Abstract:
To provide an image signal recording system for compressing image signals and storing compressed image data onto a storage-medium PC card; which prevents at least occurrence of an abnormal interruption of recording operation in the system. Conventionally, if a write data transfer rate of the PC card is relatively slow, full-motion picture data recording is disabled to cause an abnormal interruption of recording operation in the image signal recording system. Although there are conventional arrangements specifically designed for use with a dedicated card having a high rate of write data transfer, any arrangement applicable to write data transfer rates of various kinds of general-purpose PC cards has not been devised yet. The present invention provides an image signal recording system which is capable of detecting a write data transfer rate of each kind of PC card for inhibiting full-motion picture data recording or selecting a write data transfer rate meeting the detected transfer rate, thereby accomplishing above object.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to image signal recording systems, and more particularly to an image signal recording system for storing image signals of full-motion pictures or still pictures onto removable storage media. 
     2. Description of Related Art 
     An image signal recording system for storing full-motion picture image signals or still picture image signals is reported in IEEE Transaction on Consumer Electronics, Vol. 42, No. 3, August 1996, p. 776-p. 779, for example, in which image signals acquired through an image sensor or image signals received from an external image signal source such as VCR are converted into digital signals and then, after correction of a picture size and the number of vertical lines, these digital signals are stored as full-motion or still picture data. 
     In Japanese Non-examined Patent Publication No. 253251/1994, there is also disclosed a digital camera which has a compact circuit including a line memory and a frame memory for compressing full-motion pictures or still pictures and storing them onto a removable memory card. 
     As a removable memory card, there is a PC card meeting the PC Card Standards. For storing data, a hard disk card, SRAM card, flash memory card, etc. are available. 
     As a full-motion picture data compression method, the MPEG (Moving Picture coding Experts Group)  1  and MPEG 2  are standardized, for example. Even in the MPEG 1  which provides relatively slow transfer of data, a write data transfer rate of approx. 1.5 Mbits/s is employed in common applications. For realtime recording, it is required for a storage medium to support a write data transfer rate sufficiently higher than that of image signals. 
     A write data transfer rate of said hard disk card and SRAM card is approx. 15 Mbits/s, which poses no problem in image data storage, whereas a write data transfer rate of most types of flash memory cards having ATA interface is less than 1 Mbit/s, which is not suitable for storage of full-motion picture data. Even for still picture data, a certain limitation is imposed inconveniently on an interval between shots in a continuous shot operation due to an inadequate write data transfer rate of a storage medium employed. 
     Conventionally, however, any arrangement applicable to write data transfer rates of various kinds of general-purpose storage media has not been devised yet. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to obviate the abovementioned disadvantage by providing an image signal recording system which is capable of performing optimum storage setting for full-motion or still picture data to meet a write data transfer rate of each kind of storage medium employed. 
     In accomplishing this object of the present invention and according one aspect thereof, there is provided an image signal recording system comprising data transfer rate detecting means for detecting a write data transfer rate of each kind of storage medium employed and recording mode selector means for selecting an optimum recording mode for said storage medium based on the detected write data transfer rate thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a circuit block diagram showing one preferred embodiment of an image signal recording system according to the present invention; 
     FIG. 2 is a flowchart showing part of sequence in a first preferred embodiment of the present invention; 
     FIG. 3 is a flowchart showing part of sequence in a second preferred embodiment of the present invention; 
     FIG. 4 is a flowchart showing part of sequence in a third preferred embodiment of the present invention; and 
     FIG. 5 is a circuit block diagram showing said third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in further detail by way of example with reference to the accompanying drawings. 
     Referring to FIG. 1, there is shown a basic configuration block diagram of an image signal recording system in a preferred embodiment of the present invention, in which numeral  1  indicates an entire arrangement of the image signal recording system, numeral  2  indicates a lens, numeral  3  indicates an image sensor, numeral  4  indicates a camera signal processing circuit, numeral  5  indicates an image signal compression circuit, numeral  6  indicates a recording mode selector circuit, numeral  7  indicates a card identifying circuit, numeral  8  indicates a system controller, numeral  9  indicates a monitor screen, numeral  10  indicates a card socket, numeral  11  indicates a PC card, and numeral  12  indicates a reference information storage circuit. 
     An image converged through the lens  2  is formed on the image sensor  3 , in which it is converted into an electrical image signal. After processed through the camera signal processing circuit  4  including such known circuits as a white balance circuit, etc., the image signal is compressed as still or full-motion picture data by the compression circuit  5 . Then, through the socket  10 , the compressed still or full-motion picture data is stored onto the PC card  11 . An image being recorded is displayed on the monitor screen  9  so that an operator of the image signal recording  1  can monitor the image. 
