JP2005086630A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus for selecting a signal used as an image signal from a signal imaged by a different photoelectric conversion characteristic for each luminance range. <P>SOLUTION: A solid-state imaging element alternately applies logarithmic conversion and linear conversion to an image signal and thereafter stores the image signal at the logarithmic conversion and linear conversion for each pixel into a memory in a gradation conversion circuit. Then the gradation conversion circuit selects and outputs the image signal subjected to the linear conversion applied to the pixels within a luminance range lower than a prescribed luminance and selects and outputs the image signal subjected to the logarithmic conversion applied to the pixels within a luminance range higher than the prescribed luminance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a photoelectric conversion between a linear conversion operation that outputs an electric signal linearly changing with respect to an incident light amount and a logarithmic conversion operation that outputs an electric signal that naturally changes logarithmically with respect to the incident light amount. The present invention relates to an imaging apparatus capable of switching a plurality of photoelectric conversion characteristics, such as an imaging apparatus capable of switching a conversion operation and an imaging apparatus capable of switching different photoelectric conversion characteristics by changing an exposure amount.

  Conventionally, in a solid-state imaging device that performs a linear conversion operation that linearly converts the amount of incident light, its dynamic range is as narrow as two orders of magnitude, so when imaging a subject that constitutes a luminance distribution in a wide luminance range, other than the dynamic range The luminance information in the range is not output. Further, as a conventional solid-state imaging device, there is one that performs a logarithmic conversion operation for logarithmically converting the amount of incident light (see Patent Document 1). In this solid-state imaging device, the dynamic range is as wide as 5 to 6 digits. Therefore, even if an image of a subject constituting a luminance distribution in a slightly wide luminance range is captured, all luminance information in the luminance distribution is converted into an electrical signal. Can be output. However, since the imageable area becomes wider with respect to the luminance distribution of the subject, an area without luminance data is formed in the low luminance area or the high luminance area in the imageable area. On the other hand, the present applicant has proposed what can switch between the above-described linear conversion operation and logarithmic conversion operation (see Patent Document 2).

In addition, the present applicant has proposed an imaging apparatus that includes a solid-state imaging device capable of switching between a linear conversion operation and a logarithmic conversion operation and can automatically switch photoelectric conversion characteristics of the solid-state imaging device according to various conditions. (See Patent Documents 3 to 6). According to Patent Document 3, according to the brightness of the subject to be imaged, according to Patent Document 4, according to the luminance range of the subject to be imaged, and according to Patent Document 5, according to the distance to the subject and the imaging magnification. 6 automatically switches the photoelectric conversion characteristics of the solid-state imaging device in accordance with the measured luminance distribution shape of the subject.
JP-A-11-313257 JP 2002-77733 A JP 2001-8110 A JP 2001-16507 A JP 2001-28712 A JP 2001-197370 A

  However, in Patent Documents 3 to 6, although the photoelectric conversion characteristics can be set according to the subject to be imaged, all the image signals output from the solid-state image sensor are obtained by the same photoelectric conversion characteristics. It becomes. Therefore, the image signal obtained when the solid-state image sensor performs linear conversion operation has a narrow dynamic range, and the image signal obtained when the solid-state image sensor performs logarithmic conversion operation is Since the gradation is poor as compared with the case where the linear conversion is performed, the image signal has poor contrast.

  In view of such a problem, an object of the present invention is to provide an imaging apparatus that selects a signal used as an image signal for each luminance range from signals obtained by imaging with different photoelectric conversion characteristics.

  In order to achieve the above object, an imaging apparatus according to the present invention is an imaging apparatus including a solid-state imaging element having a plurality of pixels that output image signals corresponding to n types of photoelectric conversion characteristics, and the n types of photoelectric conversion characteristics. A memory that stores n types of image signals obtained from the solid-state imaging device that has been switched for each pixel, a luminance range confirmation unit that confirms a luminance range of each pixel, and n types of images stored in the memory A selection unit that selects an image signal corresponding to the luminance range confirmed by the luminance range confirmation unit from the image signal of the pixel, and the selection unit selects the n types of photoelectric signals according to the luminance range of each pixel. By selecting an image signal based on conversion characteristics for each pixel, an image signal in which the n types of image signals are combined is output.

  In such an imaging apparatus, the first to nth photoelectric conversion characteristics are used as the n types of photoelectric conversion characteristics, and the luminance ranges corresponding to the first to nth photoelectric conversion characteristics are set to the first to nth photoelectric conversion characteristics. A luminance range is set, and the image signals obtained by the first to n-th photoelectric conversion characteristics are defined as first to n-th image signals. At this time, the photoelectric conversion characteristic of the solid-state imaging device is switched between the first to nth photoelectric conversion characteristics. Then, by storing the image signal whose photoelectric conversion characteristics are switched in the memory for each pixel, the first to nth image signals are stored in the memory for each pixel. Thereafter, the luminance range confirmation unit confirms which one of the first to nth luminance ranges for each pixel. At this time, when it is confirmed that the luminance range is s (s is a natural number of 1 ≦ s ≦ n), the s-th image signal is selected from the memory. In this way, by selecting an image signal having n types of photoelectric conversion characteristics for each pixel, an image signal in which the n types of image signals are combined is generated.

  In such an imaging apparatus, for each image signal, an image of a pixel whose luminance range is confirmed by a relative relationship with an image signal of a peripheral pixel centered on the pixel whose luminance range is confirmed by the luminance range confirmation unit. A low-pass filter for newly setting a signal is provided, and the luminance range confirmation unit confirms the luminance range of each pixel from the image signal of each pixel given from the low-pass filter. That is, in the low-pass filter, the input image signal and the image signal in the second pixel around the first pixel that outputs the input image signal are weighted for each of the first to n−1th image signals. By adding, an image signal with a reduced noise component is generated and sent to the luminance range confirmation unit. Therefore, the luminance range confirmation unit confirms the luminance range based on the first to n−1th image signals newly generated by the low-pass filter.

  In such an imaging apparatus, the solid-state imaging device changes from a first state in which an image signal linearly changing with respect to the amount of incident light is output to a second state in which an image signal that changes logarithmically with respect to the amount of incident light is output. The photoelectric conversion characteristics may be switched. At this time, when switching between two types of photoelectric conversion characteristics, the photoelectric conversion characteristics may be used only in the first state or only in the second state, and the first state and the second state may be switched alternately. I do not care. The photoelectric conversion characteristics of the solid-state image sensor may be switched by switching the exposure amount of the solid-state image sensor to each pixel.

  In such an imaging apparatus, the solid-state imaging device may include a plurality of types of color filters and output a plurality of types of color signals as the image signals.

