Electronic still camera with multi-area light metering and gray scale modification

An electronic still camera for recording stationary images comprises a light metering device for light-metering a plurality of portions of an object to be photographed and outputting a pluraltiy of signals corresponding to the quantities of light of the portions, an image pickup device for converting the image of the object to be photographed into an image signal, a contour enhancing device provided with a plurality of selectable contour enhancement degrees and enhancing the contour of the image signal, and a selecting device for effecting calculation on the basis of the outputs from the light metering device and selecting one of the plurality of contour enhancement degrees provided in the contour enhancing device on the basis of the result of the calculation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electronic still camera for recording 
stationary images. 
2. Related Background Art 
FIG. 1 of the accompanying drawings is a block diagram showing the 
construction of an electronic still camera according to the prior art 
using a contour enhancement circuit. 
In FIG. 1, an object to be photographed, not shown, has its quantity of 
light adjusted by a stop member 2 and is imaged on the image pickup 
surface of an image pickup element 3 by an optical lens 1, and the light 
signal of the image is converted into an electrical signal. The image 
pickup element 3 comprises various solid state image pickup elements such 
as a CCD (charge coupled device), an MOS device and an SIT. The output of 
the image pickup element 3 is connected to a sample hold circuit 5. A 
drive pulse generator 4 generates a pulse for driving the image pickup 
element 3 to the image pickup element 3, and generates a sample pulse for 
sampling and holding to the sample hold circuit 5. The sample hold circuit 
5 samples and holds the output signal from the image pickup element 3 at 
the timing of the sampling pulse from the drive pulse generator 4, and 
outputs an analog image signal to an amplifier circuit 6. The image signal 
amplified by the amplifier circuit 6 is then input to a contour 
enhancement circuit 7, in which the process of enhancing the change of the 
image signal is carried out. The output signal of the contour enhancement 
circuit 7 is input to a level adjustment circuit 8 for adjusting the white 
clip level and the set up level, and the output signal of the level 
adjustment circuit 8 is input to a recording portion 9. 
The reference numeral 13 designates a light metering element for metering 
the quantity of light of the object to be photographed before 
photographing. The light metering element 13 is designed such that the 
image of the object to be photographed is formed thereon by a condensing 
lens 12. The image formed on the light metering element 13 is converted 
into an electrical signal by the photoelectric converting function of the 
light metering element 13 and is output to an amplifier 15. The electrical 
signal amplified by the amplifier 15 and logarithmically compressed is 
converted into a digital signal by an A/D converter 16 and is input to a 
central calculation processing portion 10. Also, a stroboscopic lamp 11 
which is a light emitting device is provided to momentarily illuminate the 
object to be photographed when it is dark. 
A release button 18 is a switch for the user to make the camera ready to 
photograph, and is operatively associated with contacts 17a, 17b and 17c. 
The contacts 17a, 17b and 17c are connected to the central calculation 
processing portion 10. When the release button 18 is depressed lightly, 
the contacts 17a and 17b are closed and the central calculation processing 
portion 10 performs a photographing preparation operation such as light 
metering. When the release button 18 is further depressed and the contacts 
17b and 17c are closed, the central calculation processing portion 10 
performs photographing operations such as the charge accumulation of the 
image pickup element 3 and the recording of the image signal. 
The central calculation processing portion 10 connected to the recording 
portion 9 and the drive pulse generator 4 controls the operation of the 
present apparatus, determines the size of the aperture diameter of the 
stop member 2 and the charge accumulation time in the image pickup element 
3 from the output signal of the light metering element 13 converted by the 
amplifier 15 and the A/D converter 16, controls the light emission of the 
stroboscopic lamp 11, controls the generation of pulse to the drive pulse 
generator 4, and causes the recording portion 9 to record the output 
signal from the level adjustment circuit 8. 
In the above-described construction, when in photographing, the release 
button 18 is depressed lightly by the user and the contacts 17a and 17b 
are closed, the quantity of light of the object to be photographed, not 
shown, is metered by the light metering element 13, and the size of the 
aperture diameter of the stop member 2 and the charge accumulation time in 
the image pickup element 3 are determined. When the central calculation 
processing portion 10 judges that the object to be photographed is dark 
and sufficient exposure will not be obtained, the preparation for the 
light emission of the stroboscopic lamp 11 is effected. When the release 
button is then depressed deeply, the contacts 17b and 17c are closed, and 
the light from the object to be photographed, not shown, enters the image 
pickup element 3 through the optical lens 1 and the stop member 2, and as 
previously described, the image signal provided by the image pickup 
element 3 and the sample hold circuit 5 is input to the amplifier circuit 
6. The image signal is electrically amplified in conformity with the 
predetermined amplification degree of the amplifier circuit 6 and 
subsequently, has its white clip level and set up level adjusted by the 
level adjustment circuit 8, and is recorded by the recording portion 9. 
