Patent Application
20060268154
This application is based on Japanese Patent Application No. 2005-152082 filed on May 25, 2005, in Japanese Patent Office, the entire content of which is hereby incorporated by reference.
apparatus and more particularly to an image pickup apparatus having an image pickup device for switching a logarithmic conversion operation and a linear conversion operation.
Conventionally, in imaging by an image pickup apparatus such as a digital camera or a camera unit cooperated in a mobile camera, when the circumference of a photographic subject is dark, an auxiliary light source such a strobo device or a high-brightness LED is used.
When imaging using such an auxiliary light source, by predetermined algorithm such as setting the photographic subject positioned in the neighborhood of the center of the picked-up image as a main photographic subject, the main photographic subject is decided and then the irradiation light quantity (for example, the strobo light quantity) by the auxiliary light source is adjusted so as to optimize the exposure quantity of the main photographic subject.
On the other hand, an image pickup device (linear log sensor) for switching a linear conversion operation and a logarithmic conversion operation of an electric signal according to the incident light quantity is proposed (Patent Document 1). According to such an image pickup device, as compared with an image pickup device (linear sensor) for performing only the linear conversion operation, the dynamic range of the electric signal is wide, so that even when a photographic subject having a wide brightness distribution is imaged, all the brightness information can be expressed by the electric signal. Furthermore, a switching point (an inflection point) for switching the linear conversion operation to the logarithmic conversion operation can be changed.
Patent Document 1: Japanese Laid-Open Patent Application 2004-088312
However, when picking up an image by using such an image pickup device and an auxiliary light source as usual, even if the main photographic subject is decided beforehand and strobo light is irradiated to it so as to optimize the exposure quantity of the photographic subject, the linear conversion operation and logarithmic conversion operation are switched according to the incident light quantity, and the electric signal is outputted, so that unless the switching point (inflection point) is considered at time of strobo-imaging, the contrast cannot be made uniform even for the same photographic subject and there is a possibility that an image with a sense of incompatibility may be obtained.
For example, in
When a linear sensor is used under such a condition, there are possibilities that the main photographic subject a may use the log area or extending over the linear area and log area. As a result, a problem arises that in an obtained picked-up image, the contrast of the main photographic subject a gets worse or does not become uniform, thus no satisfactory image can be obtained.
A problem of the present invention is to provide an image pickup apparatus, when executing imaging by an image pickup device (linear log sensor) recently introduced using an auxiliary light source, for enabling imaging capable of obtaining a good contrast for a main photographic subject. In view of forgoing, one embodiment according to one aspect of the present invention is an image pickup apparatus, comprising:
an image pickup device provided with a plurality of pixels for picking up an image of a photographic subject, the image pickup device which has a linear conversion operation in which incident light is linearly converted to an electric signal and a logarithmic conversion operation in which the incident light is logarithmically converted to the electric signal, the liner conversion operation and the logarithmic conversion operation being switchable according to an amount of incident light;
a light irradiation section which throws irradiation light when picking up the image of the photographic subject; and
an inflection point changing section, in case of conducting the picking up the image of the photographic subject, which sets an inflection point which is a boundary between a liner area where the linear conversion operation is functional and a logarithmic area where the logarithmic conversion operation is functional in a manner of keeping a distribution of brightness of a main photographic subject within the linear area.
The embodiment of the present invention will be explained with reference to the accompanying drawings.
An image pickup apparatus 1 relating to this embodiment is a compact type digital camera and the image pickup apparatus of the present invention includes electronic devices having imaging functions such as a single-lens reflex digital camera, a portable telephone with camera, and a mobile camera and also a camera unit incorporated in the electronic devices such the portable telephone and mobile camera.
