Patent Publication Number: US-7218343-B2

Title: Image sensing apparatus using a non-interlace scanning type image sensing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a divisional application under 37 C.F.R. §1.53(b) of U.S. patent application Ser. No. 08/736,259, filed on Oct. 24, 1996 now U.S. Pat. No. 6,611,286, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an image sensing apparatus and, more particularly, to an image sensing apparatus, using a non-interlace scanning type image sensing device, capable of encoding image data obtained by the image sensing device in accordance with movement of an object sensed, and outputting a smooth moving image when reproducing image data recorded on a recording medium. 
     Recently, a non-interlace scanning type image sensing device capable of sequentially reading signals of all the pixels has been developed with the progress of semiconductor manufacturing technique. 
     The non-interlace scanning type image sensing device has an advantage in that a higher resolution image can be obtained with less blurring than an image sensed by using a conventional interlace scanning type image sensing device even when sensing a moving object. 
     In the interlace scanning type image sensing device, a frame image is composed of two field images which are sensed at different times, usually at a field period interval. Accordingly, there is a problem in which, when sensing a fast moving object, there are notches on edges of the object and perhaps of the background in a frame image because of the time gap between the two field images composing a frame image. 
     If a frame image is made of image data of a single field image to overcome the aforesaid problem, there would not be notches on edges, however, since the amount of image information in the vertical direction is halved compared to a frame image composing of two field images, the vertical resolution of the obtained frame image is also halved. 
     In contrast, with a non-interlace scanning type image sensing device, it is possible to sense a frame image in the same time period as that for sensing a field image by an interlace scanning type image sensing device, thus, the above problem does not arise. By taking this advantage of the non-interlace scanning type image sensing device, it is applied to a still image camera and an input device for use with a computer, for example. 
     Further, in a still image output device, such as a video printer, which has rapidly spread in the market in these days, a user can arbitrary pick up a desired scene out of images which are sensed as a moving image. Accordingly, there is a demand to use the non-interlace scanning type image sensing device as an image sensing unit of a video camera capable of sensing both a moving image and a still image. 
     When a non-interlace scanning type image sensing device is used as an image sensing unit of a video camera capable of sensing both a moving image and a still image, as described above, a couple of methods for generating moving image signals can be considered. 
     A case where a non-interlace scanning type image sensing device is used in a digital video camera of NTSC standard, as shown in  FIG. 7 , will be explained as an example. A non-interlace scanning type image sensing device  1  has a structure to output signals by two channels, and each channel always outputs either image signals of even lines or image signals of odd lines of the non-interlace type image sensing device  1 . 
     Further, in  FIG. 7 , image signals of the even lines and odd lines are alternatively outputted from each channel of the non-interlace scanning type image sensing device  1  in each field period in accordance with timing signals generated by a timing signal generator (TG)  15 . For example, referring to one of the two output channels, when image signals of even lines are outputted from one of the channel in a given field period, image signals of odd lines are outputted in the next field period, then image signals of even lines are outputted in the following field period. Image signals read out from the non-interlace scanning type image sensing device  1  are respectively inputted to correlated double sampling (CDS) circuits  201  and  202 . The signals outputted from the CDS circuits  201  and  202  are inputted to automatic gain controllers (AGCs)  301  and  302 , thereafter enter analog-digital (A/D) converters  401  and  402 , respectively. 
     Then, after the analog signals are converted into digital signals by the A/D converters  401  and  402 , enter a camera signal processing circuit  5 . The camera signal processing circuit  5  performs signal processes, such as color separation, edge enhancement, and color correction, after the image data of the even lines and odd lines are applied with dot sequential processing. 
     After the aforesaid processes are completed, the camera signal processing circuit  5  divides a frame image, and image data of one field (e.g., image data of even lines) is outputted from the first channel ch 1 , and image data of the other field (e.g., image data of odd lines) is outputted from the second channel ch 2 . Similarly, for the next frame image, image data of alternate fields are outputted from the first and second channels ch 1  and ch 2 . For example, image data of odd lines is outputted from the first channel ch 1 , and image data of even lines is outputted from the second channel ch 2 . 
     The non-interlace scanning type image sensing device  1  can generate a frame image in one field period, however, a recording device (e.g., a digital VTR) can record only a field image in one field period. 
     Accordingly, as shown in  FIG. 8A , by using either the image signals outputted from the first channel ch 1  or the image signals outputted from the second channel ch 2 , an image of a single field is outputted in each field period (a mode for performing the aforesaid operation is called “field image sensing mode”, hereinafter). 
     Referring to  FIG. 8A , the camera signal processing circuit  5  sequentially writes field image data of a first frame image # 1  and of a second frame image # 2  outputted from the first channel ch 1  to a first frame memory  601  in the first and second field periods in accordance with a control signal C 1 . 
     Meanwhile, if image data is written in a second frame memory  602 , the image data of one previous frame period is sent to an encoding processing circuit  7  in accordance with a control signal C 2 . In the encoding processing circuit  7 , the image data is applied with processes, such as discrete cosine transform (DCT) and shuffling, thereafter, stored in a magnetic tape  9  by a recording head  8  as digital image signals in a recording method complying with a format. 
