JP2806287B2 - Image quality evaluation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality evaluation apparatus, and more particularly, to an image quality evaluation apparatus for quantitatively evaluating the extent to which the image quality of a decompressed image obtained by expanding a highly efficient coded compressed image is lower than that of an original image. About.

[0002]

2. Description of the Related Art In general, the following is known as an image quality evaluation apparatus for quantitatively evaluating the degree of image deterioration.

(1) A difference between an image to be evaluated and a reference image is obtained for each pixel, and a numerical value indicating a deterioration amount of the entire image (for example, a root mean square error of the difference for each pixel) is obtained from the result. A device that seeks. (2) As shown in JP-A-4-15882, for example, after converting an image to be evaluated to reflect the distortion of the contour shape of the object constituting the image,
A device that compares a reference image with a pixel unit and obtains a numerical value indicating the amount of deterioration of the entire image. (3) As shown in, for example, Japanese Patent Application Laid-Open No. 1-298890, the area of the degraded portion in the image to be evaluated is obtained, and the area is obtained in the same manner as (1) according to this area. Device that corrects the numerical value indicating the amount of deterioration of the entire image.

[0004]

In general, when digital image data is subjected to lossy compression using a high efficiency coding technique based on DCT (Discrete Cosine Transform),
The error that occurs between the original image and the encoded image (the image obtained by expanding the compressed image) is 8 × from the encoding process.
It is generated in units of blocks such as 8 pixels or 16 × 16 pixels. This is a DCT based MPEG
In the case of high-efficiency coding technology such as JPEG or JPEG, the coding process is performed in units of blocks in which the set of pixels is one block at the time of coding, and the deterioration is peculiar to the coded image called block distortion. belongs to.

In the conventional apparatus (1), which is generally known as an apparatus for quantifying the deterioration of image quality, the amount of deterioration of the entire screen can be evaluated, but the degree of deterioration of each block is quantitatively evaluated. It is not possible. Further, in the conventional apparatus (2), the point that the image quality is evaluated by focusing on the outline of the image is described, but the evaluation cannot be performed by focusing on a portion other than the outline. I can not cope. Furthermore, the conventional device (3) merely corrects the entire amount of deterioration according to the deteriorated area, and cannot detect block distortion. That is, the conventional device is suitable for evaluating the entire image because it is assumed that the deterioration amount of the entire image is obtained. However, it can be used for evaluating the deterioration of the image quality of each individual part, particularly, a block unit. Can not.

An object of the present invention is to provide an image quality evaluation apparatus suitable for quantitatively evaluating the deterioration of the image quality of an encoded image in units of blocks, that is, the block distortion.

It is another object of the present invention to provide an image quality evaluation device having a function of displaying and displaying the distribution of block distortion.

[0008]

SUMMARY OF THE INVENTION The present invention quantitatively evaluates the amount of deterioration of an encoded image obtained by decompressing a compressed image obtained by dividing an original image into a plurality of blocks and performing high-efficiency encoding. in the image quality evaluation apparatus, in order to be able to quantitatively evaluate the block distortion of the encoding process image, or
In addition, the distribution of block distortion can be graphically displayed.
In order to achieve this, a block processing unit that divides the coded image and its original image into a plurality of blocks as in the high-efficiency coding process, and a deterioration amount for each of the blocks divided by the blocking unit. Means for calculating the amount of deterioration to be calculated;
One-to-one correspondence with the position of each block in the coded image
Encoding the calculated degradation amount.
A deterioration amount storage means for storing the area corresponding to the position of the target block in the image, stored in the degradation amount storing means
Input the amount of deterioration, and
The above-mentioned encoding processing is performed on a deterioration amount distribution diagram in which the distribution of the deterioration amount is plotted.
Display control means for displaying the image on the screen of the display device so as to overlap the image .

[0009]

[0010]

[0011]

In the image quality evaluation apparatus of the present invention, the blocking means divides the coded image and the original image into a plurality of blocks which are the same as those used in the high-efficiency coding, and the deterioration amount calculating means The deterioration amount is calculated for each of the blocks thus determined, and the deterioration amount storage means stores the calculated deterioration amount. Further, the display control means inputs the deterioration amount stored in the deterioration amount storage means, and displays a deterioration amount distribution diagram in which the distribution of the deterioration amount of each block of the coded image is plotted on the screen of the display device.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, an image quality evaluation apparatus according to one embodiment of the present invention includes an original image data file 1, an encoded image data file 2, a frame memory 3, 4, a blocking means 5, 6, and a deterioration amount. It comprises a calculation means 7, an output file 8, a display control means 9, and a display device 10.