  At this time, all types of the color signals are generated for each of the pixels constituting the solid-state imaging device and stored in the memory, and the luminance range confirmation unit determines the color signals of the pixels. After confirming the luminance range every time, the selection unit may select, for each color signal, the color signal obtained from the photoelectric conversion characteristics corresponding to the confirmed luminance range from the memory. That is, when a color signal that is an RGB signal is output from the solid-state imaging device, the luminance range of the RGB signal of a certain pixel is the x-th luminance range, the y-th luminance range, and the z-th luminance range, respectively. When confirmed by the range confirmation unit, in the selection unit, the R signal is an R signal that is an xth image signal, the G signal is a G signal that is a yth image signal, and the B signal is a B signal that is a zth image signal. Each signal is selected.

  According to the present invention, not all image signals of the same frame are formed by image signals having the same photoelectric conversion characteristics, but image signals having different photoelectric conversion characteristics can be selected for each luminance range of each pixel. Therefore, it is possible to select an optimal photoelectric conversion characteristic according to the luminance range of each pixel without narrowing the entire dynamic range. Furthermore, it is possible to image in such a wide dynamic range, and in the luminance range in which the photoelectric conversion characteristic that is the linear conversion characteristic is selected, it is possible to output a high-contrast image with rich gradation. it can. Further, by providing a signal for confirming the luminance range through the low-pass filter, it is possible to confirm the luminance range of each pixel by a signal in which the influence of the noise component is reduced.

<Configuration of imaging device>
A configuration of an imaging apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating an internal configuration of the imaging apparatus.

  1 is output from an optical system 1 composed of a plurality of lenses, a solid-state image sensor 2 that converts an incident light amount of light incident through the optical system 1 into an electrical signal, and the solid-state image sensor 2. An amplifier 3 for amplifying the electric signal, an AD conversion circuit 4 for converting the electric signal amplified by the amplifier 3 into a digital signal, a black reference correction circuit 5 for setting a minimum level of the digital signal from the AD conversion circuit 4, An FPN correction circuit 6 that removes FPN (Fixed Pattern Noise) due to the sensitivity of each pixel of the solid-state imaging device 2 from the digital signal corrected by the black reference value in the black reference correction circuit 5, and the FPN correction circuit 6 An AE / WB evaluation value detection circuit 7 for detecting respective evaluation values for performing automatic exposure control (AE) and white balance (WB) from the digital signal from which FPN has been removed at Based on the WB control circuit 8 that performs correction for each color signal so that the color balance of the digital signal from which FPN is removed by the FPN correction circuit 6 is obtained, and the color signals of a plurality of adjacent pixels output from the WB control circuit 8. The color interpolation circuit 9 that interpolates each color signal, the color correction circuit 10 that corrects the hue of each color signal output from the color interpolation circuit 9 for each pixel by another color signal, and the color correction circuit 10 output the color signal. A gradation conversion circuit 11 that performs gradation conversion of a digital signal, a coring circuit 12 that performs processing such as edge enhancement on the digital signal output from the gradation conversion circuit 11, and an overall control unit 13 that controls each block An aperture control unit 14 for controlling the exposure amount by the aperture 1 a provided in the optical system 1, and a clock for supplying a clock for operation timing to the solid-state imaging device 2 and the AD conversion circuit 4. It includes a timing generating circuit 15, a.

  In the imaging apparatus configured as described above, when light is incident on the solid-state imaging device 2 having a different color filter for each pixel through the optical system 1, a photoelectric conversion operation is performed in each pixel. An analog signal that is a different color signal for each pixel is output. That is, as shown in FIG. 2, when a color filter having a Bayer array with RGB is provided in the solid-state imaging device 2, an R signal representing red is a color that becomes G from a pixel provided with an R color filter. A G signal representing green is outputted from the pixel provided with the filter, and a B signal representing blue is outputted from the pixel provided with the color filter B. As will be described later, in the solid-state imaging device 2, the luminance position at which the linear conversion operation and the logarithmic conversion operation are switched is changed by changing the driving condition by the overall control unit 13. As a result, the dynamic range of the solid-state imaging device 2 changes. The dynamic range becomes wider as the switching point becomes the higher luminance side.

  The R signal, the G signal, and the B signal that are serially output from the solid-state imaging device 2 are amplified by the amplifier 3 and then converted into a digital signal by the AD conversion circuit 4. When the R signal, the G signal, and the B signal thus converted into digital signals are supplied to the black reference correction circuit 5, the black level that becomes the minimum luminance value based on the dynamic range control signal supplied from the overall control unit 13 is obtained. Is corrected to the reference value (0). That is, since the black level varies depending on the dynamic range of the solid-state imaging device 2, the signal level that becomes the black level is subtracted from the signal levels of the R signal, the G signal, and the B signal output from the AD conversion circuit 4. Thus, the reference value correction is performed.

  The FPN component is removed from the R signal, the G signal, and the B signal subjected to the black reference correction by subtracting the FPN component stored in the FPN correction circuit 6. This FPN component is an offset variation caused by a threshold variation of MOS transistors constituting each pixel in the solid-state imaging device 2. When extracting the FPN component, for each of the RGB signals, an offset based on the difference in transmittance of the color filter is subtracted from the image signal for each pixel output from the solid-state imaging device 2 during uniform light irradiation. At this time, the offset based on the transmittance of each color filter is determined by the average value of each RGB signal at the time of uniform light irradiation, and each average value is subtracted from the RGB signal at the time of uniform light irradiation. The FPN component of the pixel may be extracted. The R signal, G signal, and B signal from which the FPN component has been removed in this way are supplied to the AE / WB evaluation value detection circuit 7 and the WB control circuit 8.

  The AE / WB evaluation value detection circuit 7 calculates the average value distribution range of the luminance representing the luminance range of the subject by confirming the luminance value of the image signal composed of the given R signal, G signal, and B signal, It is sent to the overall control unit 13 as an AE evaluation value for setting the exposure amount. Based on this AE evaluation value, the overall control unit 13 controls the aperture of the diaphragm 1a, whereby the exposure amount is controlled. The AE / WB evaluation value detection circuit 7 confirms the respective luminance ratios and luminance differences from the given R, G, and B signals, and calculates a WB evaluation value that is a reference value for white balance. And sent to the overall control unit 13. The WB control circuit 8 performs white balance processing based on the WB evaluation value and dynamic range data given from the overall control unit 13 so that the R signal, the G signal, and the B signal have the same photoelectric conversion characteristics. Is done.

  The R, G, and B signals that have been subjected to white balance processing by the WB control circuit 8 are subjected to color interpolation processing by the color interpolation circuit 9. When a color filter having a Bayer-type arrangement using RGB as shown in FIG. 2 is provided in the solid-state imaging device 2, the color signal output from each pixel is only the color signal from the color filter provided with the pixel. Therefore, the color interpolation circuit 9 performs color interpolation processing by generating other color signals from the color signals of adjacent pixels.

