JP6593417B2 - Image compression apparatus and program - Google Patents

Description

  The present invention relates to an image compression apparatus and a program.

  A technique for generating information for quantitatively evaluating block distortion of a compressed image based on the original image and a reproduced image obtained by decoding the compressed image obtained by compressing the original image is disclosed (for example, see Patent Document 1). ).

JP 05-219384 A

  The image quality of the compressed image changes under the influence of the external environment such as the amount of movement of the imaging target and the brightness of the imaging area including the imaging target. The optimum compression parameter that defines the compression condition of the image differs depending on the amount of movement of the imaging object and the brightness of the imaging area. Therefore, when the imaging object is imaged at a place affected by the external environment, there is a problem that the image quality of the compressed image may be deteriorated with a change in the external environment.

  Therefore, the present invention has been made in view of these points, and an object thereof is to provide an image compression apparatus that compresses an image so that the image quality of the image after compression becomes a desired image quality.

  An image compression apparatus according to a first aspect of the present invention includes an acquisition unit that acquires image data, a compression unit that compresses the image data based on a predetermined compression parameter, and a compressed image after the compression unit compresses the image data A difference between an image quality evaluation unit that evaluates the image quality of data, a target information acquisition unit that acquires target information indicating the image quality target of the compressed image data, and an evaluation result by the image quality evaluation unit and a target indicated by the target information A parameter adjusting unit that adjusts the compression parameter based on

  The target information acquisition unit acquires the target information in association with at least some of the plurality of regions of the image data, and the parameter adjustment unit includes the target information acquisition unit that has acquired the target information. The compression parameter may be adjusted based on a difference between the evaluation result of the image quality of the compressed image data in at least a part of the area and the target.

  The image compression apparatus may further include a storage unit that stores the evaluation result, and the parameter adjustment unit may adjust the compression parameter based on the evaluation result stored by the storage unit.

  For example, the storage unit stores the evaluation result in association with the feature of the image data or the compressed image data, and the parameter adjustment unit is a feature close to the feature of the compressed image data generated by the compression unit. The compression parameter is adjusted based on the evaluation result associated with.

  The parameter adjustment unit may specify the feature of the compressed image data based on a tendency of an increase or decrease in the data amount of the compressed image data.

  According to a second aspect of the present invention, there is provided a computer program including an acquisition unit that acquires image data, a compression unit that compresses the image data based on a predetermined compression parameter, and compressed image data after the compression unit compresses An image quality evaluation unit that evaluates the image quality of the image, a target information acquisition unit that acquires target information indicating a target of the image quality of the compressed image data, and a difference between an evaluation result by the image quality evaluation unit and a target indicated by the target information And function as a parameter adjustment unit for adjusting the compression parameter.

  According to the present invention, there is an effect that the image can be compressed so that the image quality of the compressed image becomes a desired image quality.

It is a figure for demonstrating the outline | summary of a video recording system. It is a figure which shows the function structure of an image compression apparatus. It is a figure which shows typically the graph which plotted the evaluation result which evaluated the image after compression for every flame | frame. It is a figure for demonstrating the process which associates with a one part area | region and acquires target information. It is a figure for demonstrating the change of an evaluation result. It is a flowchart of the process which adjusts a compression parameter. It is a figure which shows the function structure of the image compression apparatus which concerns on 2nd Embodiment. It is a figure which shows typically the data table which shows the accumulated evaluation result. It is a figure which shows typically the data table which linked | related the evaluation result, the characteristic of image data, and the used compression parameter.

<First Embodiment>
FIG. 1 is a diagram for explaining the outline of the video recording system S. The video recording system S includes a camera 2 that captures an imaging target, an image compression device 1 that compresses a captured image generated by the camera 2, and a video storage device 3. The image compression apparatus 1 and the camera 2 are connected via a network. Similarly, the image compression apparatus 1 and the video storage apparatus 3 are connected via a network. The network is, for example, the Internet.

  The image compression apparatus 1 acquires an image obtained by imaging the imaging target by the camera 2 and generates a compressed image that is compressed with a predetermined compression parameter. The image compression device 1 transmits the generated compressed image to the video storage device 3. The video storage device 3 stores the compressed image received from the image compression device 1 in a storage medium such as a hard disk. A person who monitors an area captured by the camera 2 (hereinafter referred to as a user) can check the state of the area captured by the camera 2 by visually recognizing the compressed image stored in the video storage device 3.