As shown in
Further, as shown in
Further, as shown in
Furthermore, inside the frame 2 included in the image pickup apparatus 1, a circuit substrate (not drawn) including circuits such as a system control unit 8 and a signal processing unit 9 (both are shown in
Further, as shown in
Further, in the neighborhood of the upper end of the back of the image pickup apparatus 1, a zoom button W13. (wide angle) and a zoom button T14 (telephoto) for adjusting zooming are installed. Further, on the back of the image pickup apparatus 1 and above the position of the lens unit 3, an optical finder 15 for confirming a photographic subject from the back side of the frame 2 is arranged.
Furthermore, in the neighborhood of the central part of the back of the image pickup apparatus 1, a selection cross key 16 having a cross key for moving a cursor or a window displayed on the screen of the monitor 12 or changing the designation range of the window is installed. Further, at the central part of the selection cross key 16, a decision key for deciding the contents designated by the cursor or window is installed.
Further, on the top of the image pickup apparatus 1 and between the battery 10 and the lens unit 3, a release switch 17 for releasing the shutter is installed. The release switch 17 can perform an operation of “half pressing” of pressing part of the way and an operation of “full pressing” of pressing furthermore.
Further, in the neighborhood of the top end of the frame 2, a power switch 18 for turning on (start) or off (stop) the power source of the image pickup apparatus 1 by pressing down is installed.
Further, in the neighborhood of the upper end of one side of the frame 2, a USB terminal 19 for connecting a USB cable for connecting the image pickup apparatus 1 to a personal computer is installed.
Next, the functional constitution of the image pickup apparatus 1 is shown in
As mentioned above, the image pickup apparatus 1 has the system control unit 8 on the circuit substrate inside the frame 2. The system control unit 8 is composed of a central processing unit (CPU), a random access memory (RAM) composed. of a rewritable semiconductor device, and a read only memory (ROM) composed of a nonvolatile semiconductor memory.
Further, to the system control unit 8, the components of the image pickup apparatus 1 are connected and the system control unit 8 stores a processing program recorded in the ROM in the RAM, executes the processing program by the CPU, thereby drives and controls the components.
As shown in
The lens unit 3 is composed of a plurality of lenses for focusing an optical image of a photographic subject on the image pickup screen of the image pickup device 4 and a stop for adjusting the quantity of light focused by the lenses.
The stop control unit 20 drives and controls the stop for adjusting the quantity of light focused by the lenses of the lens unit 3. Namely, the stop control unit 20, on the basis of a control value input from the system control unit 8, closes the stop after a lapse of predetermined exposure time after opening the stop immediately before start of the image pickup operation of the image pickup device 4 and at time of non-image pickup, interrupts incident light to the image pickup device 4, thereby controls the incident light quantity.
The image pickup device 4 converts photoelectrically and fetches incident light of each color component of R, G, and B of the optical image of the photographic subject to an electric signal.
As shown in
Each of the pixels G11 to Gmn converts photoelectrically incident light and outputs an electric signal. These pixels G11 to Gmn can switch the conversion operation of an electric signal according to an incident light quantity and more in detail, switch a linear conversion operation for linearly converting incident light to an electric signal and a logarithmic conversion operation for logarithmically converting it. Further, in this embodiment, linear conversion or logarithmic conversion of incident light to an electric signal is linear conversion to an electric signal for changing linearly a time integral value of the light quantity or logarithmic conversion to an electric signal for changing logarithmically it.
On the side of the lens unit 3 of the pixels G11 to Gmn, a filter (not drawn) of one color among red, green, and blue is respectively arranged. Further, to the pixels G11 to Gmn, as shown in
The signal impression lines LA1to LAn, LB1 to LBn, and LC1 to LCn give signals φV, φVD, and φVPS (refer to
To the signal reading lines LD1 to LDm, an electric signal generated by each of the pixels G11 to Gmn is derived. To the signal reading lines LD1 to LDm, constant-current sources D1 to Dm and selection circuits S1 to Sm are connected. Further, to one end of each of the constant-current sources D1 to Dm (the lower ends shown in the drawing), a DC voltage VPS is impressed.