  When the RGB color filters are arranged in the pixels G11 to G44 as shown in FIG. 2, the R signals r11, r31, r13, and r33 are converted from the pixels G11, G31, G13, and G33 to the pixels G21, G41, and G33, respectively. G signals G21, g41, g12, g32, g23, g43, g14, g34 from G12, G32, G23, G43, G14, G34, and B signals b22, b42, b24, b44 from pixels G22, G42, G24, G44. Is output. At this time, RGB signals of the pixels G22, G23, G32, and G33 are expressed by the following equations.

R signal r22, G signal g22, B signal b22 of pixel G22
r22 = (r11 + r31 + r13 + r33) / 4
g22 = (g21 + g12 + g32 + g23) / 4
b22 = b22
R signal r32, G signal g32, B signal b32 of the pixel G32
r32 = (r31 + r33) / 2
g32 = g32
b32 = (b22 + b42) / 2
R signal r23, G signal g23, B signal b23 of pixel G23
r23 = (r13 + r33) / 2
g23 = g23
b23 = (b22 + b24) / 2
R signal r33, G signal g33, B signal b33 of pixel G33
r33 = r33
g33 = (g32 + g23 + g43 + g34) / 4
b33 = (b22 + b42 + b24 + b44) / 4

  By performing pixel interpolation processing in this way, when RGB signals are obtained for each pixel, the RGB signals of each pixel are given to the color correction circuit 10 and color correction processing for emphasizing the color of each pixel is performed. Is done. At this time, each of the RGB signals is subjected to color correction by the values of other color signals. That is, by substituting the RGB signals rkl, gkl, bkl of the pixel Gkl into the following expression, the RGB signals rxkl, gxkl, bxkl of the pixel Gkl subjected to the hue correction are generated. At this time, the matrix coefficients of a1 to a3, b1 to b3, and c1 to c3 are switched based on the dynamic range control signal input from the overall control unit 13, and the hue of the RGB signals of each pixel is emphasized.

rxkl = a1 * rkl + a2 * gkl + a3 * bkl
gxkl = b1 * rkl + b2 * gkl + b3 * bkl
bxkl = c1 * rkl + c2 * gkl + c3 * bkl

  The RGB signal subjected to the color correction by the color correction circuit 10 is given to the gradation conversion circuit 11 so that the dynamic range control signal and the AE evaluation value are input from the overall control unit 13 so as to obtain an appropriate output level. Based on the above, the gradation characteristics are changed by a change based on the γ curve or a change in digital gain. Details of the gradation conversion circuit 11 will be described later. Then, as shown in FIG. 3, for the edge component, the noise superimposed on each of the RGB signals in the coring circuit 12 having level conversion characteristics for converting all outputs within a predetermined range to the reference signal level as seen from the reference signal level. The components are removed, and edge components are extracted and subjected to edge enhancement processing.

<Configuration example of solid-state imaging device>
The configuration of the solid-state imaging device 2 in the imaging apparatus configured as shown in FIG. 1 will be described with reference to the drawings. FIG. 4 is a block diagram schematically showing a part of the configuration of the solid-state imaging device of this example, and FIG. 5 is a circuit diagram showing the configuration of each pixel.

  As shown in FIG. 4, in the solid-state imaging device 2, G11 to Gmn represent pixels arranged in a matrix (matrix arrangement). Reference numeral 21 denotes a vertical scanning circuit, which sequentially scans rows (lines) 23-1, 23-2,..., 23-n that apply a signal φV to each pixel and lines 24-1 and 24-2. ,..., 24-n, and a signal φVD is applied to each pixel via lines 25-1, 25-2,. A horizontal scanning circuit 22 sequentially reads out photoelectric conversion signals derived from the pixels to the output signal lines 26-1, 26-2, ..., 26-m in the horizontal direction for each pixel. Reference numeral 20 denotes a power supply line. For each pixel, not only the lines 23-1 to 23-n, 24-1 to 24-n, 25-1 to 25-n, the output signal lines 26-1 to 26-m, and the power supply line 20, but also These lines (for example, a clock line and a bias supply line) are also connected, but these are omitted in FIG.

  Also, constant current sources 27-1 to 27-m are connected to the output signal lines 26-1 to 26-m, and pixels are provided via the signal lines 26-1 to 26-m, respectively. Selection circuits 28-1 to 28-m for sample-holding image signals and noise signals supplied from G11 to Gmn are provided. Then, when the image signal and the noise signal are sequentially transmitted from the selection circuits 28-1 to 28-m to the correction circuit 29, the correction circuit 29 performs correction processing and outputs the image signal from which noise has been removed to the outside. Is done. The DC voltage VPS is applied to one end of the constant current sources 27-1 to 27-m.

  In such a solid-state imaging device, an image signal and a noise signal output from the pixel Gab (a natural number of a: 1 ≦ a ≦ m, b: 1 ≦ b ≦ n) are respectively output signal lines 26- The signal is output via a and amplified by a constant current source 27-a connected to the output signal line 26-a. The image signal and noise signal output from the pixel Gab are sequentially sent to the selection circuit 28-a, and the sent image signal and noise signal are sampled and held in the selection circuit 28-a. Thereafter, after the sampled and held image signal is sent to the correction circuit 29 from the selection circuit 28-a, the same sampled and held noise signal is sent to the correction circuit 29. The correction circuit 29 corrects the image signal given from the selection circuit 28-a based on the noise signal similarly given from the selection circuit 28-a, and outputs the noise-removed image signal to the amplifier 3.

  In the solid-state imaging device 2 having such a configuration, as shown in FIG. 5, the pixels G11 to Gmn have the drain of the MOS transistor T1 connected to the anode of the photodiode PD to which the DC voltage VPD is applied to the cathode. The gate and drain of the MOS transistor T2 and the gate of the MOS transistor T3 are connected to the source of T1. The gate of the MOS transistor T4 and the drain of the MOS transistor T5 are connected to the source of the MOS transistor T3, and the drain of the MOS transistor T6 is connected to the source of the MOS transistor T4. The drain of the MOS transistor T6 is connected to the output signal line 26 (corresponding to the output signal lines 26-1 to 26-m in FIG. 4). The MOS transistors T1 to T6 are P-channel MOS transistors.

  The signal φVPS is input to the source of the MOS transistor T2 via the line 25 (corresponding to the lines 25-1 to 25-n in FIG. 4), and the DC voltage VPD is applied to the drains of the MOS transistors T3 and T4. Further, the other end of the capacitor C to which the signal φVD is applied via the line 24 (corresponding to the lines 24-1 to 24-n in FIG. 4) is connected to the source of the MOS transistor T3. The DC voltage VRG is input to the source of the MOS transistor T5, and the signal φRS is input to the gate thereof. Further, signals φS and φV are input to the gates of the MOS transistors T1 and T6, respectively.