  The image quality of the compressed image compressed by the image compression apparatus 1 varies depending on the external environment such as the amount of movement of the imaging target and the brightness in the area including the imaging target when the camera 2 captures the imaging target. Therefore, in order to obtain the desired image quality of the compressed image, it is necessary to adjust the compression parameter that defines the compression condition of the image according to the imaging target and the external environment. The desired image quality is, for example, an image quality target set by a user who monitors the status of an area including an imaging target using a compressed image.

  Therefore, the image compression apparatus 1 adjusts the compression parameter based on the difference between the evaluation result obtained by evaluating the image quality of the compressed image after compression and a predetermined image quality target. Specifically, the image compression apparatus 1 adjusts the compression parameter so that the difference between the evaluation result and the target becomes small. By doing in this way, the image compression apparatus 1 can make the image quality of the post-compression image a desired image quality by adjusting the compression parameters even if the imaging target and the external environment change.

  FIG. 2 is a diagram illustrating a functional configuration of the image compression apparatus 1. The image compression apparatus 1 includes an acquisition unit 11, a compression unit 12, an image quality evaluation unit 13, a target information acquisition unit 14, and a parameter adjustment unit 15. The acquisition unit 11 acquires image data V0 from the camera 2. The acquisition unit 11 notifies the acquired image data V0 to the compression unit 12 and the image quality evaluation unit 13.

  The compression unit 12 compresses the image data V0 based on a predetermined compression parameter, and generates compressed image data V1. The compression standard when the compression unit 12 compresses image data is, for example, H.264. However, the present invention is not limited to this. The compression parameters are various setting values that determine the image quality of the compressed image. Specifically, the compression parameter is that the compression standard is H.264. H.264, the number of macroblocks per second, the number of macroblocks per frame, and the bit rate. Further, the compression parameter may include a GOP (Group Of Picture) and I frame (Key frame) insertion interval.

  The image quality evaluation unit 13 evaluates the image quality of the compressed image data V1 after being compressed by the compression unit 12. For example, the image quality evaluation unit 13 calculates a mean square error (MSE) between the uncompressed image data V0 and the compressed image data V1 after the compression unit 12 compresses the compressed image. The image quality of the data V1 is evaluated. Note that the image quality evaluation unit 13 evaluates that the lower the MSE value, the higher the image quality.

  The image quality evaluation unit 13 may evaluate the image quality level based on the MSE value. For example, the image quality evaluation unit 13 evaluates the image quality level in 10 stages. The image quality evaluation unit 13 evaluates, for example, MSE less than 50 as level 0, MSE from 50 to less than 100 as level 1, and MSE from 100 to less than 150 as level 2. The image quality evaluation unit 13 increases the level by one step every time MSE increases by 50, and evaluates MSE from 400 to less than 450 as level 8 and MSE from 450 to level 9.

  FIG. 3 is a diagram schematically showing a graph plotting evaluation results of evaluating the compressed image for each frame. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the evaluation result (MSE value). In FIG. 3, the target image quality level of the evaluation result determined by the target indicated by the target information is indicated by a broken line. In FIG. 3, the time indicated by arrows I0 and I1 is the timing of the I frame. Since the I frame is not affected by the data error in the other frame, the evaluation result is better than that of the other frame.

  In FIG. 3, evaluation results R1 and evaluation results R2 indicated by solid lines are results obtained by evaluating a compressed image obtained by compressing a video captured by the camera 2 for each frame. The evaluation result R1 is an evaluation result obtained by evaluating a compressed image obtained by compressing a video with little change between images. The image quality evaluation unit 13 evaluates the evaluation result R1 as image quality level 1.

  The evaluation result R2 is an evaluation result obtained by evaluating a post-compression image obtained by compressing a video having a large change between images. For example, the image quality evaluation unit 13 evaluates the evaluation result R2 as the image quality level 3 based on the average MSE value obtained by averaging the MSE values within a predetermined average period, which is indicated by a one-dot chain line M in FIG. The average period is, for example, a period from an I frame to the next I frame, but is not limited thereto, and may be set as appropriate by a business operator who operates the video recording system S.

