JP2001292381A - Receiving device, reception system, receiving method and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiving device capable of providing video with less uncomfortable feeling for a user by relieving a freeze (stop) state of an outputted video signal due to channel hopping with inexpensive hardware structure. SOLUTION: When the switching of channels at a channel switching means 120 is generated, a control means 140 makes reproduction speed at a reproducing means 154 lower than reproduction speed based on video frame rate information of channel data (TS data in MPEG 2 format). The channel switching means 120 executes the switching of channels from storage of prescribed quantity of channel data by a storage means 130 to completion of reproduction of the prescribed quantity of channel data by a reproducing means 140.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a computer which can read out a receiving device, a receiving system, a receiving method, and a processing step for implementing the same, which are used in a device or a system for receiving digital television broadcasting. Related to the storage medium stored in the storage medium.

[0002]

2. Description of the Related Art In Japan in recent years, for example, M
CS (Communic) adopting the PEG2 encoding method
Digital satellite broadcasts such as digital satellite broadcasts have been realized.

[0003]

However, in a conventional receiving apparatus for digital television broadcasting, when switching channels, a freeze (stop) state of an output video signal occurs due to a phenomenon called channel hopping. Was a problem. The main cause of channel hopping is that it takes time for the tuner switching operation to stabilize the tuner decoding operation. MPEG2 encoded data is transferred as packet data having no continuity on the time axis and the space axis.
And the like.

[0004] The freeze (stop) state of the output video signal due to the channel hopping as described above gives the user embarrassment for a short time and impairs the operability.

In order to solve the above problem, it is conceivable that the tuner and the decoder unit for MPEG2 encoded data have two systems each, and when the channels are switched, the systems are operated so as to overlap each other. In such a configuration, the cost of the tuner and the decoder section increases, and it is difficult to say that the cost is high enough to improve the operability.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to eliminate the above-mentioned drawbacks, and reduces the freeze (stop) state of an output video signal due to channel hopping by using an inexpensive hardware configuration, and performs channel switching. Even at times, it is possible to provide images with less discomfort for users,
It is an object of the present invention to provide a storage medium in which a receiving device, a receiving system, a receiving method, and processing steps for executing the receiving device, a receiving method, and a computer are stored in a computer-readable manner. In particular, an object of the present invention is to reduce the time related to channel switching operation and settling among the main causes of channel hopping.

[0007]

For such a purpose,
A receiving device according to a first aspect of the present invention includes a receiving unit that receives desired channel data from a plurality of channel data, a channel switching unit that switches a receiving channel,
Storage means for storing the channel data switched by the channel switching means; playback means for playing back video data included in the channel data stored in the storage means; and a video frame rate information included in the channel data. And control means for controlling a playback speed of the playback means, wherein the control means, when a channel changeover by the channel switching means occurs, sets the playback speed of the playback means to the video frame rate information. The speed is lower than the reproduction speed based on

According to a second aspect of the present invention, in the receiving apparatus according to the first aspect, the channel switching means is configured such that the storage means controls the reproduction means at a low reproduction speed by the control means, After the channel data is stored, the channel switching is performed between the time when the reproducing means finishes reproducing the predetermined amount of channel data stored in the storing means, and the control means controls the channel switching means. When the channel switching is completed, the playback speed of the playback unit is set to a speed based on video frame rate information included in channel data to be played back by the playback unit.

According to a third aspect of the present invention, there is provided a receiving apparatus for selectively switching arbitrary channel data from a plurality of channel data and outputting the channel data, and a channel output from the selective switching means. Accumulating means for temporarily accumulating data; base clock reproducing means for reproducing a base clock used as a reference clock for decoding the channel data from clock reproduction information included in the channel data; Base clock frequency dividing means for dividing the base clock obtained by the above at an arbitrary frequency dividing ratio, and channel data stored in the storage means based on the frequency-divided clock obtained by the base clock frequency dividing means. Decoding means for decoding at least video data; A frequency dividing ratio setting means for setting a frequency dividing ratio in the lock frequency dividing means, and when a switching operation by the selection switching means occurs, by changing a frequency dividing ratio set by the frequency dividing ratio setting means, Setting the decoding processing speed in the decoding means to a value relatively lower than the video decoding frame rate included in the channel data to be decoded, causing the selection switching means to execute a switching operation, Control means for setting the decoding processing speed of the decoding means to a value equal to the video decoding frame rate included in the channel data to be decoded by changing the division ratio set by the ratio setting means again. It is characterized by having.

