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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electronic still camera for recording images
on a semiconductor memory card used as a recording medium.
2. Description of the Related Art
Recently, electronic still cameras which use a solid state imaging device,
such as a charge coupled device (CCD) for photographing still images of
subjects and recording the still images on rotatable magnetic recording
medium, are considered to replace conventional still cameras for
photographing and recording still images by use of the photosensitivity of
photographic films, and they have been merchandised. However, since this
type of electronic still camera uses the rotatable magnetic recording
medium, a driving unit for driving the rotatable magnetic recording medium
relative to the recording head must be provided inside the camera, thus
making it difficult to reduce the size of the camera. A solid state
electronic still camera system for recording image signals on a memory
card using a semiconductor memory has been proposed, as a system which has
no driving unit and is suitable for small sized cameras, by the same
applicant (Minoru Sasaki U.S. application No. 073.160). An example of this
type of electronic still camera is shown in FIG. 13.
An image of the subject is transmitted via lens 121, diaphragm 122 and
color filter 120, formed on CCD 126 used as the imaging device in which
the image is subjected to the photoelectric conversion. An output signal
of CCD 126 is subjected to a predetermined process in pre-processing
circuit 127, converted into a digital signal by means of analog-to-digital
(A/D) converter 128, and then recorded on memory card 115. In this case, a
signal of each picture element of the imaging device is recorded in the
digital form on memory card 115. The signal of each picture element of the
imaging device is subjected to a predetermined process such as
amplification, white-balance correction and .gamma. correction as the
pre-processing noted above. Picture element data which has been subjected
to the pre-processing in a sequence according to the picture element array
is recorded on memory card 115. In the reproduction mode, memory card 115
is set in a reproducing unit, and data stored in memory card 115 is
subjected to a predetermined signal processing and digital-to-analog (D/A)
conversion, and then supplied to a TV (television) monitor which in turn
displays the data as an image. In FIG. 13, case 110, release switch 111,
battery 123 used as a power source, shutter control circuit 124 for
controlling diaphragm 122 and electronic shutter operation, CCD driving
circuit 125, and monitoring unit 130 are also shown. CCD driving circuit
125 is used to control and drive shutter control circuit 124, CCD 126,
pre-processing circuit 127, A/D converter 128 and memory card 115.
Monitoring unit 130 displays the photographed image based on signals
transmitted via pre-processing circuit 127 at the time of photographing
and is used as a view.
As described above, wherein data corresponding to each picture element of
the solid state imaging device is recorded on the memory card, the signal
processing is simple and the device is simple in construction. However, if
the recording conditions, such as the number of picture elements and the
arrangement of color filters of the solid state imaging device of the
electronic still camera, are changed, for example, the arrangement of data
recorded on the memory card will be changed accordingly. Therefore, the
recorded memory card is not interchangeably used for another type of
electronic still camera system, that is, an electronic still camera having
a different number of picture elements and arrangement of color filters
from those of the electronic still camera originally used for recording
the image data on the memory card.
If a single electronic still camera is designed so as to record an image
under different recording conditions, the recorded memory card may be
interchangeably used to some extent. However, in this case, the memory
capacity required for recording one frame of image data of the
photographed still image varies depending on the recording conditions set
at the time of photographing. Therefore, in a case where new image data is
written into a recording area in which one frame of image data has been
recorded and erased, the memory capacity may some sometimes be
insufficient for recording the new image data, thus making it impossible
to record the new image data.
SUMMARY OF THE INVENTION
An object of this invention is to provide a new electronic still camera and
an image recording method by which a memory card recorded by the
electronic still camera of this invention can be used for a desired
reproducing unit for image reproduction, the memory capacity required for
recording one frame of data can be changed as required, the number of
images to be recorded on the memory card can be changed according to the
image quality, and new image data can be recorded in a recording area in
which one frame of image data has been previously recorded and erased.