  Note that the image quality evaluation unit 13 may evaluate the image quality level based on the maximum value of the MSE values within the average period. When the image quality level is evaluated based on the maximum value of the MSE within the average period, the image quality evaluation unit 13 evaluates the evaluation result M2 as the image quality level 4.

  The image quality evaluation unit 13 may evaluate the image quality by calculating not only the MSE but also a peak signal-to-noise ratio or SSIM (structural similarity). The image quality evaluation unit 13 notifies the parameter adjustment unit 15 of the calculated evaluation result.

  The target information acquisition unit 14 acquires target information indicating an image quality target of the compressed image data V1. The target information is, for example, text or a numerical value indicating an image quality level indicating an image quality target input by the user. In the following description, it is assumed that the target information acquisition unit 14 has acquired 2 as a numerical value indicating the image quality level input by the user. Note that the target information acquisition unit 14 may determine the target value of the MSE value based on a numerical value indicating the image quality level input by the user.

  The target information acquisition unit 14 may acquire target information in association with at least some of the plurality of regions of the image data V0. FIG. 4 is a diagram for explaining a process of acquiring target information in association with a partial area. In FIG. 4, it is assumed that the image data A is divided into six regions from region A1 to region A6. The user can select at least one of the six areas from the area A1 to the area A6. The target information acquisition unit 14 acquires information indicating the area selected by the user.

  The target information acquisition unit 14 notifies the parameter adjustment unit 15 of the acquired target information. When the target information acquisition unit acquires target information in association with a partial area, the target information acquisition unit notifies the parameter adjustment unit 15 of the acquired target information and information indicating the partial area selected by the user.

  The parameter adjustment unit 15 adjusts the compression parameter based on the difference between the evaluation result by the image quality evaluation unit 13 and the target indicated by the target information. For example, the parameter adjustment unit 15 changes the compression parameter so that the difference between the evaluation result and the target becomes small. Specifically, the parameter adjustment unit 15 adjusts the compression parameter so that the difference between the image quality level corresponding to the evaluation result and the image quality level indicated by the target becomes small. For example, the parameter adjustment unit 15 adjusts the value of the compression parameter so that the value obtained by subtracting the target value of MSE determined by the target from the value of MSE that is the evaluation result becomes smaller. Further, the parameter adjustment unit 15 may not adjust the compression parameter if the MSE value is equal to or less than the target value.

  FIG. 5 is a diagram for explaining a change in the evaluation result. In FIG. 5, the horizontal axis indicates time, the vertical axis indicates the evaluation result (MSE value), and the image quality level determined by the target indicated by the target information is indicated by a broken line. An evaluation result M1 indicated by a solid line is a graph in which an average value of MSE values is plotted against time.

The parameter adjustment unit 15 adjusts the compression parameter so that the difference between the evaluation result (image quality level 7) in the period T1 and the target (image quality level 2) becomes small at time t _i . Similarly, the parameter adjustment unit 15 adjusts the compression parameter at time t _{i + 1} so that the difference between the evaluation result (image quality level 4) and the target (image quality level 2) in the period T2 becomes small. The parameter adjustment unit 15 adjusts the compression parameter so that the difference between the evaluation result (image quality level 3) and the target (image quality level 2) in the period T3 becomes small at time t _{i + 2} . The parameter adjustment unit 15 does not adjust the compression parameter at time t _{i + 3} because there is no difference between the evaluation result (image quality level 2) and the target (image quality level 2) in the period T4. In this way, the parameter adjustment unit 15 can compress the image with the image quality desired by the user.

  Further, the parameter adjustment unit 15 may adjust the compression parameter based on the difference between the evaluation result of the image quality of the compressed image data V1 and the target in at least a part of the region where the target information acquisition unit 14 has acquired the target information. Good. For example, the parameter adjustment unit 15 adjusts the compression parameter so that the difference between the evaluation result of at least a part of the area and the target associated with the part of the area becomes small. Specifically, the parameter adjustment unit 15 adjusts the compression parameter so that the MSE value, which is the evaluation result of the partial area, is included in the target range of the MSE determined by the target associated with the partial area. To do.

