Image encoding and recording apparatus and method

Abstract: An image coding apparatus comprises: a) first means for fixing or limiting quantity of code produced by compressively coding a given image data, independent of the image; and b) second means for conducting valiable length compression of which quantity of code produced varies according to the image; and selection means for selecting the first and second means.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an image encoding apparatus for variable lenght compression encoding of image signal and an image recording apparatus for recording image signal. Related Background Art Conventional image recording apparatus, for example still video camera, is based for example on analog signal recording on floppy disks or recording of digital image data, compressed by fixed length encoding, in semiconductor memory cards. The fixed length encoding means a compression encoding in such a manner that the amount of compressed codes of an image frame becomes equal to a predetermined value. Such conventional image signal recording methods can guarantee the number of images recordable per recording medium, because the capacity thereof required for recording image data of an image frame is predetermined. However, for example in a digital still video camera employing image data compression with a fixed length encoding method, the rate of compression can empirically be only increased to the order of 8 bit/pixel, including the luminance and the color information, in order to guarantee the quality of compressed image for various image data, for example those involving fine patterns. Thus the fixed length encoding cannot achieve a sufficiently high compression rate. On the other hand, a variable length encoding method can achieve efficient compression while guaranteeing sufficient image quality. The variable length encoding generates codes of variable length depending on the image, and empirically provides an encoding rate of 2 - 4 bit/pixel, including the luminance and color information and guaranteeing the image quality. In this case, however, it is not possible to guarantee the total number of images recordable per recording medium, because the total amount of codes varies according to the image. Also if the capacity of the recording medium is limited, the image may not be recordable on the recording medium. Consequently, such variable length encoding method, if employed in a recording apparatus, results in a significant inconvenience as the user is unable to recognize, in advance, the number of images still recordable on the recording medium. EP-A-0323194 describes a digital image recording apparatus wherein image data is stored in a buffer memory in either encoded or unencoded form, and the data is transferred from the buffer memory to a storage device such as a memory card, without further processing of the data. As explained in the foregoing, a system employing fixed length encoding has been unable to guarantee the image quality, while a system employing variable length encoding has been unable to guarantee the number of recordable images. Thus either system has been inconvenient for the user. SUMMARY OF THE INVENTION In consideration of the foregoing an object of the present invention is to provide an image encoding method or apparatus, or an image recording method or apparatus, capable of individually or collectively resolving the drawbacks mentioned above. Another object of the present invention is to provide an apparatus allowing the operator to know, prior to a recording operation, whether such recording operation is possible or not. Still another object of the present invention is to provide an image recording apparatus employing a variable length encoding method and still convenient for use. The above-mentioned objects can be attained, according to a preferred embodiment of the present invention, by a method and an apparatus recording to the appended claims. Still another object of the present invention is to provide an image encoding method or apparatus which is convenient for use and still allows efficient use of the recording capacity of the recording medium. Still another object of the present invention is to provide a novel image recording apparatus having image taking capability. Still other objects of the present invention, and the advantages thereof, will become fully apparent from the following description of the embodiments thereof, to be taken in conjunction with the attached drawings, in which Fig. 1 is a block diagram of an embodiment of the present invention; Fig. 2 is a timing chart showing the function of the apparatus shown in Fig. 1; Fig. 3 is a flow chart of the control sequence of the apparatus shown in Fig. 1; Figs. 4 and 5 are flow charts showing details of parts of the flow chart shown in Fig. 3; Figs. 6-1 and 6-2 are flow charts of the control sequence of another embodiment of the present invention; and Figs. 7A and 7B are charts for explaining the embodiment corresponding to Fig. 6. In the drawings, Fig. 1 is a block diagram of an embodiment of the present invention. Other parts of the camera not directly related to the present invention, such as the diaphragm and the shutter, are naturally provided but not shown. An optical image of an object, formed by a lens 1, is converted into an electrical image signal by an image pickup device 2, such as a charge-coupled device (CCD), positioned behind said lens. Said device 2 effects accumulation of charges corresponding to the optical image of the object and readout of image signal, in response to control signals given by a control unit 7. The obtained image signal is converted into a digital signal by an A/D converter 3. Between the image pickup device 2 and the A/D converter 3, there are provided means for regulating the image signal such as gamma correction, formation and separation of color signals, white balance process etc. though such means are not illustrated. The digital image signal is stored in an image memory 4. A compression encoding circuit 5 effects compression encoding on the image data read from the image memory 4 and sends the