  The signal φVPS is a binary voltage signal. When the amount of incident light exceeds a predetermined value, the voltage for operating the MOS transistor T2 in the subthreshold region is VL, and the voltage higher than this voltage is used for the MOS transistor T2. The voltage for making the conductive state is VH. The signal φVD is a ternary voltage signal, the voltage value when integrating the capacitor C is set to the highest Vh, the voltage value when reading the image signal is set to Vm lower than Vh, and the noise signal is read The voltage value is set to Vl lower than Vm.

  The operation of the pixels G11 to Gmn in the solid-state imaging device 2 configured as described above will be described with reference to the time chart of FIG. First, when a pulse signal φVD having a voltage value Vm and a pulse signal φV are supplied and an image signal is output, the signal φVD is set to Vh, then the signal φS is set high to turn off the MOS transistor T1, and the reset operation is performed. Begins. Next, the signal φVPS applied to the source of the MOS transistor T2 is set to VH, and the source voltage of the MOS transistor T2 is increased, so that negative charges accumulated in the gate and drain of the MOS transistor T2 and the gate of the MOS transistor T3 are accumulated. Are quickly recombined. At this time, the signal φRS is set to low, the MOS transistor T5 is turned on, and the voltage at the connection node between the capacitor C and the gate of the MOS transistor T4 is initialized.

  Then, the signal φVPS applied to the source of the MOS transistor T2 is set to VL to return the potential state of the MOS transistor T2 to the original state, and then the signal φRS is set to high to turn off the MOS transistor T5. Thereafter, the capacitor C performs an integration operation, and the voltage at the connection node between the capacitor C and the gate of the MOS transistor T4 becomes in accordance with the reset gate voltage of the MOS transistor T2. Then, the pulse signal φV is applied to the gate of the MOS transistor T6 to turn on the MOS transistor T6 and set the voltage value of the signal φVD to Vl. At this time, since the MOS transistor T4 operates as a source follower type MOS transistor, a noise signal appears on the output signal line 26 as a voltage signal. Thereafter, the pulse signal φRS is again applied to the MOS transistor T5 to reset the voltage at the connection node between the capacitor C and the gate of the MOS transistor T4, and then the signal φS is set low to turn on the MOS transistor T1 to perform the imaging operation. Make it ready.

  After the noise signal is output in this way, the imaging operation is started when the MOS transistor T1 is turned on. At this time, the signal φRS is set high and the MOS transistor T5 is turned off. Further, the signal φVPS applied to the source of the MOS transistor T2 is set to VL, and the voltage value of the signal φVD applied to the capacitor C is set to Vh to perform the integration operation. When photocharge corresponding to the amount of incident light flows from the photodiode PD into the MOS transistor T2, the MOS transistor T2 is in a cut-off state, so that the photocharge is accumulated at the gate of the MOS transistor T2.

  Therefore, when the brightness of the subject to be imaged is low and the amount of incident light entering the photodiode PD is small, a voltage corresponding to the amount of photocharge accumulated at the gate of the MOS transistor T2 appears at the gate of the MOS transistor T2, A voltage that changes linearly with respect to the integrated value of the amount of light appears at the gate of the MOS transistor T3. Also, when the luminance of the subject to be imaged is high and the amount of incident light entering the photodiode PD is large, and the voltage according to the amount of photocharge accumulated at the gate of the MOS transistor T2 increases, the MOS transistor T2 operates in the subthreshold region. Therefore, a voltage that changes logarithmically with respect to the amount of incident light appears at the gate of the MOS transistor T3.

  Since a drain current that is linearly or naturally logarithmically changed with respect to the incident light amount flows from the capacitor C, the gate voltage of the MOS transistor T4 is set to the integrated value of the incident light amount. Thus, the voltage changes linearly or in a natural logarithm. Then, by setting the voltage value of the signal φVD to Vm and applying the pulse signal φV to the MOS transistor T6, a source current corresponding to the gate voltage of the MOS transistor T4 flows to the output signal line 6 via the MOS transistor T6. . At this time, since the MOS transistor T4 operates as a source follower type MOS transistor, an image signal appears as a voltage signal on the output signal line 6. Thereafter, the signal φV is set high to turn off the MOS transistor T6, and the voltage value of the signal φVD is set to Vh.

  When operating in this way, the voltage value VL of the signal φVPS at the time of imaging decreases, and the potential difference between the gate and the source of the MOS transistor T2 increases as the difference from the voltage value VH of the signal φVPS at the time of reset increases. The ratio of subject luminance at which the MOS transistor T2 operates in the cutoff state increases. Therefore, as shown in FIG. 7, the lower the voltage value VL, the larger the ratio of subject luminance to be linearly converted. Therefore, for example, the luminance range of the subject is detected, and if the luminance range of the subject is narrow, the voltage value VL is lowered to widen the luminance range for linear conversion, and if the luminance range of the subject is wide, the voltage value VL is increased. By widening the luminance range for logarithmic conversion, photoelectric conversion characteristics that match the characteristics of the subject can be obtained. It should be noted that when the voltage value VL is minimized, it is possible to always perform linear conversion. When the voltage value VL is maximized, it is possible to always perform logarithmic conversion.

  The solid-state image pickup device in which the dynamic range can be switched according to the luminance range of the subject by the overall control unit 13 switching the voltage value VL of the signal φVPS given to the pixels G11 to Gmn of the solid-state image pickup device 2 operating in this way. 2 can be used. That is, the inflection point (luminance value) for switching from the linear conversion operation to the logarithmic conversion operation in the pixels G11 to Gmn of the solid-state imaging device 2 can be set by switching the voltage value VL of the signal φVPS. it can. Note that the amount of photoelectric charge flowing into the MOS transistor T2 until reaching the gate voltage of the MOS transistor T2 when changing to the logarithmic conversion operation at the time of imaging is the same in all the pixels.

  In this configuration example, a solid-state imaging device including pixels configured as shown in FIG. 5 is used. However, the present invention is not limited to this configuration, and linear conversion operation and logarithmic conversion operation are automatically performed in each pixel. As long as it can be switched to the above, it may be composed of a pixel having another configuration such as a pixel having a configuration as shown in Patent Document 2. In addition, the inflection point between the linear conversion operation and the logarithmic conversion operation is changed by changing the voltage value VL of the signal φVPS at the time of imaging. However, the linear value can be changed by changing the voltage value VH of the signal φVPS at the time of resetting. The inflection point between the conversion operation and the logarithmic conversion operation may be changed. The inflection point may be changed by changing the reset time. Further, although each pixel is provided with an RGB filter, other color filters such as cyan, magenta, and yellow may be provided.