The prior art as described above has suffered from the following problems. 
When in general photographing, the difference in quantity of light between 
the light portion and the dark portion of an object to be photographed is 
small, for example, as in a scene during cloudy weather, if contour 
enhancement is done at the standard contour enhancement degree in the 
contour enhancement circuit, the contrast of the image will be too weak 
and modulation will become null and therefore, a visually good image will 
not be obtained. Also, when the difference in quantity of light between 
the light portion and the dark portion of an object to be photographed is 
great, such as when a figure is photographed during fine weather or when a 
stroboscopic lamp is used, if contour enhancement is done at the standard 
contour enhancement degree in the contour enhancement circuit, the 
contrast of the image will be too strong and modulation will become too 
strong and again, a visually good image will not be obtained. 
As described above, in the prior art, the setting of the contour 
enhancement degree is fixed in the contour enhancement circuit and contour 
enhancement is done always at the same enhancement degree, and this has 
led to the problem that contour enhancement matching an object to be 
photographed is not done and depending on the situation of the object to 
be photographed, a visually good image of good contrast is not always 
obtained. 
FIG. 2 of the accompanying drawings is a block diagram showing the 
construction of an electronic still camera according to the prior art 
using a gray scale modification circuit. 
In FIG. 2, optical members and circuits given reference numerals identical 
to those in FIG. 1 are identical to those in FIG. 1 and therefore need not 
be described. 
The output signal of the contour enhancement circuit 7 is input to a gray 
scale modification circuit 19, in which gamma correction is effected so 
that the image may assume the standard gray scale. The output signal of 
the gray scale modification circuit 19 is input to the level adjustment 
circuit 8 for adjusting the white clip level and the set up level, and the 
output signal of the level adjustment circuit 8 is input to the recording 
portion 9. 
The image signal is electrically amplified in conformity with the 
predetermined amplification degree of the amplifier circuit 6, and has 
predetermined contour enhancement applied thereto by the contour 
enhancement circuit 7. Subsequently, modification of the gray scale is 
effected by gamma correction at the standard .gamma. value preset in the 
gray scale modification circuit 19, and then the image signal has its 
white clip level and set up level adjusted by the level adjustment circuit 
8 and is recorded in the recording portion 9. 
The prior art as described above has suffered from the following problems. 
When in general photographing, the difference in quantity of light between 
the light portion and the dark portion of an object to be photographed is 
small, for example, as in a scene during cloudy weather, if gray scale 
modification by gamma correction at the standard .gamma. value is effected 
in the gray scale modification circuit, the contrast will be weak and 
therefore, a visually good image will not be obtained. Also, when the 
difference in quantity of light between the light portion and the dark 
portion of an object to be photographed is great, such as when a figure is 
photographed during fine weather or when a stroboscopic lamp is used, if 
gray scale modification by gamma correction at the standard .gamma. value 
is effected in the gray scale modification circuit, the contrast will be 
strong and therefore, a visually good image will not be obtained. 
As described above, in the prior art, gray scale modification by gamma 
correction always at the standard .gamma. value is effected in the gray 
scale modification circuit and therefore, the gray scale modification 
characteristic is fixed and gray scale modification matching the object to 
be photographed is not done, and this has lead to the problem that 
depending on the situation of the object to be photographed, a visually 
good image cannot always be obtained. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of such problems peculiar to 
the prior art and an object thereof is to provide an electronic still 
camera which can always obtain a visually good image of good contrast 
irrespective of the distribution of the light portion and the dark portion 
of an object to be photographed in the photographing picture plane. 
To achieve the above object, the electronic still camera of the present 
invention has light metering means for light-metering a plurality of 
portions of an object to be photographed in the photographing picture 
plane and outputting a plurality of signals corresponding to the 
quantities of light of said portions, image pickup means for converting 
the image of the object to be photographed into an image signal, contour 
enhancing means provided with a plurality of selectable contour 
enhancement degrees and enhancing the contour of the image signal, and 
selecting means for selecting one of said plurality of contour enhancement 
degrees of said contour enhancing means, and effects calculation in said 
selecting means on the basis of the outputs of said light metering means 
and selects one of said plurality of contour enhancement degrees on the 
basis of the result of the calculation. The electronic still camera also 
has light emitting means for illuminating the object to be photographed, 
and selects one of said plurality of contour enhancement degrees in 
conformity also with the presence or absence of the light emission by said 
light emitting means. 
By the construction as described above, when the difference in quantity of 
light between said portions of the object to be photographed in the 
photographing picture plane is great, the contour enhancement degree can 
be made weak during the contour enhancement of the image signal by said 
contour enhancing means, and when the difference in quantity of light 
between said portions of the object to be photographed is small, the 
contour enhancement degree can be made strong and therefore, an image of 
good contrast can always be obtained from any object to be photographed. 