obtained codes to a recording unit 6. The control unit 7 is so constructed as to control the recording and reproducing for example with MS-DOS commands through the recording unit 6. The compression is conducted by a variable length encoding or a fixed length encoding, for example by DCT conversion of the image as will be explained later, followed by entropy encoding. Also there is provided a function of counting the amount of compressed codes without the supply thereof to the recording unit 6. For this purpose there is provided a counting circuit 16 for counting the amount of compressed encoded data prior to the supply thereof to the recording unit 6. The recording unit 6 is provided with a recording medium such as a semiconductor memory or a tape-shaped medium, is capable of information exchange with the control unit, of recording or reading of arbitrary digital data at an arbitrary physical address of the recording medium, and of counting the empty capacity of said recording medium. The control unit 7 controls the entire apparatus by controlling the units 2 - 6, and is also capable of controlling the image data files in the recording medium, through the recording unit. More specifically the control unit 7 correlates the file information with the physical addresses on the recording medium, as in a disk operating system employed in a computer system, and is therefore capable of controlling the mode of recording of files (compressed image data) on the recording medium, and also the empty capacity thereof. If the compressed codes have to be stored in divided plural parts with a limited recording unit each, the control unit 7 causes the recording unit 6 to record the compressed codes by designating the physical address on the medium and the data length for each recording unit. When an image file is recorded in plural positions on the recording medium, the control unit 7 also records information indicating said positions, on the recording medium. A man-machine interface (MMIF) 8 includes an operation member 9 for actuating switches SW1, SW2 for shutter releasing and other switches to be explained later, and display devices 10 including a display in the view finder, an external LCD display, a buzzer etc. In an actual phototaking operation, the number of recordable images is displayed as will be explained in the following, with reference to a flow chart shown in Fig. 3. (1) At first the control unit 7 sends commands DIR, CHK, DSK to the recording unit 6 to release the empty capacity therefrom (S1). When a shutter release button is depressed by a half stroke (switch SW1 on) for a phototaking operation, the control unit effects focusing by driving the lens 1, then activates the diaphragm and the shutter thereby exposing the image pickup device (S5), fetches the image information in the memory (S7), and effects compression encoding (S9). The control unit causes the counting circuit 16 to count the amount of codes of the image data, also causes the recording unit to count the empty capacity, and calculates, from thus obtained data, the number of frames that can be recorded (S11). Said number is obtained for example by dividing the empty capacity with the amount of codes of image data. Thus calculated value is informed to the user by a display device 10 provided in the view finder (S13). The display is continued while the switch SW1 is closed (S15, S17). When the shutter releasing button is depressed deeper for the phototaking operation, the sequence branches from the step S17 to steps S19, S21 and S23 to effect similar operations as those in the steps S5, S7 and S9, thereby fetching anew an image to be actually recorded. (2) When a continuous phototaking mode is not selected, the sequence branches from a step S25 to the step S3. On the other hand, when said mode is selected, the empty capacity of the recording medium will decrease with the phototaking operations, and the amount of codes of image data per frame may also vary. Thus, after the recording of the first frame in said mode, the empty capacity and the amount of image codes to be recorded next are counted after the recording of each frame (S23), and the decreasing number of recordable images is continuously displayed in the view finder (S29). Thus, in the present embodiment, if the continuous recording mode is selected and while the switch SW2 is kept closed, the images are fetched in the memory, encoded and stored in succession. In this operation, the number of recordable images is calculated from the amount of codes of the image recorded immediately before and the empty capacity of the recording medium, and the decreased number of recordable images is displayed, in the present embodiment, in succession in the view finder. However such display need not necessarily be made in the view finder. The details of the steps S21, S23 in Fig. 3 are shown in Fig. 4. The sequence shown in Fig. 4 is conducted after the step S23 in Fig. 3, namely storage of the image data in the memory 4. Referring to Fig. 4, the image signal stored in the memory 4 is read and compression encoded in the encoding circuit 5, and thus compression encoded data are counted by the counting circuit 16 (S41). Then the amount of the compressed codes is compared with the empty capacity of the recording medium in the recording unit 6 (S43), and, if there is an enough empty capacity, a gate 18 is so controlled as to read the image signal again from the memory 4, to effect the compression encoding and to send the data to the recording unit 6 for recording. In this case the control unit 7 instructs the image memory to effect the readout of the image data, the compression encoding circuit 5 to release the compressed codes, the recording unit 6 to record the compressed codes, and the gate 18 to open the gate. It also designates the physical address and the data length on the medium for each recording unit to the recording unit 6 thereby recording the compressed codes. Unless a recording command is given by the control unit 7, the recording unit 6 does not request the data output from the compression encoding circuit 5, so that the function of said circuit 5 and