The original image data file 1 is a file for storing original image data, and the encoded image data 2 is a highly efficient encoding of the original image stored in the original image data file 1 such as MPEG or JPEG based on DCT. It is a file that performs lossy compression with the technology and stores data of an encoded image that is an image decompressed with the technology. The original image data and the encoded image data stored in these files 1 and 2 are recorded in the frame memories 3 and 4 at the time of evaluation.

The block dividing means 5 divides the original image in the frame memory 3 into a plurality of blocks as shown in FIG. 2, similarly to the block division performed at the time of encoding the original image data. Also, as shown in FIG. 2, the coded image in the frame memory 4 is similarly divided into a plurality of blocks.

The deterioration amount calculating means 7 comprises blocking means 5,
The deterioration amount of the coded image is calculated based on the original image data for each block divided by 6. That is, as shown in FIG. 2, one block is extracted from the original image and the coded image divided into blocks, and a difference between corresponding pixels is obtained for each block on a pixel-by-block basis. Is detected. For this reason, as shown in FIG. 1, the deterioration amount calculating means 7 calculates the difference of each pixel in each block unit.
1 and an error detecting means 72 for obtaining the amount of deterioration per block from the obtained difference value. The deterioration amount for each block obtained by the deterioration amount calculating means 7 is output to and stored in the output file 8 constituting the deterioration amount storing means.

The display control means 9 inputs the deterioration amount of each block stored in the output file 8 and displays a deterioration amount distribution diagram showing the distribution of the deterioration amount of each block of the coded image on the display device 10. Display on the screen. In this embodiment,
The coded image data is input, and the coded image is displayed together on the same screen as the deterioration amount distribution diagram. Then, in this case, the deterioration amount distribution map is
Are displayed in a superimposed manner.

FIG. 3 is a schematic flowchart of the above embodiment. At the time of evaluation, the original image data of the original image data file 1 and the encoded image data of the encoded image data file 2 are read into the frame memories 3 and 4 (S1,
S2). Next, the first block when the block is divided from the original image data in the frame memory 3 by the blocking unit 5 is read, and similarly, the block is divided from the coded image data in the frame memory 4 by the blocking unit 6. The first block of the case is read (S3, S4). Then, the block of the original image read by the blocking unit 5 and the block of the coded image read by the blocking unit 6 are input to the difference detection unit 71 of the deterioration amount calculation unit 7, and The difference value of the pixel at the same position is obtained by the following equation (S5).

C _{i, j} = A _{i, j} −B _{i, j} (1) where C _{i, j} ; difference value A _{i, j} ; pixel value of original image data (for example, luminance) B _{i, j} A pixel value (for example, luminance) of the encoded image data

FIG. 4 is a flow chart showing the processing of the difference detecting means 71 as described above. The blocks of the original image data are inputted from the blocking means 5 and the blocks of the coded image data are inputted from the blocking means 6. Then, one pixel of the original image data and one pixel of the corresponding coded image are read from the blocks (S13, S14), and the above equation (1) is input. Calculates the difference value (S15). Then, it is determined whether or not the pixel processed this time is the last pixel in the block (S16). If there is a remaining pixel instead of the last pixel, attention is shifted to the next pixel (S17), and the process returns to step S13, and Repeat the process. This is repeated until the remaining pixels are exhausted, thereby obtaining all the difference values for one block, and outputting the result to the error detecting means 72 (S18).

In the error detecting means 72, the difference detecting means 71
The deterioration amount N per block is obtained from the difference value C _{i, j for} one block passed from (S6 in FIG. 3). In this embodiment, the deterioration amount N is obtained by the following equation using the root mean square method.

(Equation 1) (2) where n and m are constants representing the number of vertical and horizontal pixels of the block, respectively.

The deterioration amount N may be obtained by other average errors such as the absolute value average error method other than the root mean square error method.

When the deterioration amount N per block is obtained by the error detecting means 72, if the block processed this time is not the last block but there are remaining blocks (S in FIG. 2).
(NO in 7), the focus is shifted to the next block (S8), the process returns to step S3, and the above operation is repeated. Then, the processing is performed for all the remaining blocks, and when the deterioration amounts of all the blocks of the image are obtained, they are output to the output file
(S9).