The selection circuits S1 to Sm sample-hold noise signals given from the pixels G11 to Gmn via the signal reading lines LD1 to LDm and an electric signal at time of image pickup. To the selection circuits S1 to Sm, a horizontal scanning circuit 28 and a correction circuit 29 are connected. The horizontal scanning circuit 28 switches sequentially the selection circuits S1 to Sm for sample-holding an electric signal and transmitting it to the correction circuit 29 in the Y direction. Further, the correction circuit 29, on the basis of noise signals transmitted from the selection circuits S1 to Sm and the electric signal at time of image pickup, remove the noise signals from the concerned electric signal.
Further, for the selection circuits S1 to Sm and the correction circuit 29, the ones disclosed in Japanese Patent Application 2001-223948 can be used. Further, in this embodiment, the case that for the whole selection circuits S1 to Sm, one correction circuit 29 is installed is described, though one correction circuit 29 may be installed for each of the selection circuits S1 to Sm.
Then, the pixels G11 to Gmn included in the image pickup device 4 will be explained.
Each of the pixels G11 to Gmn, as shown in
To the photodiode P, light passing through the lens unit 3 is irradiated. To an anode PA of the photodiode P, a DC voltage VPD is impressed and to a cathode PK, a drain T1D of the transistor T1 is connected.
To a gate T1G of the transistor T1, a signal φS is input and to a source T1S, a gate T2G and a drain T2D of the transistor T2 are connected.
To a source T2S of the transistor T2, a signal impression line LC (equivalent to LC1 to LCn shown in
To the source T1S of the transistor T1, a gate T3G of the transistor T3 is connected.
To a drain T3D of the transistor T3, a DC voltage VPD is impressed. Further, to a source T3S of the transistor T3, one end of the capacitor C, a drain T5D of the transistor T5, and a gate T4G of the transistor T4 are connected.
To the other end of the capacitor C, a signal impression line LB (equivalent to LB1 to LBn shown in
To a source T5S of the transistor T5, a DC voltage VRG is input and to a gate T5G thereof, a signal φRS is input.
To a drain T4D of the transistor T4, the DC voltage VPD is impressed in the same as with the drain T3D of the transistor T3 and to a source T4S thereof, a drain T6D of the transistor T6, is connected.
To a source T6S of the transistor T6, a signal reading line LD (equivalent to LD1 to LDm shown in
By use of such a circuit constitution, the pixels G11 to Gmn perform the following reset operation.
Firstly, as shown in
Concretely, in the state that the signal φS is low, and the signal φV is high, and the signal φVPS is very low, and the signal φRS is high, and the signal φVD is very high, the vertical scanning circuit 27 gives the pulse signal φV and the pulse signal φVD of the voltage Vm to the pixels G11 to Gmn so as to output an electric signal to the signal reading line LD and then makes the signal φS high and turn off the transistor T1.
Next, when the vertical scanning circuit 27 makes the signal φVPS very high, the negative charges accumulated in the gate T2G and drain T2D of the transistor T2 and the gate T3G of the transistor T3 are recoupled promptly. Further, when the vertical scanning circuit 27 makes the signal φRS low and turns on the transistor T5, the voltage of the node between the capacitor C and the gate T4G of the transistor T4 is initialized.
Next, the vertical scanning circuit 27 makes the signal φVPS very low, thereby returns the potential state of the transistor T2 to its original state, then makes the signal φRS high, and turns off the transistor T5. Next, the capacitor C performs the integral operation. By doing this, the voltage of the node between the capacitor C and the gate T4G of the transistor T4 corresponds to the gate voltage of the transistor T2.
Next, when the vertical scanning circuit 27 gives the pulse signal φV to the gate T6G of the transistor T6, the transistor T6 is turned on and the pulse signal φVD of the voltage V1 is impressed to the capacitor C. At this time, the transistor T4 operates as a source follower type MOS transistor, so that a noise signal appears on the signal reading line LD as a voltage signal.
