Abstract: Automatic white balancing and/or autoexposure as useful in a digital camera extracts color channel gains from comparisons of image colors with reference colors under various color temperature illuminants and/or extracts exposure settings from illuminance mean, illuminance variance, illuminance minimum, and illuminance maximum in areas of an image with a trained neural network.

Abstract: An image processing apparatus, which performs an orthogonal transformation on an image signal and which compresses the image signal, includes a control unit for controlling a range of the image signal based on a coefficient of a DC component of an output of the orthogonal transformation before the orthogonal transformation.

Abstract: The image sensing device adapted to compose an appropriate single picture from a plurality of pictures of different exposures obtained from the same subject, wherein the camera operation is controlled using as a reference the signal of one of said plurality of pictures of different exposures.

Abstract: A method of creating an image 4 obtained from say a camera 1 to obtain a substantially linear representation of the brightness of the image includes, for each of a set of pixels (x, y) in a two dimensional array, calculating, in a computer 3, an estimate of the true image intensity (ixy) as a weighted average of n samples of the apparent image intensity (&ngr;n,xy).

Abstract: A monochrome camera system, includes a processor for producing an image signal, a first circuit for selectively adjusting an overall gain of the image signal produced by the processor, and a second circuit, coupled to the processor. The second circuit selectively adjusts a gain of a portion of the image signal within a predefined region of a field of the image without affecting an overall gain set by the first circuit of other portions of the image field.

Abstract: An embodiment of the invention is a method of generating a final exposure setting, including, (a) selecting one of a number of predetermined exposure settings as a current exposure setting for a solid state camera having a camera imager, (b) generating a captured scene by the camera imager using the current exposure setting, (c) selecting according to an automated search methodology another one of the exposure settings to be the current setting in response to the captured scene being underexposed or overexposed, and, (d) repeating (b) and (c) until the captured scene is neither underexposed or overexposed.

Abstract: A camera comprises a beam splitter configured to divide an incident light from a subject through a photographing lens, an eyepiece lens configured to observe the incident light divided by the beam splitter with a viewfinder, a relay lens provided between the beam splitter and the eyepiece lens, and a shutter provided in a vicinity of the relay lens and configured to cut a reverse-incident light from the eyepiece lens.

Abstract: A visual sensor capable of expanding a dynamic range with a little load of processing for arithmetic operations and performing a stable detection not affected by change of conditions such as ON/OFF state of projection of reference light. A multiplying parameter A (A>1) and the number N of times of image capturing are set in accordance with ON/OFF state of the reference light projection. N images are captured with a shutter speed varying by successively multiplying an initial value by (1/A). Values of density of each pixel in the captured images are summed. Values of constants B and C in equations: 1=B·Zmax+C; 0=B·Zmin+C are obtained based on the maximum value Zmax and the minimum value Zmin of the summed values of densities of all the pixels. An output value Z′ of each pixel is obtained according to an equation: Z′=B·Z+C, using the determined values of B and C.

Abstract: An image pickup apparatus which can produce an image provided with exposure suitable for both a backlighted object and its background without requiring a mechanical member, such as an iris or the like. The image pickup apparatus has a photoelectric conversion section for photoelectrically converting a light image so as to accumulate light information and to output the light information every unit light accumulation period which forms one picture. A digital camera signal processing circuit processes an output from the photoelectric conversion section to output a video signal. A timing signal generator outputs a plurality of timing signals for setting light information accumulation time every unit light accumulation period which is set in the photoelectric conversion section.

Abstract: A photographic image is divided into a central area and a surrounding area, and video signals for the central and surrounding areas are integrated by an area integrator circuit. When an operator of video camera attached to a notebook personal computer is to photograph himself/herself with an imager of the video camera pointing toward the operator, a control microcomputer causes the integration result for the former to be multiplied by a larger weighting before both are summed. The control microcomputer generates exposure information according to the result, and compares the exposure level indicated by this information with the reference level to control an electronic shutter of an imaging device and the gain of an amplifier circuit so that the exposure level matches the reference level. Thus, the exposure of the video camera can be adjusted to an appropriate level. If the imager points towards an object on the opposite side of the operator, exposure control is performed as usual.