In an electronic still camera of this invention, an image signal subjected
to the photoelectric conversion by a solid state imaging device is
converted into a digital signal by a signal processing circuit and coded
and then the coded digital data is recorded on a memory card. Further, in
the electronic still camera, the image signal is converted into a
luminance signal and two color difference signals which are in turn
recorded on the memory card. The luminance signal and two color difference
signals may be recorded on the memory card after the total bit capacity
thereof for recording one frame of image has been reduced by changing the
sampling number and non-linearly quantizing differences between the
luminance signal and two color difference signals and corresponding
prediction signals to reduce the number of bits required for representing
one sampling data. Thus, the number of frames of images to be recorded on
the memory card can be changed as required.
Further, the electronic still camera can divide the memory area of the
memory card into a plurality of blocks of a preset memory capacity in each
of which a block number or name is set, record each frame of data on a
plurality or blocks, and record the block number of name of a starting
block and the number of blocks used for recording each frame of data.
Therefore, even when a memory having different memory capacities for each
frame is used, data can be easily written, read out, erased or re-written.
The electronic still camera of this invention effectively solves the
problem that the image cannot be restored based on data read out from the
memory card because of the difference in the number of picture elements
and the arrangement of color filters of the imaging device. Further, the
electronic still camera can efficiently change the number of images to be
recorded on the memory card according to the picture quality and record
the image data of different modes on a single memory card. The electronic
still camera can easily erase only one frame of data and record new image
data in a corresponding memory area. Therefore, according to this
invention, an electronic still camera and an image recording method
thereof, which can attain a high versatility of a system including the
memory card as the recording medium, can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing an appearance of an electronic still
camera according to an embodiment of this invention;
FIG. 2 is a diagram schematically showing the construction of the
electronic still camera shown in FIG. 1;
FIG. 3 is a perspective view illustrating the basic construction of a
semiconductor memory card used in the electronic still camera shown in
FIG. 1;
FIG. 4 is a diagram illustrating the detail construction of the memory card
shown in FIG. 3;
FIG. 5 is a diagram showing the modeled construction of a CCD array used in
the electronic still camera shown in FIG. 1;
FIGS. 6A and 6B are diagrams showing the detail construction of the
electronic still camera shown in FIG. 2;
FIGS. 7 and 8 are views illustrating the sampling points of the image data
in the electronic still camera shown in FIG. 1 on the assumption that the
positions thereof lie on a 2-dimensional plane;
FIGS. 9A to 9E are views illustrating the recording formats of the memory
card used in the electronic still camera shown in FIG. 1;
FIG. 10 is a flowchart showing the process in detail at the time of
photographing effected by the electronic still camera shown in FIG. 1;
FIG. 11 is a block diagram showing the schematic construction of a
reproducing unit for reproducing an image from the memory card recorded by
the camera of this invention;
FIGS. 12A and 12B are block diagrams showing the detail construction of an
electronic still camera according to another embodiment of this invention;
and
FIG. 13 is a diagram showing the construction of the conventional
electronic still camera.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There will now be described an electronic still camera according to an
embodiment of this invention with reference to the accompanying drawings.
An electronic still camera system as used hereinafter is defined as
including, an electronic still camera and a reproducing unit. The
electronic still camera is used to take a picture of a subject and record
the image on a semiconductor memory card used as recording medium, and the
reproducing unit is used to read out image information from the memory
card and transfers the image information to TV receiver or the like for
display.
FIG. 1 is a perspective view of the electronic still camera as viewed from
the rear upper point thereof, the explanation of portions of the
electronic still camera which have the same functions as those of an
ordinary still camera (using a photographic film) being omitted.
Electronic still camera 10 includes release 11, photographing mode switch
12 and photographed picture number displaying unit 13. Further, insertion
slot 14 is provided for permitting insertion of semiconductor memory card
15 on the right side of electronic still camera 10. Shutter speed
selection dial 18 is disposed on the upper surface of electronic still
camera 10. These elements will be described in more detail later.
FIG. 2 schematically shows the basic construction of electronic still
camera 10. In the photographing operation, focusing is effected by means
of lens system 21 and the shutter speed is adequately set by operating
shutter speed selection dial 18 in the same manner as in the ordinary
still camera. Diaphragm 22 is controlled by means of control circuit 24,
and the shutter speed is adjusted by a so-called electronic shutter. The
electronic shutter adjusts the shutter speed by controlling the charge
storing time in CCD array 26 used as an imaging device. An image of a
subject is formed on CCD array 26 via lens system 21.