And, the vertical scanning circuit 27 gives the pulse signal φRS to the gate T5G of the transistor T5, resets the voltage of the node between the capacitor C and the gate T4G of the transistor T4, and then makes the signal φS low, and turns on the transistor T1. By doing this, the reset operation is completed and the pixels G11 to Gmn enter the image pickup ready state.
Further, the pixels G11 to Gmn perform the following image pickup operation.
When an optical charge according to the incident light quantity flows into the transistor T2 from the photodiode P, the optical charge is accumulated in the gate T2G of the transistor T2.
Here, when the brightness of a photographic subject is low and the incident light quantity to the photodiode P is smaller than the predetermined incident light quantity th, the transistor T2 is in the cut-off state, so that a voltage according to the optical charge quantity accumulated in the gate T2G of the transistor T2 appears in the concerned gate T2G. Therefore, on the gate T3G of the transistor T3, the voltage for linearly converting the incident light appears.
On the other hand, when the brightness of the photographic subject is high and the incident light quantity to the photodiode P is larger than the predetermined incident light quantity th, the transistor T2 operates in the sub-threshold area. Therefore, in the gate T3G of the transistor T3, the voltage for converting natural-logarithmically the incident light appears.
Further, in this embodiment, between the pixels G11 to Gmn, the predetermined value is equal.
When the voltage appears in the gate T3G of the transistor T3, the current flowing from the capacitor C to the drain T3D of the transistor T3 is amplified according to the voltage. Therefore, in the gate T4G of the transistor T4, the voltage for linearly or logarithmically converting the incident light of the photodiode P appears.
Next, the vertical scanning circuit 27 sets the voltage of the signal φVD to Vm and makes the signal φV low. By doing this, a source current according to the gate voltage of the transistor T4 flows to the signal reading line LD via the transistor T6. At this time, the transistor T4 operates as a source follower type MOS transistor, so that in the signal reading line LD, the electric signal at time of image pickup appears as a voltage signal. Here, the signal value of the electric signal outputted via the transistors T4 and T6 is a value in proportion to the gate voltage of the transistors T4, so that the concerned signal value is a value when the incident light of the photodiode P is converted linearly or logarithmically.
And, the vertical scanning circuit 27 sets the voltage of the signal φVD to Vh and makes the signal φV high, thus the image pickup operation ends.
When such an operation is performed, the voltage VL of the signal φVPS at time of image pickup is lowered, and as the difference from the voltage VH of the signal φVPS at time of reset is increased, the difference in the potential between the gate and the source of the transistor T2 is increased, and the rate of the brightness of the photographic subject when the transistor T2 operates in the cut-off state is increased. Therefore, as shown in
Therefore, for example, when the brightness range of the photographic subject is narrow, the voltage VL is lowered so as to extend the linear conversion brightness range, and when the brightness range of the photographic subject is wide, the voltage VL is increased so as to extend the logarithmic conversion brightness range, thus a photoelectric conversion characteristic in accordance with the characteristic of the photographic subject can be set. Further, when minimizing the voltage VL, the linear conversion state can be set always and when maximizing the voltage VH, the logarithmic conversion state can be set always.
When switching the voltage VL of the signal φVPS given to the pixels G11 to Gmn of the image pickup apparatus 1 operating like this, the dynamic range can be switched. Namely, when the system control unit 8 switches the voltage VL of the signal φVPS, the inflection point where the linear conversion operation of the pixels G11 to Gmn is switched to the logarithmic conversion operation can be changed.
Further, the image pickup device 4 relating to this embodiment may automatically switch the linear conversion operation and logarithmic conversion operation for each pixel and it may have pixels using a different constitution from that shown in
Further, in this embodiment, the value VL of the signal φVPS at time of image pickup is changed, thus the linear conversion operation and logarithmic conversion operation are switched. However, the value VL of the signal φVPS at time of reset is changed, thus the inflection point between the linear conversion operation and the logarithmic conversion operation may be changed. Furthermore, the reset time is changed, thus the inflection point between the linear conversion operation and the logarithmic conversion operation may be changed.