     After image data of one frame is written in the first frame memory  601 , the camera signal processing circuit  5  sequentially writes field image data of the third frame image # 3  and of the fourth frame image # 4  outputted from the first channel ch 1  to the second frame memory  602  in the third and fourth field periods in accordance with the control signal C 2 . 
     Meanwhile, the image data of one previous frame period is sent to the encoding processing circuit  7  in accordance with a control signal C 2 . In the encoding processing circuit  7 , the image data is applied with the same processes as described above, thereafter, stored in the magnetic tape  9  by the recording head  8  as digital image signals in the recording method complying with the format. 
     The image signals which are recorded as above is processed as shown in  FIG. 8B  when they are reproduced. First, the image signals read from the magnetic tape  9  by the read head  10  are sent to a decoding processing circuit  11  in the first and second field periods, and applied with signal processes, such as inverse discrete cosine transform (I-DCT) and de-shuffling. Thereafter, the image signals are written to a third frame memory  121  in accordance with a control signal C 3 . 
     Meanwhile, if image data is written in a fourth frame memory  122 , the decoding processing circuit  11  reads image data from the fourth memory  122  in accordance with a control signal C 4 , and reproduces an image by an even line field and an odd line field separately. 
     In the third and fourth field periods, the image signals read from the magnetic tape  9  by the read head  10  are transmitted to the decoding processing circuit  11  where the image signals are applied with the I-DCT, deshuffling, and so on, then written to the fourth frame memory  122 . 
     Meanwhile, the decoding processing circuit  11  reads image data from the third memory  121  in accordance with the control signal C 3 , and reproduces an image of the even line field and the odd line field separately. 
     In the decoding processing circuit  11  used in the aforesaid conventional example, image signals outputted from the first channel ch 1  and the second channel ch 2  are of the even line field and the odd line field of the non-interlace scanning type image sensing device  1 , shown in  FIG. 10 . Therefore, the field image sensing mode can be used for moving image sensing operation. 
     However, according to the aforesaid example, the vertical resolution is about the same as that of a conventional image sensing device which outputs image data after adding charges stored in two adjacent pixels in the vertical direction. Accordingly, when outputting an image of a moving object obtained by using the non-interlace scanning type image sensing device  1  in the field image sensing mode as a still image from a video printer, or the like, only a poor still image can be obtained because of blurring. 
     Thus, as a method of effectively using an advantage of the non-interlace scanning type image sensing device, i.e., to output a frame image in a field period, the one shown in  FIG. 9A  has been suggested. 
     In this case, the camera signal processing circuit  5  writes field image data of the even line field of the frame image # 1  outputted from the first channel ch 1  and field image data of the odd line field of the frame image # 1  outputted from the second channel ch 2  to the first frame memory  601  in the first and second field periods, respectively, in accordance with the control signal C 1 . 
     Then a frame image # 2  sensed in the second field period is not stored, and the first frame image sensed in the first field period is used as a moving image of a frame period (this image sensing operation is called “frame image sensing mode”, hereinafter). 
     Meanwhile, if image data has been written in the second frame memory  602 , the image data of one previous frame is sent to the encoding processing circuit  7  in accordance with the control signal C 2  and processed with DCT, shuffling, and so on. Thereafter, the processed image data is recorded as digital image signals on the magnetic tape  9  by the recording head  8  in a recording method complying with a format. 
     When image data of a single frame is written in the first frame memory  601 , the camera signal processing circuit sequentially writes even line field image data of the third frame image # 3  outputted from the first channel ch 1  and odd line field image data of the third frame image # 3  outputted from the second channel ch 2  to the second frame memory  602  in the third and fourth field periods in accordance with the control signal C 2 . 
     Meanwhile, the image data of one previous frame written in the first frame memory  601  is send to the encoding processing circuit  7  where it is applied with the same processes as described above, then recorded on the magnetic tape  9  by the recording head  8  in a recording method complying with a format as digital image signals. 
     The image signals recorded as described above are applied with processes as shown in  FIG. 9B  when they are reproduced. First, the image signals read from the magnetic tape  9  by the read head  10  are transmitted to the decoding processing circuit  11  where they are processed with I-DCT, deshuffling, and so on. Then, the image signals are written to the third frame memory  121  in accordance with the control signal C 3  in the first and second field periods. 
     Meanwhile, if image data is written in the fourth frame memory  122 , the decoding processing circuit  11  reads image data from the fourth memory  122  in accordance with the control signal C 4 , and reproduces an image by an even line field and an odd line field separately. 
     In the third and fourth field periods, the image signals read from the magnetic tape  9  by the read head  10  are transmitted to the decoding processing circuit  11  where they are applied with the I-DCT, deshuffling, and so on. Thereafter, the images are written to the fourth frame memory  122  in accordance with the control signal C 4 . 
     Meanwhile, the decoding processing circuit  11  reads image data from the third memory  121  in accordance with the control signal C 3 , and reproduces an image using the even line field and the odd line field separately. 