Also, when the object to be photographed is dark and is illuminated by 
said light emitting means, the difference in quantity of light between 
said portions of the object to be photographed becomes great and 
therefore, the contour enhancement degree can be made weak during the 
contour enhancement of the image signal by said contour enhancing means. 
It is also an object of the present invention to provide an electronic 
still camera which can always obtain a visually good image irrespective of 
the situation of an object to be photographed. 
To achieve the above object, the electronic still camera of the present 
invention has light metering means for light-metering a plurality of 
portions of an object to be photographed in the photographing picture 
plane and outputting a plurality of signals corresponding to the 
quantities of light of said portions, image pickup means for converting 
the image of the object to be photographed into an image signal, gray 
scale modification means provided with a plurality of selectable gray 
scale modification characteristics and modifying the gray scale of the 
image signal, and selecting means for selecting one of said plurality of 
gray scale modification characteristics of said gray scale modification 
means, and effects calculation in said selecting means on the basis of the 
outputs of said light metering means, and selects one of said plurality of 
gray scale modification characteristics on the basis of the result of the 
calculation. The electronic still camera also has light emitting means for 
illuminating the object to be photographed, and selects one of said 
plurality of gray scale modification characteristics by said selecting 
means in conformity also with the presence or absence of the light 
emission by said light emitting means. 
By the construction as described above, when the difference in quantity of 
light between said portions of the object to be photographed in the 
photographing picture plane is great, the gray scale is modified so as to 
weaken the contrast during the gray scale modification of the image signal 
by said gray scale modification means, and when the difference in quantity 
of light is small, the gray scale is modified so as to strengthen the 
contrast, whereby an image of good contrast can be obtained from any 
object to be photographed. Also, when the object to be photographed is 
illuminated by said light emitting means, the difference in quantity of 
light between said portions of the object to be photographed becomes great 
and therefore, the gray scale is modified so as to weaken the contrast 
during the gray scale modification of the image signal by said gray scale 
modification means, whereby an image of good contrast can always be 
obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will hereinafter be described with 
reference to FIG. 3. 
FIG. 3 is a block diagram showing the construction of an electronic still 
camera according to a first embodiment of the present invention. In FIG. 
3, optical members and circuits given reference numerals identical to 
those in FIG. 1 are identical to those in FIG. 1 and therefore need not be 
described. 
In FIG. 3, the output terminal 20a of the amplifier circuit 6 is 
parallel-connected with switches 20b-20d. These switches 20b-20d are 
connected to respective contour enhancement circuits 20e-20g. In the 
contour enhancement circuits 20e-20g, the respective contour enhancement 
degrees are set so as to be one time, two times and four times. The first 
to third switches 20b-20d and the first to third contour enhancement 
circuits 20e-20g together constitute a contour enhancement circuit 20, and 
the first to third switches 20b-20d are controlled by the central 
calculation processing portion 10 so that any contour enhancement degree 
may be selected. 
The image of an object to be photographed is formed on a light metering 
member 21 through the condensing lens 12. The light metering member 21 is 
comprised of five light metering elements 21a-21e to light-meter the 
object to be photographed in five divisions. The outputs of the light 
metering elements are amplified by amplifiers 22a-22e and logarithmically 
compressed, and are converted into digital signals by A/D converters 
23a-23e and input to the central calculation processing portion 10. 
Description of the operation of the electronic still camera constructed as 
described above will first be made with respect to a case where the 
difference in quantity of light between portions of the object to be 
photographed is great. 
When the release switch 18 is depressed lightly by the user and the 
contacts 17a and 17b are closed, the central calculation processing 
portion 10 examines the output values of the light metering elements 
21a-21e converted through the amplifiers 22a-22e and the A/D converters 
23a-23e, and when the difference between the greatest output and the 
smallest output among them, i.e., the difference in quantity of light, is 
greater than the maximum value prestored in the central calculation 
processing portion 10, it is judged that the difference in quantity of 
light of the object to be photographed is great, and the switch 20b is 
closed and the other switches 20c and 20d are opened so that the contour 
enhancing process may be carried out by the first contour enhancement 
circuit 20e of the smallest contour enhancement degree. 
Also, the central calculation processing portion 10 examines the outputs of 
the light metering elements 21a-21e converted through the amplifiers 
22a-22e and the A/D converters 23a-23e, and determines the size of the 
aperture diameter of the stop member 2 and the charge accumulation time of 
the image pickup element 3 so that proper charge accumulation in the image 
pickup element 3 may be effected. 