When the photographing operation is started and release 11 is set into the
halfway position (the release button is depressed halfway) by an operator
or user, the power source voltage from power source 23 using a battery is
supplied to the respective electronic circuit sections. The amount of
incident light is measured by exposure sensor 19, and control circuit 24
controls diaphragm 22 according to the measured amount of incident light.
The external color temperature is measured by white balance sensor 17, and
control circuit 24 generates a white balance control signal according to
the measured color temperature.
When release 11 is further depressed from the halfway position to the fully
depressed position (the release button is fully depressed), control
circuit 24 produces a shutter pulse. In response to the shutter pulse,
driving circuit 25 supplies control signals to CCD array 26,
pre-processing circuit 27, A/D conversion circuit 28 and signal processing
circuit 31 which are in turn operated in response to the respective
control signal. An image information signal formed of an analog signal
from CCD array 26 is supplied to A/D conversion circuit 28 via
pre-processing circuit 27 and is converted into a corresponding digital
signal. The image information signal thus converted into the digital form
is subjected to a predetermined signal processing by signal processing
circuit 31. A digital image information signal from signal processing
circuit 31 is supplied to semiconductor memory card 15 together with a
control signal with an address signal. In this way, the image information
signal corresponding to the photographed still image is stored in
semiconductor memory card 15.
Prior to the photographing, the user can selectively set the format of data
to be stored in semiconductor memory card 15 by operating mode switch 12.
Mode switch 12 is used to select and set a desired one of a plurality of
modes for different image qualities. Mode selection by mode switch 12
makes it possible to change the amount of digital data required for
storing one frame image, i.e., the number of image frames which can be
stored in one memory card 15. For example, when mode "1" or high image
quality mode is set, one frame image is stored as digital data of 640
Kbytes with the highest image quality. When mode "2" is set, one frame
image is stored as digital data of 320 Kbytes with the second highest
image quality, and when mode "3" is set, one frame image of 160 Kbytes is
stored with the third highest image quality. Further, when mode "4" or low
image quality mode is set, one frame image of 80 Kbytes corresponding to
the smallest memory space for one frame is stored. If memory card 15 is
provided with a memory of 2.56 Mbytes, for example, it is possible to
store 4, 8, 16 and 32 frames into one memory card 15 in modes "1", "2",
"3"and "4", respectively. The operation will be described later.
FIG. 3 shows the basic construction of memory card 15. Memory card 15 is
constituted by a printed circuit board having a plurality of random access
memory (RAM) chips 36 mounted thereon. External terminals including data
terminals, address terminals and control terminals, and power source
terminals 33 are provided on one side of memory card 15. For use of memory
card 15, it is inserted into electronic still camera 10 or a reproducing
unit. Supply of the power source voltage to memory card 15 is achieved via
power source terminals 33, and transfer of signals with respect to memory
card 15 is effected via external terminals 32. Exclusive battery 34, used
for maintaining stored data, is built in memory card 15. Further, memory
card 15 includes power source switching circuit 35 which switches the
power source of RAM chip 36 from built-in battery 34 to power source 23 of
electronic still camera 10 or the power source of the reproducing unit
when memory card 15 is inserted into electronic still camera 15 or the
reproducing unit.
FIG. 4 shows an example of memory card 15 having 20 1M-byts RAM chips
36.sub.1 to 36.sub.20. External terminals 32.sub.1 to 32.sub.3 and power
source terminals 33 are provided on one side of memory card 15. External
terminals 32.sub.1 to 32.sub.3 include 8-bit data terminals 32.sub.1,
address terminals 32.sub.2 for receiving address information A0 to A20 and
control terminals 32.sub.3. Memory card 15 of FIG. 4 has a memory capacity
of 20 Mbytes (2.56 Mbytes). Control terminals 32.sub.3 include terminal CS
for selection of RAM chips 36, write pulse terminals WP and card selection
terminals CE for selecting one of cards when a plurality of cards are
used. One of decoders 121.sub.1 and 121.sub.2 is selected by an input
supplied to terminals CS. Decoders 121.sub.1 and 121.sub.2 respectively
correspond to RAM chips 36.sub.1 to 36.sub.10 and 36.sub.11 to 36.sub.20.