     In this method, it is possible to store an image of high resolution without blurring when sensing a moving object. Therefore, the method can be used when sensing a still image. However, when the stored image data is reproduced as a moving image, image data of fields as shown in  FIG. 9B  is outputted, thus the displayed image is of frame images sensed in frame period. In this method, therefore, it is possible to obtain an image of high resolution, however, when the image data of a faster moving object is reproduced as a moving image, for example, the displayed image has gaps in time and only a poor moving image can be obtained. 
     The present invention is addressed to solve this problem. 
     Further, as the digital signal processing technique improves, many image sensing apparatuses adopting digital recording and reading technique in the recording and reproducing unit have been proposed. In these image sensing apparatuses, image signals are compressed and encoded as well as modulated to a format suitable for digital recording in a recording unit, then recorded in a data storage medium. Further, when reproducing image signals, read data is demodulated and decoded in a process in opposite to the recording process, then outputting reproduced image signals. 
       FIG. 11  is a block diagram illustrating a configuration of a conventional image sensing apparatus. In  FIG. 11 , reference numeral  501  denotes an image sensing unit whose focus, zoom ratio, and iris diaphragm, and so on, are controlled by an image sensing controller  503 , and which generates known digital standard image data S 1   p , such as parallel data conforming with SMPTE (Society of Motion Picture and Television Engineers) 125M. 
     A block division unit  502  divides the digital image data S 1   p  into blocks consisting of a plurality of pixels, further applies processes, such as shuffling and noise reduction, on the divided digital image data. 
     The image data S 2   p  divided into a plurality of blocks by the block division unit  502  is provided to a motion detector (MD)  505 . 
     The MD  505  generates information S 3   p  on movement of image data on the basis of the input image data S 2   p  and outputs it to a system controller  509 . The MD  505  detects movement in an image by detecting differences between field image data of each image blocks. 
     Reference numerals  506  and  507  denote discrete cosine transform (DCT) units which compress information by using correlation between neighboring pixels of the image data. The first DCT unit  506  performs DCT on image data by an area, e.g., 8×8 pixel block, of a frame image. 
     Further, the second DCT unit  507  performs DCT on image data by an area, e.g., by 8×4 pixel block, of an odd line field image, and 8×4 pixel block of an even line field image. 
     The system controller  509  outputs a switching signal S 4   p  in accordance with information on movement, thereby controls a switch  508  to switch between the first DCT unit  506  and the second DCT unit  507 . 
     Here, in a case where no movement is detected in the block image data S 2   p , in other words, movement determination information S 3   p  shows “not moving”, the switch  508  switches to the terminal  508   a . In contrast, in a case where movement is detected in the block image data S 2   p , i.e., the movement determination information S 3   p  shows “moving”, the switch  508  switches to the terminal  508   b . Thus, DCT processes can be switched for a frame image and for a field image in accordance with the movement determination information S 3   p.    
     In a case where there is a large movement in the block image data S 2   p , since correlation between fields is low, vertical components of the DCT coefficients reach high frequency range if an image is processed as a frame image, and encoding efficiency drops extremely. 
     Therefore, when the movement determination information S 3   p  shows “moving”, it is controlled so that odd line field image data and even line field image data are separately applied with orthogonal transformation. As described above, by properly switching the DCT between the one for a frame image and the one a field image in accordance with a state, “moving” or “not moving” shown by the movement determination information S 3   p , effective encoding is performed. 
     Data S 5   p  processed with the DCT by the first DCT unit  506  or the second DCT unit  507  is quantized by a quantization unit  510 . Processes at each step of quantization are adjusted in accordance with the precision of the image data, and an image of low frequency is quantized closely, whereas an image of high frequency is quantized roughly. 
     This is because distinguishable ability of human eyes is keen for an image of low frequency, in contrast, it is dull for an image of high frequency. Therefore, by quantizing image data of low frequency range closely and image data of high frequency range roughly, distortion of an image caused by the quantization is concentrated on the high frequency components, thereby reducing deterioration of a visual image quality. 
     An encoding unit  511  scans the block data arranged in two dimension in zig-zag scanning from the low space frequency portion to the high space frequency portion to obtain linear data, encodes zero coefficients by run-length coding and non-zero coefficients by two dimensional Huffman coding into variable length codes, then outputs encoded data S 6   p.    
     In the run-length coding, image data is applied with lossless compression in accordance with a zero-run count. In the Huffman coding, short codes are assigned to data whose occurrence probability is high, whereas long codes are assigned to data whose occurrence probability is low, thereby shortening the total code length. 
     A flag controller  512  is for generating a system information flag S 7   p  used when writing information outputted from the system controller  509  to a recording medium. 
     In an image sensing apparatus adopting digital recording and reading technique, not only a moving image but also a still image can be recorded in high precision. Further, it is possible to record a still image of high precision (still image recording mode) while recording a moving image (moving image recording mode) depending upon an image sensing mode. 
     The conventional image sensing apparatus as described above determines movement based on correlation of block image data between fields, a proper DCT method performed by frame or by field is selected on the basis of the detected result. 
     However, upon sensing and recording a still image of high precision by using a progressive or non-interlace scanning type CCD, since information on the vertical resolution of the image contains higher frequency components than that of an image sensed by using an interlace scanning type CCD, it becomes very difficult to determine movement. For example, when a fine stripe pattern is in an image and differences between even line field data and odd line field data of the image are calculated to be used for detecting movement, since the differences between the field data would be large because of the high vertical resolution, there would be more chance for the image to be misjudged as a moving image. Accordingly, there are more cases in which a still image is misjudged as a moving image, thereby encoding efficiency drops. 