Further, the image pickup device 4 of this embodiment has the R, G, and B filters for each pixel, though it may have filters of other colors such as cyan, magenta, and yellow.
In
Among them, the amplifier 30 amplifies an electric signal outputted from the image pickup device 4 to a predetermined specified level and compensates for the insufficient level of a picked-up image.
Further, the A-D converter 31 (ADC) converts the electric signal amplified by the amplifier 30 from an analog signal to a digital signal.
Further, the black reference correction unit 32 corrects the black level which is a lowest brightness value to the reference value. Namely, the black level varies with the dynamic range of the image pickup device 4, so that the signal level of the black level is subtracted from the signal level of each of R, G, and B signals outputted from the A-D converter 31, thus the black reference correction is performed.
Further, the AE evaluation calculation unit 33 detects an evaluation value necessary for automatic exposure (AE) from an electric signal after black reference correction. Namely, it confirms the brightness value of the electric signal composed of the primary color components of R, G, and B, thereby calculates a mean value distribution range of the brightness indicating the brightness range of the photographic subject, and outputs it to the system control unit 8 as an AE evaluation value for setting the incident light quantity.
Further, the WB processing unit 34 calculates a correction coefficient from the electric signal after black reference correction, thereby adjusts the level ratios of the color components of R. G, and B of the picked-up image (R/G, B/G), and correctly displays the white.
Further, the color interpolation unit 35, when signals obtained from the pixels of the image pickup device 4 are composed of only one or two colors among the primary colors, to obtain color component values of R, G, and B of each pixel, performs a color interpolation process of interpolating the missing color component(s) for each pixel.
Further, the color correction unit 36 corrects the color component values for each pixel of the image data input from the color interpolation unit 35 and generates an image emphasizing the color tone of each pixel.
Further, the gradation conversion unit 37, to faithfully reproduce an image and to realize an ideal gradation reproduction characteristic assuming the gamma as 1 between input of the image and final output thereof, performs a gamma correction process of correcting the gradation response characteristic of the image to an optimum curve according to the gamma value of the image pickup apparatus 1.
Further, the color space conversion unit 38 converts the color space from R, G, and B to Y, U. and V. To Y, U, and V, a control method for representing a color by two chromaticities of a brightness (Y) signal, a blue color difference (U, Cb), and a red color difference (V, Cr) is applied and when the color space is converted to Y, U, and V, data compression of only a color difference signal can be performed easily.
Next, the timing generation unit 21 controls the image pickup operation (accumulating charge on the basis of exposure and reading the accumulated charge) by the image pickup device 4. Namely, on the basis of an image pickup control signal from the system control unit 8, the timing generation unit 21 generates a predetermined timing pulse (a pixel drive signal, a horizontal synchronous signal, a vertical synchronous signal, a horizontal scanning circuit drive signal, a vertical scanning circuit drive signal, etc.) and outputs it to the image pickup device 4. Further, the timing generation unit 21 generates an A-D conversion timing signal used by the A-D converter 31.
The recording unit 11 is a recording memory composed of a semiconductor memory and has an image data recording area for recording image data input from the signal processing unit 9. The recording unit 11, for example, may be a built-in memory such as a flash memory or a removable memory card or memory disk and may be a magnetic recording medium such as a hard disk or a floppy (registered trademark) disk.
The monitor 12 fulfills a function as a display unit and displays a preview image of a photographic subject and a text screen such a menu screen to select a function by a user.
The operation unit 22 is composed of a zoom button W13, a zoom button T14, the selection cross key 16, the release switch 17, and the power switch 18. When a user operates the operation unit 22, an instruction signal corresponding to each button or switch function is transmitted to the system control unit 8 and according to the instruction signal, each component of the image pickup apparatus 1 is driven and controlled.
