided with a detecting means (100) which detects a quantization step from a bit stream of the image encoded in a first stage, a quantization step control means (103) which performs control of the detected quantization step, and a selection means (102) which performs the second stage encoding to the image by using the controlled quantization step and selects either image of the image encoded in the first stage and the image encoded in the second stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for encoding a still image and a moving image, and more particularly to a process for encoding image data of a specific area with higher image quality than other areas.

[0002]

2. Description of the Related Art At present, JP is used as a still image encoding method.
The EG coding method is widely used. This encoding method is based on ISO (International Orgnization for Standardizat)
ion: standardized by the International Organization for Standardization). Motion JPEG which uses this JPEG encoding method as an intra-frame encoding method as a moving image encoding method.
Is generally known. Furthermore, with the spread of the Internet in recent years, higher performance and higher image quality encoding than the conventional JPEG encoding method is required. Therefore IS
In O, work is being carried out to formulate the standardization of a new still image coding method. This activity is generally "JPEG2000"
is called. In particular, ROI (Region Of Interesting) in the JPEG2000 encoding method is a new function and a useful technique.

[0003] An image coding apparatus for realizing an ROI will be described below with reference to FIG.

[0004] First, an image to be encoded is input to an image input unit 1001 in raster scan order, and its output is output as a discrete wavelet transform unit 100 as an image signal.
2 is input. Discrete wavelet transform unit 1002
Performs two-dimensional discrete wavelet transform processing on an input image signal, calculates transform coefficients, and outputs the result. FIG. 9 shows a configuration example of a two-level conversion coefficient group obtained by a two-dimensional conversion process. An image signal is decomposed into coefficient strings HH1, HL1, LH1,..., LL in different frequency bands. In the following description, these coefficient sequences are called subbands. The coefficient of each subband is calculated by the following quantization unit 1.
003.

[0005] An area designating unit 1011 is an input means including a pointing device such as a keyboard and a mouse. A user can use the input means to input an image to be encoded into an image.
A region to be decoded with higher image quality compared to the surrounding portion (RO
I) can be indicated and determined. Then, when discrete wavelet transform is performed on the image to be encoded, mask information indicating which coefficient belongs to the specified area is generated. FIG. 10A shows an example when mask information is generated. When a star-shaped area is specified in the image by the image input unit 1001 as shown on the left side of the drawing, the area specifying unit 1011 performs discrete wavelet transform on the image including this specified area, and the specified area is Calculate the part occupying the subband. The area indicated by the mask information is a range including surrounding transform coefficients necessary for restoring an image signal on the boundary of the specified area.

An example of the mask information calculated in this way is shown on the right side of FIG. In this example, mask information when a two-level discrete wavelet transform is performed on the image on the left side of the figure is calculated as shown in the figure. In the figure, the star-shaped portion is a designated area, and the bits of the mask information in this area are 1 and the bits of the other mask information are 0. Since the entirety of the mask information is the same as the configuration of the transform coefficient by the two-dimensional discrete wavelet transform,
By examining the bits in the mask information, it is possible to identify whether or not the coefficient at the corresponding position belongs to the designated area. The mask information generated in this way is output to quantization section 1003.

[0007] The quantization unit 1003 quantizes the input transform coefficient by a predetermined quantization step, and outputs an index for the quantized value. Next, the quantization unit 1003
Changes the quantization index by the following equation based on the above-described mask information input from the area specifying unit 1011.

Q ′ = q * 2 ^ W; inside the area (Equation 1) q ′ = q; outside the area (Equation 2) q is the quantization step before the change, and q ′ is the quantization step after the change. A ＾ b represents a raised to the power of b.

By the above processing, only the quantization index belonging to the specified area in the area specifying unit 1011 is shifted up by W bits. Note that W is a positive integer.

FIGS. 10 (b) and 10 (c) show the change of the quantization index due to the shift up. In FIG. 6B, the subband has a quantization index, and the shifted quantization index is as shown in FIG. The quantization index changed in this way is output to the subsequent variable length coding unit 1004.

The variable length coding unit 1004 decomposes the input quantization index into bit planes, performs binary arithmetic coding on a bit plane basis, and outputs a bit stream. FIGS. 11A and 11B show the variable length coding unit 10.
FIG. 4 is a diagram for explaining the operation of No. 04. In this example, 4x
There are three non-zero quantization indices in the region within the sub-band having a size of 4, and each has a +1
It has a value of 3, −6, +3. Variable length encoding unit 10
Reference numeral 04 scans this area to find the maximum value M and calculates the required number of bits S.