[0010] In a fourth aspect of the present invention, in the receiving apparatus according to the first or third aspect, the reception channel data is M
It is characterized by including data according to the PEG encoding method.

A fifth invention is a receiving system in which a plurality of devices are communicably connected to each other, wherein at least one of the plurality of devices is one of the first to fourth inventions. It has a function of a receiving device.

A sixth invention is a receiving method including a processing step of receiving a plurality of channel data, selectively switching an arbitrary channel from the received channel, and reproducing at least video data included in the data of the switched channel. The processing step includes a storage step of storing the switching channel data, a reproduction step of reproducing and outputting video data of the channel data stored in the storage step, and channel data to be reproduced in the reproduction step. Based on the video frame rate information included in the, including a control step of controlling the playback output speed in the playback step, the control step, when the channel switching occurs, the playback output speed in the playback step, Playback based on the above video frame rate information Characterized in that it comprises a step of relatively lower speed than the speed.

[0013] In a seventh aspect based on the sixth aspect,
In the processing step, in a state where the reproduction output speed in the reproduction step is controlled to a low speed by the control step, a predetermined amount of channel data is accumulated in the accumulation step, and then the predetermined amount of By the time the channel data is finished reproducing and outputting
Performing the channel switching, wherein the control step, when the channel switching is completed, changes the reproduction output speed in the reproduction step to the video frame rate information included in the channel data to be reproduced in the reproduction step. And a step of setting a speed based on the speed.

[0014] A receiving method according to an eighth aspect of the present invention is a selection switching step of selecting and switching arbitrary channel data from a plurality of channel data, and outputting the channel data, and a buffer memory for storing the output channel data. An accumulation step of temporarily accumulating the data, a base clock reproduction step of reproducing a base clock used as a reference clock for decoding the channel data from the clock reproduction information included in the channel data, and a base clock reproduction step. A base clock dividing step of dividing the obtained base clock by an arbitrary dividing ratio; and at least one of the channel data stored in the buffer memory based on the divided clock obtained by the base clock dividing step. Decode video data Decoding step, a dividing ratio setting step of setting a dividing ratio in the base clock dividing step, and, when a switching operation by the selection switching means occurs, the dividing step is performed as a first step. By changing the division ratio set in the ratio setting step, the decoding processing speed in the decoding step is set to a relatively lower value than the video decoding frame rate included in the channel data to be decoded, As a second step, the switching operation is executed, and as a third step, the frequency division ratio set in the frequency division ratio setting step is changed again, so that the decoding processing speed in the decoding step is reduced. Setting a value equal to the video decoding frame rate included in the channel data to be processed.

A ninth invention is characterized in that, in the sixth or eighth invention, the reception channel data includes data according to the MPEG coding system.

A storage medium according to a tenth aspect of the present invention is the storage medium according to the first aspect.
A processing program for implementing the function of the receiving device according to any one of the above-described aspects or the function of the receiving system according to the fifth aspect, is readable by a computer.

A storage medium according to an eleventh aspect of the present invention is the storage medium according to claim 6.
The processing steps of the receiving method according to any one of the above-described items are stored in a computer-readable manner.

More specifically, for example, in a digital television broadcast receiving apparatus employing the MPEG2 encoding system, when a channel change by a user operation occurs, a decoding clock supplied to an MPEG2 video decoder section (reproducing means, decoding means). Is lower than the default value. Thus, the MPEG2 video decoder section
In order to perform decoding processing of video data using a low-frequency decoding clock, that is, decoding processing of an MPEG2 video stream is performed at a speed lower than a predetermined decoding processing speed for a certain period, a reception buffer (accumulating means) A certain amount of MPEG2 video stream (channel data) can be stored.