CCD array 26, which is a solid state imaging device, is used as an imaging
device for photographing still frame images, for example. A frame
interline type CCD may be suitable for the CCD array 26 used in the
electronic still camera of this invention, for example.
FIG. 5 shows the modeled construction of one example of a frame interline
type CCD solid state imaging device.
The CCD array has image receiving portions 51 formed of photoelectric
conversion elements such as photodiodes arranged in a matrix form.
Vertical transferring portions 52 are arranged along and adjacent to the
columns of image receiving portions 51. Charges in each of image receiving
portions 51 are transferred to a corresponding one of vertical
transferring portions 52 in response to field shift pulse .phi.v1, and
then transferred from one end thereof to charge storage section 54 acting
as a frame memory section via transfer gate 53. Signal charges in charge
storage section 54 are transferred to output circuit 56 via horizontal
transferring section 55 and then output as an electrical signal. Drain
portion 57 is arranged adjacent to the other ends of vertical transferring
sections 52.
In a case where only one CCD array of this type is used to derive out a
color image signal, an optical color filter for separating light
components of red (R), green (G) and blue (B) is disposed on each image
receiving portion 51. Various types and arrangements of the optical color
filters are known in the art, and any type and arrangement may be used in
the electronic still camera of this invention.
Referring to FIGS. 6A and 6B, electronic still camera 10 of this invention
is explained in more detail.
The user can select a desired mode by operating mode switch 12 prior to the
operation of release 11 by taking the quality of image stored in the
memory card and the number of frames stored in the memory card into
consideration. A selected mode signal is supplied from central processing
unit (CPU) 24.sub.1 to switch 31.sub.5.
When release 11 is depressed halfway, information of external color
temperature and the information of light exposure are supplied from white
balance sensor 17 and exposure sensor 19 to CPU 24.sub.1 via interface
(I/F) 24.sub.2. CPU 24.sub.1 controls diaphragm driving circuit 24.sub.5
in response to the information of light exposure so as to drive diaphragm
22. Further, CPU 24.sub.1 controls CCD driving circuit 25.sub.2 via I/F
24.sub.3 and signal generator 25.sub.1 according to the information of
white balance and light exposure so as to drive CCD array 26. Flash
driving circuit 24.sub.4 is controlled by a signal supplied from CPU
24.sub.1 via I/F 24.sub.3, and it is determined whether or not flash 16
such as an electronic flash should be driven by flash driving circuit
24.sub.4 at the photographing time. Amplifier circuit 27.sub.1 and color
separation.multidot..gamma. correction.multidot.white balance circuit
27.sub.2 are each controlled by a signal supplied from CPU 24.sub.1 via
I/F 24.sub.3 and a signal supplied CPU 24.sub.1 via I/F 24.sub.3 and
signal generator 25.sub.1.
When release 11 is further depressed to a fully depressed position, signal
generator 25.sub.1 supplies respective driving signals to CCD array 26,
amplifier 27.sub.1, color separation.multidot..gamma.
correction.multidot.white balance circuit 27.sub.2, A/D conversion circuit
28, signal processing circuit 31.sub.1, filter 31.sub.2, sub-sampling
circuit 31.sub.3, data compression circuit 31.sub.4, switch 31.sub.5, and
memory interface (memory I/F) 31.sub.7.