In FIG. 11A, S is 4 because the maximum coefficient value is 13, and the 16 quantization indices in the sequence correspond to four bit planes as shown in FIG. Processing is performed as a unit. First, the variable length coding unit 1004 determines the most significant bit plane (MS in FIG.
B) (binary arithmetic coding) and output as a bit stream. Next, the bit plane is lowered by one level, and similarly, each bit in the bit plane is encoded and output to the code output unit 1005 until the target bit plane reaches the least significant bit plane (represented by LSB in the figure). At this time, the code of each quantization index is subjected to variable-length coding immediately after the first non-zero bit is detected in the bit plane scanning.

In this variable length coding, the code length can be adjusted by appropriately terminating the coding on the way.

[0014]

However, in such a configuration, for example, when a low-capacity line is used for communication in a network, a case where only a part of the ROI's attention area is transmitted and the transmission is completed is ended. A phenomenon occurs in which only the ROI portion is transmitted and information other than the ROI cannot be transmitted at all. This is because the number of bits required for the bit shift is set so that bit planes do not overlap inside and outside the ROI area. If all bits of the ROI are not decoded, other bits are not decoded at all.

In addition, when JPEG2000 is applied to moving picture coding as intra-frame coding, rate control is required, and the number of bit planes that can be transmitted depending on the picture when adjusting the code amount may vary greatly. There is. In other words, it is conceivable that the ROI region and the other region can be reproduced in a certain frame, but only the ROI region is reproduced in a certain frame and the other regions are black. Further, since the phenomenon differs for each frame, a problem occurs that a reproduced image is largely disturbed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problem, and has a further advantage of controlling a code amount of a region for encoding with higher image quality than surrounding portions to thereby achieve encoding with higher image quality than surrounding portions. It is an object of the present invention to reduce the deviation of the image quality between the image of the region to be performed and the image of the other region.

[0017]

In order to achieve the object of the present invention, for example, an image coding apparatus of the present invention has the following arrangement. That is, an image encoding apparatus for encoding an image including an area for encoding with higher image quality than a surrounding portion, wherein a quantization step is performed from a bit stream of the image encoded in the first stage. Detecting means for detecting, and a quantization step control means for controlling the detected quantization step, performing a second stage encoding on the image using the controlled quantization step, the A selecting unit for selecting any one of the image encoded in the first step and the image encoded in the second step;

In order to achieve the object of the present invention, for example, an image coding apparatus of the present invention has the following arrangement. That is, an image encoding apparatus that performs encoding on an image including an area for encoding with higher image quality than a designated surrounding part, and uses an area of the image and an area of the area to determine an index. A calculating means for calculating; and a quantization step control means for controlling a quantization step using the index.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail according to preferred embodiments with reference to the accompanying drawings. [First Embodiment] FIG. 1 is a block diagram showing a configuration of an image coding apparatus according to the present embodiment.

An image input unit 1 inputs an image to be encoded, divides the image into blocks of a predetermined size, and outputs an image signal in block units, and 2 performs a discrete wavelet transform on the image signal. A discrete wavelet transform unit that outputs a transform coefficient as a result, 3 quantizes the transform coefficient after the discrete wavelet transform, and generates and outputs a quantization index. Is a variable-length encoding unit that makes a variable-length bit stream, and 5 is a code output unit that outputs a bit stream. Reference numeral 6 denotes an area specifying unit for specifying a desired ROI in the image. Reference numeral 7 denotes a quantization step updating unit for controlling the final generated code amount from the code amount from the code output unit 5.

The operation of the image coding apparatus according to the present embodiment having such a configuration will be described with reference to FIG. 7 and FIG. 1 showing a flowchart of this operation.

First, an image to be encoded is input to the image input unit 1 in raster scan order (step S).
701). Then, the image input unit 1 divides the input image into blocks of a predetermined size, and an image signal in block units is input to the discrete wavelet transform unit 2.

The discrete wavelet transform unit 2 performs a two-dimensional discrete wavelet transform process on the input image signal, and calculates a transform coefficient (step S702). The transform coefficient is output to the subsequent quantization unit 3.