the image memory 4 is interrupted. Thus the control unit 7 can achieve the recording operation through the control of the functions of the compression encoding circuit 5 and the image memory 4, by designating the physical address and the data length on the recording medium for each recording unit according to the filing format, to the recording unit. The recording operation is completed when all the compressed codes are recorded. Fig. 2 shows the communication protocol between the control unit 7 and the recording unit 6. In Fig. 2, there are shown a data output request signal D-Req from the recording unit 6 to the control unit 7, a signal D-Ack supplied from the control unit 7 to the recording unit 6 and indicating that the data from the compression encoding circuit 5 to the recording unit 6 are effective; and 8-bit parallel output data D0 - D7 supplied from the compression encoding circuit 5 to the recording unit 6. Fig. 2 shows the output of data of one byte each, through the exchange of signals D-Req and D-Ack between the control unit 7 and the recording unit 6. Referring to Fig. 2, the data receiver (namely recording unit 6) shifts the signal D-Req from the high level state to the low level state, thereby requesting the data transmitter (namely encoding circuit 5) to release the data. Detecting the low level state of said signal D-Req, the data transmitter release the data on the data bus (D0-D7), and shifts the signal D-Ack from the high to the low level state when the values of said data are fixed. The data receiver fetches the signals on the data bus when the signal D-Ack is shifted to the low level state, and returns the signal D-Req to the high level state. The data transmitter terminates the data output to the data bus when the signal D-Req is shifted to the high level state, and returns the signal D-Ack to the high level state. The data transfer is thus conducted by matching the function of the transmitter and the receiver through the above-explained hand-shake communications of the signals Req and Ack. Consequently the compression encoding circuit 5 need not generate the compressed codes with a fixed transfer rate, and the eventual variation in the code length depending on the image does not cause any inconvenience. Now referring to Fig. 4 again, if the sequence proceeds from the step S43 to a step S47, the control unit causes the display unit 10 of the man-machine interface 8 to display that the recording operation is not possible because of an insufficient empty capacity of the recording medium, thereby requesting the user to select either one of the following three options: (1) to interrupt the recording operation; (2) to exchange the recording medium; and (3) to erase one of the image files in the currently mounted recording medium. For this purpose the control unit 7 executes the steps S49, S51 and S53. If the option (1) is selected by the user, all the functions are interrupted from the step S49. If the option (2) is selected by the user, namely if the recording unit 6 detects the replacement of the recording medium and informs the control unit 7 of that effect, the sequence returns to the step S43. If the option (3) is selected by the user, the control unit 7 displays the number of recorded images on the display unit 10 (S55), and requests the user to enter the sequential number of the image to be erased. In response to the entry by the user of the number of the image to be erased with the operation switches (S57), the control unit 7 erases the corresponding image file (S59) and the sequence returns to the step S43. The replacement of the recording medium may be mechanically detected by the recording unit as disclosed in the Japanese Laid-open Patent Sho 61-182669. The control unit 7 can make access to the information on the presence of such replacement through the recording unit 6. The above-explained control shown in Fig. 4 can ensure image recording to the user, even with a compression method with codes of variable length, thereby proving a system of improved convenience of use and still capable of guaranteeing the image quality. Now reference is made to Fig. 5 for explaining the method of displaying the number of recordable images, executed in the steps S11, S13 in Fig. 3. The control unit 7 releases a command for detecting the empty capacity, thereby causing the recording unit 6 to count the empty capacity of the recording medium (S61), and calculates the number of images recordable on the recording medium, from said empty capacity and the pre-stored representative value of the compression rate of the variable length encoding method (S63). As an example, a variable length encoding method disclosed in the Japanese Laid-open Patent Sho 63-124680 provides a code length of bit/pixel in average or 4.5 bit/pixel at longest. Thus a step S65 displays, on the display unit 10, a standard number of recordable images calculated from the average code length of 2 bit/pixel, and a minimum guaranteed number of recordable images calculated from 4.5 bit/pixel. Naturally it is possible to display only either of said numbers. The display device 10 is composed for example of a liquid crystal display (LCD) or light-emitting diodes (LED), and can provide display in the upper part of the apparatus and/or in the view finder. The above-explained embodiment provides a digital image recording apparatus employing variable length encoding, provided with means for counting the empty capacity of the recording medium and capable of storing the representative amount of compressed codes in variable length encoding, thereby calculating the number of images recordable on the recording medium from said calculated empty capacity and said representative amount, and further provided with means for displaying the calculated number of recordable images, thereby displaying a standard number and/or a minimum guaranteed number of images recordable on said recording medium. Also in the above-explained embodiment, the empty capacity of the recording medium is detected not only in the step S1 in Fig. 3 but also in the steps S11, S13 of which details are shown in Fig. 5. Thus said empty