Abstract: In a method for determining the frame rate and exposure time for each frame of a video collection, an image capture system acquires at least two successive frames of a scene, separated in time. The two images are compared to determine if objects in the scene are in motion. If motion is detected, then the speed and displacement of the objects that are moving is determined. If the speed of the fastest moving object creates an unacceptable amount of image displacement, then the frame rate for the next frame is changed to one that produces an acceptable amount of image displacement. Also, if the speed of the fastest moving object creates an unacceptable amount of motion blur, then the exposure time for the next frame is changed to one that produces an acceptable amount of motion blur.

Abstract: An adaptive peak value detector, wherein the peak value for a peak hold section is detected, the peak hold section being selected by a peak hold control circuit. A solid-state imaging sensor generates pixel signals representative of an image and the peak value of portions of the pixel signals is detected. The exposure time of the sensor is adjusted as a function of the detected peak value and auto-focusing of the image for the camera is carried out on the basis of the image received during the adjusted exposure time.

Abstract: Briefly, a camera for film photography and electronic photography in accordance with the present invention comprising film photography mechanism for exposing a subject image on a film; a digital photography mechanism for picking up the subject image with a CCD and converting it into a digital image signal; a photometry element for measuring the brightness of the subject; a photometry unit for obtaining the subject brightness based on the image signal obtained by the digital photography mechanism; first setting means for setting the exposure conditions of the film based on the photometry results of the photometry element; second setting means for setting the image-pickup pickup conditions of the digital photography mechanism based on the photometry results of the photometry unit; control means for controlling the film photography mechanism based on the exposure conditions and controlling the digital photography mechanism based on the image-pickup conditions during a release operation; and initial conditions se

Abstract: In a video monitoring method, each of a series of frame outputs generated by a video camera is defined with a number of image regions. Each of the image regions contains a predetermined segment of a predetermined set of horizontal scan lines of the corresponding frame output. A reference brightness value is obtained for each of the image regions of a reference one of the frame outputs. A current brightness value is then obtained for each of the image regions of a current one of the frame outputs. Each of the current brightness values is compared with a respective one of the reference brightness values to detect movement of an object into one of the image regions of the current one of the frame outputs.

Abstract: Wide dynamic range operation is used to write a signal in a freeze-frame pixel into the memory twice, first after short integration and then after long integration. The wide dynamic range operation allows the intra-scene dynamic range of images to be extended by combining the image taken with a short exposure time with the image taken with a long exposure time. A freeze-frame pixel is based on voltage sharing between the photodetector PD and the analog memory. Thus, with wide dynamic range operation, the resulting voltage in the memory may be a linear superposition of the two signals representing a bright and a dark image after two operations of sampling.

Abstract: A method of improving a signal in an image sequence acquired with a digital color video camera creating a digital video signal (1) including a brightness signal component (3) and a color signal component (4) includes the steps (6, 7) of continuously evaluating the brightness signal component (3) to calculate maximum brightness values and minimum brightness values at least within a first predetermined image sector and at least for a partial sequence of images, continuously calculating offset values on the basis of at least two previously calculated minimum brightness values, continuously calculating gain values based on differences between at least to previously calculated maximum brightness values and the associated minimum brightness values, continuously modifying the brightness signal component (3) by subtracting the last calculated offset value therefrom and by then multiplying it with the last gain value, and continuously modifying the color signal component (4) by multiplying it with the last calculated

Abstract: In an image sensing system having an image sensing optical system, and an image sensing element for photoelectrically converting incoming light from the image sensing optical system, a predetermined pattern image for adjustment, which is specified in advance, is read by the image sensing element, and the image sensing element is driven to adjust its position on the basis of an output from said image sensing element, thereby adjusting the relative position of the image sensing element with respect to the image sensing optical system prior to an image sensing operation.

Abstract: An embodiment of the invention is a method of generating a final exposure setting, including, (a) selecting one of a number of predetermined exposure settings as a current exposure setting for a solid state camera having a camera imager, (b) generating a captured scene by the camera imager using the current exposure setting, (c) selecting according to an automated search methodology another one of the exposure settings to be the current setting in response to the captured scene being underexposed or overexposed, and, (d) repeating (b) and (c) until the captured scene is neither underexposed or overexposed.

