JP3754812B2 - Negative film imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative film imaging apparatus that captures a negative photographic film and outputs a positive image signal.
[0002]
[Prior art]
Conventionally, in an imaging apparatus such as a video camera, a means for taking a photographic film and viewing it on a television monitor or taking it into a computer or the like has been devised. Hereinafter, a conventional example will be described with reference to the drawings.
[0003]
(Conventional example 1)
FIG. 10 is a block diagram showing the configuration of the photographic negative film imaging apparatus of Conventional Example 1. In FIG. In FIG. 10, 501 is a light source for film irradiation, 502 is a negative photographic film (hereinafter referred to as negative film), 503 is an imaging lens, 504 is an aperture for exposure control, and 505 is an image sensor that photoelectrically converts incident light. 506, a gain control amplifier, 507, an inverting circuit for converting a negative image into a positive image, 508, a clamp circuit, 509, a signal processing circuit including white balance processing, gamma processing, an encoder circuit, and the like, 510 drives an aperture 504 An aperture driving circuit 511 is an exposure control circuit.
[0004]
FIG. 11 is a diagram for explaining the processing process of the video signal level in the first conventional example. (E1) is the video level of the negative film before exposure control, the upper part of the frame is the upper limit of the dynamic range, the lower part is the lower limit, (e2) is the video signal that is at the appropriate level as a result of exposure control, (e3 ) Is a video signal as a result of the inversion process, and (e4) is a video signal as a result of the clamp process performed on (e3).
[0005]
Light from the film irradiation light source 501 passes through the negative film 502, passes through an imaging lens 503, and is adjusted to an exposure amount by a diaphragm 504 and then imaged on an image sensor 505. The video signal photoelectrically converted by the image sensor 505 is amplified by the gain control amplifier 506 and supplied to the exposure control circuit 511 (see e1, the same applies hereinafter). Here, the exposure control circuit 511 drives the aperture 504 via the aperture drive circuit 510 so that the video signal level becomes an appropriate level. Here, the feedback-controlled video signal (e2) having an appropriate level is supplied to the inverting circuit 507. The inversion circuit 507 inverts the level of the video signal at an appropriate level. At this time, the upper limit of the dynamic range of the circuit is converted into the lower limit and the lower limit is converted into the upper limit, and the white peak portion of the video signal becomes the dark peak. However, in this state, the difference from the white peak of the video signal before inversion to the upper limit of the dynamic range becomes the signal level of the dark peak after inversion as it is (e3). The clamp circuit 508 detects a dark peak of the inverted video signal and performs a clamp process so that the level is optimized. For example, in the case of a luminance signal, if it is assumed that a black level signal is included in the video signal, a video signal of an appropriate level is obtained by performing a clamping process so that the luminance signal of the black portion becomes a pedestal level. Can be obtained (e4). Hereinafter, this clamping process is referred to as dark clamping.
[0006]
FIG. 12 is a graph showing the clamp reference level of Conventional Example 1. CLmin is always given as the clamp reference level of the clamp circuit 508 regardless of conditions, and dark clamping is performed so that the dark peak portion becomes equal to CLmin.
[0007]
(Conventional example 2)
FIG. 13 is a block diagram showing a configuration of a photographic negative film imaging apparatus of Conventional Example 2. In FIG. 13, reference numeral 601 denotes a film irradiation light source, 602 a negative photographic film, 603 an imaging lens, 604 an aperture for exposure control, 605 an image pickup device that photoelectrically converts incident light, and 606 a gain control amplifier. 607 is an inverting circuit for converting a negative image into a positive image, 608 is a clamp circuit, 609 is a signal processing circuit including white balance processing, gamma processing, an encoder circuit, 610 is an aperture driving circuit for driving the aperture 604, 611 is An exposure control circuit 614 is an average value detection circuit.
[0008]
FIG. 14 is a diagram for explaining the process of the video signal level in the second conventional example. (G1) is the image level of the negative film before exposure control, and the upper limit of the frame is the upper limit of the dynamic range and the lower limit is the lower limit. The negative film is a state in which a photosensitive material is applied to an orange base film, and the density of the base varies depending on the film. When the density is low, the signal level is generally increased. (G2) is a video signal that is at an appropriate level as a result of exposure control, (g3) is a video signal as a result of inversion processing, and (g4) is a video as a result of clamping processing on (g3). Signal.