Further, the switching operation is actually executed when the MPEG2 video stream of an amount sufficient to allow for the settling time until the switching of the channel data and the operation is stabilized is accumulated in the receiving buffer. As a result, during the period from when the switching operation is performed to when the operation is stabilized, a new MPEG2 video stream is not transferred to the reception buffer, so that the MPEG2 video stream stored in the reception buffer is subjected to a predetermined decoding process. By performing the decoding process at a speed lower than the speed, it is possible to prevent the screen from freezing (still image display).

During the above period, the image update speed is originally M
Although it is lower than that obtained by decoding the PEG2 video stream in accordance with the default value, since the moving image is displayed, the sense of incongruity is less than when the screen is frozen (still image display). In addition, during the above-mentioned period, special hardware is used by maintaining the frame rate of the video signal supplied to the display unit constant by, for example, outputting the same frame at a fixed interval. And a moving image can be displayed on the display unit. Further, during the above-mentioned period, lip synchronization with the audio signal corresponding to the video signal to be reproduced (displayed) cannot be obtained, so that the audio signal is, for example, muted (silent state) or Like the video signal, decoding is performed at a low decoding processing speed.

When the channel switching and operation are stabilized, the frequency of the decoding clock supplied to the MPEG2 video decoder is returned to a predetermined value, thereby shifting to a normal reception state.

Therefore, according to the present invention, the display image does not freeze (still image display) as in the related art when the channel is switched.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

The present invention is applied to, for example, a digital television broadcast receiving apparatus 100 as shown in FIG. As shown in FIG.
Antenna 110 for receiving digital television broadcast radio waves, tuner 120 for switching received radio waves at antenna 110 (channel switching) to output stream data of received radio waves, and temporarily storing output data of tuner 120 Buffer 130 and Buffer 1
The apparatus 100 includes a decoder 150 that acquires and outputs an audio signal and a video signal from the data stored in the device 30, and a control unit 140 that controls the operation of the entire device 100.

<Outline of Operation of Receiving Apparatus 100> Controller 14
Numeral 0 controls the operation of the entire apparatus 100 by a microcontroller (CPU: not shown) provided therein. For example, the control unit 140 controls the entire operation of the apparatus 100 by reading and executing a processing program stored in the internal memory in advance by the CPU. This allows
The receiving device 100 operates as follows.

The tuner 120 selects an arbitrary wave from a plurality of received radio waves (carriers) supplied via the antenna 110, and uses the selected carrier as a TS in the MPEG2 encoding system including a plurality of program streams. (Tran
(Sport Stream) data.

The buffer (FIFO memory) 130 temporarily stores the TS data in the MPEG2 encoding system supplied from the tuner 120.

The decoder 150 is a decoder unit corresponding to the MPEG2 encoding method, and decodes an arbitrary program stream from a plurality of program streams included in TS data supplied via the buffer 130.

Specifically, the decoder 150 includes a demultiplexer 151, a decoding base clock reproducing unit 152, a frequency divider 153, a video decoder 154, and an audio decoder 155.

Under the control of the control unit 140, the demultiplexer (separation unit) 151 selects a specific PID (Packet Identifier) from a plurality of program streams contained in the TS data from the buffer 130.
session: stream identification information), and obtains a plurality of PES (Packetized Elements) constituting the program stream.
Entry stream packets and packet headers are filtered to obtain video packets, audio packets, SI (Service Information).
on) and PCR (Program Clock P)
reference: program time reference value) or SC
R (System Clock Preference:
Information such as a system time reference value is acquired. The demultiplexer 151 supplies the video packet to the video decoder 154, the audio packet to the audio decoder 155, the information such as PCR and SCR to the decoding base clock reproducing unit 152, and the SI information to the control unit 140.

The video decoder 154 outputs a video packet (video stream) from the demultiplexer 151.
Is decoded into a baseband video signal (video signal) and output. The audio decoder 155 decodes the audio packet (audio stream) from the demultiplexer 151 into a baseband audio signal (audio signal) and outputs it.

The decoding base clock reproducing unit 152 generates a 27 MHz reference clock necessary for decoding a video stream and an audio stream from information such as PCR and SCR from the demultiplexer 151.