The area designating section 6 provides an area (R) to be decoded with higher image quality compared to the surrounding area in the image to be encoded.
OI) is determined, and mask information indicating which transform coefficient belongs to the ROI when the image is subjected to discrete wavelet transform is generated (step S703). Each bit constituting the mask information has a one-to-one correspondence with the transform coefficient, and the bit corresponding to the transform coefficient belonging to the ROI is 1 and the bit not belonging to the ROI is 0. Further, when an image including this ROI is subjected to discrete wavelet transform, R
Calculate the portion that OI occupies in each subband. The mask information is encoded by the variable length encoding unit 4 and sent to the code output unit 5.

The quantizing section 3 quantizes the input transform coefficient by a predetermined quantization step QP, and outputs an index (quantization index) for the quantized value (step S704). Next, the quantization unit 3 changes the quantization index according to Expressions (1) and (2) based on the mask information input from the region specification unit 6. That is,
Only the quantization index belonging to the ROI is shifted up by W bits (step S705).

FIGS. 2A, 2B and 2C show how the quantization unit 3 changes the quantization index when W = 8. FIG. 2A shows the original quantization index, and the center halftone dot represents the ROI. In FIG. 2B, the ROI is shifted upward by 8 bits. Further, a portion indicated by a dotted frame in FIG. Also, the number of each bit plane is set to 15 from the highest order to 0 from the lowest order.
The quantization index changed in this way is output to the subsequent variable length coding unit 4, and the quantization index is stored in a RAM (not shown).

The variable length coding unit 4 decomposes the input quantization index into a plurality of bit planes in the same manner as in the conventional example (step S706),
Value arithmetic coding is performed, and a bit stream for each bit plane is output (step S707).

In the quantization step updating section 7, the code output section 5
, And calculates a new quantization step by a method described later, and outputs the new quantization step to the quantization unit 3.

FIG. 3 shows the internal operation of the quantization step updating section 7.

After the input of the bit stream from the code input unit 101, the quantization step detector 100 detects the quantization step QP included in the bit stream (step S708), and furthermore, the ROI outside area code amount detector 10
The presence / absence of a block outside the ROI range is detected for the bit stream input in step 2 (step S709).
When each block is arranged one-dimensionally in advance, RO
It is assumed that the blocks exist in the order of the blocks included in I and the blocks not included in the ROI. In the method of determining the inside / outside of the ROI range for each block, for example, if the ratio of the ROI overlapping the block is equal to or more than a predetermined ratio, it is preferable to determine that the block is within the ROI range.

The non-ROI region code amount detector 102 detects the ROI
If a block outside the range is detected, an instruction not to update the quantization step QP is sent to the quantization step calculator 103, and as a result, the quantization step update unit 7 does not output anything, and thus the quantization step QP Is not updated. On the other hand, when the ROI outside area code amount detector 102 detects a block within the ROI range, the ROI outside area code amount detector 1
02 sends an instruction to update the quantization step QP to the quantization step calculator 103.

The quantization step calculator 103 updates the quantization step QP to a new quantization step QP_NEW (step S710), and outputs it to the quantization step output unit 104. The relationship between QP and QP_NEW is shown below.

QP_NEW = QP + 1 Next, QP_NEW is substituted for QP (step S71).
1) Encoding is again performed on the quantization index stored in the RAM (not shown).

As described above, in the quantization step updating unit 7,
The update of the quantization step QP_NEW (QP) is repeated until a block outside the ROI range is obtained for the block of the code output unit 5. Then, the result of this encoding is connected to the result of encoding outside the ROI. As a result, since the coarse quantization is performed in the ROI, the image has a lower image quality than when the quantization is performed in the quantization step QP.

That is, by reducing the image quality in the ROI, the code amount of the ROI is further reduced, the difference from the image quality in the area other than the ROI is also reduced, and the bias of the image quality of the entire image is reduced. become.

In this embodiment, the discrete wavelet transform is used as a method of transforming an image into a frequency space (orthogonal transform), but another transform may be used.

Further, in the present embodiment, the quantization step updating section 7 updates the quantization step QP_NEW by +1 and repeats it, but the update amount may be another value having a relationship of QP <QP_NEW.

As described above, according to the image encoding apparatus and method of the present embodiment, the code amount of the ROI can be further reduced, and
Image quality bias between the ROI image and the image in the other area can be reduced.

The program code according to the flowchart shown in FIG. 7 is stored in a ROM (not shown).

[Second Embodiment] In the first embodiment,
Although the ROI encoding involves a plurality of encoding processing steps, in the present embodiment, the quantization step is determined in advance, so that the ROI encoding processing step is performed once. The method will be described with reference to the flowchart of the operation of the image coding apparatus according to the present embodiment shown in FIG. Steps S1201 to S12
Steps up to 03 are the same as steps S1 to S3, and a description thereof is omitted.