Abstract: A preferred embodiment of the present invention provides a method and apparatus for correcting the offset induced by Field Effect Transistor (FET) photo-conductive effects in a solid state X-ray detector. The method and apparatus include reading out twice as many rows (scan lines) as actually exist in the X-ray detector. The additional rows may be read out between the actuation of “real” scan lines on the X-ray detector. The additional row times may be used to measure the “signal” induced by FET photo-conductivity. In a preferred embodiment, the “real” rows may be actuated during odd lines, and even lines will be used to measure the signal induced by FET photo-conductivity. To correct for the offset induced by photo-conductive FETs, an even row signal may be subtracted from the preceding odd row signal. The correction for the offset induced by photo-conductive FETs may occur in addition to normal offset correction.

Abstract: An image frame of a long-time exposure video signal from a solid stage imaging device outputting the long-time exposure video signal and a short-time exposure video signal on a time division basis is divided into a plurality of predetermined areas, and a first area in which a luminance level of the long-time exposure video signal becomes minimal is detected from a plurality of areas of the image frame. Different weighting is applied to the long-time exposure video signal of the first area and to the long-time exposure video signal of a second area other than the detected first area among a plurality of areas of the image frame, and an iris of a lens for condensing the light beams is controlled in accordance with the long-time exposure video signal so weighted.

Abstract: The exposure control apparatus comprises screen divider which divides the screen into a many areas, and high luminance decider which decides, for each area of the screen, whether a main subject having a high luminance exists within that area. Further, average luminance calculator calculates average luminance in that area of the screen which is decided as including the main subject, and exposure value determiner determines the exposure value based on the calculated average luminance.

Abstract: A digital camera has a correcting process determining section for determining an image correcting process in accordance with the metering type uses in capturing the image. In the case where spot metering is performed, a correcting process for making a metering area proper is determined, thereby making an image correction in which intention of the user is reflected. In the case where multi-area metering is performed, a metering value and a result of scene determination are transferred from an exposure determining section to a correction controlling section. By using the information obtained in the metering process also for the image correction, the correction time can be shortened.

Abstract: A light level detecting method uses an automatic gain control of an electrically transformed image signal, thereby obviating the need for a separate light sensor. Instead, the method makes use of the image signal in the recording process. The light detecting and indicating method includes the steps of: (a) setting up a reference value corresponding to an amount of light which requires an automatic gain control; (b) measuring the amount of light of an optical input signal; (c) calculating a comparative value corresponding to the amount of light, where the comparative value controls the performance of the automatic gain control; (d) comparing the reference value with the comparative value; and (e) determining that the amount of light is insufficient when the result of the comparing step falls within a predetermined gain control range.

Abstract: Apparatus for displaying a combined image of an auxiliary image and a main image includes a source of a main image signal and a source of samples representing an auxiliary image signal. A quincunx subsampler is coupled to the auxiliary image sample source and the quincunx subsampler. The sample combiner combines the main image signal and a signal representing the quincunx subsampled samples to generate a signal representing a combined image of the main and auxiliary images.

Abstract: It is an object of this invention to provide an apparatus which can properly expose a main object regardless of the background conditions. In order to achieve this object, there is provided an apparatus comprising a photometric unit for receiving object light and converting the object light into luminance signals of a plurality of areas, and a control unit for calculating the histogram of the luminance distribution on the basis of the luminance signals of the plurality of areas converted by the photometric unit, and controlling the operation of an illumination device for illuminating the object on the basis of the calculation result.

Abstract: A digital camera with an anti-blur function is provided with simple structures. The digital camera comprises an automatic exposure control mechanism for an automatic exposure mode and inclinometer. As sub-modes, the automatic exposure mode comprises a normal program mode and a high-shutter-speed priority program mode. Output of the inclinometer is repeatedly checked at a predetermined period to detect camera-shake. Camera-shake is determined by stable or unstable output from the inclinometer. When the output is unstable, it is determined that camera-shake exists, and the high-shutter-speed priority program mode is selected. Contrarily, when it is stable, it is determined that no camera-shake exists, and the normal program mode is selected. Attitude of the camera, which is sensed by the inclinometer, is recorded to a detachable PC card with the image data when camera-shake is not detected. If camera-shake is detected, the sensed attitude data is invalidated.

Abstract: Based on the output signal of an area sensor 1, a level adjustment circuit 2 adjusts the bias voltage fed to the transistors provided within the individual pixels of the area sensor 1 and operating in a subthreshold region and thereby adjusts the level of the output signal of the area sensor 1. According to whether the subject is illuminated with intense or dim light, the level of the output signal is lowered or raised, respectively.