When the release button 18 is then depressed deeply and the contacts 17b 
and 17c are closed, the photographing operation is entered. Thereupon, the 
light passed through the optical lens 1 passes through the stop member 2 
which has assumed a predetermined aperture diameter and is imaged on the 
image pickup element 3. Charge accumulation in the image pickup element 3 
is effected for the charge accumulation time determined in the central 
calculation processing portion 10. The charge accumulated in the image 
pickup element 3 is subjected to predetermined amplification as an image 
signal by the amplifier circuit 6 via the sample hold circuit 5. The image 
signal then passes through the switch 20b and is subjected to the weakest 
contour enhancement by the first contour enhancement circuit 20e. Thereby, 
contour enhancement is done weakly for an object to be photographed having 
a great difference in quantity of light, i.e., so-called high contrast, 
and therefore, it never happens that the image becomes unnatural. The 
output signal is subjected to the adjustment of the white clip level and 
set up level in the white clip level and set up level adjustment circuit 
8, and is recorded on a recording medium in the recording portion 9. 
Description will now be made of the operation when the difference in 
quantity of light between portions of the object to be photographed is of 
a medium degree. 
When the release switch 18 is depressed by the user and the contacts 17a 
and 17b are closed, the central calculation processing portion 10 examines 
the output values of the light metering elements 21a-21e converted through 
the amplifiers 22a-22e and the A/D converters 23a-23e. If the difference 
between the greatest output and the smallest output among them is between 
the maximum value and the minimum value prestored in the central 
calculation processing portion 10, it is judged that the difference in 
quantity of light between the portions of the object to be photographed is 
of a medium degree, and the switch 20c is closed and the other switches 
20b and 20d are opened so that the contour enhancing process may be 
carried out in the second contour enhancement circuit 20f of a medium 
contour enhancement degree. The operation until the image signal is 
thereafter recorded in the recording portion 9 is as previously described. 
If the difference in quantity of light is small, the operation is likewise 
as follows. The central calculation processing portion 10 examines the 
output values of the light metering elements 21a-21e converted through the 
amplifiers 22a-22e and the A/D converters 23a-23e, and if the difference 
between the greatest output and the smallest output among them is smaller 
than the minimum value prestored in the central calculation processing 
portion 10, it is judged that the difference in quantity of light between 
the portions of the object to be photographed is small, and the switch 20d 
is closed and the other switches 20b and 20c are opened so that the 
contour enhancing process may be carried out in the third contour 
enhancement circuit 20g of the strongest contour enhancement degree. The 
operation until the image signal is thereafter recorded in the recording 
portion 9 is as previously described. 
Thus, in the case of an object to be photographed having a small difference 
in quantity of light, the strongest contour enhancement is effected so 
that modulation may be visually provided. When the difference in quantity 
of light is of a medium degree, a medium degree of contour enhancement is 
effected within a range which is not unnatural. 
Description will now be made of a case where the object to be photographed 
is dark and the stroboscopic lamp 11 is used. 
When the release button 18 is depressed and the contacts 17a and 17b are 
closed, the central calculation processing portion 10 examines the outputs 
of the light metering elements 21a-21e converted through the amplifiers 
22a-22e and the A/D converters 23a-23e, and if it is judged that the 
outputs are small, that is, the object to be photographed is dark and 
proper exposure cannot be accomplished unless the stroboscopic lamp 11 is 
made to emit light, the preparation for the light emission of the 
stroboscopic lamp, for example, the charging of a capacitor, not shown, is 
effected. When the release button 18 is depressed deeply and the contacts 
17b and 17c are closed, the photographing operation is performed. In this 
case, the light emission of the stroboscopic lamp 11 is effected during 
the charge accumulation in the image pickup element 3. At this time, the 
central calculation processing portion 10 closes the switch 20b and opens 
the other switches 20c and 20d so that the contour enhancing process may 
be carried out in the first contour enhancing circuit 20e of the smallest 
contour enhancement degree, at the stage whereat the central calculation 
processing portion 10 has examined the outputs of the light metering 
elements 21a-21e converted through the amplifiers 22a-22e and the A/D 
converters 23a-23e. This is because if photographing is effected by the 
use of the stroboscopic lamp 11 approximate to a point source of light, 
the contrast of the object to be photographed and the shadow formed in the 
background of the object to be photographed will be strong and an image 
having a great difference in quantity of light will be recorded and so, it 
will provide a visually good image to make the contour enhancement 
weakest. The sequence thereafter is as previously described. 
The case of the light emission of the stroboscopic lamp has been described 
with respect to a case where the outputs of all the light metering 
elements 21a-21e are small, but even when only the output of one of the 
light metering elements 21a-21e, for example, the light metering element 
21c which is the light metering element for light-metering the central 
portion, is small and it is judged that photographing will be effected in 
a backlight condition, a visually good image can be photographed without 
the central object to be photographed becoming dark if the stroboscopic 
lamp 11 is made to emit light to the central object to be photographed. In 
such case, by the stroboscopic lamp 11 being made to emit light, the 
difference in quantity of light between the background and the main object 
to be photographed becomes relatively small and therefore, design is made 
such that the contour enhancement circuit 20f having a medium contour 
enhancement degree is selected. 