[0009]
Light from the film irradiation light source 601 passes through the negative film 602, passes through an imaging lens 603, is adjusted in exposure amount by a diaphragm 604, and then imaged on an image sensor 605. The video signal photoelectrically converted by the image sensor 605 is amplified by the gain control amplifier 606 and supplied to the average value detection circuit 614 (g1). The average value detection circuit 614 samples the signal level of the entire image and outputs the average value as the video signal level. The detected average value corresponds to the “average value” of (g1). Here, the exposure control circuit 611 drives the aperture 604 via the aperture drive circuit 610 so that the video signal level supplied from the average value detection circuit 614 becomes an appropriate level. This appropriate level corresponds to the “target value” in (g2). Here, the feedback-controlled video signal (g2) having an appropriate level is supplied to the inverting circuit 607, and the inverting circuit 607 inverts the level of the video signal having an appropriate level. At this time, the upper limit of the dynamic range of the circuit is converted into the lower limit and the lower limit is converted into the upper limit, and the white peak portion of the video signal becomes the dark peak. However, in this state, the difference from the white peak of the video signal before inversion to the upper limit of the dynamic range becomes the signal level of the dark peak after inversion as it is (g3). The clamp circuit 608 detects the dark peak of the inverted video signal and performs a clamp process so that the level is optimized. For example, in the case of a luminance signal, if it is assumed that a black level signal is included in the video signal, an image with an appropriate level is obtained by performing a clamping process so that the luminance luminance signal of the black portion becomes a pedestal level. A signal can be obtained (g4).
[0010]
[Problems to be solved by the invention]
However, in the case of the negative film imaging device of the conventional example 1, when a negative film with a low contrast is photographed, the exposure control circuit may not be able to control to an appropriate level. There was a problem that the video was low, and the original video could not be obtained.
[0011]
FIG. 11B is a diagram for explaining the process of processing the video signal level when a negative film with a low contrast is photographed. (F1) is the video level of the negative film before exposure control, the upper part of the frame is the upper limit of the dynamic range, the lower part is the lower limit, and (f2) is the video signal that is at the appropriate level as a result of exposure control, (f3 ) Is the video signal resulting from the inversion process, and (f4) is the video signal resulting from the dark clamp process performed on (f3). If exposure control is performed within the range of the dynamic range for the negative film of (f1), the state of (f2) becomes the limit. When this image is inverted (h3) and the above-described dark clamp processing of the conventional example 1 is performed, the result is as shown in (f4), and the exposure control is not properly performed with the image level being low as a whole.
[0012]
Further, in the negative film imaging apparatus of the conventional example 2, since exposure control is performed so that the average level before reversal is constant, there is a problem that the image level after reversing and clamping is not known, depending on the type of negative film In some cases, the original video could not be obtained because the video level was not stable due to the difference in the density of the base and the exposure state during photography.
[0013]
FIG. 14B is a diagram for explaining the processing process of the video signal level when a negative film base having a high density is photographed. (H1) is the image level of the negative film before exposure control, the upper limit of the dynamic range is above the frame and the lower limit is the lower limit. When the base density is high, the signal level is overall compared to (g1). It becomes low. (H2) is a video signal at an appropriate level as a result of exposure control, (h3) is a video signal as a result of inversion processing, and (h4) is a video as a result of clamping processing on (h3). Signal. When exposure control is performed so that the average level becomes an appropriate value for the negative film of (h1), the state of (h2) becomes appropriate. When this image is inverted (h3) and clamp processing is performed, the result is as shown in (h4), and this does not allow proper exposure control with a high image level as a whole.
[0014]
The present invention has been made under such circumstances, and an object of the present invention is to provide a negative film imaging apparatus that can always obtain a video signal of an appropriate level.
[0015]
[Means for Solving the Problems]
  SaidSolve the problemTherefore, in the present invention, the negative film imaging device is the following (1),(2)Configure as follows.