Abstract: An automatic exposure control apparatus comprises a skin color extracting circuit for extracting a skin-colored portion from an input video signal and a focus condition detecting circuit for detecting a focus condition of the skin-colored portion. Exposure is controlled based on outputs of the two circuits. That is, when a skin-colored portion is extracted and it is detected that the skin-colored portion is in an in-focus condition, exposure is controlled so as to be appropriate with respect to the skin-colored portion.

Abstract: In an image pickup apparatus, a level of an output signal from an image pickup device is detected. A first quantity of exposure of the image pickup device is determined such that a maximum value of the output signal from the image pickup device does not exceed a saturation level. And a first image signal picked up by the image pickup device with the first quantity of exposure is synthesized with at least one second image signal picked up with a second quantity of exposure which is larger than the first quantity of exposure.

Abstract: An image pickup apparatus and method for controlling an exposure so as to maintain proper brightness for a target or desired object regardless of the background brightness. Such image pickup apparatus may include a level sensing unit having a number of level sensing or detecting devices including a first level sensing device for sensing an imaging output level of a specific luminance level area on an imaged screen and a second level sensing device for sensing an imaging output level of a skin tone area on the imaged screen. The image pickup apparatus may further include a control device for controlling the quantity of light received in an image pickup unit in accordance with the sensed or detected output levels. Additionally, the present color image pickup apparatus may be operable in a plurality of exposure modes in accordance with the imaging condition. As a result, an imaging output may be provided which has relatively high or excellent image quality.

Abstract: An image pickup apparatus wherein plural elements simultaneously pick up the image and the state of the incident light includes a plurality of image pickup elements for generating an object image signal on the basis of a signal output from at least one of the plurality of image pickup elements, and for generating an incident light state signal on the basis of a signal from another image pickup element having substantially the same photographing region as a photographing region of said at least one image pickup element which generates the object image signal. A read-out period for one frame of said at least one image pickup element which generates the object image signal being different from the read-out period for one frame of said another image pickup signal which generates the incident light state signal.

Abstract: An image sensing device, such as an electronic camera, has different operating modes that are suited for sensing images of documents and sensing images of landscapes and the like. In the document mode, since information in the document is important, the image sensor is set at a maximum resolution. In the landscape mode, the resolution is varied in accordance with image brightness, to optimize the exposure conditions. Additional image processing is carried out in the document mode to enhance the sensed image and increase the efficiency with which memory is utilized.

Abstract: An exposure control device includes a first exposure control circuit which is arranged to keep constant an average signal level of an image signal corresponding to the whole of an image sensing plane, and a second exposure control circuit which is arranged to compensate the average signal level according to the level of an image signal corresponding to a light measuring area set in a part of the image sensing plane. The second exposure control circuit has a response characteristic arranged to have its exposure control action performed at a slower response speed than the first exposure circuit.

Abstract: An adaptive peak value detector, wherein the peak value for a peak hold section is detected, the peak hold section being selected by a peak hold control circuit. A solid-state imaging sensor generates pixel signals representative of an image and the peak value of portions of the pixel signals is detected. The exposure time of the sensor is adjusted as a function of the detected peak value and auto-focusing of the image for the camera is carried out on the basis of the image received during the adjusted exposure time.

Abstract: When a selecting unit selects a second mode for sensing a document or the like, image signals obtained by exposing an exposing unit enters a second mode unit through a clamping unit and the selecting unit. High resolution image signals are generated in the second mode unit. Meanwhile, levels of the electrical image signals are detected by a detecting unit, and a control unit performs either exposure control by the exposing unit and gain control by a gain control unit or both in accordance with a peak level of the detected levels of the electrical image signals. At the same time, a correction unit sets a target value for the levels of the electrical image signals in accordance with a selected mode. The electrical image signals are controlled so that the detected levels approach the target value, thereby a document, an illustration, and the like can be sensed in high resolution and an image of high quality can be obtained regardless of character density in the document.

Abstract: A camera includes an exposure part arranged to cause a film loaded on the camera to be exposed to light, an image sensor arranged to convert an object image into an electrical signal, a signal processing circuit arranged to carry out predetermined processes on the signal outputted from the image sensor, the signal processing circuit being arranged to perform the processes for obtaining an object image which is nearly equivalent to an image of a picture to be obtained when a specific film is exposed to light under set exposure conditions, and a display device arranged to display the object image by using the signal processed by the signal processing circuit.