The setting of the contour enhancement degree by the aforedescribed central 
calculation processing portion 10 will be now described with reference to 
the flow chart shown in FIG. 4. In FIG. 4, P.sub.1 -P.sub.5 are the 
outputs of the A/D converters 22a-22e, respectively, .sigma..sub.MAX is 
the maximum allowable value of the luminance difference, and 
.sigma..sub.MIN is the minimum allowable value of the luminance 
difference. 
When the release switch 18 is depressed lightly by the user and the 
contacts 17a and 17b are closed, the central calculation processing 
portion 10 starts the contour enhancement set up routine at a step 1 (S1). 
At a step 2 (S2), whether the object field is dark is judged on the basis 
of whether the weighted mean value and the normal mean value of the 
outputs P.sub.1 -P.sub.5 of the A/D converters 22a-22e are lower than a 
predetermined value. If the object field is dark, at a step 3 (S3), the 
light emission of the stroboscopic lamp is prepared, and at a step 4 (S4), 
the switch 20b is closed and the first contour enhancement circuit 20e 
which is small in the contour enhancement degree is selected, and at a 
step 5 (S5), return is made. 
If at the step 2, it is judged that the object field is not dark, at a step 
6 (S6), whether the light is backlight is judged. The judgement as to 
whether the light is backlight is done, for example, on the basis of 
whether the difference between the luminance of the central light metering 
area 21c and the average luminance of a plurality of marginal light 
metering areas 21a, 21b, 21d and 21e exceeds a predetermined value. If at 
the step 6 (S6), it is judged that the light is backlight, at a step 7 
(S7), the light emission of the stroboscopic lamp is prepared, and at a 
step 8 (S8), the switch 20c is closed, and the second contour enhancement 
circuit 20f of a medium contour enhancement degree is selected and at a 
step 5 (S5), return is made. 
If at the step 6, it is judged that the light is not backlight, at step 
9(S9), the maximum value of the absolute values of luminance differences 
.vertline.P.sub.i -P.sub.j .vertline. (i=1-5, j=1-5) is defined as a 
maximum luminance difference .sigma.. Subsequently, at a step 10 (S10), 
the maximum luminance difference .sigma. is compared with the maximum 
allowable value .sigma..sub.MAX of the luminance difference prestored in 
the central calculation processing portion 10, and if the maximum 
luminance difference .sigma. is greater than the maximum allowable value 
.sigma..sub.MAX of the luminance difference, at a step 11 (S11), the 
switch 20b is closed and the first contour enhancement circuit 20e of a 
small contour enhancement degree is selected, and at the step 5 (S5), 
return is made. 
If at the step 10 (S10), the maximum luminance difference .sigma. is equal 
to or less than the maximum allowable value .sigma..sub.MAX of the 
luminance difference, at a step 12 (S12), the maximum luminance difference 
.sigma. is compared with the minimum allowable value .sigma..sub.MIN of 
the luminance difference prestored in the central calculation processing 
portion 10. If the maximum luminance difference .sigma. is greater than 
the minimum allowable value .sigma..sub.MIN of the luminance difference, 
at a step 13 (S13), the switch 20c is closed and the second contour 
enhancement circuit 20f of a medium contour enhancement degree is 
selected, and at the step 5 (S5), return is made. 
If at the step 12 (S12), the maximum luminance difference .sigma. is equal 
to or less than the minimum allowable value .sigma..sub.MIN of the 
luminance difference, at a step 14 (S14), the switch 20d is closed and the 
third contour enhancement circuit 20g of a great contour enhancement 
degree is selected, and at the step 5 (S5), return is made. 
In the present embodiment, a change-over system using switches is adopted 
so that the contour enhancement degree may be stepwisely changed, but 
alternatively, design may be made such that the contour enhancement degree 
is continuously changed. Also, as regards the use of the stroboscopic 
lamp, provision may be made of a selection switch for determining the 
presence or absence of light emission not only by the judgment of the 
central calculation processing portion, but also by the user's judgment, 
and design may be made such that the contour enhancement degree is changed 
over in response to this switch. 
Also, in the present embodiment, selection of the contour enhancement 
degree is effected on the basis of the difference between the maximum 
value and the minimum value of the output values from the light metering 
means, whereas the method of calculation is not restricted thereto, but 
conversion tables corresponding to the output values from the light 
metering means may be memorized by the central calculation processing 
portion and selection of the contour enhancement degree may be effected on 
the basis of such conversion tables. 