  (1) A negative film imaging apparatus for photographing a negative photographic film and outputting a positive image signal,
Imaging means for converting the image irradiated through the negative photographic film into a video signal;
Exposure control means for adjusting the level of the video signal converted by the imaging means;
Contrast detection means for detecting a contrast level of a video signal whose exposure is controlled by the exposure control means;
Reversing means for reversing the level of the exposure-controlled video signal;
Clamp level control means for changing the clamp reference level to increase as the contrast level detected by the contrast detection means becomes smaller than a predetermined value;
Clamp means for clamping the signal level of the video signal inverted by the inversion means to a clamp reference level changed by the clamp level control means,
A negative film imaging device.
(2) A negative film imaging device for photographing a negative photographic film and outputting a positive image signal,
Imaging means for converting the image irradiated through the negative photographic film into a video signal;
Exposure control means for adjusting the level of the video signal converted by the imaging means;
Exposure level detection means for detecting a difference between an average level and a peak level of the video signal exposure controlled by the exposure control means as an exposure level;
Reversing means for reversing the level of the exposure-controlled video signal;
Clamp level control means for changing the clamp reference level so as to increase the clamp reference level as the exposure level detected by the exposure level detection means becomes smaller than a predetermined value;
Clamp means for clamping the signal level of the video signal inverted by the inversion means to a clamp reference level changed by the clamp level control means,
A negative film imaging device.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to examples of negative film imaging devices.
[0027]
【Example】
(Example 1)
FIG. 1 is a block diagram illustrating a configuration of a “negative film imaging apparatus” according to the first embodiment. This apparatus includes a negative film image contrast detection device and a clamp level control device, and enables an appropriate video signal level, that is, optimum exposure control, by changing the clamp level in accordance with the contrast level.
[0028]
In FIG. 1, 101 is a light source for film irradiation, 102 is a negative film, 103 is an imaging lens, 104 is a diaphragm for controlling exposure, 105 is an image sensor that photoelectrically converts incident light, and 106 is a gain control amplifier. 107 is an inverting circuit for converting a negative image into a positive image, 108 is a clamp circuit, 109 is a signal processing circuit including white balance processing, gamma processing, an encoder circuit, etc. 110 is a diaphragm driving circuit for driving the diaphragm 104, 111 is An exposure control circuit, 112 is a contrast detection circuit, and 113 is a clamp level control circuit.
[0029]
The signal processing process of the present embodiment will be described with reference to FIG. 2A for a negative film having sufficient contrast. The light from the film irradiation light source 101 passes through the negative film 102 and is an imaging lens. An image is formed on the image sensor 105 after the exposure amount is adjusted by the diaphragm 104 through 103. The video signal photoelectrically converted by the image sensor 105 is amplified by the gain control amplifier 106 and supplied to the exposure control circuit 111 (see a1, the same applies hereinafter). Here, the exposure control circuit 111 drives the aperture 104 via the aperture drive circuit 110 so that the video signal level becomes an appropriate level. The video signal (a2) that has been feedback-controlled and has reached an appropriate level is supplied to the inverting circuit 107. The inversion circuit 107 inverts the level of the video signal at an appropriate level. At this time, the upper limit of the dynamic range of the circuit is converted into the lower limit and the lower limit is converted into the upper limit, and the white peak portion of the video signal becomes the dark peak. However, in this state, the difference from the white peak of the video signal before inversion to the upper limit of the dynamic range becomes the signal level of the dark peak after inversion as it is (a3). The contrast detection circuit 112 detects the contrast level of the video signal (a2) after exposure control, and supplies the contrast level signal to the clamp level control circuit 113.
[0030]
FIG. 3 is a graph for explaining the operation of the clamp level control circuit 113 of this embodiment. When the contrast level in the figure is supplied from the contrast detection circuit 112, a clamp level corresponding to the contrast level is output to the clamp circuit. In the case of the image shown in FIG. 2 (a2), the contrast level is sufficiently larger than Cth shown in FIG. 3, so that the clamp level output is the minimum value CLmin. The clamp circuit 108 detects the dark peak of the inverted video signal and performs dark clamp processing so that the level becomes a level given from the clamp level control circuit 113 (a4).
[0031]
Next, with reference to FIGS. 2B and 2C, the signal processing process of this embodiment will be described for a negative film having a low contrast. The negative contrast film (b) is exposed to the dynamic range limit (b2) and then inverted (b3). Here, when the contrast level of (b2) is equal to or lower than Cth in FIG. 3, the clamp level control circuit 113 outputs a level between CLmin and CLmax. The clamp circuit 508 of the conventional example 1 is clamped to the level (b4). However, in this embodiment, the clamp circuit 508 is clamped according to the output of the clamp level control circuit 113, so the level is (b4 '). In (b4), the overall video is low in level, but in (b4 ′), the average level of the video is increased, so that a video signal with an appropriate level close to the original subject can be obtained.