     The present invention is also addressed for solving the above problem. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of aforesaid situation, and has as its object to obtain a moving image of natural movement and of high resolution even in a case where frame images are recorded by using a non-interlace or progressive scanning type image sensing device. 
     According to the present invention, the foregoing object is attained by providing an image sensing apparatus which has a reproduction function comprising: 
     image sensing means for generating image signals by sequentially reading all the pixels of the image sensing means in non-interlace scanning in one field period; camera signal processing means for generating first image signals and second image signals based on television signal standard; output signal selection means for selecting the first image signals or the second image signals outputted by the camera signal processing means; signal recording means for recording a type signal showing a type of the image signals selected by the output signal selection means in a sub-cord recording area of a recording medium; 
     an interpolation filter for interpolating image data between consecutive images sensed at different times; and interpolation filter control means for controlling whether or not to perform interpolation of image data using the interpolation filter, wherein, when the type signal recorded in the sub-cord recording area indicates a frame image sensing mode in which frame images are sensed in every other field period and the first image signals are recorded in a given field period and the second image signals are recorded in the next field period, and when the sensed image signals are to be outputted as a moving image, the interpolation filter control means controls the interpolation filter to perform interpolation of image data. 
     According to the aforesaid configuration, when a moving image is sensed in the frame image sensing mode which is essentially suitable for still image sensing, by interpolating field images between consecutive frame images sensed at different times, it is possible to make a moving image continue smoothly. Therefore, if all the recorded image data is of still frame images, it is possible to display it as a moving image of high resolution continuing naturally. 
     It is another object of the present invention to prevent drop of coding efficiency caused by misdetection of movement in a still image when coding the still image of high precision obtained by non-interlace scanning. 
     According to the present invention, the foregoing object is attained by providing an image sensing apparatus comprising: image sensing means for generating image signals by sequentially reading all the pixels of the image sensing means in non-interlace scanning in one field period; image sensing mode selection means for selecting an image sensing mode performed by the image sensing means out of a plurality of image sensing modes; and movement determination means for performing movement determination processes in accordance with the image sensing mode selected by the image sensing mode selection means. 
     With the aforesaid configuration, upon sensing an image by using an image sensing device which sequentially outputs signals generated at each pixel without adding the signals, movement is detected in accordance with the image sensing mode, i.e., a moving image sensing mode or a still image sensing mode. Thereby, it is possible to reduce a chance to misdetect the movement in a still image caused by different features between the moving and still image sensing modes. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram showing main functions of an image sensing apparatus according to the first embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a configuration of the image sensing apparatus according to the first embodiment of the present invention; 
         FIG. 3  is an explanatory view showing an operation of the image sensing apparatus according to the first embodiment; 
         FIG. 4  is a block diagram illustrating a configuration of an image sensing apparatus according to the second embodiment of the present invention; 
         FIG. 5  is a block diagram illustrating an example of a configuration of movement detector; 
         FIG. 6  is a block diagram illustrating another example of a configuration of movement detector; 
         FIG. 7  is a block diagram illustrating a configuration of a conventional image sensing apparatus; 
         FIGS. 8A and 8B  are explanatory views showing operations of the conventional image sensing apparatus; 
         FIGS. 9A and 9B  are explanatory views showing operations of the conventional image sensing apparatus; 
         FIG. 10  is an explanatory view showing outputs from a non-interlace scanning type image sensing device; 
         FIG. 11  is a block diagram illustrating a configuration of a conventional image sensing apparatus; 
         FIG. 12  is a flowchart showing an operation of image reproduction performed by the image sensing apparatus according to the first embodiment of the present invention; 
         FIG. 13  is a flowchart showing an operation of the movement detector according to the second embodiment of the present invention; and 
         FIG. 14  is a flowchart showing an operation of another movement detector according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail in accordance with the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a block diagram illustrating a brief configuration of an image sensing apparatus according to the first embodiment of the present invention. In  FIG. 1 , reference numeral  1001  denotes an image sensing unit;  1002 , a camera signal processing unit;  1003 , an output signal selection unit;  1004 , a signal recording unit;  1005 , a recording medium;  1006 , a signal reading and reproduction unit;  1007 , an interpolation filter; and  1008 , an interpolation filter controller. 
     The image sensing unit  1001  has a non-interlace scanning type image sensing device, and sequentially reads out signals of each pixel and generates image signals. 
     The camera signal processing unit  1002  generates first image signals and second image signals conforming to television standard from the image signals outputted from the image sensing unit  1001 . 
     The output signal selection unit  1003  selects either the first image signals or the second image signals outputted from the camera signal processing unit  1002  to be recorded. 
     The signal recording unit  1004  records the type of the image signals selected by the output signal selection unit  1003  in a sub-cord recording area (not shown) of the recording medium  1005  as a sub-cord signal. 