An image information signal is output from CCD array 26 in response to the
above described operation of release 11. The image information signal is
amplified to a preset level by amplifier 27.sub.1, and R, G and B signals
are supplied in parallel to A/D conversion circuit 28 via color
separation.multidot..gamma. correction.multidot.white balance circuit
27.sub.2 including a color separation circuit, white balance circuit and
.gamma. correction circuit. R, G and B digital signals output in parallel
from A/D conversion circuit 28 are converted into luminance signal Y1 and
color difference signals CR1 and CB1 by signal processing circuit
31.sub.1, and color difference signals CR1 and CB1 are supplied to
low-pass filter 31.sub.2 after the sampling number thereof is reduced to
one half. In this case, luminance signal Y1 is supplied to low-pass filter
31.sub.2 with the sampling number kept unchanged. Thus, luminance signal
Y1 and color difference signals CR1 and CB1 are obtained as linearly
quantized data with each sampled value represented by 8 bits. FIG. 7 shows
the relation between the sampling points of luminance signal Y1 and those
of color difference signals CR1 and CB1. Low-pass filter 31.sub.2 is a
pre-low-pass filter for sub-sampling. Luminance signal Y1 and color
difference signals CR1 and CB1 are supplied to sub-sampling circuit
31.sub.3 via low-pass filter 312. In sub-sampling circuit 31.sub.3,
luminance signal Y1 is subjected to a line-offset sampling process and
converted into luminance signal Y2 whose sampling number is reduced to one
half, and color difference signals CR1 and CB1 are sampled in every other
line and converted into color difference signals CR2 and CB2 whose
sampling number is reduced to one half. FIG. 8 shows the relation between
the sampling data points of the signals. Luminance signal Y2 and color
difference signals CR2 and CB2 are supplied to data compression circuit
31.sub.4. As described before, luminance signal Y2 and color difference
signals CR2 and CB2 are linearly quantized using 8 bits for each sampled
value, but the data bit number for each sampling value is reduced in data
compression circuit 31.sub.4. In this embodiment, differential pulse code
modulation (DPCM) is used, for example, as the data compression system to
effect the data compression. The data compression by DPCM is well known in
the art, each sampling data is quantized by nonlinearly compressing a
difference between the sampling data and receding sampling data. For
example, in the case of luminance signal Y12 of FIG. 8, a difference
between luminance signals Y11 and Y12 is non-linearly quantized, and each
sampling value is represented by 4 or 2 bits. Likewise, color difference
signals CR1 and CB1 are compressed and each sampling value is represented
by 4 or 2 bits. The luminance signal thus compressed is denoted by Y3, and
the color difference signals thus compressed are denoted by CR3 and CB3.
Switch 31.sub.5 is used to select the luminance signal and color difference
signals according to the set mode. In a case where mode (A) is set, for
example, signal Y1, CR1 and CB1 supplied from signal processing circuit
31.sub.1 are selected by switch 31.sub.5 and stored into memory card 15
via buffer memory 31.sub.6. Buffer memory 31.sub.6 can store at least one
frame of data. Likewise, in mode (B), signals Y2, CR2 and CB2 supplied
from sampling circuit 31.sub.3 are selected by switch 31.sub.5, in mode
(C), signals Y3, CR3 and CB3 compressed by data compression circuit
31.sub.4 to represent each sampling value by 4 bits are selected by switch
31.sub.5, and in mode (D), signals Y3 CR3 and CB3 compressed by data
compression circuit 31.sub.4 to represent each sampling value by 2 bits
are selected by switch 31.sub.5. The signals selected by switch 31.sub.5
are stored in memory card 15 via buffer memory 31.sub.6.
In addition to image data, information relating to the selected mode is
also stored into memory card 15 together with the image data. (For
example, in modes (A) and (B), "001" and "010" are stored in the form of
binary code indicating the selected mode numbers).
For example, it is also possible to store imaging data, such as data
relating to use of the flash, white balance control data, exposure data
(or aperture data) and shutter speed data, in the form of binary code as
well as the selected mode. The imaging data is displayed on display unit
13 by the control of CPU 24.sub.1, thereby permitting the user or operator
to recognize the imaging data by observing display unit 13.
A method of storing data into memory card 15 is explained in detail with
reference to FIGS. 9A to 9E. In this example, a memory card of 20 Mbits or
2.56 Mbytes which has 20 RAMs or static RAMs (SRAM) of 1 Mbits mounted
thereon as shown in FIG. 4 is used.