[0032]
In this way, by changing the clamp level according to the contrast level, even a negative film with low contrast can be photographed with an appropriate exposure amount without lowering the video signal level.
[0033]
Although the present embodiment has been described with respect to the luminance signal, it goes without saying that the same processing can be performed with a plurality of color signals and color difference signals, and the clamp level of the color signal can be controlled using the contrast level of the luminance signal. . Further, the relationship between the contrast level and the clamp level may not be the same as that in the graph of FIG.
[0034]
(Example 2)
FIG. 4 is a block diagram illustrating a configuration of a “negative film imaging apparatus” according to the second embodiment. This apparatus includes a negative film image exposure level detection device and a clamp level control device, and enables an appropriate video signal level, that is, optimal exposure control by changing the clamp level in accordance with the exposure level.
[0035]
In FIG. 4, 201 to 211 are the same as 101 to 111 in FIG. 1, respectively, 212 is an exposure level detection circuit, and 213 is a clamp level control circuit.
[0036]
The operation will be described with reference to FIG.
[0037]
The flow of video signals 201 to 211 in the figure is the same as that of 101 to 111 in FIG. The exposure level detection circuit 212 detects the overall average level and white peak of the video signal (a2) after exposure control, and supplies the difference as an exposure level signal to the clamp level control circuit 313. The white peak in (a2) corresponds to the dark peak after inversion, and the difference between this and the average level is equal to the average level of the entire image after the inversion. A condition for setting the video signal level to an appropriate level is that the overall average level after inversion is an appropriate value.
[0038]
FIG. 5 is a graph for explaining the operation of the clamp level control circuit 213 of this embodiment. When the exposure level in the drawing is supplied from the exposure level detection circuit 212, a corresponding clamp level is output to the clamp circuit 208. In the case of the image of FIG. 2 (a2), it can be said that the exposure level is sufficiently higher than Eth of FIG. 5, that is, the overall average level after inversion is an appropriate value, and the clamp level output is the minimum value CLmin. The clamp circuit 208 detects the dark peak of the inverted video signal and performs dark clamp processing so that the level becomes a level given from the clamp level control circuit 213 (a4).
[0039]
Next, the signal processing process of this embodiment will be described for a negative film having a low exposure level. The negative film (b1) having a low exposure level is controlled to the limit of the dynamic range (b2) and then inverted (b3). Here, when the exposure level in (b2) is equal to or lower than Eth in FIG. 5, the clamp level control circuit 213 outputs a level between CLmin and CLmax. The clamp level control circuit 213 of the conventional example 1 outputs a level between CLmin and CLmax. The clamp circuit 508 of the conventional example 1 is clamped to the level (b4). However, in this embodiment, the level is set to (b4 ′) because the clamp is performed according to the output of the clamp level control circuit 213. In (b4), the overall video is low in level, but in (b4 ′), the average level of the video is increased, so that a video signal with an appropriate level close to the original subject can be obtained.
[0040]
Thus, by changing the clamp level in accordance with the exposure level, it is possible to shoot a negative film with a low exposure level without deteriorating the video signal level with an appropriate exposure amount.
[0041]
Although the present embodiment has been described with respect to the luminance signal, it goes without saying that the same processing can be performed with a plurality of color signals and color difference signals, and the clamp level of the color signal can be controlled using the exposure level of the luminance signal. . Further, the relationship between the exposure level and the clamp level may not be the same as the graph of FIG.
[0042]
(Example 3)
FIG. 6 is a block diagram illustrating a configuration of a “negative film imaging apparatus” according to the third embodiment. This device comprises a negative film image peak level detection device and an average value detection device, and enables an appropriate video signal level, that is, optimal exposure control by making the difference between the peak value and the average value appropriate. .