     The signal reading and reproduction unit  1006  reads signals recorded on the storage medium  1005  and applies predetermined signal processes on them, and outputs the reproduced image signals to the interpolation filter  1007  as well as outputs the sub-cord signal stored in the sub-cord recording area to the interpolation filter controller  1008 . 
     A signal recorded in the sub-cord recording area of the recording medium  1005  is either of the following two types: one is the field image sensing mode in which, out of image signals of a frame image obtained in a field period, image signals corresponding to the even line field or the odd line field of the image sensing unit  1001  are recorded in a field period; or the other is the frame image sensing mode in which, out of image signals of a frame image obtained in a field period, image signals corresponding to the even line field or the odd line field of the image sensing unit  1001  are recorded in a given field period and image signals corresponding to other field are recorded in the next field period. 
     The interpolation filter  1007  is for interpolating field images between consecutive frame images sensed at different times in accordance with the sub-cord signal stored in the sub-cord area of the recording medium  1005 . 
     The interpolation filter controller  1008  controls the ON and OFF state of the interpolation filter  1007  in accordance with the sub-cord signal stored in the subcord recording area of the recording medium  1005 . 
     Referring to  FIG. 12 , a brief operation of reproduction performed by the image sensing apparatus having the aforesaid configuration will be explained below. First at step S 21 , image signals and sub-cord signal stored in the recording medium  1005  are read out. When moving image output is requested (YES at step S 22 ), the process proceeds to step S 23 . If the sub-cord signal shows the frame image sensing mode (NO at step S 23 ), the interpolation filter  1007  is turned ON and field images are interpolated between consecutive frame images sensed at different times (this operation will be explained later in detail) (step S 24 ). Whereas, if the sub-cord signal shows the field image sensing mode (YES at step S 23 ), the interpolation filter  1007  is turned OFF (step S 25 ). In contrast, when still image output is designated, regardless of which image sensing mode the sub-cord signal shows, the interpolation filter  1007  is turned off (step S 25 ). 
     According to the image sensing apparatus having the aforesaid configuration, when images are sensed in the frame image sensing mode which is basically a mode for sensing a still image, it is possible to output the recorded images as a smooth and continuous moving image by interpolating field images between consecutive frame images sensed at different times by the interpolation filter  1007 . 
     Thus, if all the image data recorded on the recording medium  1005  is of frame still images, it is possible to reproduce a moving image of high resolution which moves naturally. 
     Note, in a domestic use digital TVR standard, a moving image mode and a still image mode are set, and these modes can be distinguished from each other when reproducing recorded images by recording a signal showing whether a still image is recorded or a moving image is recorded when recording images on a recording medium (e.g., a magnetic tape). Thus, the sub-cord signal is merely for distinguishing either the still image mode or the moving image mode when reproducing the image signals. 
     A more detailed configuration and operation of the image sensing apparatus according to the first embodiment of the present invention will be described with reference to drawings. 
       FIG. 2  is a block diagram showing a configuration of the image sensing apparatus of the first embodiment. In  FIG. 2 , the same units and elements as those in  FIG. 7  showing the conventional image sensing apparatus are referred by the same reference numerals and explanation of those are omitted. The non-interlace scanning type image sensing device  1  has a structure to output signals by two channels, and each channel always outputs either image signals of even lines or image signals of odd lines of the non-interlace type image sensing device  1 . Further, the recording and reproducing unit is a digital VTR, for instance. 
     The image signals of the even lines and odd lines are alternatively outputted from each channel of the non-interlace scanning type image sensing device  1  in each field period in accordance with timing signals generated by the TG  15 . Image signals read out from the non-interlace scanning type image sensing device  1  are respectively inputted to the correlated double sampling (CDS) circuits  201  and  202 . These CDS circuits  201  and  202  perform correlated double sampling for removing a clock and reset noises from the image signals outputted from the non-interlace scanning type image sensing device  1 . 
     The image signals applied with predetermined signal processes by the CDS circuits  201  and  202  enter the AGCs  301  and  302  where their gains are controlled. Thereafter, the image signals enters the A/D converters  401  and  402  where the image signals are converted into digital signals. 
     The camera signal processing circuit  5  receives the digital signals from the A/D converters  401  and  402 , in turn, performs point sequential operation on the even line field image signals and odd line field image signals, further performs signal processes, such as color separation, edge enhancement, and color correction. 
     A signal selection circuit  14  selects whether the image data to be transmitted to the encoding processing circuit  7  is of signals sensed in the field image sensing mode or signals sensed in the frame image sensing mode in accordance with an image sensing mode set by a mode switch (not shown). Further, the signal selection circuit  14  transmits a control signal S 1  to the camera signal processing circuit  5 . At the same time, the signal selection circuit  14  generates a sub-cord signal S 2  and outputs it to the encoding processing circuit  7 . 
     The control signal S 1  is transmitted to be used for selecting processes, either processes for the frame image sensing mode or processes for the field image sensing mode, performed by the camera signal processing circuit  5  in the first embodiment. Detailed explanation of the control signal S 1  is omitted here. 
     When both the control signal S 1  and the sub-cord signal S 2  show the field image sensing mode, the processes in field image sensing mode which are explained with reference to  FIGS. 8A and 8B  are performed. Therefore, the explanation of the processes are omitted here. 