  For example, when the target information acquisition unit 14 acquires a target associated with the region A5, the parameter adjustment unit 15 determines whether the image quality evaluation unit 13 evaluates the image quality in the region A5 and the target associated with the region A5. Adjust compression parameters to reduce the difference. In addition, when the target information acquisition unit 14 acquires the target associated with the region A5 and the target associated with the region A6, the parameter adjustment unit 15 determines the difference between the evaluation result of the region A5 and the target, and the region A6. The compression parameter is adjusted so that the difference between the evaluation result and the target becomes small. For example, the parameter adjustment unit 15 adjusts the compression parameter so that the MSE value of the region A5 is included in the target range of the region A5 and the MSE value of the region A6 is included in the target range of the region A6.

  The parameter adjustment unit 15 may adjust the compression parameter so that the difference between the average of the evaluation results obtained by evaluating the image quality in each of the plurality of regions and the target becomes small. Specifically, the parameter adjustment unit 15 has a predetermined difference between the average value of the MSE value as the evaluation result of the region A5 and the MSE value as the evaluation result of the region A6 and the target value of the MSE determined by the target. The compression parameter is adjusted to be equal to or less than the threshold value. By doing in this way, the image compression apparatus 1 can compress the image so that the image quality of the region focused on by the user becomes the image quality desired by the user, and can reduce the processing amount.

  FIG. 6 is a flowchart of a process for adjusting the compression parameter. Hereinafter, the flow of processing in which the image compression apparatus 1 adjusts the compression parameter will be described with reference to FIG. First, the acquisition unit 11 acquires image data V0 obtained by imaging the imaging target by the camera 2 (step S1). The compression unit 12 compresses the image data V0 acquired by the acquisition unit 11 and generates compressed image data V1 (step S2). The image quality evaluation unit 13 evaluates the image quality of the compressed image data V1 (step S3).

  Subsequently, the target information acquisition unit 14 acquires target information indicating an image quality target of the compressed image data V1 input by the user (step S4). The parameter adjusting unit 15 adjusts the compression parameter based on the difference between the evaluation result and the image quality target (step S5). The image compression apparatus 1 can adjust the compression parameters of the image data V0 captured by the camera 2 so that the image quality of the compressed image data V1 becomes the target image quality by repeating steps S1 to S5. . Note that the image compression apparatus 1 may execute either the process of step S1 or the process of step S4 first, or the process of steps S1 to S3 and the process of step S4 are executed in parallel. May be.

[Effect of the image compression apparatus 1 according to the first embodiment]
As described above, the parameter adjustment unit 15 of the video recording system S adjusts the compression parameter based on the difference between the evaluation result of evaluating the image quality of the compressed image data V1 and the image quality target of the compressed image data V1. To do. In this way, the video recording system S can set the image quality of the image after being compressed by the compression unit 12 to the image quality desired by the user.

<Second Embodiment>
In addition to the above configuration, the image compression apparatus 1 may have a configuration for accumulating evaluation results. FIG. 7 is a diagram illustrating a functional configuration of the image compression apparatus 1 according to the second embodiment. The image compression apparatus 1 according to the second embodiment further includes an accumulation unit 16 that accumulates evaluation results. For example, the storage unit 16 stores the evaluation result in association with the date and time when the image data was captured.

  FIG. 8 is a diagram schematically showing a data table showing the accumulated evaluation results. FIG. 8A is a diagram schematically showing a data table showing the evaluation results accumulated in association with the date and time. A graph in which the evaluation results accumulated in association with the date and time are plotted against time is, for example, a graph as shown in FIG.

  The parameter adjustment unit 15 adjusts the compression parameter based on the evaluation result accumulated by the accumulation unit 16. For example, the parameter adjustment unit 15 refers to the evaluation result stored in the storage unit 16 in association after the same time as the current time of another day, and compresses the difference between the referred evaluation result and the target to be small. Adjust the parameters. By doing in this way, the parameter adjustment part 15 can change a compression parameter previously according to the tendency for an evaluation result to change.