Among the aforementioned units, the zoom button W13, when pressed, fulfills a function for adjusting the zoom and displaying small a photographic subject and the zoom button T14, when pressed, fulfills a function for adjusting the zoom and displaying large a photographic subject.
Further, the selection cross key 16, when the cross key is pressed, moves the cursor, selects the image pickup mode or strobo mode, and when the central part is pressed, can confirm the selection contents.
Further, the release switch 17 starts the beam measurement operation by “half pressing” and starts a series of imaging operations including preliminary imaging and real imaging by “full pressing”.
Further, the power switch 18, whenever pressed, sequentially repeats to turn the power source of the image pickup apparatus 1 on or off.
The strobo device as an irradiation unit 6, at time of preliminary imaging, irradiates preliminarily the light quantity of 1/n of the irradiation quantity at time of real irradiation. The irradiation quantity at this time is desirably a one of almost preventing saturation of the output of the image pickup device 4. Further, the strobo device as an irradiation unit 6, when the brightness of the surrounding environment is insufficient at time of real imaging, performs real irradiation at predetermined irradiation timing and at a predetermined irradiation quantity.
The irradiation control circuit 23 accumulates a charge in order to allow the irradiation unit 6 to irradiate and on the basis of an instruction signal from the system control unit 8, allows the irradiation unit 6 to irradiate.
The light sensor 7 detects strobo light irradiated from the irradiation unit 6 and outputs the detection results to the light control circuit 24.
The light control circuit 24, to integrate the output from the light sensor 7 and dim the irradiation quantity of the irradiation unit 6, outputs the integral value to the irradiation control circuit 23.
The line sensor 5 is, for example, an area sensor or a surface sensor, and as shown in
The system control unit 8, when the power source of the image pickup apparatus 1 is turned on, picks up images by the image pickup device 4 every predetermined cycle, for example, every 15 fps and successively displays the picked-up images on the monitor 12 as preview screens. In this case, automatic exposure can be performed every time.
Further, the system control unit 8, from the AE evaluation value obtained from the picked-up images of the preview screens, for example, the mean brightness value of all the screens of the monitor 12, decides the stop value, shutter speed, and imaging sensitivity which are exposure conditions of the real imaging.
Further, the system control unit 8 judges whether or not to use the strobo device as an irradiation unit 6 at time of imaging. For example, the system control unit 8 calculates the mean brightness value of all the preview screens from the AE evaluation value and when the mean brightness value is not larger than a predetermined brightness value, judges use of the strobo device at time of imaging.
Further, the system control unit 8, in the preliminary imaging, executes imaging without using the strobo device under the exposure condition at time of the real imaging and then executes imaging by preliminary irradiation at a light quantity of 1/n of that of the real irradiation. And, the system control unit 8, when receiving, from the line sensor 5, a sensor received light quantity (i) of reflected light of a photographic subject in imaging when the strobo device is not used and a sensor received light quantity (ii) of reflected light of a photographic subject in imaging after preliminary irradiation, obtains the difference between the sensor received light quantity (i) and the sensor received light quantity (ii), thereby calculates a reflected light quantity X according to the distance of the photographic subject in the respective areas A to E. The reflected light quantity X is reduced as the distance between the image pickup apparatus 1 and the photographic subject is increased and here, the intrinsic reflection factor of the photographic subject is not considered. In
Furthermore, the system control unit 8 decides the main photographic subject of a picked-up image on the basis of the reflected light quantity X according to the distance of the photographic subject. Namely, among the areas existing within the range where the strobo light reaches appropriately, the photographic subject in the area where the reflected light quantity X according to the distance of the photographic subject is largest is decided as a main photographic subject. In this embodiment, in
Further, the system control unit 8 sets the irradiation quantity of the irradiation unit so as to make the exposure quantity of the main photographic subject appropriate.