[0043]
In FIG. 6, 301 is a film irradiation light source, 302 is a negative film, 303 is an imaging lens, 304 is a diaphragm for exposure control, 305 is an image sensor that photoelectrically converts incident light, 306 is a gain control amplifier, Reference numeral 307 denotes an inversion circuit that converts a negative image into a positive image, 308 denotes a clamp circuit, 309 denotes a signal processing circuit including white balance processing, gamma processing, an encoder circuit, and the like, 310 denotes an aperture driving circuit that drives the aperture 304, and 311 denotes exposure. A control circuit, 312 is a screen division integration circuit that divides an image, samples and integrates, 313 is a peak value detection circuit that outputs a value of a region having the highest video level in the image, and 314 outputs an average level of the entire image An average value detection circuit 315 is an arithmetic circuit that subtracts the average value from the peak value and outputs an exposure level.
[0044]
FIG. 7 is a diagram for explaining the processing process of the video signal level of this embodiment. (C1) is the image level of the negative film before exposure control. The upper limit of the frame is the upper limit of the dynamic range and the lower limit is the lower limit. The negative film is a state in which a photosensitive agent is applied to an orange base film, and the density of the base varies depending on the film. When the density is low, the signal level is generally high. (C2) is a video signal at an appropriate level as a result of exposure control, (c3) is a video signal as a result of inversion processing, and (c4) is an appropriate exposure as a result of performing clamp processing on (c3). This is a video signal.
[0045]
Light from the film irradiation light source 301 passes through the negative film 302, passes through an imaging lens 303, is adjusted in exposure amount by a diaphragm 304, and is imaged on an image sensor 305. The video signal photoelectrically converted by the image sensor 305 is amplified by the gain control amplifier 306 and supplied to the screen division integration circuit 312 (c1). The screen division integration circuit 312 divides the image into 128 regions, and samples and integrates the signals in each region. The peak value detection circuit 113 outputs the maximum value among the integration values of each area of the screen division integration circuit 112 as a peak value. The detected peak value corresponds to the “peak value α” in (c1). The average value detection circuit 314 calculates the average signal level of the entire image by adding all integral values of 128 regions and dividing by 128, and outputs the average signal level as an average value. The detected average value corresponds to “average value β” in (c1). The arithmetic circuit 315 subtracts the average value β supplied by the average value detection circuit 314 from the peak value α supplied by the peak value detection circuit 313, and outputs the result as an exposure level (α−β). This exposure level corresponds to the level δ from the pedestal level to the average value of all the images in the signal (c4) which is inverted and clamped later. Here, the exposure control circuit 311 drives the diaphragm 304 via the diaphragm drive circuit 310 so that the exposure level supplied from the arithmetic circuit 315 becomes an appropriate level. This appropriate level corresponds to the “target level γ” in (c2). The video signal (c2) that has been feedback-controlled and has reached an appropriate level is supplied to the inverting circuit 307, and the inverting circuit 307 inverts the level of the video signal that has reached the appropriate level. At this time, the upper limit of the dynamic range of the circuit is converted into the lower limit and the lower limit is converted into the upper limit, and the white peak portion of the video signal becomes the dark peak. However, in this state, the difference from the white peak of the video signal before inversion to the upper limit of the dynamic range becomes the signal level of the dark peak after inversion as it is (c3). The clamp circuit 108 detects the dark peak of the video signal after inversion, and performs a clamp process so that the level becomes optimum. For example, in the case of a luminance signal, if it is assumed that a black level signal is included in the video signal, a video signal of an appropriate level is obtained by performing a clamping process so that the luminance signal of the black portion becomes a pedestal level. Can be obtained (c4). By the way, apart from taking a negative film, as a means for controlling exposure in an image pickup apparatus such as a normal video camera or electronic camera, generally, a method of making the average level and the center level of an image constant is taken. In the case of the present embodiment, if the average level δ becomes constant in (c4) after the clamping process, the same control result as the general exposure control is achieved. However, as described above, (c2) and ( between c4)
(Target level γ) = (Average level δ)
In (c2)
(Peak value α) − (Average value β) = (Target level γ)
This case corresponds to this state.
[0046]
Next, the signal processing process of this embodiment will be described for a negative film having a high film base density. The negative film (d1) having a higher film base density than (c1) is smaller in both peak level and average level than (c1), but exposure control is performed so that the difference is equal to the target level γ in (c2). (D2). After that, it is inverted (d3), and the clamp circuit 308 performs the clamping process so that the dark peak level of the video signal becomes optimum, so that the level becomes (d4). In conventional example 2, as shown in FIG. 14 (h4), the entire image is high in level, but in (d4) of this embodiment, the average level of the image is equal to (c4) and is close to the original subject. A video signal at an appropriate level can be obtained.