  Since the solid-state imaging device 2 including the pixels G11 to Gmn as described above circulates and switches n photoelectric conversion characteristics for each frame, the voltage value VL of the signal φVPS is set to n values VL1 to VLn. The Since the voltage values VL1 to VLn of the signal φVPS are switched every frame and supplied to the pixels G11 to Gmn, the pixels G11 to Gmn operate with the same photoelectric conversion characteristics every n frames. Below, two photoelectric conversion characteristics are assumed to be switched cyclically for each frame, and one photoelectric conversion characteristic is a photoelectric conversion characteristic based on a logarithmic conversion characteristic as shown in the graph a1 in FIG. 7, and the other photoelectric conversion characteristic is As shown in a graph a4 in FIG.

  Therefore, the signal φVPS is switched every frame, and the photoelectric conversion characteristics of the pixels G11 to Gmn are switched between the logarithmic conversion characteristic and the linear conversion characteristic every frame. That is, the next frame of the frame when the photoelectric conversion characteristic of the pixels G11 to Gmn is imaged as the logarithmic conversion characteristic is imaged with the photoelectric conversion characteristic of the pixels G11 to Gmn as the linear conversion characteristic. The next frame after the image captured with the photoelectric conversion characteristic as the linear conversion characteristic is imaged with the photoelectric conversion characteristic of the pixels G11 to Gmn as the logarithmic conversion characteristic. At this time, the graph of FIG. 8 shows the relationship between the signal level of the RGB signal and the luminance value when the solid-state imaging device 2 is operated with the logarithmic conversion characteristic and the linear conversion characteristic. The graph of FIG. 8 shows the relationship between the signal level of the R signal and the luminance value. In the following, the R signal will be described as a representative.

  When the solid-state imaging device 2 is linearly converted, the output changes as shown by the graph b2 in FIG. 8, and the output of the pixel in the solid-state imaging device 2 is saturated at the luminance value Lmaxr. Saturates. Further, when the solid-state imaging device 2 is subjected to logarithmic conversion operation, it changes as shown in the graph b1 in FIG. 8, and therefore, when the luminance value is Lmaxr, the signal level of the R signal is lower than the signal level Vmaxr1 when the signal level Vmaxr1 is operated linearly. It becomes. Therefore, the signal level Vmaxr1 of the R signal during the linear conversion operation and the signal level Vmaxr2 of the R signal during the logarithmic conversion operation with respect to the luminance value Lmaxr where the output of the pixel is saturated when the solid-state imaging device 2 is linearly operated. The difference ΔVmaxr is Vmaxr1−Vmaxr2.

  Similarly, the signal levels of the linearly converted GB signal when the pixel output is saturated when the linear conversion operation is performed are Vmaxg1 and Vmaxb1, respectively, and the luminance values at that time are Lmaxg and Lmaxb for the GB signals, respectively. And The signal levels of the GB signal logarithmically converted for the luminance values Lmaxg and Lmaxb are Vmaxg2 and Vmaxb2, respectively. At this time, the difference ΔVmaxg in the G signal level between the linear conversion operation and the logarithmic conversion operation at the luminance value Lmaxg is Vmaxg1−Vmaxg2, and the signal level of the B signal at the linear conversion operation and the logarithmic conversion operation at the luminance value Lmaxb. The difference ΔVmaxb is Vmaxb1−Vmaxb2.

<First Example of Tone Conversion Circuit>
A first example of the gradation conversion circuit in the imaging apparatus configured as shown in FIG. 1 will be described in detail below with reference to the drawings. FIG. 9 is a block diagram illustrating an example of an internal configuration of the gradation conversion circuit.

  As shown in FIG. 9, the gradation conversion circuit 11 of this example includes a memory 111 a that stores RGB signals of a frame when the photoelectric conversion characteristics of the solid-state image sensor 2 are linear conversion characteristics, and the solid-state image sensor 2. The memory 111b that stores the RGB signal of the frame when the photoelectric conversion characteristic is the logarithmic conversion characteristic, and the signal level of the RGB signal that is saturated when the solid-state imaging device 2 performs the photoelectric conversion operation by the linear conversion characteristic (linear) (Saturation level at the time of operation) and the comparison units 112r, 112g, and 112b that respectively compare the signal levels of the RGB signals from the memory 111a, and the output is saturated when the solid-state imaging device 2 performs a photoelectric conversion operation by linear conversion characteristics. The difference (offset) of the signal level between the logarithmic conversion operation and the linear conversion operation with respect to the luminance value Lmax is determined for each of the RGB signals from the memory 111b. Adders 113r, 113g, and 113b that add to the signal level of, and selection units 114r, 114g, and 114b that select and output the RGB signals from the memory 111a and the RGB signals from the adders 113r, 113g, and 113b, A gradation characteristic conversion unit 115 that performs gradation conversion on the RGB signals selected by the selection units 114r, 114g, and 114b according to the gradation characteristic in the reproduction output device.

  The operation of the gradation conversion circuit 11 configured as described above will be described below with reference to the timing chart of FIG. First, RGB signals of N frames obtained by the solid-state imaging device 2 performing a linear conversion operation are color-interpolated by the color interpolation circuit 9, and RGB signals are obtained for all the pixels G11 to Gmn. The RGB signals are color-corrected by the color correction circuit 10 and input to the gradation conversion circuit 11. The N-frame linearly converted RGB signals of N frames are stored in areas corresponding to the pixels G11 to Gmn in the memory 111a. When all the N-frame RGB signals are output from the solid-state imaging device 2, the reset is performed so as to perform the logarithmic conversion operation, the logarithmic conversion operation is performed, and the N + 1-frame RGB signal is output. At this time, the RGB signals of the pixels G11 to Gmn color-corrected by the color correction circuit 10 are stored in areas corresponding to the pixels G11 to Gmn in the memory 111b.

  As described above, the RGB signal obtained by the solid-state imaging device 2 performing the linear conversion operation is stored in the memory 111a, and the RGB signal obtained by the solid-state imaging device 2 performing the logarithmic conversion operation is stored in the memory 111b. Are stored in the memory 111a, the N + 2 frame RGB signal is read from the memory 111a and the N + 2 frame RGB signal is read from the memory 111b. N + 1 frames of RGB signals are read out. Then, for each of the pixels G11 to Gmn, the comparison unit 112r, 112g, 112b confirms whether or not the RGB signal is at the saturation level during the linear operation, and the comparison result in the comparison unit 112r, 112g, 112b is obtained. In response, the selectors 114r, 114g, and 114b select N frames of RGB signals from the memory 111a or N + 1 frames of RGB signals from the adders 113r, 113g, and 113b, respectively.

  Specifically, the N frame R signal read from the memory 111a is stored in the comparison unit 112r and the selection unit 114r, and the N frame G signal read from the memory 111a is stored in the comparison unit 112g and the selection unit 114g. The B signals of N frames read from 111a are output to the comparison unit 112b and the selection unit 114b, respectively. Further, the N + 1 frame R signal read from the memory 111b is sent to the selection unit 114r via the adder 113r, and the N + 1 frame G signal read from the memory 111b is sent to the selection unit 114g via the adder 113g. The B signals of N + 1 frames read from the memory 111b are output to the selection unit 114b via the adder 113b.