The frequency divider 153 frequency-divides the reference clock supplied from the decoding source clock reproducing unit 152 at an arbitrary frequency division ratio set by the control unit 140, and decodes the video stream and the audio stream. Are supplied to the video decoder 154 and the audio decoder 155, respectively. Therefore, the video decoder 154 and the audio decoder 155 respectively
The video stream and the audio stream are decoded according to the decoding clock from the frequency divider 153.

The control unit 140 includes an interface for receiving a signal from a remote control device (remote controller) operated by a user, and an LED for displaying a channel.
Based on the SI information from the demultiplexer 151, control for the channel selection and switching operation by the remote control operation and the like is performed.

<The most characteristic operation of the receiving apparatus 100>
FIG. 2 is a flowchart illustrating the channel switching operation of the receiving apparatus 100. FIG. 3 shows the receiving apparatus 1
It schematically shows the frame rate of the decoded video signal in the channel switching operation at 00, and shows the correspondence with the processing steps in the flowchart of FIG. FIG. 4 schematically shows the average remaining amount of TS data in the buffer 120, and illustrates the correspondence with the processing steps in the flowchart of FIG.
The channel switching operation shown in FIGS. 2 to 4 is performed as follows by operation control of the present apparatus 100 by the control unit 140.

Here, for simplicity of explanation, the current channel is CH-A, which is referred to as channel CH-A.
Switch to B. Also, the current decoding processing speed (moving image output speed) depends on the channel (CH-
It is assumed that the frame rate is 30 fps corresponding to the video reproduction frame rate indicated by information such as PCR and SCR in the program stream of A).

First, when channel switching (switching from CH-A to CH-B) occurs due to a remote control operation or the like from the user (step S201), it is determined whether or not it is necessary to change the transponder selection. It is determined (step S202). If it is determined that there is no need to change the transponder selection, the process proceeds to step S210, which will be described later.

On the other hand, if the result of determination in step S202 is that transponder switching is necessary, the audio signal output is first muted (step S203). For example,
Although not shown, a mute circuit for the audio signal is provided at a stage subsequent to the audio decoder 155, and the mute circuit mutes the audio signal output.

Next, the dividing ratio of the frequency divider 153 is, for example,
By setting to ２, the decoding processing speed in the video decoder 154 is changed from 30 fps to 15 fps (step S204). In this state, a period until the amount of TS data sufficient to allow for the time required for the channel switching operation and stabilization of the tuner 120 is accumulated in the buffer 130 (here, 200 ms, see FIGS. 3 and 4 described above). ), The decoding processing and display of the video stream are performed at a low decoding processing speed (15 fps, which is relatively lower than 30 fps corresponding to the video reproduction frame rate indicated by information such as PCR and SCR in the CH-A program stream). Do.

When a certain amount of TS data is accumulated in the buffer 130, that is, when 200 ms has elapsed (step S205), the tuner 120 performs a transponder selection and switching operation (step S206). The transponder selection and replacement operations are realized by, for example, changing the transmission frequency of the local oscillator supplied to the mixer inside the tuner 120 by the control unit 140, not shown.

Next, a standby state is set until the operation of the tuner 120 is stabilized (step S207).
When the operation of 0 is stabilized, the TS data of the old channel (CH-A) remaining in the buffer 120 is flushed out (step S208). The determination of whether or not the operation of the tuner 120 has been stabilized is, for example, not shown,
This can be realized by confirming that the demodulation PLL inside the tuner 120 is locked and valid data is output from a signal processing circuit such as the FEC.

Next, by setting the frequency division ratio of the frequency divider 153 to 1/1, the decoding processing speed of the video decoder 154 is changed from 15 fps to 30 fps (step S).
209). As a result, the speed is returned to the normal video stream decoding processing speed (30 fps).

If the transponder selection does not need to be changed or the transponder selection needs to be changed according to the result of the determination in step S202 described above, after the processing of steps S203 to S209 is executed, a new The program stream of the channel (CH-B) to be reproduced is obtained from the TS data including the plurality of program streams obtained from the selected transponder, and set to the demultiplexer 151 (step S210). After that, the process ends (step S
211).