As described above, according to the first embodiment, a plurality of 
portions of an object to be photographed are light-metered by the light 
metering means and the contour enhancement degree is changed in conformity 
with the difference in quantity of light, whereby a good image visually 
free of unnaturalness of contrast can always be obtained from any object 
to be photographed. Also, even when the object to be photographed is 
illuminated by the light emitting means and the difference in quantity of 
light becomes great, a good image visually free of unnaturalness of 
contrast can be obtained by weakening the contour enhancement degree. 
A second embodiment of the present invention will now be described with 
reference to FIG. 5. 
FIG. 5 is a block diagram showing the construction of an electronic still 
camera according to the second embodiment of the present invention. In 
FIG. 5, optical members and circuits given the same reference numerals as 
those in FIG. 2 are the same as those in FIG. 2 and therefore need not be 
described. 
In FIG. 5, the output terminal 24 of the contour enhancement circuit 7 is 
parallel-connected to three switches 24b-24d. These switches 24b-24d are 
connected to respective gray scale modification circuits 24e-24g. The gray 
scale modification circuits 24e-24g are set such that their respective 
gray scale modification characteristics are .gamma.1, .gamma.2 and 
.gamma.3 shown in FIG. 6. 
The gray scale modification characteristic of FIG. 6 represents the input 
and output characteristics of gamma correction, and is expressed as the 
following equation (1) when the input of the horizontal axis (the output 
of the contour enhancement circuit 7) is x and the output of the vertical 
axis (the output of the gray scale modification circuit 24) is y: 
EQU y=x.sup..gamma. (1) 
Characteristic curves .gamma.1, .gamma.2 and .gamma.3 shown in FIG. 6 show 
the cases where in the equation (1), .gamma.=1, .gamma.=0.7 and 
.gamma.=0.45, respectively. 
When gray scale modification is effected, the greater is the .gamma. value, 
the stronger becomes contrast, and the smaller is the .gamma. value, the 
weaker becomes contrast. 
The first to third switches 24b-24d and the first to third gray scale 
modification circuits 24e-24g together constitute the gray scale 
modification circuit 24, and the first to third switches 24b-24d are 
designed such that they are controlled by the central calculation 
processing portion 10 and any gray scale modification characteristic is 
selected. 
The image of the object to be photographed is formed on a light metering 
member 21 through the condensing lens 12. The light metering member 21 is 
comprised of five light metering elements 21a-21e to light-meter the 
object to be photographed in five divisions. The outputs of the light 
metering elements are amplified by amplifiers 22a-22e, respectively, and 
logarithmically compressed, and are converted into digital signals by A/D 
converters 23a-23e and input to the central calculation processing portion 
10. 
The operation of the electronic still camera constructed as described above 
will first be described with respect to a case where the difference in 
quantity of light between portions of the object to be photographed is 
great. 
When the release switch 18 is depressed lightly by the user and the 
contacts 17a and 17b are closed, the central calculation processing 
portion 10 examines the output values of the light metering elements 
21a-21e converted through the amplifiers 22a-22e and the A/D converters 
23a-23e, and if the difference between the greatest output and the 
smallest output among them, i.e., the difference in quantity of light, is 
greater than the maximum value prestored in the central calculation 
processing portion 10, it is judged that the difference in quantity of 
light between the portions of the object to be photographed is great, and 
the switch 24d is closed and the other switches 24b and 24c are opened so 
that the gray scale modifying process may be done by the third gray scale 
modification circuit 24g having the characteristic of .gamma.3 which is 
smallest in .gamma. value. 
Also, the central calculation processing portion 10 examines the outputs of 
the light metering elements 21a-21e converted through the amplifiers 
22a-22e and the A/D converters 23a-23e, and determines the size of the 
aperture diameter of the stop member 2 and the charge accumulation time of 
the image pickup element 3 so that proper charge accumulation in the image 
pickup element 3 may be effected. 
When the release button 18 is then depressed deeply and the contacts 17b 
and 17c are closed, the photographing operation is entered. Thereupon, the 
light passed through the optical lens 1 passes through the stop member 2 
which has assumed a predetermined aperture diameter, and is imaged on the 
image pickup element 3. Charge accumulation in the image pickup element 3 
is then effected for the charge accumulation time determined in the 
central calculation processing portion 10. The charge accumulated in the 
image pickup element 3 passes as an image signal through the sample hold 
circuit 5, is subjected to predetermined amplification by the amplifier 
circuit 6, and is contour-enhanced by the contour enhancement circuit 7. 
Then it passes through the switch 24d and has its gray scale modified by 
the characteristic of .gamma.3 which is smallest in .gamma. value in FIG. 
6. Thereby, the image signal in which the gray scale expression for an 
object to be photographed having a great difference in quantity of light, 
i.e., so-called high contrast, has become impossible is corrected with a 
result that moderate contrast is provided and therefore, it never happens 
that the image becomes unnatural. Then, the white clip level and the set 
up level are adjusted in the level adjustment circuit 8, and the image 
signal is recorded on a recording medium in the recording portion 9. 