     Further, when both the control signal S 1  and the sub-cord signal S 2  show the frame image sensing mode, in the recording operation, the processes in the frame image sensing mode explained in the background of the invention with reference to  FIG. 9A  are performed, and the explanation of the processes are omitted. 
     The image signals recorded as shown in  FIG. 9A  are processed as shown in  FIG. 3  upon reproducing the images when the control signal S 1  and the sub-cord signal S 2  indicate the frame image sensing mode and the recorded images are to be reproduced as a moving image. 
     First, image signals obtained from the magnetic tape  9  by the read head  10  are transmitted to the decoding processing circuit  11  where the signals are applied with I-DCT, deshuffling, and so on, in the first and second frame periods, then written to the third frame memory  121  in accordance with the control signal C 3 . 
     Meanwhile, if image data is written in a fourth frame memory  122 , the decoding processing circuit  11  reads image data from the fourth memory  122  in accordance with the control signal C 4 , and reproduces an image by an even line field and an odd line field separately. 
     In the third and fourth field periods, the image signals read from the magnetic tape  9  by the read head  10  are transmitted to the decoding processing circuit  11  where the image signals are applied with the I-DCT, deshuffling, and so on, then written to the fourth frame memory  122 . 
     Meanwhile, the decoding processing circuit  11  reads image data from the third memory  121  in accordance with the control signal C 3 , and reproduces an image of the even line field and the odd line field separately. 
     A linear interpolation circuit  13  receives the image signals reproduced as described above, and controls the ON and OFF state of the interpolation filter which interpolates field images between consecutive frame images sensed at different times in accordance with a control signal S 3 . In the example shown in  FIG. 3 , a reproduced image signal is first outputted in the third field period. In this field period, the interpolation filter is turned OFF in accordance with the control signal S 3 , and even line field image data of the frame image # 1  is outputted sequentially from the third frame memory  121 . 
     In the fourth field period, the interpolation filter is turned ON in accordance with the control signal S 3 , and the linear interpolation circuit  13  generates image data interpolated between frame images # 1  and # 3  on the basis of the odd line field image data of the frame image # 1  stored in the third frame memory  121  and the odd line field image data of the frame image # 3  stored in the fourth frame memory  122 . With this interpolation, field image data of a field image which is virtually generated during a time period between the sensing of a given frame image and the next sensing of the frame image (virtual odd line field data, frame image # 2 ). 
     In the fifth field period, the interpolation filter is turned OFF in accordance with the control signal S 3 , and the even line field data of the frame image # 3  are sequentially read from the fourth frame memory  122 . 
     In the sixth field period, the interpolation filter is turned ON in accordance with the control signal S 3 , and the linear interpolation circuit  13  generates image data interpolated between frame images # 3  and # 5  on the basis of the odd line field image data of the frame image # 3  stored in the fourth frame memory  122  and the odd line field image data of the frame image # 5  stored in the third frame memory  122 . With this interpolation, field image data of a field image which is virtually sensed during a time period between when a given frame image is sensed and when the next frame image is sensed (virtual odd line field data, frame image # 4 ). 
     By interpolating field images between consecutive frame images as described above in every other field period, time gaps between images are filled and a moving image looks continuing smoothly. Thus, it is possible to obtain a smooth moving image even though the moving image is reproduced on the basis of still images. 
     Further, in order to output image signals from a video printer as a still image, the linear interpolation circuit  13  controls interpolation filter so as to ignore the control signal S 3 . By doing so, it is possible to output the still image directly. 
     Note, two frame memories are used as image memories for reproducing images in the first embodiment, since it is assumed that deshuffling is performed by frame. Therefore, if deshuffling is performed by field, the image memories can be used only for configuring the interpolation filter, thereby it is possible to configure the image sensing apparatus by using two field memories for reproduction. 
     Further, a linear field interpolated image is generated on the basis of field image data of two consecutive frame images, however, by using image data of a greater number of fields, it is possible to generate a more natural field interpolated image. 
     According to the first embodiment as described above, a sub-cord signal showing whether image signals recorded on a recording medium are sensed in the field image sensing mode or in the frame image sensing mode is recorded in a sub-cord recording area of the recording medium. Therefore, by applying predetermined processes on the image signals reproduced from the recording medium on the basis of the sub-cord signal, it is possible to reproduce a natural moving image of high time resolution. 
     More precisely, an interpolation filter which interpolates field images between consecutive frame images sensed at different times in accordance with the sub-cord signal stored in the sub-cord recording area of the recording medium and an interpolation filter controller for controlling ON/OFF of the interpolation filter are provided, and since the interpolation filter controller turns on the interpolation filter when the sub-cord signal indicates that the frame image sensing mode and a moving image output is requested, it is possible to obtain a natural moving image of high resolution even if all the image data recorded on the recording medium are sensed in the frame image sensing mode which is basically for sensing still image. 
     Second Embodiment 
     A second embodiment of the present invention will be described with reference to drawings. 
       FIG. 4  is a block diagram illustrating a brief configuration of an image sensing apparatus according to the second embodiment of the present invention. 