  Then, the comparison unit 112r checks whether or not the signal level of the R signal of each pixel in the N frame is the saturation level Vmaxr1 at the time of linear operation, and the comparison unit 112g determines the signal of the G signal of each pixel in the N frame. It is confirmed whether or not the level is a saturation level Vmaxg1 at the time of linear operation, and the comparison unit 112b confirms whether or not the signal level of the B signal of each pixel in the N frame is the saturation level Vmaxb1 at the time of linear operation. . The adder 113r adds the offset ΔVmaxr to the signal level of the R signal of each pixel in the N + 1 frame, and the adder 113g adds the offset ΔVmaxg to the signal level of the G signal of each pixel in the N + 1 frame. In 113b, the offset ΔVmaxb is added to the signal level of the B signal of each pixel in the N + 1 frame.

  Further, in the selection unit 114r, the comparison result for each of the linearly converted R signals of the pixels G11 to Gmn in the comparison unit 112r is input, and the signal level of the linearly converted R signal of the pixel Gab is smaller than the saturation level Vmaxr1. In this case, the R signal of the N-frame pixel Gab read from the memory 111a is selected as the R signal of the pixel Gab, and the signal level of the linearly converted R signal of the pixel Gab is equal to the saturation level Vmaxr1. When it is a value, the R signal of the pixel Gab from the adder 113r of the N + 1 frame is selected as the R signal of the pixel Gab.

  Similarly, in the selection unit 114g, when the signal level of the linearly converted G signal of the pixel Gab is smaller than the saturation level Vmaxg1, the N-frame pixel Gab read from the memory 111a as the G signal of the pixel Gab. When the signal level of the linearly converted G signal of the pixel Gab is equal to the saturation level Vmaxg1, the G signal of the pixel Gab is used as the G signal of the pixel Gab from the adder 113g of the N + 1 frame. Select the G signal. Further, in the selection unit 114b, when the signal level of the linearly converted B signal of the pixel Gab is smaller than the saturation level Vmaxb1, the N-frame pixel Gab read from the memory 111a is read as the B signal of the pixel Gab. When the B signal is selected and the signal level of the linearly converted B signal of the pixel Gab is equal to the saturation level Vmaxb1, the B signal of the pixel Gab from the adder 113g of the N + 1 frame is used as the B signal of the pixel Gab. Select a signal.

  As described above, when the RGB signal of N + 2 frame is output from the solid-state imaging device 2, at the same time, first, for each RGB signal of each pixel, the comparison unit for whether the signal level of the linearly converted N frame has reached the saturation level. Confirm with 112r, 112g, and 122b, respectively. If the signal level of the linearly converted N frame does not reach the saturation level, the linearly converted N frame signal is selected by the selection units 114r, 114g, and 114b, and the linearly converted N frame signal is selected. When the level has reached the saturation level, the selectors 114r, 114g, and 114b select N + 1 frame signals that have been logarithmically converted and that have been offset by the adders 113r, 113g, and 113b.

  Therefore, as shown in FIG. 11, the RGB signals of the respective pixels selected and output by the selection units 114r, 114g, and 114b are linearly converted in the luminance range lower than the luminance Lmaxr, Lmaxg, and Lmaxb, and the luminance Lmaxr , Lmaxg, and Lmaxb or higher in the luminance range, the logarithmically converted signal is obtained. 11 shows the state of the R signal output from the selection unit 114r with respect to the R signal changing as shown in FIG. 9, the signal level Vmaxr1 at the luminance value Lmaxr is also shown for each GB signal. Are changed to the signal level Vmaxg1 at the luminance value Lmaxg and the signal level Vmaxb1 at the luminance value Lmaxb, but can be expressed in the same manner as the R signal in FIG.

  As described above, when the RGB signals output from the selection units 114r, 114g, and 114b are supplied to the gradation / gradation characteristic conversion unit 115, the luminance values of the RGB signals are converted into gradation levels based on the gradation characteristics in the reproduction output device. Key conversion is performed. That is, when the reproduction output device is a CRT monitor, γ correction is performed on each of the RGB signals in order to obtain gradation characteristics suitable for the CRT monitor.

  In this way, when the RGB signal of N + 2 frame is output from the solid-state imaging device 2, the RGB signal of N frame and N + 1 frame is selected for each pixel and gradation conversion is performed, and the coring circuit 12 in the subsequent stage is selected. Output. At this time, the linearly converted N-frame RGB signal is deleted from the memory 111a, and the linearly converted N + 2 frame RGB signal is stored in the memory 111a.

  After that, when the logarithmically converted N + 3 frame RGB signal is output from the solid-state imaging device 2, the gradation conversion circuit 11 reads the logarithmically converted N + 1 frame RGB signal from the memory 111b and linearly converts N + 2 The RGB signal of the frame is read from the memory 111a. The selectors 114r, 114g, and 114b select the RGB signal of the N + 1 frame from the adders 113r, 113g, and 113b and the RGB signal of the N + 2 frame from the memory 111a for each pixel, and a gradation characteristic conversion unit. The gradation is converted at 115 and output to the coring circuit 12 at the subsequent stage. At this time, the logarithmically converted N + 1 frame RGB signal is deleted from the memory 111b, and the logarithmically converted N + 3 frame RGB signal is stored in the memory 111b.

  As shown in FIG. 10, when N-frame RGB signals are output from the solid-state imaging device 2, the linearly converted N-2 frame RGB signals are read from the memory 111 a and logarithmically converted N−1. After the RGB signal of the frame is read from the memory 111b, it is selected by the selection units 114r, 114g, and 114b. When the RGB signal of N + 1 frame is output from the solid-state image sensor 2, the linearly converted N frame RGB signal is read from the memory 111a, and the logarithmically converted N-1 frame RGB signal is read from the memory 111b. After being read out, it is selected by the selection units 114r, 114g, and 114b.

  By repeating the operation shown in the timing chart of FIG. 10, the solid-state imaging device 2 alternately outputs a linearly converted RGB signal and a logarithmically converted RGB signal for each frame, and for each RGB signal of each pixel, In the luminance range lower than the luminance Lmaxr, Lmaxg, and Lmaxb, a signal that is linearly converted and stored in the memory 111a is selected to perform gradation conversion. The stored signal is selected, gradation-converted, and output to the coring circuit 12 at the subsequent stage.