Abstract: An intelligent flash system for a digital camera having components including an image optical pickup, an interface circuit, a flash unit and a processor. Upon activation of the camera, ambient lighting conditions are evaluated and if flash energy is required, a first low energy pre-flash is radiated, the reflected light received by the optical pickup having a multiplicity of pixels, and the output of the pixels converted to image intensity data by the interface circuit. The processor samples the image intensity data, weighing the center image area more heavily, and creates a histogram plot of quantity of pixels v.s. intensity, and separates the plot into a bar graph from which a determination of exposure is obtained. The histogram is then used to calculate a multiplicative scaling factor used to multiply the first flash energy to an estimate of a flash energy for correct exposure. Conditions of extreme over and under exposure result in the activation of a second flash at an adjusted energy level.

Abstract: A reproduced still picture having a comparatively high picture quality is obtained irrespective of the luminance of the subject. In an interval photography mode, photography is performed one time in a plurality of fields at a relatively high shutter speed of 1/250 of a second to obtained a first video signal, and photography is performed at an ordinary shutter speed of 1/60 of a second in other fields to obtain a second video signal. These video signals are amplified at mutually different first and second amplification factors (6 dB and 18.4 dB, respectively) in conformity with the shutter speed, by an AGC. The first and second amplification factors are varied in dependence upon the illumination of the subject in such a manner that the average levels of the first and second video signals are maintained at a fixed level.

Abstract: A hand held label reader is capable of illuminating a label, capturing a digital image of two-dimensional information indicia on the label, and decoding the digital image to provide decoded output data to a terminal. The target label is illuminated by a low variation illuminator that includes a circular LED array mounted behind a plano-concave dispersing lens. The automatic electronic camera, which includes a CCD camera and control circuitry, uses three images to adjust the intensity of the digital image and store a properly exposed image of the label in video RAM. The intensity of the digital image is adjusted by controlling the video system gain via adjusting the CCD array's integration time, the gain of a video amplifier, and the gain provided by an analog-to-digital converter. The gain provided by the analog-digital-converter is adjusted to compensate for the attenuation of light through the camera's lens assembly. For the first image, the digital image is obtained using a default setting for the gain.

Abstract: An exposure control device for performing exposure control on the basis of a video signal obtained from a light measuring area set within an image sensing plane is provided with a determining circuit which determines the position of a photographed object within the image sensing plane from the values of a specific component of the video signal obtained from the inside and outside of a detection area the position of which is variably set within the image sensing plane. The light measuring area is set in the object's position within the image sensing plane detected by the determining circuit. The exposure control device is provided further with a changing circuit which detects the size of the object on the image sensing plane and changes the size of the light measuring area accordingly, and a weighting circuit which performs for light measurement a weighting operation on video signals obtained from the inside and outside of the light measuring area.

Abstract: Video signals are recorded in such a manner that prints having a high picture quality can be obtained while not interfering with playback of images in the form of a movie. A CCD is controlled in such a manner that exposure is performed at a shutter speed of 1/250 of a second one time in exposures performed a plurality of times in succession and at a shutter speed of 1/60 of a second at other times. The video signal outputted by the CCD is applied to a combining circuit via a CDS, AGC and signal processing circuit for an image sensing system. A PI signal generating circuit outputs a PI signal, which represents inhibition of printing, in the case where exposure is carried out at the shutter speed of 1/60 of a second, and the combining circuit superposes the PI signal upon the video signal, which has been obtained by exposure at the shutter speed of 1/60 of a second, in the vertical blanking interval of this video signal.

Abstract: A method of filming a scene with a video camera whereby the brightness and/or colour of at least one selected area of a video image is adjusted by processing the video image data representing the video image prior to the video amplifier stage of the video camera. There is also provided a video apparatus having a processing means connected between the imaging device and the video amplifier and processor of a video camera.

Abstract: Image processing parameters for gradation correction of a digital image from a scene, which includes specular reflections may be seriously influenced by the presence of those specular reflections. Therefore, a method is developed to detect the presence of specular reflections in a scene, to modify the exposure time of the photo-sensitive means, which converts a luminous image to electronic image signals and to apply a gradation correction to the image data thus acquired. In one embodiment a digital camera is used to capture the image data, a cumulative histogram is built and two characteristic cumulative frequencies are used to determine via the histogram specular densities and highlight densities. The relative position of these density values indicates whether specular reflections are present, and give suitable parameters for setting an optimal exposure time and for computing a gradation correction curve.