  The storage unit 16 may store the evaluation results in association with the characteristics of the image data V0 or the compressed image data V1. The characteristic is, for example, weather such as clear weather, cloudy weather, rainy weather, and snowy weather. The feature may be a time zone or brightness. FIG. 8B schematically shows a data table in which the image data V0, the compressed image data V1, the characteristics of the compressed image data V1, and the evaluation result of the compressed image data V1 are associated with each other. It is.

  When the storage unit 16 stores the characteristics of the image data V0 or the compressed image data V1 in association with the evaluation results, the parameter adjustment unit 15 is close to the characteristics of the compressed image data V1 generated by the compression unit 12. The compression parameter is adjusted based on the evaluation result associated with the feature. First, the parameter adjustment unit 15 analyzes the compressed image data V1 generated by the compression unit 12, and specifies the characteristics of the compressed image data V1. The method for specifying the characteristics of the compressed image data V1 is arbitrary, and details will be described later. The parameter adjustment unit 15 refers to the evaluation result stored in association with the identified feature, for example, the evaluation result stored in the storage unit 16 in association with the current time on the other day after the same time as the current time. The compression parameter is adjusted so that the difference between the referred evaluation result and the target is reduced.

  The accumulating unit 16 may store the compression parameter used when the evaluation result is obtained. FIG. 9 is a diagram schematically illustrating a data table in which evaluation results, characteristics of the image data V0, and used compression parameters are associated with each other.

  When the storage unit 16 stores the compression parameter in association with the feature of the image data V0, the parameter adjustment unit 15 has one or more associated with the same feature as the feature of the compressed image data V1 generated by the compression unit 12. Among the evaluation results, a compression parameter associated with the evaluation result that satisfies the image quality target is selected. For example, when the feature of the compressed image data V1 is “clear sky”, the parameter adjustment unit 15 evaluates M11 (image quality level 4) and M12 (image quality level) associated with the same feature “sunny” as the compressed image data V1. 2), the compression parameter “a” corresponding to the evaluation result M11 that satisfies the image quality target (image quality level 2) is selected. In this way, the parameter adjustment unit 15 can adjust the compression parameter based on the compression parameter used in the past, and thus shortens the time until the image quality of the compressed image becomes a desired image quality. be able to.

[Method for identifying image data characteristics]
Hereinafter, a specific example will be given for a method in which the parameter adjustment unit 15 specifies the characteristics of the image data V0 or the compressed image data V1 based on the data amount of the compressed image data V1 and the MSE value. explain.

  Since the image data V0 captured when it is raining contains raindrops, movement occurs in the entire image. Therefore, both the data amount of the compressed image data V1 and the MSE value are increased. Therefore, if the data amount of the compressed image data V1 is equal to or greater than the first data threshold and the MES value is equal to or greater than the first evaluation threshold, the parameter adjusting unit 15 characterizes the image data V0 and the compressed image data V1. Is identified as rainy.

  The image data V0 captured when the image is clear has little motion and can be compressed at a high compression rate even when the image quality is high, so both the data amount of the compressed image data V1 and the MES value are small. Therefore, if the data amount of the compressed image data V1 is equal to or smaller than the second data threshold smaller than the first data threshold, and the MSE value is smaller than the second evaluation threshold smaller than the first evaluation threshold, the parameter adjusting unit 15 The features of the image data V0 and the compressed image data V1 are specified as clear sky.

  Further, if a sudden movement occurs in the image data V0 captured when it is clear, the MSE value increases even if the data amount of the compressed image data V1 is small. Therefore, the parameter adjustment unit 15 specifies that the characteristics of the image data V0 and the compressed image data V1 are clear when the data amount is equal to or smaller than the second data threshold and the MES value is equal to or larger than the second evaluation threshold. To do. The parameter adjustment unit 15 does not specify a feature when the data amount is equal to or greater than the first data threshold value and the MES value is equal to or less than the second evaluation threshold value.

  The parameter adjustment unit 15 may specify the characteristics of the compressed image data V1 based on the tendency of the increase or decrease in the data amount of the compressed image data V1. For example, when the data amount of the compressed image data V1 and the MSE value tend to increase, the parameter adjustment unit 15 indicates that the weather when the image data V0 is captured has changed from sunny to rainy. Is specified. Further, when the data amount of the compressed image data V1 and the value of MSE tend to decrease, the parameter adjustment unit 15 indicates that the weather when the image data V0 is captured has changed from rainy weather to sunny weather. Is specified.