[0047]
By controlling the exposure of the difference between the peak value and the average value to an appropriate level, it becomes possible to photograph with an appropriate exposure amount regardless of the film base density.
[0048]
Although the present embodiment has been described with negative films having different film base densities, it is possible to compensate for a negative film state due to overexposure or underexposure during photography, or a difference in exposure state due to contrast of a subject. Although exposure control in this embodiment is performed by an optical aperture, it goes without saying that means such as a gain control amplifier or an electronic shutter may be used.
[0049]
(Example 4)
FIG. 8 is a block diagram illustrating a configuration of a “negative film imaging apparatus” according to the fourth embodiment. This device includes a negative film image peak level detection device and a center-weighted average device, and enables an appropriate video signal level, that is, optimum exposure control by making the difference between the peak value and the average value appropriate. .
[0050]
Reference numerals 401 to 411 in FIG. 6 are the same function parts as 301 to 311 in FIG. 6, respectively. 413 is a peak hold circuit for peak-holding the video signal in the image and outputting the highest video level value. 414 is the entire image. A center-weighted average circuit 415 for outputting the center-weighted average level is an arithmetic circuit 415 that outputs the exposure level by subtracting the center-weighted average value from the peak value.
[0051]
The operation will be described with reference to FIG. The flow of video signals 401 to 411 in the figure is the same as 301 to 311 in FIG. The video signal amplified by the gain control amplifier 406 is supplied to the peak hold circuit 413 and the center weighted average circuit 314 (c1). Peak hold and output the highest video level. The detected peak value corresponds to the “peak value α” in (c1). The center-weighted average circuit 314 assigns weights to the central portion of the image (see FIG. 9A), calculates the average signal level of the entire image (FIG. 9B), and outputs it as the center-weighted average value. The detected center-weighted average value corresponds to “average value β” in (c1). The arithmetic circuit 415 subtracts the average value β supplied from the center-weighted average circuit 414 from the peak value α supplied from the peak hold circuit 413, and outputs the result as an exposure level (α−β). This exposure level corresponds to the level δ from the pedestal level to the center-weighted average value of all the images in the signal (c4) that is inverted and clamped later. Here, the exposure control circuit 411 drives the diaphragm 404 via the diaphragm drive circuit 410 so that the exposure level supplied from the arithmetic circuit 415 becomes an appropriate level. This appropriate level corresponds to the “target level γ” in (c2). The video signal (c2) that has been feedback-controlled and has reached an appropriate level is supplied to the inverting circuit 307, and the inverting circuit 307 inverts the level of the video signal that has reached the appropriate level. At this time, the upper limit of the dynamic range of the circuit is converted into the lower limit and the lower limit is converted into the upper limit, and the white peak portion of the video signal becomes the dark peak. However, in this state, the difference from the white peak of the video signal before inversion to the upper limit of the dynamic range becomes the signal level of the dark peak after inversion as it is (c3). The clamp circuit 408 detects a dark peak of the inverted video signal and performs a clamp process so that the level is optimized. For example, in the case of a luminance signal, if it is assumed that a black level signal is included in the video signal, a video signal of an appropriate level is obtained by performing a clamping process so that the luminance signal of the black portion becomes a pedestal level. Can be obtained (c4).
[0052]
By the way, in addition to negative film shooting, as a means of exposure control in an imaging device such as a normal video camera or electronic camera, the main subject is often located at the center of the screen, so the center weight of the image is generally used. A technique is used to keep the average level constant. By using the center-weighted average value instead of the overall average value, exposure control becomes more accurate when shooting in backlight or when the surroundings are dark. In this embodiment, center-weighted average metering is employed in order to obtain such an effect even during negative film photography. In the case of the present embodiment, if the center-weighted average level δ becomes constant in (c4) after the clamping process, the same control result as the general exposure control is achieved, but as described above (c2) And (c4)
(Target level γ) = (Average level δ)
In (c2)
(Peak value α) − (Average value β) = (Target level γ)
This case corresponds to this state.