<Second Example of Tone Conversion Circuit>
A second example of the gradation conversion circuit in the imaging apparatus configured as shown in FIG. 1 will be described in detail below with reference to the drawings. FIG. 12 is a block diagram illustrating an example of the internal configuration of the gradation conversion circuit. In the gradation conversion circuit of FIG. 12, the same components as those of the gradation conversion circuit of FIG. 9 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 12, the gradation conversion circuit 11 of this example includes memories 111a and 111b, comparison units 112r, 112g, and 112b, adders 113r, 113g, and 113b, selection units 114r, 114g, and 114b, A low-pass filter (LPF) 116r, 116g, 116b for each of 5 pixels × 5 pixels, which is supplied with each of the RGB signals output from the memory 111a and output to the comparison units 112r, 112g, 112b; Is provided. By providing the LPFs 116r, 116g, and 116b in this way, the signal levels of a plurality of pixels around the pixels of the RGB signals selected and output by the selection units 114r, 114g, and 114b are reflected in the comparison results of the comparison units 112r, 112g, and 112b. Is done.

When configured in this way, the pixels G (a-2) (b-2), G (a-1) (b-2), Ga (b-2), G (a + 1) (b-2) , G (a + 2) (b-2), G (a-2) (b-1), G (a-1) (b-1), Ga (b-1), G (a + 1) (b-1), G (a + 2) (b-1), G (a-2) b, G (a-1) b, Gab, G (a + 1) b, G (a + 2) b, G (a-2) (b + 1), G (a-1) (b + 1), Ga (b + 1), G (a + 1) (b + 1), G (a + 2 ) (b + 1), G (a-2) (b + 2), G (a-1) (b + 2), Ga (b + 2), G (a + 1) (b + 2), The RGB signals of G (a + 2) (b + 2) are input to the LPFs 116r, 116g, and 116b. The LPFs 116r, 116g, and 116b multiply the RGB signals of the above-described 25 pixels by the pixels Gab and the 24 pixels around the pixel Gab by multiplying by a predetermined coefficient and then add them. At this time, when the pixels G (a-2) (b-2) to G (a + 2) (b + 2) are multiplied by the coefficients A11 to A55, the pixels G (a-2) (b− The relationship between 2) to G (a + 2) (b + 2) and the coefficients A11 to A55 is as follows. The sum of the coefficients A11 to A55 is set to 1. The coefficients A11 to A55 may be different or the same for the LPFs 116r, 116g, and 116b.
Positional relationship of pixels G (a-2) (b-2) to G (a + 2) (b + 2) G (a-2) (b-2) G (a-1) (b-2) Ga (b-2) G (a + 1) (b-2) G (a + 2) (b-2)
G (a-2) (b-1) G (a-1) (b-1) Ga (b-1) G (a + 1) (b-1) G (a + 2) (b-1)
G (a-2) b G (a-1) b Gab G (a + 1) b G (a + 2) b
G (a-2) (b + 1) G (a-1) (b + 1) Ga (b + 1) G (a + 1) (b + 1) G (a + 2) (b + 1)
G (a-2) (b + 2) G (a-1) (b + 2) Ga (b + 2) G (a + 1) (b + 2) G (a + 2) (b + 2)

Positional relationship between coefficients A11 to A55 and pixels G (a-2) (b-2) to G (a + 2) (b + 2)
A11 A21 A31 A41 A51
A12 A22 A32 A42 A52
A13 A23 A33 A43 A53
A14 A24 A34 A44 A54
A15 A25 A35 A45 A55

  That is, the signal levels of the RGB signals obtained by performing weighted averaging with the signal levels of the RGB signals of the surrounding 24 pixels in the LPFs 116r, 116g, and 116b are output to the comparison units 112r, 112g, and 112b. Therefore, the comparison units 112r, 112g, and 112b compare the signal levels obtained by weighted averaging of the RGB signals of 25 pixels centered on the output pixels with the saturation levels Vmaxr1, Vmaxg1, and Vmaxb1, and the comparison result. Is output to the selection units 114r, 114g, and 114b. As described above, when the LPFs 116r, 116g, 116b and the comparison units 112r, 112g, 112b operate, the addition units 113r, 113g, 113b, the selection units 114r, 114g, 114b, and the gradation characteristic conversion unit 115 are the same as those in the first example. The same operation is performed.

  By providing the LPFs 116r, 116g, and 116b in the previous stage of the comparison units 112r, 112g, and 112b as in this example, when the signal levels of the RGB signals are confirmed by the comparison units 112r, 112g, and 112b, they are superimposed on each signal. Noise signal can be removed and confirmed. Therefore, the influence on noise can be reduced as compared with the first example described above.

  In the present embodiment, a single-plate solid-state image sensor having a plurality of types of color filters provided in one solid-state image sensor is used. For example, a three-plate solid-state image sensor having a solid-state image sensor for each RGB color filter As described above, a solid-state imaging device having the same color filter may be provided for each type of color filter. Furthermore, a solid-state imaging device that outputs a monochrome image signal without a color filter may be used. Further, in each of the above-described examples, the two photoelectric conversion characteristics of the linear conversion characteristic and the logarithmic conversion characteristic are switched, but an image in which the exposure time (integration time) of the solid-state imaging device is changed in the linear conversion characteristic is synthesized. Anyway. An embodiment in this case will be described below.

  The configuration of the pixels G11 to Gmn provided in the solid-state imaging device 2 that switches the photoelectric conversion characteristics according to the exposure time in this way is, for example, as shown in FIG. In the pixel shown in FIG. 13, the MOS transistor T1 is omitted from the pixel shown in FIG. 5, and one end is connected to the source of the MOS transistor T3 and the DC voltage VPS is applied to the other end. A MOS transistor T7 having a drain connected and a source connected to the gate of the MOS transistor T4 is added. A signal φSW is applied to the gate of the MOS transistor T7, and a signal φD is applied to the drain of the MOS transistor T3. The MOS transistor T7 is a P-channel MOS transistor.

  When the pulse signal φV is applied to the gate of the MOS transistor T6 and the output signal is read, first, a reset operation is performed with the signal φVPS as VH. At this time, first, a high level pulse signal φD is given to the drain of the MOS transistor T3, whereby the charge accumulated in the capacitor C1 is discharged to the signal line of the signal φD through the MOS transistor T3, and the capacitor C1 and the MOS transistor T3 are discharged. Reset the voltage of the connection node with the source of Further, the capacitor C is reset by applying a pulse signal to the signal φRS.

  The reset gate voltage of the MOS transistor T2 is applied to the gate of the MOS transistor T3, and a drain current corresponding to the gate voltage of the MOS transistor T2 flows to the capacitor C1 through the MOS transistor T3. Therefore, the capacitor C1 and the MOS transistor T3 The voltage at the connection node with the source of the transistor corresponds to the gate voltage of the reset MOS transistor T2. Then, the signal φVPS is set to VL to prepare for the next imaging operation. The operations of the signals φD and φVPS are simultaneously performed for all the pixels G11 to Gmn in FIG.