Description will now be made of the operation when the difference in 
quantity of light between the portions of the object to be photographed is 
of a medium degree. 
When the release switch 18 is depressed by the user and the contacts 17a 
and 17b are closed, the central calculation processing portion 10 examines 
the output values of the light metering elements 21a-21e converted through 
the amplifiers 22a-22e and the A/D converters 23a-23e. If the difference 
between the greatest output and the smallest output among them is between 
the maximum value and the minimum value prestored in the central 
calculation processing portion 10, it is judged that the difference in 
quantity of light between the portions of the object to be photographed is 
of a medium degree, and the switch 24c is closed and the other switches 
24b and 24d are opened so that gray scale modification may be done in the 
second gray scale modification circuit 24f having the characteristic of 
.gamma.2 which is medium in .gamma. value in FIG. 6. The operation until 
the image signal is thereafter recorded in the recording portion 9 is as 
previously described. 
The operation when the difference in quantity of light is small is likewise 
as follows. The central calculation processing portion 10 examines the 
output values of the light metering elements 21a-21e converted through the 
amplifiers 22a-22e and the A/D converters 23a-23e, and if the difference 
between the greatest output and the smallest output among them is smaller 
than the minimum value prestored in the central calculation processing 
portion 10, it is judged that the difference in quantity of light between 
the portions of the object to be photographed is small, and the switch 24b 
is closed and the other switches 24c and 24d are opened so that gray scale 
modification may be done in the first gray scale modification circuit 24e 
having the characteristic of .gamma.1 which is greatest in .gamma. value 
in FIG. 6. The operation until the image signal is thereafter recorded in 
the recording portion 9 is as previously described. 
In the case of such an object to be photographed having small difference in 
quantity of light, gray scale modification by the characteristic which is 
greatest in .gamma. value is effected so that modulation may be visually 
provided and that finally appropriate contrast may be provided. 
Description will now be made of a case where the object to be photographed 
is dark and the stroboscopic lamp 11 is used. 
When the release button 18 is depressed and the contacts 17a and 17b are 
closed, the central calculation processing portion 10 examines the outputs 
of the light metering elements 21a-21e converted through the amplifiers 
22a-22e and the A/D converters 23a-23e, and if it judges that the outputs 
are small, that is, the object to be photographed is dark and proper 
exposure cannot be accomplished unless the stroboscopic lamp 11 is made to 
emit light, the preparation for the light emission of the stroboscopic 
lamp, for example, the charging of a capacitor, not shown, is effected. 
When the release button 18 is then depressed deeply and the contacts 17b 
and 17c are closed, the photographing operation is performed. In this 
case, the light emission of the stroboscopic lamp 11 is effected during 
the charge accumulation in the image pickup element 3. At this time, the 
central calculation processing portion 10 closes the switch 24d and opens 
the other switches 24b and 24c so that gray scale modification may be done 
in the third gray scale modification circuit 24g which is smallest in 
.gamma. value, at the stage whereat the central calculation processing 
portion 10 has examined the outputs of the light metering elements 21a-21e 
converted through the amplifiers 22a-22e and the A/D converters 23a-23e. 
This is because if photographing is effected by the use of the 
stroboscopic lamp 11 approximate to a point source of light, the contrast 
of the object to be photographed and the shadow formed in the background 
thereof will be strong and an image having a great difference in quantity 
of light will be output and therefore, if the .gamma. value in gray scale 
modification is made small, moderate contrast will finally be provided and 
a visually good image will be provided. The operation thereafter is as 
previously described. 
The case of the light emission of the stroboscopic lamp has been described 
with respect to a case where the outputs of all the light metering 
elements 21a-21e are small, but even when only the output of one of the 
plurality of light metering elements, for example, the light metering 
element 21c which is the light metering element for light-metering the 
central portion, if small, that is, when it is judged that photographing 
will be effected in a backlight condition in which the background is light 
and the central object to be photographed is dark, a visually good image 
can be photographed without the central object to be photographed becoming 
dark if the stroboscopic lamp 11 is made to emit light to the central 
object to be photographed (the main object to be photographed). In such 
case, by the stroboscopic lamp 11 being made to emit light, the difference 
in quantity of light between the background and the main object to be 
photographed becomes relatively small and therefore, design is made such 
that the gray scale modification circuit 24f having a medium degree of 
.gamma. value is selected. 
The setting of .gamma. by the aforedescribed central calculation processing 
portion 10 will hereinafter be described with reference to the flow chart 
shown in FIG. 7. In FIG. 7, steps given the same symbols as those in FIG. 
4 are the same steps as those in FIG. 4. 