[0053]
Next, the signal processing process of this embodiment will be described for a negative film having a high film base density. The negative film (d1) having a higher film base density than (c1) is smaller than (c1) in both the peak level and the center-weighted average level, but the difference is equal to the target level γ in (c2). It is controlled as shown in (d2). After that, it is inverted (d3), and the clamp circuit 308 performs the clamping process so that the dark peak level of the video signal becomes optimum, so that the level becomes (d4). In Conventional Example 2, as shown in (h4) of FIG. 14, the entire image has a high level, but in this example, the center-weighted average level of the image is equal to (c4) as shown in (d4). Thus, it is possible to obtain a video signal of an appropriate level close to the original subject.
[0054]
By controlling the exposure of the difference between the peak value and the center weighted average value to an appropriate level, it is possible to photograph with an appropriate exposure amount with high accuracy regardless of the film base density.
[0055]
Although the present embodiment has been described with negative films having different film base densities, it is possible to compensate for a negative film state due to overexposure or underexposure during photography, or a difference in exposure state due to contrast of a subject. The center-weighted average of this embodiment simply averages two regions with different weights, but this may be any commonly used method. Not only the central weighted average but also a simple average can be used. Needless to say, the exposure control of this embodiment may use means such as a gain control amplifier and an electronic shutter performed by an optical aperture.
[0056]
【The invention's effect】
  As explained above,Claim 1According to the inventionIfLamp reference levelSince the image is changed so as to increase as the contrast decreases, for example, a video signal having an appropriate level can always be obtained even with a negative film having a low contrast.
[0057]
  According to the invention of claim 2,Since the clamp reference level is changed so as to increase as the exposure level decreases, for example, even a negative film with a low exposure level can always obtain a video signal of an appropriate level.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a first embodiment.
FIG. 2 is an operation explanatory diagram of the first embodiment.
FIG. 3 is a correlation graph between the contrast level and the clamp level in Example 1.
FIG. 4 is a block diagram showing the configuration of the second embodiment.
FIG. 5 is a correlation graph between the exposure level and the clamp level in Example 2.
FIG. 6 is a block diagram showing the configuration of the third embodiment.
FIG. 7 is an operation explanatory diagram of the third embodiment.
FIG. 8 is a block diagram showing the configuration of the fourth embodiment.
9 is a conceptual diagram of center-weighted average metering in Example 4. FIG.
FIG. 10 is a block diagram showing the configuration of Conventional Example 1
11 is an operation explanatory diagram of Conventional Example 1. FIG.
12 is a correlation graph between contrast level and clamp level in Conventional Example 1. FIG.
FIG. 13 is a block diagram showing the configuration of Conventional Example 2
FIG. 14 is an operation explanatory diagram of Conventional Example 2;
[Explanation of symbols]
105 Image sensor
107 Inversion circuit
108 Clamp circuit
111 Exposure control circuit
112 Contrast detection circuit
113 Clamp level control circuit

Claims (2)

A negative film imaging device for photographing a negative photographic film and outputting a positive image signal,
Imaging means for converting the image irradiated through the negative photographic film into a video signal;
And exposure control means for adjusting the level of the converted video signal by the image pickup means,
Contrast detecting means for detecting the contrast level of the exposure control video signal by the exposure control means,
Reversing means for reversing the level of the exposure-controlled video signal;
Clamp level control means for changing the clamp reference level to increase as the contrast level detected by the contrast detection means becomes smaller than a predetermined value;
And clamping means for clamping the signal level of the video signal which is inverted by said inverting means to the clamp reference level is varied by the clamp level control means,
Negative film imaging apparatus comprising: a. A negative film imaging device for photographing a negative photographic film and outputting a positive image signal,
Imaging means for converting the image irradiated through the negative photographic film into a video signal;
And exposure control means for adjusting the level of the converted video signal by the image pickup means,
And exposure level detecting means for detecting a difference between the average level and the peak level of the exposure control video signal by the exposure control means as an exposure level,
Reversing means for reversing the level of the exposure-controlled video signal;
Clamp level control means for changing the clamp reference level so as to increase the clamp reference level as the exposure level detected by the exposure level detection means becomes smaller than a predetermined value ;
Clamp means for clamping the signal level of the video signal inverted by the inversion means to a clamp reference level changed by the clamp level control means,
Negative film imaging apparatus comprising: a.

Images