FIG. 4 is a block diagram showing the configuration of the image coding apparatus according to the present embodiment.

4, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

Reference numeral 200 denotes a quantization step updating unit that calculates a quantization step for an image input to the image input unit 1 from the ROI mask information from the area specifying unit 6.

In such a configuration, the quantization step calculation unit 200 obtains the area in the ROI based on the ROI mask information from the area designation unit 6, and calculates the quantization step based on the ratio to the area of the entire image.

FIG. 5 shows the internal operation of the quantization step calculator 200.

The ROI area area calculator 301 obtains the above-mentioned area ratio based on the mask information from the area specifying unit 6 input to the mask information input unit 300. The area ratio at this time is shown below.

Area in ROI / Area of entire image =
A Next, the quantization step calculator 302 updates the predetermined quantization step QP to a new quantization step QP_NEW (step S1204), and outputs the result from the quantization step output unit 303. The relationship between QP and QP_NEW is shown below.

QP_NEW = QP × (1 + A) Using the quantization step QP_NEW, the same encoding processing as the processing from step S4 to step S6 is performed (step S1206).

As described above, the area ratio A and the updated quantization step NEW_QP
, The quantization becomes coarser as a whole, but as a result, the code amount of the ROI is further reduced, and
The deviation of the image quality between the OI image and the image in the other area could be reduced.

In the present embodiment, the discrete wavelet transform is used as a method for transforming an image into a frequency space (orthogonal transform), but another transform may be used.

Further, in this embodiment, the area ratio in the quantization step updating unit 7 may have a certain multiplier, and QP and Q
The relational expression of P_NEW may be any other one as long as QP_NEW> QP.

As described above, according to the image coding apparatus and method of the present embodiment, a quantization step corresponding to the area of the ROI is obtained in advance, and coding is performed using this quantization step, thereby obtaining the ROI. Can be performed once.

[Third Embodiment] In the present embodiment, the first and second embodiments
14 shows a computer functioning as an image encoding device according to the second embodiment.

FIG. 6 is a block diagram showing the configuration of a computer according to this embodiment.

Reference numeral 500 denotes a central processing unit (CPU) for controlling the entire computer and performing various processes. Reference numeral 501 provides an operating system (OS) required for controlling the computer, software, data, and a storage area required for calculation. Memory. It is also used as a work area when the CPU 500 performs various processes.

Reference numeral 502 denotes a bus for connecting various devices and exchanging data and control signals; 503, a storage device for storing various software; 504, a storage device for storing moving image data; 505, a system from an image or a computer; It is a monitor that displays messages and the like.

Reference numeral 508 denotes a communication circuit, which includes a LAN, a public line, a wireless line, a broadcast wave, and the like. A communication interface 507 transmits encoded data to the communication circuit 508. 506 starts the computer,
A terminal for setting various conditions such as a bit rate.

The memory 501 controls the entire computer, stores an OS for operating various software and operating software, stores an image area for reading image data for encoding, and a code for temporarily storing code data. There is a working area for storing areas, parameters for various calculations, and the like.

In such a configuration, prior to the processing,
The terminal 506 selects moving image data to be encoded from the moving image data stored in the storage device 504, and instructs activation of the computer. Then, the software stored in the storage device 503 is transferred to the memory 5 via the bus 502.
01 and the software is started.

Then, the storage device 50 by the CPU 500
4 performs processing according to the flowchart shown in FIG. 7 or 12, and in this processing, FIG. 7 shows a program code according to the flowchart shown in FIG. Software) will be executed.

As described above, the computer according to the present embodiment functions as the image encoding device according to the first and second embodiments.

[Other Embodiments] Even if the first to third embodiments are applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a camera, a printer, etc.), one embodiment will be described. The present invention may be applied to a device including a device (for example, a copying machine, a facsimile device, a video camera, and the like).

Further, the first to third embodiments are to provide a storage medium (or a storage medium) in which a program code of software for realizing the functions of the above-described embodiment is recorded to a system or an apparatus, and the system or the apparatus is provided. The computer (or CPU or MPU) reads and executes the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the first to third embodiments. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. This also includes a case where some or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, This includes a case where a CPU or the like provided in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the function of the above-described implementation.

When the above-described first to third embodiments are applied to the above-described storage medium, the storage medium stores program codes corresponding to the above-described flowcharts (shown in FIG. 7 or 12). Will be.