     Referring to FIG. 2, there is shown a recording mode setup procedure. The following describes the recording mode setup procedure to be taken when the PC card is used as a storage medium. 
     The PC card is provided with a connector pin for checking whether the connector of the PC card is inserted into the card socket. By monitoring connection of this connector pin, it is detected that the PC card is mounted on the card socket (S 2 ). 
     Then, card attribute information held in an attribute memory (CIS: Card Information Structure) is verified (S 3 ). The PC cards include hard disk cards and memory cards for storing data, modem cards, LAN cards, etc. The CIS contains inherent information on functions of each card, and therefore any card improper for storing data can be rejected first by checking the CIS. Still more, the CIS contains information “CISTPL_MANFID, CISTPL_VER_ 1 ” indicating a card manufacturer, card designation, etc. Using this information, a manufacturer and model code of each card can be attained. 
     In the reference information storage circuit  12 , write data transfer rates of various kinds of PC cards are pre-stored together with information on manufacturers, model codes, etc. thereof. By comparing these reference information registered in the reference information storage circuit  12  with the contents of CIS, a write data transfer rate of each PC card mounted on the card socket can be identified (S 4 ). 
     In a situation that a full-motion picture data transfer rate is fixed in the image signal recording system shown in FIG. 1, the following operations are performed: If a write data transfer rate of the PC card is found to be sufficiently higher than that required for full-motion picture data recording, it is decided to allow recording full-motion pictures. If the write data transfer rate of the PC card is found to be slower than that required for full-motion picture data recording, it is decided to allow recording still pictures only. If the PC card is found to be improper for storing data, the PC card is decided to be invalid (S 5 ). 
     The result of decision is output to the recording mode selector circuit  6  (S 6 ). According to said result of decision, the recording mode selector circuit  6  supplies the image signal compression circuit  5  with a control signal indicating any one of the following conditions; both full-motion picture recording and still picture recording are allowed, still picture recording only is allowed, and image signal compression is inhibited due to invalidity for picture data storage. Besides, the recording mode selector circuit  6  may be arranged to let the operator of the image signal recording system know which recording mode is selectable (not illustrated). 
     Although the recording mode selector circuit  6  and the card identifying circuit  7  are provided separately for ease of understanding in the preferred embodiment shown in FIG. 1, these circuits may be implemented in the system controller  8  in common practice. 
     As mentioned above, according to the present preferred embodiment, the operator of the image signal recording system can know whether each PC card is suitable for full-motion picture recording or still picture recording just by mounting the PC card on the recording system without having to remember suitability thereof or refer to any suitability reference information table. 
     For any data-storage PC card that will be put on the market after the reference information is registered in the image signal recording system, i.e., a PC card whose reference information is not contained in the reference information storage circuit  12 , presetting may be made so that recording both full-motion and still pictures is allowed or recording still pictures only is allowed. If a write data transfer rate of said PC card is sufficiently high, full-motion pictures can be recorded normally. If not, full-motion picture recording is interrupted prematurely. Even in the latter case, however, the reference information storage circuit  12  may be arranged so that the contents thereof can be updated on the instant, thereby making it possible to prevent recurrence of such an inconvenient condition. 
     After the image signal recording system described in the present preferred embodiment is placed on the market, the reference information storage circuit  12  designed on a basis of software can be updated with ease. 
     Furthermore, while the present preferred embodiment has been described in connection with the PC cards including memory cards and hard disk cards, it is to be understood that the invention is applicable to other kinds of storage media through the PC Card Standard interface. 
     Referring to FIG. 3, there is shown a flowchart indicating another preferred embodiment different from the abovementioned embodiment shown in FIG.  2 . Although the hardware structure is the same as shown in FIG. 1, the image signal recording system in the preferred embodiment shown in FIG. 3 is arranged so that it has a functional feature permitting a variable rate of full-motion picture data transfer. 
     A card detection step (S 11 ), CIS read step (S 12 ), and reference information comparison step (S 13 ) are the same as those in the preferred embodiment shown in FIG.  2 . Description of these steps is therefore omitted here. 
     After the reference information comparison step (S 13 ), decision is made to identify any one of the following PC card categories; PC card capable of high-quality full-motion picture recording at a registered transfer rate, PC card which is not capable of high-quality full-motion picture recording but supports low-quality full-motion picture recording at a decreased transfer rate, PC card which allows recording still pictures only at a low transfer rate, and PC card not suitable for storing picture data such as a modem card. The result of decision is output to the recording mode selector circuit  6  (S 15 ). 