     In  FIG. 4 , reference numeral  101  denotes an image sensing unit having a so-called progressive or non-interlace scanning type CCD. A focus, zooming ratio, light exposure, and so on, of the image sensing unit  101  is controlled by the image sensing controller  103 , and the image sensing unit  101  outputs known digital standard image signals S 10 , e.g., parallel data conforming with SMPTE (Society of Motion Picture and Television Engineers) 125M. 
     The block division unit  102  divides the digital image data S 10  into blocks consisting of a plurality of pixels, further applies processes, such as shuffling and noise reduction, on the divided digital image data. 
     The image data S 20  divided into a plurality of blocks by the block division unit  102  is provided to a motion detector (MD)  105 . 
     Reference numeral  104  denotes an image sensing mode selector which outputs an image sensing mode signal S 80 , showing whether an image sensing mode performed by using the image sensing unit  101  is a moving image mode or a still image mode, to the MD  105 . The image sensing mode signal S 80  is “H” to indicate the moving image mode and “L” to indicate the still image mode, in the second embodiment. 
     The MD  105  detects differences between fields of a block image on the basis of the input image data S 20 , for example, and determines movement in a block image on the basis of the differences and the image sensing mode signal S 80  inputted from the image sensing mode selector  104 . Further, it generates movement determination information S 30  and outputs it to a system controller  109 . In the second embodiment, when the MD  105  determines that there is movement in the input data S 20 , the movement determination information S 30  is “H”, whereas when the MD  105  determines that there is no movement in the input data S 20 , the movement determination information S 30  is “L”. 
     Reference numerals  106  and  107  denote discrete cosine transform (DCT) units which compress information by using correlation between the image data of neighboring pixels. The first DCT unit  106  performs DCT on image data by pixel block, e.g., by 8×8 pixel block. 
     Further, the second DCT unit  107  performs DCT on image data by pixel block, e.g., by 8×4 pixel block for an odd field and by 8×4 pixel block for an even field. 
     The system controller  109  outputs a switching signal S 40  in accordance with the movement determination information S 30 , thereby controls a switch  108 A to switch between the first DCT unit  106  and the second DCT unit  107 . 
     In the second embodiment, in a case where no movement is detected in the block image data S 20 , i.e., movement determination information S 30  is “L”, the switch  108 A switches to the terminal  108   a . In contrast, in a case where movement is detected in the block image data S 20 , i.e., movement determination information S 30  is “H”, the switch  108 A switches to the terminal  108   b . Thus, DCT processes can be switched between the one for a frame image and the one for a field image in accordance with the movement determination information S 30 . 
     In a case where there is a big movement in the block image data S 20 , since correlation between fields is low, vertical components of the DCT coefficients reach high frequency range if an image is processed as a frame image, and encoding efficiency drops extremely. 
     Therefore, when the movement determination information S 30  is “H”, it is controlled so that odd line field image data and even line field image data are separately applied with orthogonal transformation. As described above, by properly switching the DCT between the one for a frame image and the one a field image in accordance with a state, “H” or “L” shown by the movement determination information S 30 , effective encoding is performed. 
     Image data S 50  processed with the DCT by the first DCT unit  106  or the second DCT unit  107  is quantized by a quantization unit  110 . Processes in each step of quantization are adjusted in accordance with the precision of the image data, and an image of low frequency is quantized closely, whereas an image of high frequency is quantized roughly. 
     The encoding unit  111  scans the block data arranged in two dimensions in zig-zag scanning from the low space frequency portion to the high space frequency portion to obtain linear data, encodes zero coefficients by run-length coding and non-zero coefficients by two dimensional Huffman coding into variable length codes, then outputs encoded data S 60 . 
     In the run-length coding, image data is applied with lossless compression in accordance with a zero-run count. In the Huffman coding, short codes are assigned to data whose occurrence probability is high, whereas long codes are assigned to data whose occurrence probability is low, thereby shortening the total code length. 
     A flag controller  112  is for generating a system information flag S 70  used for writing information outputted from the system controller  109  to a recording medium. 
       FIG. 5  is a block diagram illustrating an example of a configuration of the MD  105 . In  FIG. 5 , reference numeral  203  denotes a field separator which reads block image data from a memory (not shown) and outputs odd line field data S 100  and even line field data S 110 . 
     Reference numeral  205  denotes a subtractor for taking differences between the field data S 100  and S 110 , and it serves as a difference data operator. 
     Reference numeral  205  denotes an absolute value circuit;  206 , an accumulator; and  207 , a determinator. The absolute value circuit  205  and the accumulator  206  consist an absolute field difference value accumulator. 
     Further, the image sensing mode signal S 80  outputted from the image sensing mode selector  104  enters a buffer circuit  208 , and outputted to an AND circuit  209  as an image sensing mode signal S 120 . The AND circuit  209  is provided as movement information generator and outputs the movement determination information S 30  as the image sensing mode signal S 120  and the determination result S 130  from the determinator  207  are inputted. 
     Next, an operation of the MD  105  having the aforesaid configuration will be explained with reference to  FIG. 13 . The image data S 20  which is divided into blocks by the block division circuit  102  is further separated into the odd line field data S 100  and the even line field data S 110  by the field separator  203  (step S 31 ). These field data S 100  and S 110  enter the subtractor  204 . 