As shown in FIG. 9A, all the memory space is divided respectively into
directory area, a file allocation table (FAT) and a data area. As shown in
FIG. 9B, there are stored in the directory area various items of 1-byte
information which include information indicating a file number or image
(frame) number in the case where the file is image data; information
indicating data classfication or the classification of image data, voice
data or other data; information indicating the imaging system, that is,
the 525 (lines)/60 (fields) system or 625 (lines)/50 (fields) system in
the case of image data; information indicating the imaging mode or image
compression method (including the case where on data compression is
effects); information indicating the voice mode or compression method in
the case of voice data; information indicating the year in which the
recording or photographing was effected; information indicating the month
in which the recording was effected; information indicating the date on
which the recording was effected; information indicating the hour at which
the recording was effected; and information indicating the minute at which
the recording was effected. Further, the entry block number of the file
(image data file) and the number of data blocks used for storing the file
are stored into the directory area. The directory area has 16 bytes for
each file, and 256 files (256 frames in the case of image data) are
allotted thereto. As a result, the directory area has a memory capacity of
4 Kbytes. FIGS. 9C and 9D respectively show the FAT area and data area.
256 bytes are allotted to the FAT area, and addresses from 00H to FFH are
assigned thereto. The data area is divided into blocks each having 10
Kbytes, and block numbers 00H to FFH are assigned to the respective
blocks.
In order to clarify the explanation, assume that approx. 40 Kbytes are
necessary to store one frame data, for example. Then, the entry block
number or 11H and the number of available blocks of 04H are written into
the directory area, for example. 12H, 13H, 2AH and FFH are written into
addresses 11H, 12H, 13H and 2AH. Image data of one frame is written into a
40-Kbyte area obtained by linking block numbers 11H, 12H, 13H and 2AH of
the data area. FFH written into the address of 2AH of the FAT area
indicates the last block. FIG. 9E shows the 40-Kbyte memory area obtained
by linking the blocks. In the first block or 256-byte block of block
number 11H, data indicating the presence or absence of the flash (or
information as to whether the flash has been used or not), white balance
data, and photographing condition data including the exposure value (or
aperture value) and shutter speed are recorded, and the remaining 252-byte
area is used as a user area for recording the title, for example. Image
data may be successively recorded in an area from 257 th byte to block
number 2AH. 64 blocks, 32 blocks, 16 blocks and 8 blocks are used
respectively in modes (A), (B), (C) and (D).
In this method, when a variable length coding system in which the memory
capacity for each frame attained after the coding operation may be varied
is used, data can be recorded on the memory card without causing any
problem. That is, after the coding operation, data is temporarily stored
in buffer memory 31.sub.6. The memory capacity necessary for storing one
frame data is determined according to the application condition of buffer
memory 31.sub.6, and therefore it is possible to calculate the number of
data blocks to be used. When the number of available data blocks is not
sufficient, the image data is kept stored in buffer memory 31.sub.6 and
the next photographing is inhibited until a new memory card is set.
Now, the processing for effecting the above recording operation is
explained in detail with reference to FIG. 10 showing the flowchart.
When an operation input of release 11 determining the photographing timing
is supplied (step ST1), the photographing information to be written into
the directory area of memory card 15 and directory information of memory
card 15 set in the device are fetched (step ST2). The photographing
information includes mode information, information indicating the presence
or absence of the flash, white balance information, information indicating
the exposure value (or aperture value), shutter speed information, year
information, month information, date information and time information. The
entry block number of memory card 15 is determined based on the above
information (step ST3). Further, the number of data blocks used to store
image to be photographed is determined based on the mode information (step
ST4). The available memory capacity of memory card 15 is checked. In a
case where it is detected that a sufficient number of data blocks for
recording an image cannot be obtained in memory card 15 (step ST5),
necessary information is displayed on display unit 13 or alarm is sounded,
for example, to inform the user that memory card 15 should be replaced,
and, at the same time, one frame of data is stored in buffer memory
31.sub.6. If a new memory card is set (step ST8), step ST2 is effected
again. In a case where a sufficient number of data blocks for recording an
image are available in memory card 15 set in the device (step ST5),
address allocation to the FAT in memory card 15 is effected (step ST6) and
image data and photographing data, which have been stored in buffer memory
31.sub.6, are stored in memory card 15 (step ST7).
Next, the reproducing unit for reading out the image data from memory card
15 and displays video image on a TV monitor or the like is explained with
reference to FIG. 11.
When memory card 15 is inserted into reproducing unit 90 and keyboard 104
is operated to specify a file number (image number), then CPU 102 reads
out information from the directory area in the memory card via card
interface (card I/F) 91. CPU 102 determines whether the information
classification of the specified file number is image data or not, the type
of imaging system, and the type of c | | |