capacity can be confirmed not only when the switch SW1 is closed but also in a continuous recording operation. Also the present embodiment can improve the convenience of use and still can guarantee the image quality even with a variable length encoding method, since the amount of recorded images or the number of images recordable on the recording medium can be guaranteed and informed to the user. Also in the present embodiment, the amount of encoded data is calculated, prior to the recording operation by the recording unit 6, by actual variable length encoding of the image signal which is obtained by photoelectric conversion of the object image and stored in the memory 4, but the present invention is not limited to such embodiment and said amount of encoded data may be obtained without actual variable length encoding. Therefore the prediction of data amount from a simplified encoding is also included in the present invention. Also the control unit 7 for executing the sequence shown in Fig. 4 controls said memory 4 according to the comparison of thus generated signal and said data amount. As explained in the foregoing, the present embodiment controls means for storing in advance the information to be stored in the recording medium, according to the comparison of the empty capacity of said recording medium and the amount of encoded data to be recorded, and can therefore continue the storage of said information in said storage means, if necessary. Also the present embodiment allows to know in advance the number of recordable images. Also as explained in the foregoing, the present embodiment generates a value corresponding to the amount of variable length data by conversion of the object image prior to the recording operation by the recording unit, so that certain measures can be taken in advance if the recording operation is impossible due to an excessively large amount of encoded data. The variable length compression encoding in the present embodiment may be conducted in other various encoding methods. For example there may be employed an entropy encoding on the DCT encoded data. There may be employed any encoding method as long as fixed length compression encoding and variable length compression encoding can be switched, so that both encodings need not be conducted by a same method. In the present embodiment the recording unit 6 is composed of a data memory device controlled by an MS-DOS system, but there may also be employed other media, such as a semiconductor memory or a tape-shaped medium. If the recording medium is composed of a floppy disk of vertical recording type, a capacity of 5 M Bytes can be sufficiently provided with a diameter of 2 inches. In such case the present embodiment can guarantee the recording of 55 television field images at standard or 22 images at minimum. In the present embodiment, the control unit 7 sends the commands to the recording unit 6 for obtaining the information on the empty capacity of the memory means, but the control unit 7 may directly detect the unrecorded area of the memory means, namely an unrecorded area for example on a tape. Though the foregoing embodiment has been limited to so-called still video apparatus for recording still images on a recording medium, the present invention is not limited to such embodiment and is likewise applicable to a facsimile apparatus, an electronic image file or the like.

Claims: An image recording method for use with an image recording apparatus comprising an image pickup device (2), a holding means (4) for holding image data generated by said image pickup device (2), variable-length coding means for encoding said image data to produce encoded data, storing means (6) for storing said encoded data and display means (10) for displaying information to a user, the method comprising the steps of: generating image data in the image pickup device (2); holding said image data in the holding means (4) in unencoded form; generating an amount signal indicating an amount of encoded data to be obtained when said image data held in said holding means (4) is variable-length encoded; generating information relating to a recordable capacity of said storing means (6); characterised by the steps of: comparing said information relating to recordable capacity with said amount signal; and either: variable-length encoding said image data and storing said encoded image data in said storing means (6) if the amount of encoded data does not exceed the recordable capacity; or if the amount of encoded data exceeds the recordable capacity, holding said unencoded image data in said holding means (4) and indicating the insufficiency of capacity on said display means (10). An image recording apparatus comprising: an image pickup device (2) for generating image data; a holding means (4) for holding image data generated by said image pickup device (2) in unencoded form; variable-length coding means for encoding said image data to produce encoded data; storing means (6) for storing said encoded data; display means (10) for displaying information to a user; and controlling means (7) for controlling said holding means and said storing means (6) and said display means (10), wherein said controlling means is operable to generate an amount signal indicating an amount of encoded data to be obtained when said image data held in said holding means (4) is variable-length encoded, and to generate information relating to a recordable capacity of said storing means (6), and to compare said information relating to recordable capacity with said amount signal, and either: to cause said variable-length coding means to encode said image data, and to store said encoded data in said storing means (6) if the amount of encoded data does not exceed the recordable capacity; or if the amount of encoded data exceeds the recordable capacity, to cause said holding means (4) to hold said unencoded image data and to indicate the insufficiency of capacity on said display means (10).

Inventors: KOSUGI MASATO, YAMAGAMI TAKU, KOSUGI, MASATO, YAMAGAMI, TAKU
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: H04N1
IPC codes: H04N5, H04N7, H04N9, H04N1