  When the imaging operation is started with the signal φVPS as VL, a voltage that changes linearly or in a natural logarithm with respect to the amount of light incident on the photodiode PD appears at the gates of the MOS transistors T2 and T3. A drain current obtained by amplifying the voltage linearly or naturally logarithmically with respect to the incident light quantity in the MOS transistor T3 flows to the capacitor C1, and the voltage at the connection node between the capacitor C1 and the source of the MOS transistor T3. Is a voltage that changes linearly or in a natural logarithm with respect to the integrated value of the incident light quantity.

  Then, by applying a low level pulse signal φSW to the gate of the MOS transistor T7, the MOS transistor T7 becomes conductive, and the voltage at the connection node between the capacitor C1 and the source of the MOS transistor T3 is sampled by the capacitor C. Therefore, the voltage at the connection node between the capacitor C and the gate of the MOS transistor T4 becomes a voltage that is linearly or naturally logarithmically proportional to the integrated value of the incident light quantity. Note that the operation from the start of the imaging operation to the application of the pulse signal φSW is performed simultaneously for all of the pixels G11 to Gmn in FIG.

  Thereafter, the low-level pulse signal φV is applied to the gate of the MOS transistor T6, and the signal φVD is set to the voltage value Vm, thereby reading the video signal at the time of imaging. At this time, the voltage at the connection node between the capacitor C and the gate of the MOS transistor T4 is amplified by the MOS transistor T4. The output current amplified by the MOS transistor T4 is output to the output signal line 6 via the MOS transistor T6.

  When the solid-state imaging device 2 includes such a pixel, by controlling the time from when the capacitor C1 is reset by the signal φD until the movement of the electric charge to the capacitor C is completed by the signal φSW, the solid-state imaging device 2 The exposure time (integration time) is controlled. Therefore, by controlling the exposure time (integration time), the inflection point in the photoelectric conversion characteristic of the solid-state imaging device 2 and the amplification factor in the linear conversion characteristic (corresponding to the gradient of the difference for linear conversion) can be switched.

  By doing so, for example, as shown in FIG. 14, the photoelectric conversion characteristics of the solid-state imaging device 2 have linear conversion characteristics in the entire luminance range, and the integration time is increased to increase the amplification factor (slope). In addition, the amplification time (slope) can be reduced by shortening the integration time. As shown in FIG. 14, when synthesizing an image signal whose exposure time is switched as a linear conversion characteristic, in other words, an image signal whose photoelectric conversion characteristic is switched as described above, the photoelectric conversion characteristic having a longer integration time on the low luminance side. By using the image signal obtained by the above, it is possible to output a high-contrast image with linear characteristics as much as possible.

  Further, the photoelectric conversion characteristics may be switched by switching the exposure amount to each pixel of the solid-state imaging device. At this time, the photoelectric conversion characteristics can be switched by switching the aperture ratio of the lens by the diaphragm and the exposure time. Furthermore, in the present embodiment, the linearly converted signal is used as the low luminance side image signal and the logarithmically converted signal is used as the high luminance side image signal. However, the linear conversion is performed as the high luminance side image signal. It is also possible to use a logarithmically converted signal as an image signal on the low luminance side as well as using the converted signal. At this time, when imaging with high luminance using a photoelectric conversion characteristic that is a linear characteristic, it is necessary to reduce the exposure amount by shortening the exposure time or by reducing the aperture ratio of the lens by the diaphragm.

These are block diagrams which show the structure of the imaging device of this invention. These are figures which show the arrangement | sequence of the color filter provided in a solid-state image sensor. These are graphs showing level conversion characteristics for edge components in a coring circuit. These are block circuit diagrams for demonstrating the whole structure of a solid-state image sensor. These are circuit diagrams which show one structural example of the pixel which comprises the solid-state image sensor of FIG. These are timing charts showing the operation of the pixel of FIG. These are graphs showing the relationship between the luminance of a subject and the output of a pixel. These are graphs showing the relationship between the luminance value of the R signal and the signal level at the time of linear conversion and logarithmic conversion. These are block diagrams showing an example of the internal configuration of the gradation conversion circuit. These are timing charts showing the operation of the gradation conversion circuit. These are graphs showing the relationship between the luminance value of the R signal after selection unit output and the signal level. These are block diagrams which show the other example of the internal structure of a gradation conversion circuit. These are circuit diagrams which show the other structural example of the pixel which comprises the solid-state image sensor of FIG. These are graphs showing the relationship between the luminance of a subject and the output of a pixel when the photoelectric conversion characteristic is a linear conversion characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical system 2 Solid-state image sensor 3 Amplifier 4 AD conversion circuit 5 Black reference correction circuit 6 FPN correction circuit 7 AE / WB evaluation value detection circuit 8 WB control circuit 9 Color interpolation circuit 10 Color correction circuit 11 Gradation conversion circuit 12 Coring Circuit 13 Overall control unit 14 Aperture control unit 15 Timing generation circuit

Claims (6)

In an imaging apparatus including a solid-state imaging device having a plurality of pixels that output image signals corresponding to n types of photoelectric conversion characteristics,
A memory that stores, for each pixel, n types of image signals obtained from the solid-state imaging device in which the n types of photoelectric conversion characteristics are switched;
A luminance range confirmation unit for confirming the luminance range of each pixel;
A selection unit that selects an image signal corresponding to the luminance range confirmed by the luminance range confirmation unit from n types of image signals stored in the memory;
With
The selection unit outputs an image signal obtained by combining the n types of image signals by selecting an image signal based on the n types of photoelectric conversion characteristics for each pixel according to a luminance range of each pixel. An imaging device that is characterized. A low pass for newly setting an image signal of a pixel for checking the luminance range by a relative relationship with an image signal of a peripheral pixel around the pixel whose luminance range is confirmed by the luminance range confirmation unit for each image signal With a filter,
The imaging apparatus according to claim 1, wherein the luminance range confirmation unit confirms a luminance range of each pixel from an image signal of each pixel given from the low-pass filter.   Switching the photoelectric conversion characteristics of the solid-state imaging device from a first state in which an image signal linearly changing with respect to an incident light quantity is output to a second state in which an image signal changing logarithmically with respect to the incident light quantity is output. The imaging device according to claim 1 or 2, wherein   The imaging apparatus according to any one of claims 1 to 3, wherein the photoelectric conversion characteristics of the solid-state imaging device are switched by switching an exposure amount of the solid-state imaging device to each pixel.   The imaging device according to claim 1, wherein the solid-state imaging device includes a plurality of types of color filters and outputs a plurality of types of color signals as the image signals. For each of the pixels constituting the solid-state imaging device, all kinds of the color signals are generated and stored in the memory,
In the luminance range confirmation unit, after confirming the luminance range for each color signal of each pixel,
6. The imaging apparatus according to claim 5, wherein the selection unit selects, from the memory, a color signal obtained by the photoelectric conversion characteristic corresponding to the confirmed luminance range for each color signal.

Images