When the release switch 18 is depressed lightly by the user and the 
contacts 17a and 17b are closed, the central calculation processing 
portion 10 starts the .gamma. set up routine at a step 21 (S21). 
At a step 2 (S2), whether the object field is dark is judged on the basis 
of whether the weighted mean value and the normal mean value of the 
outputs P.sub.1 -P.sub.5 of the A/D converters 22a-22e are lower than a 
predetermined value. If it is judged that the object field is dark, at a 
step 3 (S3), the light emission of the stroboscopic lamp is prepared, and 
at a step 22 (S22), the switch 24d is closed and the third gray scale 
modification circuit 24g in which .gamma.=0.45 is selected, and at a step 
5(S5), return is made. 
If at the step 2, it is judged that the object field is not dark, at a step 
6 (S6), whether the light is backlight is judged. The judgment as to 
whether the light is backlight is done, for example, on the basis of 
whether the difference between the luminance of the central light metering 
area 21c and the average luminance of the plurality of marginal light 
metering areas 21a, 21b, 21d and 21e exceeds a predetermined value. If at 
the step 6 (S6), it is judged that the light is backlight, at a step 7 
(S7), the light emission of the stroboscopic lamp is prepared, and at a 
step 23 (S23), the switch 24c is closed and the second gray scale 
modification circuit 24f in which .gamma.=0.7 is selected, and at the step 
5 (S5), return is made. 
If at the step 6, it is judged that the light is not backlight, at a step 9 
(S9), the maximum value of the absolute values of luminance differences 
.vertline.P.sub.i -P.sub.j .vertline. (i=1-5, j=1-5) is defined as a 
maximum luminance difference .sigma.. Subsequently, at a step 10 (S10), 
the maximum luminance difference .sigma. is compared with the maximum 
allowable value .sigma..sub.MAX of the luminance difference prestored in 
the central calculation processing portion 10, and if the maximum 
luminance difference .sigma. is greater than the maximum allowable value 
.sigma..sub.MAX of the luminance difference, at a step 24 (S24), the 
switch 24d is closed and the third gray scale modification circuit 24g in 
which .gamma.=0.45 is selected, and at the step 5 (S5), return is made. 
If at the step 10 (S10), the maximum luminance difference .sigma. is equal 
to or less than the maximum allowable value .sigma..sub.MAX of the 
luminance difference, at a step 12 (S12), the maximum luminance difference 
.sigma. is compared with the minimum allowable value .sigma..sub.MIN of 
the luminance difference prestored in the central calculation processing 
portion 10. If the maximum luminance distance .sigma. is greater than the 
minimum allowable value .sigma..sub.MIN of the luminance difference, at a 
step 25 (S25), the switch 24c is closed and the second gray scale 
modification circuit 24f in which .gamma.=0.7 is selected, and at the step 
5 (S5), return is made. 
If at the step 12 (S12), the maximum luminance difference .sigma. is equal 
to or less than the minimum allowable value .sigma..sub.MIN of the 
luminance difference, at a step 26 (S26), the switch 24b is closed and the 
first gray scale modification circuit in which .gamma.=1 is selected, and 
at the step 5 (S5), return is made. 
In the present embodiment, the change-over system using switches is adopted 
so that the degree of the gray scale modification characteristic may be 
stepwisely changed, but alternatively, design may be made such that the 
degree of the gray scale modification characteristic is continuously 
changed. Also, as regards the use of the stroboscopic lamp, provision may 
be made of a selection switch for selecting the presence or absence of 
light emission not only by the judgment of the central calculation 
processing portion, but also by the user's judgment, and design may be 
made such that the gray scale modification characteristic is changed over 
in response to this switch. 
Also, in the present embodiment, the characteristic of gamma correction is 
used as the gray scale modification means, but alternatively, any 
modification table may be memorized in a memory and any characteristic may 
be set and used, such as effecting gray scale modification on the basis of 
the modification table. 
Also, in the present embodiment, selection of the gray scale modification 
characteristic is effected on the basis of the difference between the 
maximum value and the minimum value of the output values from the light 
metering means, whereas the method of calculation is not restricted 
thereto, but conversion tables corresponding to the output values may be 
memorized by the central calculation processing portion and selection of 
the gray scale modification characteristic may be effected on the basis of 
such conversion tables. 
As described above, according to the second embodiment, a plurality of 
portions of an object to be photographed are light-metered by the light 
metering means and the gray scale modification characteristic is changed 
in conformity with the difference in quantity of light, whereby a good 
image visually free of unnaturalness and having moderate contrast can 
always be obtained from any object to be photographed. Also, even when the 
object to be photographed is illuminated by the light emitting means and 
the difference in quantity of light becomes great, a good image visually 
free of unnaturalness can be obtained by changing the gray scale 
modification characteristic to a gray scale modification characteristic 
for weakening the contrast.