Therefore, conventionally, as shown in FIG. 5, at the time of channel switching (see "" in FIG. 5),
In contrast to the freeze state of the output video signal (see “” in the figure), in the present embodiment, when a channel change occurs, the decoding playback speed is set to a relative value to the video playback frame rate in the program stream. In the meantime, the system is configured to perform decoding and reproduction of a certain amount of old channels and to perform channel switching in the meantime, so that the output video signal freezes as shown by "" in FIG. 3 and FIG. No condition occurs.

The configuration of the receiving apparatus 100 shown in FIG. 1 may be, for example, a configuration as shown in FIG. That is, the buffer 130 may not be provided before the decoder unit 150 but may be provided after the demultiplexer 151 in the decoder unit 150.

After the channel switching occurs,
The period from the start of the channel switching until the operation of the tuner is stabilized (see “” in FIGS. 3 and 4) is, for example,
The frame rate of the video signal supplied to the display unit may be kept constant by, for example, outputting the same frame at a constant interval. This makes it possible to display a moving image on the display unit without using special hardware.

Also, in the present embodiment, during the above period, it becomes impossible to lip-sync with the audio signal corresponding to the video signal to be reproduced (displayed), so that the audio signal is muted (silent state). Was configured to
The present invention is not limited to this. For example, an audio signal may be configured to be decoded at a low decoding processing speed similarly to a video signal.

Another object of the present invention is to supply a storage medium storing program codes of software for realizing the functions of the host and the terminal of the present embodiment to a system or an apparatus, and to provide a computer (or a computer) of the system or apparatus. Needless to say, the present invention can also be achieved by a CPU or an MPU) reading and executing a program code stored in a storage medium. In this case, the program code itself read from the storage medium implements the functions of the present embodiment, and the storage medium storing the program code constitutes the present invention. As a storage medium for supplying the program code, a ROM, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, or the like can be used. it can. In addition, by executing the program code read by the computer, not only the function of the present embodiment is realized, but also based on the instruction of the program code,
It goes without saying that the OS or the like running on the computer performs part or all of the actual processing, and the functions of the present embodiment are realized by the processing.
Further, after the program code read from the storage medium is written to a memory provided in an extension function board inserted into the computer or a function extension unit connected to the computer, the function extension is performed based on the instruction of the program code. C provided on board and function expansion unit
It goes without saying that a PU or the like performs part or all of the actual processing, and the processing realizes the functions of the present embodiment.

[0049]

As described above, according to the present invention, when a channel change occurs, the decoding (reproduction) speed is increased.
As the speed is relatively lower than the video playback frame rate of the channel data to be decoded, a certain amount of old channels are decoded and the channel is switched during that time. The freeze state of the signal is reduced, and even when the channel is switched, it is possible to provide a video with less discomfort to the user, and to realize comfortable operability. In addition, there is no need to adopt a configuration in which each of the receiving unit and the decoder unit has two systems and the systems operate in an overlapping manner at the time of channel switching, so that there is no increase in cost.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital television broadcast receiving apparatus to which the present invention has been applied.

FIG. 2 is a flowchart for explaining the operation of the receiving device.

FIG. 3 is a diagram for explaining a channel switching operation in the receiving device.

FIG. 4 is a diagram for explaining a state of data accumulation in a buffer in the channel switching operation.

FIG. 5 is a diagram for explaining a channel switching operation in a conventional receiving device.

FIG. 6 is a block diagram showing another configuration example of the receiving device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 receiving device 110 antenna 120 tuner 130 buffer memory 140 system control unit 150 MPEG2 decoder unit 151 demultiplexer 152 decoding decoding clock recovery unit 153 frequency divider 154 video decoder 155 audio decoder

Claims (11)