  The parameter adjustment unit 15 selects a compression parameter corresponding to the changed weather based on the relationship between the evaluation result associated with the identified feature corresponding to the changed weather and the compression parameter. By doing in this way, the parameter adjustment part 15 can adjust rapidly to the compression parameter which makes the image quality of the image after compression the image quality which a user desires, even when the weather changes.

  The parameter adjustment unit 15 may specify the feature by analyzing the image data V0 or the compressed image data V1 using a known analysis method. The analysis method is a pattern recognition method for specifying features by selecting and extracting objects having a certain rule or meaning from the image data V0.

[Effect of the image compression apparatus 1 according to the second embodiment]
As described above, the storage unit 16 of the image compression apparatus 1 stores the evaluation results. The parameter adjustment unit 15 adjusts the compression parameter based on the compression parameter corresponding to the accumulated evaluation result. By doing in this way, the parameter adjustment part 15 can shorten the time until the image quality of the compressed image becomes the image quality desired by the user.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment, A various deformation | transformation and change are possible within the range of the summary. is there. For example, the specific embodiments of device distribution / integration are not limited to the above-described embodiments, and all or a part of them may be configured to be functionally or physically distributed / integrated in arbitrary units. Can do. In addition, new embodiments generated by any combination of a plurality of embodiments are also included in the embodiments of the present invention. The effect of the new embodiment produced by the combination has the effect of the original embodiment.

DESCRIPTION OF SYMBOLS 1 Image compression apparatus 2 Camera 3 Image | video storage device 11 Acquisition part 12 Compression part 13 Image quality evaluation part 14 Target information acquisition part 15 Parameter adjustment part 16 Accumulation part

Claims (5)

An acquisition unit for acquiring image data;
A compression unit that compresses the image data based on a predetermined compression parameter;
An image quality evaluation unit that evaluates the image quality of the compressed image data after being compressed by the compression unit;
A target information acquisition unit for acquiring target information indicating a target of image quality of the compressed image data;
Weather when the image data is captured, the time zone, or a characteristic indicative of brightness of at least one, and evaluation results of the image quality evaluation unit, in association with compression parameters used in the compressed image data An accumulating unit for accumulating;
Among the one or more evaluation results stored in the storage unit in association with the same feature as the feature of the compressed image data generated by the compression unit after the storage unit stores the evaluation result , the target information A parameter adjustment unit that selects the compression parameter associated with the evaluation result that satisfies the image quality target indicated by:
An image compression apparatus. The parameter adjustment unit adjusts the compression parameter based on a difference between the evaluation result and a target indicated by the target information;
The image compression apparatus according to claim 1. The target information acquisition unit acquires the target information in association with at least some of the plurality of regions of the image data,
The parameter adjustment unit adjusts the compression parameter based on a difference between the evaluation result of the image quality of the compressed image data in the at least a part of the area where the target information acquisition unit has acquired the target information and the target. To
The image compression apparatus according to claim 1 or 2. The parameter adjustment unit specifies the characteristics of the compressed image data based on a tendency of an increase or decrease in the data amount of the compressed image data.
The image compression apparatus according to any one of claims 1 to 3. Computer
An acquisition unit for acquiring image data;
A compression unit for compressing the image data based on a predetermined compression parameter;
An image quality evaluation unit for evaluating the image quality of the compressed image data after the compression unit compresses,
The target information acquiring unit for acquiring target information indicating the target quality of the compressed image data, and weather when the image data is captured, a feature indicating at least one time zone, or brightness, the image quality the evaluation result by the evaluation unit, after the compression after compression parameters used in the image data and the evaluation result storage section for storing in association with the compression parameter is accumulated in association with, said compression unit has generated the of in association with the same characteristics as the image data after compression the said accumulation part of the stored one or more of the evaluation result, selecting the compression parameters associated with the evaluation result satisfying the target quality indicated by the target information Parameter adjustment unit to
Program to function as.

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