Abstract: In a camera having a first image pickup device arranged to pick up a still image by using a silver-halide film, a second image pickup device arranged to electrically pick up a moving image by using a photoelectric conversion element, and an image pickup optical system arranged to guide an image light flux both to the first image pickup device and the second image pickup device, the image pickup optical system includes a fixed half mirror for guiding the image light flux both to the first image pickup device and the second image pickup device, a first light quantity adjusting device provided for the first image pickup device, and a second light quantity adjusting device provided for the second image pickup device.

Abstract: A video camera includes a CCD imager, and an image corresponding to a camera signal outputted from all of charge areas of the CCD imager is outputted on a monitor in a normal mode. In a quadruplication mode, four (4) images corresponding to camera signals repeatedly outputted from one of quarter areas of the charge area are outputted on the monitor. A high-frequency luminance component value generation circuit generates a high-frequency luminance component value on the basis of a luminance signal to be outputted at a center of the monitor in the normal mode, and a high-frequency luminance component value on the basis of a luminance signal to be outputted at a center of one of quarter areas of the monitor in the quadruplication mode. A microcomputer controls a focus motor on the basis of the high-frequency luminance component values obtained in such manners so as to adjust a focus.

Abstract: An image capture apparatus (eg. a video camera) for producing video image signals includes an image sensor for producing image signals having signal values representative of radiation intensity incident on respective positions of the sensor. The apparatus is able to identify an area of the sensor at which the incident intensity exceeds a predetermined intensity and to cause a stepped reduction in the image signal values corresponding to said area. The apparatus enables a range of intensity levels above a predetermined maximum to be translated or shifted to within a range which can be accommodated, for example by a broadcast television system, in a manner equivalent to applying a negative pedestal to that range of intensity levels.

Abstract: A charge coupled device (CCD) camera includes a CCD imager circuit, a compression engine, and a control circuit coupled to both the CCD imager circuit and the compression engine. The CCD imager circuit is characterized by an integration time defined by clock pulses from the control circuit. The compression engine generates successive frame requests. The control circuit generates the clock pulses to define the integration time based on a time between the sucessive frame requests. The camera further includes a histogram accumulator and an automatic gain controlled (AGC) amplifier coupled between the CCD imager circuit and the histogram accumulator. The CCD imager circuit is characterized by a predetermined maximum imager dynamic range and generates successive frames of imager data values, each successive frame of imager data values being characterized by an imager data value dynamic range and each frame of imager data values being generated based on a corresponding integration time.

Abstract: An image pickup apparatus has an AF function which determines a focus state of an object using an image signal obtained from a signal output of an image pickup device and detects the lens position in an in-focus state. The apparatus includes an image-region setting circuit for selectively extracting an image region for detecting the lens position in an in-focus state, an optimum-exposure-amount calculation circuit for calculating an optimum amount of exposure for the image region using an image signal within the image region set by the image-region setting circuit, and a focus detection circuit for calculating the lens position in an in-focus state using an image signal within the image region exposed with the optimum amount of exposure calculated by the optimum-exposure-amount calculation circuit.

Abstract: A reproduced still picture having a comparatively high picture quality is obtained irrespective of the luminance of the subject. In an interval photography mode, photography is performed one time in a plurality of fields at a relatively high shutter speed of 1/250 of a second to obtained a first video signal, and photography is performed at an ordinary shutter speed of 1/60 of a second in other fields to obtain a second video signal. These video signals are amplified at mutually different first and second amplification factors (6 dB and 18.4 dB, respectively) in conformity with the shutter speed, by an AGC. The first and second amplification factors are varied in dependence upon the illumination of the subject in such a manner that the average levels of the first and second video signals are maintained at a fixed level.

Abstract: A back light detecting method, a back light detecting device and an image pick-up camera for detecting a back light state in view of the pick-up state of a subject. Concerning a pixel other than the pixel within the brightness level between two slice levels given from the outside, its brightness level is integrated to distinguish a subject area AR.sub.M from a background area AR.sub.L. A back light state BLS is estimated from the area HIST.sub.M and the brightness level Y.sub.M of the subject area AR.sub.M. Thereby the back light state can be detected more correctly.