[Claims] A receiving means for receiving desired channel data from a plurality of channel data; a channel switching means for switching a receiving channel; a storage means for storing the channel data switched by the channel switching means; Playback means for playing back video data included in the channel data stored in the storage means, and control means for controlling a playback speed in the playback means based on video frame rate information included in the channel data, The control means, when the channel switching by the channel switching means occurs, the reproduction speed by the reproduction means,
A receiving device, wherein the reproducing speed is lower than the reproducing speed based on the video frame rate information. 2. The channel switching means, wherein the storage means stores a predetermined amount of channel data in a state where the playback means is controlled to a low playback speed by the control means, and then the playback means stores the predetermined amount of channel data in the storage means. The channel switching is executed until the reproduction of the predetermined amount of channel data stored in the means is completed. When the channel switching by the channel switching means is completed, the control means controls the reproduction speed by the reproducing means. 2. The receiving apparatus according to claim 1, wherein the speed is set based on video frame rate information included in channel data to be reproduced by said reproducing means. 3. Selection switching means for selectively switching arbitrary channel data from a plurality of channel data and outputting the channel data, and storage means for temporarily storing the channel data output from the selection switching means. Base clock reproducing means for reproducing a base clock used as a reference clock for decoding the channel data from the clock reproduction information included in the channel data, and a base clock obtained by the base clock reproducing means, Base clock frequency dividing means for dividing by a frequency ratio; and decoding means for decoding at least video data of channel data stored in the storing means based on the frequency-divided clock obtained by the base clock frequency dividing means. The division ratio of the base clock dividing means is A dividing ratio setting means for setting, and when a switching operation in the selection switching means occurs, by changing a dividing ratio set in the dividing ratio setting means, a decoding processing speed in the decoding means is reduced. The value is set to a value relatively lower than the video decoding frame rate included in the channel data to be decoded, the switching operation is performed by the selection switching unit, and the division ratio set by the division ratio setting unit is set. A receiving apparatus comprising: a control unit that sets the decoding processing speed of the decoding unit to a value equal to a video decoding frame rate included in the channel data to be decoded by changing the setting again. 4. The receiving channel data is MPEG data.
4. The receiving device according to claim 1, wherein the receiving device includes data according to an encoding method. 5. A receiving system in which a plurality of devices are communicably connected to each other, wherein at least one device among the plurality of devices is a function of the receiving device according to claim 1. A receiving system comprising: 6. A receiving method comprising the steps of: receiving a plurality of channel data, selectively switching an arbitrary channel from the received channel, and reproducing at least video data included in the data of the switched channel; The processing step includes: an accumulation step of accumulating the switching channel data; a reproduction step of reproducing and outputting video data of the channel data accumulated by the accumulation step; and a video included in the channel data to be reproduced in the reproduction step. A control step of controlling a reproduction output speed in the reproduction step based on the frame rate information, wherein the control step includes:
A receiving method comprising: setting a playback output speed in the playback step to a speed relatively lower than a playback output speed based on the video frame rate information. 7. The method according to claim 7, wherein the controlling step controls the reproduction output speed in the reproducing step to a low speed, and stores the predetermined amount of channel data in the storing step. The step of performing channel switching until the predetermined amount of channel data is completed by the reproduction output, and the control step comprises: when the execution of the channel switching is completed, the reproduction output speed in the reproduction step: 7. The receiving method according to claim 6, further comprising the step of setting a speed based on video frame rate information included in channel data to be reproduced in said reproducing step. 8. A selection switching step of selecting and switching arbitrary channel data from a plurality of channel data and outputting the channel data, and a storage step of temporarily storing the output channel data in a buffer memory. A base clock recovery step of recovering a base clock used as a reference clock for decoding the channel data from the clock recovery information included in the channel data; and a base clock obtained by the base clock recovery step. A base clock dividing step for dividing by a dividing ratio; and a decoding step of decoding at least video data of channel data stored in the buffer memory based on the divided clock obtained in the base clock dividing step. When, A dividing ratio setting step of setting a dividing ratio in the base clock dividing step; and setting in the dividing ratio setting step as a first step when a switching operation by the selection switching means occurs. By changing the frequency division ratio, the decoding processing speed in the decoding step is set to a value relatively lower than the video decoding frame rate included in the channel data to be decoded. As a second step, Execute the above switching operation,
As a third step, by changing again the division ratio set in the division ratio setting step, the decoding processing speed in the decoding step is changed to the video decoding frame rate included in the channel data to be decoded. A control step of setting the value to an equal value. 9. The receiving channel data is MPEG data.
9. The receiving method according to claim 6, further comprising data according to an encoding method. 10. A processing program for implementing the function of the receiving device according to claim 1 or the function of the receiving system according to claim 5, readable by a computer. Storage medium. 11. A storage medium, wherein the processing steps of the reception method according to claim 6 are readable by a computer.