FIG. 5 is a diagram showing a logical configuration example of the output file 8 for storing the deterioration amount. As shown in the figure, the output file 8 has an area E corresponding to each block at the position of each block of the coded image, and the calculated degradation amount (a numerical value such as 2, 3 in the figure) Is stored in the area E corresponding to the position of the processing target block of the encoded image.

The display control means 9 inputs the deterioration amount of each block stored in a format as shown in FIG. 5 and displays a deterioration amount distribution diagram showing the distribution of the deterioration amount of each block of the coded image. Is displayed on the screen of the display device 10 (S10).

FIG. 6 is a flowchart of an example of a process for displaying a deterioration amount distribution diagram by the display control means 9. The display control means 9 reads the deterioration amount stored in the output file 8 (S2
1), input one by one sequentially from the top (S22), and determine a dot density pattern according to the input deterioration amount (S23). That is, a pattern having a higher dot density is determined as the deterioration amount increases. Here, the dot density refers to the ratio of black pixels occupied when a block of 8 × 8 pixels is filled with white pixels and black pixels. The above processing is repeated for all the deterioration amounts stored in the output file 8 (S24, S2
5). Then, the dot density pattern determined for each deterioration amount is displayed at a block position corresponding to each deterioration amount in a frame of the same size as the encoded image on the screen of the display device 10 (S26). .

FIG. 7 shows a main portion of the deterioration amount distribution diagram displayed on the screen of the display device 10 by the processing of FIG. 6, and a pattern having a higher dot density is drawn as the deterioration amount increases, whereby the deterioration The distribution of the quantities can be clearly recognized visually.

Although the above-described deterioration amount distribution diagram is prepared by using patterns having different dot densities, other types of patterns can be used. Other methods can be adopted, such as changing the type of .

[0029]

According to the image quality evaluation apparatus of the present invention described above, the following effects can be obtained.

It is possible to quantitatively calculate the local deterioration, which is unique to the coded image, called block distortion, without subjectivity of the measurer. For this reason, for example, in the design of a screen image in an information terminal device that compresses and accumulates a screen image used in a graphical user interface, and expands the image when used, the distribution of deterioration in a prototype screen image is designed. , And the operation of partially correcting the image of the part where deterioration is concentrated to an image with little deterioration can be efficiently performed.

By storing the calculated deterioration amount of each block in an area corresponding to each block position of the coded image on a one-to-one basis, it is possible to confirm the distribution state. In particular, according to the configuration in which the deterioration amount distribution diagram illustrating the distribution of the deterioration amount of each block is displayed on the screen of the display device, the distribution state of the block distortion can be visually and extremely easily grasped.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image quality evaluation device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of block division of an original image and an encoded image, and difference detection for each block.

FIG. 3 is a flowchart showing an outline of the operation of the embodiment in FIG. 1;

FIG. 4 is a flowchart illustrating a processing example of a difference detection unit.

FIG. 5 is a diagram illustrating a logical configuration example of an output file.

FIG. 6 is a flowchart illustrating a processing example of a display control unit.

FIG. 7 is a diagram showing an example of a deterioration amount distribution diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Original image data file 2 ... Encoding processing image data file 3, 4 ... Frame memory 5, 6 ... Blocking means 7 ... Deterioration amount calculation means 71 ... Difference detection means 72 ... Error detection means 8 ... Output file 9 ... Display Control means 10 ... Display device 10

Claims (3)

(57) [Claims] An image quality evaluation apparatus for quantitatively evaluating the amount of deterioration of an encoded image obtained by decompressing a compressed image obtained by dividing an original image into a plurality of blocks and performing high-efficiency encoding. Blocking means for dividing an image and its original image into a plurality of blocks same as in the high-efficiency encoding process, deterioration amount calculating means for calculating a deterioration amount for each of the blocks divided by the blocking means, One-to-one correspondence with the position of each block in the coded image
Encoding the calculated degradation amount.
A deterioration amount storage means for storing the area corresponding to the position of the target block in the image, enter the deterioration amount stored in the degradation amount storage means, said marks
A graphical representation of the distribution of the amount of degradation for each block of the decoded image
Image of the display device by superimposing the
An image quality evaluation device, comprising: display control means for displaying on a surface . 2. The image quality evaluation apparatus according to claim 1, wherein the deterioration amount distribution diagram is a diagram expressing the deterioration amount of each block in a pattern corresponding to the deterioration amount. 3. The image quality evaluation apparatus according to claim 1, wherein the deterioration amount distribution diagram is a diagram expressing the deterioration amount of each block by a color corresponding to the deterioration amount.