     According to said result of decision, the recording. mode selector circuit  6  supplies the image signal compression circuit  5  with a control signal indicating any one of the following conditions; high-quality full-motion picture recording, low-quality full-motion picture recording and still picture recording are all allowed, low-quality full-motion picture recording and still picture recording are allowed, still picture recording only is allowed, and image signal compression is inhibited due to invalidity for picture data storage. Besides, the recording mode selector circuit  6  may be arranged to let the operator of the image signal recording system know which recording mode is selectable (no illustrated). 
     Although the image signal recording system  1  in the present preferred embodiment provides two levels of write data transfer rates for high-quality full-motion picture recording and low-quality full-motion picture recording, it is to be understood that the invention is not limited in its application to selectivity of just two levels of write data transfer rates. 
     Referring to FIG. 4, there is shown a flowchart indicating another preferred embodiment different from the foregoing embodiments shown in FIGS. 2 and 3. A unique feature of the preferred embodiment shown in FIG. 4 is that a write data transfer rate of each PC card  11  mounted on the image signal recording system  1  is measured directly. FIG. 5 shows the hardware configuration of the present preferred embodiment. In this figure, the same parts as those in FIG. 1 are indicated by the same numerals. Description of these same parts is omitted here. In FIG. 5, numeral  30  indicates a reference data storage circuit, numeral  31  indicates an input/output port, numeral  32  indicates a CPU, numeral  33  indicates a timer circuit, and numeral  34  indicates a transfer rate calculating circuit. 
     In the processing flowcharted in FIG. 4, a card detection step (S 21 ), CIS read step (S 22 ), and reference information comparison step (S 23 ) are the same as those in the preferred embodiments shown in FIGS. 2 and 3. Description of these steps is therefore omitted here. At the reference information comparison step (S 23 ), if a PC card mounted on the card socket  10  is found to be any one of cards registered already (S 24 —NO), it is not necessary to measure a write data transfer rate. In this case, the result of decision is output immediately (S 30 ). 
     If the PC card mounted on the card socket  10  is found to be an unknown new-type card whose write data transfer rate is not yet registered (S 24 —YES), the CPU  32  shown in FIG. 5 issues a start-of-measurement instruction to the timer circuit  33  (S 25 ). The CPU  32  also carries out an instruction for writing a predetermined amount of test reference data from the test reference data storage circuit  30  to the PC card through the input/output port  31 . Upon completion of writing the predetermined amount of test reference data, the CPU  32  instructs the timer circuit  34  to stop measurement (S 27 ) and deliver a measured period of time to the transfer rate calculating circuit  34 . A write data transfer rate inherent to each PC card can thus be determined through dividing the amount of written data by the measured period of time. The calculated value of write data transfer rate includes a time required for execution of instructions handled between the image signal recording system  1  and the PC card, i.e., a command overhead time. Since a similar command overhead time is required when full-motion picture data is written to the PC card in actual applications, the calculated write data transfer rate represents a value that is nearer an actual write data transfer rate than a theoretical write data transfer rate of the PC card. 
     According to the result of measurement mentioned above, decision is made whether the PC card is suitable for full-motion picture recording or still-picture recording (S 28 ) and the result of decision is output to the recording mode selector circuit  6 . In addition, the result of decision is registered in the reference information storage circuit  12  for the purpose of updating (not illustrated) (S 29 ). 
     Although only one full-motion picture recording mode is provided in the present preferred embodiment, high-quality and low-quality full-motion picture recording modes may be provided as exemplified in the embodiment shown in FIG.  3 . 
     Still more, the image signal compression circuit  5  may be arranged to allow arbitrary setting of a data compression ratio thereof. In this arrangement, it is possible to output information on a write data transfer rate only to the recording mode selector circuit  6  at the decision processing step S 28  so that the recording mode selector circuit  6  sets up an optimum full-motion picture data transfer rate for each PC card  11  mounted on the card slot. 
     Although the reference information storage circuit  12  is provided in the present preferred embodiment, it is also possible to exclude the reference information storage circuit  12  for reduction in production cost of the image signal recording system since a write data transfer rate of each PC card mounted can be measured as described above. 
     According to the present preferred embodiment, applicability of the invention can be enhanced significantly since a write data transfer rate of any unknown new-type PC card can be measured. 
     As set forth hereinabove, this invention provides an image signal recording system which is capable of performing optimum storage setting for full-motion or sill picture data to meet a write data transfer rate of each kind of PC card or other storage medium employed. Further, embodiment of this invention requires a considerably low cost since it can be carried out just by incorporating additional software in card detection and CIS read functions provided in an image signal recording system using a PC card. 
     While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible of changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications as fall within the ambit of the appended claims.