     Then, difference data between the even and odd line field data is calculated by the subtractor  204 . The difference data is inputted to the absolute value circuit  205  then to the accumulator  206 , thereby the sum of absolute values of differences between field data of a block image is obtained (step S 32 ). Further, the sum of the absolute values of differences between field data is inputted to the determinator  207  where the sum is compared to a predetermined threshold (step S 33 ). Accordingly, movement in the block image data is determined. 
     As the determination result, when the sum of absolute values of differences between field data is greater than the threshold (YES at step S 33 ), it is determined that there is movement between fields of the block image data. Whereas, if the sum is less than or equal to the threshold (NO at step S 33 ), it is determined that there is no movement between two field image data of the block image. The determined result is outputted to the AND circuit  209  as a determination result information S 130 . 
     Meanwhile, the image sensing mode signal S 80  is delayed for the same time period as that required for determining movement by the buffer circuit  208  which is for delaying the signal, thereafter, outputted to the AND circuit  209  as the image sensing mode signal S 120 . The AND circuit  209  performs logical AND operation on the determination result information S 130  inputted from the determinator  207  and the image sensing mode signal S 120  inputted from the buffer circuit  212 . 
     Then, when the logic value of the image sensing mode signal S 120  is “L”, i.e., when showing the still image mode (NO at step S 34 ), the movement determination information S 30  is outputted as “L” indicating no movement in the block image, regardless of the state of the determination result information S 130 . Whereas, when the logic value of the image sensing mode signal S 12  is “H”, i.e., when showing the moving image mode (YES at step S 34 ), the state of the determination result information S 130  becomes the state of the movement determination information S 30 . 
     Next, a block diagram of other configuration of the MD  105  is shown in  FIG. 6 . Note, the same units and elements as those in  FIG. 5  are referred by the same reference numerals, and explanation of those are omitted. 
     In  FIG. 6 , reference numeral  211  denotes a determinator, and reference numeral  213  and  214  denote thresholds used for movement determination. In the following explanation, the first threshold TH 1  is less than the second threshold TH 2 . 
     Reference numeral  212  denotes a buffer circuit which outputs image sensing mode signal S 120  corresponding to the input image sensing mode signal S 80 . Reference numeral  215  denotes a threshold switch which switches between the first threshold TH 1  and the second threshold TH 2  in accordance with the image sensing mode signal S 120  outputted from the buffer circuit  212 , and selectively outputs either of the thresholds. 
     Next, an operation of the MD  105  will be explained with reference to  FIG. 14 . The image data divided into blocks is further separated into odd line field data S 100  and the even line field data S 110  (step S 41 ), then inputted to the subtractor  204 . 
     The subtractor calculates differences between the two field image data. The calculated differences enter the absolute value circuit  204  then the accumulator  206 , thereby, the sum of the absolute values of differences between field image data of the block image is obtained (step S 42 ). The sum is inputted to the determinator  211  where it is compared to the threshold S 140  which is inputted from the threshold switch  215  (step S 46 ). 
     Meanwhile, the image sensing mode signal S 80  is delayed for the same time period as that required for calculating the sum of the absolute values of differences between field data by the buffer circuit  212 , thereafter, the image sensing mode signal S 120  is outputted to the threshold switch  215 . 
     In the aforesaid threshold switch  215 , when the logic value of the image sensing mode signal S 120  is “H”, i.e., when showing the moving image mode (YES at step S 43 ), the first threshold TH 1  is outputted as the threshold S 140  for determination to the determinator  211  (step S 44 ). 
     On the other hand, when the logic value of the image sensing mode signal S 120  is “L”, i.e., when showing the still image mode (NO at step S 43 ), the second threshold TH 2  is outputted as the threshold S 140  for determination to the determinator  211  (step S 45 ). 
     The determinator  211  compares the sum of the absolute values of differences between field data to the threshold S 140 . If the sum is greater than the threshold S 140  (YES at step S 46 ), then it is determined that there is movement between field image data of the block image (step S 47 ). 
     Further, if the sum is less than or equal to the threshold S 140  (NO at step S 46 ), it is determined that there is no movement between field image data of the block image, then outputs the corresponding movement determination information S 30  (step S 48 ). 
     Here, the first threshold TH 1  is less than the second threshold TH 2 , i.e., the threshold for the still image mode is greater than the threshold for the moving image mode. Accordingly, it is possible to determine movement in the still image mode more precisely. 
     According to the second embodiment as described above, movement determination is performed differently in accordance with the image sensing mode of the image sensing unit, namely, depending upon whether an image is sensed in the moving image mode or the still image mode. Therefore, it is possible to obtain more precise movement determination information with less error in both the image sensing modes, namely, the moving image mode and the still image mode. As a result, it is possible to prevent the encoding efficiency from dropping caused by misdetection of movement especially during encoding a still image of high precision obtained by non-interlace scanning. 
     Further, according to the other advantage of the second embodiment, a threshold used by the movement detector is set in accordance with the image sensing mode, thereby it is possible to record a still image of high precision under the same condition for recording moving image by using limited hardware. 
     The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore to appraise the public of the scope of the present invention, the following claims are made.