[0066]

As is apparent from the above description, according to the present invention, by controlling the code amount of the region for encoding with higher image quality than the surrounding portion, the image is encoded with higher image quality than the surrounding portion. The effect of reducing the image quality deviation between the image in the region for the image and the image in the other region can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image encoding device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating bit shifting of a quantization index.

FIG. 3 is a diagram showing an internal operation of a quantization step updating unit 7;

FIG. 4 is a block diagram illustrating a configuration of an image encoding device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an internal operation of a quantization step calculation unit 200.

FIG. 6 is a diagram illustrating a configuration of a computer according to a third embodiment of the present invention.

FIG. 7 is a flowchart of an operation of the image encoding device according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a conventional image encoding device that realizes an ROI.

FIG. 9 is a diagram illustrating a configuration example of a two-level transform coefficient group;

FIG. 10 is a diagram illustrating shift-up of mask information and a quantization index.

FIG. 11 is a diagram for explaining the operation of the variable length coding unit 1004.

FIG. 12 is a flowchart of an operation of the image encoding device according to the second embodiment of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C059 KK01 MA00 MA24 MC11 ME11 PP04 PP21 SS08 SS20 SS26 TA46 TB04 TC04 TC06 TC32 TC43 TD09 TD18 UA02 UA34 UA38 UA39 5C078 AA04 BA58 DA01 DA02 5J064 AA01 BA09 BA16 BB12 BC01 BC01 BC01 BB03 BB04 CC05 EE02 EE05 GG01 HH27 HH30 JJ71 KK56

Claims (12)

[Claims] An image encoding apparatus for encoding an image including an area for encoding with higher image quality than a surrounding portion, comprising: Detecting means for detecting a quantization step; quantization step control means for controlling the detected quantization step; and performing a second-stage encoding on the image using the controlled quantization step. An image encoding apparatus, comprising: a selecting unit that selects any one of an image encoded in the first step and an image encoded in the second step. 2. The image encoding apparatus according to claim 1, wherein the selection unit detects whether there is a block outside the area in the bit stream. 3. The quantization step control unit updates the quantization step when the selection unit detects only blocks in the area with respect to the image. 3. The image encoding device according to 1 or 2. 4. The image encoding apparatus according to claim 3, wherein the quantization step control unit performs the update until a block outside the area is obtained. 5. The image coding apparatus according to claim 4, wherein said quantization step control means makes the value of the quantization step after the update larger than that before the update. apparatus. 6. The encoding in the second step, wherein the region of the image is encoded again using a quantization step updated by the quantization step control means. The image encoding device according to claim 1. 7. An image encoding apparatus for encoding an image including an area for encoding with higher image quality than a designated surrounding portion, wherein the image encoding apparatus uses an area of the image and an area of the area. An image coding apparatus, comprising: a calculating unit that calculates an index by using the index; and a quantization step control unit that controls a quantization step by using the index. 8. The apparatus according to claim 7, wherein the index includes a ratio of an area of the region to an area of the image. 9. An image encoding method for encoding an image including an area for encoding with higher image quality than a surrounding portion, wherein the image encoding method comprises the steps of: A detection step of detecting a quantization step; a quantization step control step of controlling the detected quantization step; and a second-stage encoding of the image using the controlled quantization step. And performing a selecting step of selecting any one of the image encoded in the first step and the image encoded in the second step. 10. An image encoding method for encoding an image including an area for encoding with higher image quality than a designated peripheral portion, wherein the image encoding method uses an area of the image and an area of the area. An image coding method, comprising: a calculation step of calculating an index by using the index; and a quantization step control step of controlling a quantization step by using the index. 11. A storage medium for storing a program code that functions as an image encoding device that encodes an image including an area for encoding with higher image quality than a surrounding portion, wherein the program code includes: A program code for a detection step for detecting a quantization step from a coded bit stream of the image; a program code for a quantization step control step for controlling the detected quantization step; and the controlled quantization Performing a second stage encoding on the image using the first and second stages, and selecting one of the image encoded in the first stage and the image encoded in the second stage. A storage medium comprising a program code. 12. A storage medium for storing a program code that functions as an image encoding device that encodes an image including an area for encoding with higher image quality than a designated surrounding portion, wherein the image code includes: A storage medium comprising: a program code of a calculation step of calculating an index using the area of the area and the area of the region; and a program code of a quantization step control step of controlling a quantization step using the index. .