The inflection point changing unit 25, in picking up an image on the preview screen and preliminary imaging, minimizes the voltage VL impressed to the image pickup device 4, thereby can always make the image pickup device 4 perform the linear conversion operation, and can put the image pickup device 4 into the state capable of performing both linear conversion operation and logarithmic conversion operation. When always performing the linear conversion operation, in picking up an image on the preview screen and preliminary imaging, the contrast of the picked-up image has privilege. Further, the inflection point changing unit 25, on the basis of the AE evaluation value calculated whenever the preview screen is picked up, to prevent the high-brightness area of an output signal of the image pickup device 4 from saturation, can be structured so as to change the inflection point every time.
Further, the inflection point changing unit 25, after preliminary imaging, changes the inflection point so as to position the brightness distribution of the main photographic subject in the linear area of the output signal of the image pickup device 4. In this embodiment, the inflection point changing unit 25 changes the inflection point so that the brightness distribution of the area D where the reflected light quantity X is largest within the range where the strobo light reaches appropriately is positioned in the linear area of the output signal of the image pickup device 4.
Therefore, as shown in
Next, the inflection point changing unit 25, to change the inflection point of the image pickup device 4, calculates a voltage VL to be set in the image pickup device 4.
As mentioned above, the image pickup device 4 of this embodiment switches the voltage VL of the signal φVPS given to the pixels G11 to Gmn shown in
Here, as a characteristic of the output signal of the image pickup device 4, as the voltage VL is lowered, the rate of the brightness of the photographic subject to be linearly converted is increased. Therefore, when moving up the inflection point, that is, when increasing the rate of the brightness of the photographic subject to be linearly converted, the voltage VL may be reduced. In this way, the inflection point changing unit 25, to change the inflection point of the image pickup device 4 to the decided inflection point, calculates the voltage VL of the signal φVPS given to the pixels G11 to Gmn.
Further, a constitution may be used that an LUT prepared beforehand by making the exposure quantity of the main photographic subject and voltage VL correspond to each other is stored in the inflection point changing unit 25 and the voltage VL is calculated using the LUT.
Furthermore, the inflection point changing unit 25 has a D-A converter 39, converts the calculated voltage VL to analog data, and inputs it to the pixels G11 to Gmn of the image pickup device 4, thus the inflection point of the image pickup device 4 is changed to an optimum inflection point. Next, the operation of the image pickup apparatus 1 of this embodiment will be explained by referring to the flow chart shown in
The system control unit 8, when the power source of the image pickup apparatus 1 is turned on, picks up images by the image pickup device 4 every predetermined cycle, for example, every 15 fps and successively displays the picked-up images on the monitor 12 as preview screens (Step S1). Further, in this image pickup, the inflection point changing unit 25 minimizes the voltage VL impressed to the image pickup device 4, thereby may always make the image pickup device 4 perform the linear conversion operation, and may put the image pickup device 4 into the state capable of performing both linear conversion operation and logarithmic conversion operation.
Then, when a user half-presses the release switch 17, the beam measurement is started. Namely, the AE evaluation value calculation unit 33 detects the AE evaluation value from the picked-up images of the preview screens and the system control unit 8, from the AE evaluation value, for example, the mean brightness value of all the screens of the monitor 12, decides the stop value, shutter speed, and imaging sensitivity which are exposure conditions of the real imaging (Step S2).
Next, the system control unit 8 judges whether or not to use the strobo device as an irradiation unit 6 at time of imaging (Step S3). In this embodiment, the system control unit 8 calculates the mean brightness value of all the preview screens from the AE evaluation value and when the mean brightness value is not larger than a predetermined brightness value, judges use of the strobo device at time of imaging. On the other hand, when the mean brightness value is the predetermined brightness value or larger, the system control unit 8 performs the ordinary image pickup operation without using the strobo device (Step S10).
Next, when the user full-presses the release switch 17, the system control unit 8 executes imaging without using the strobo device under the exposure condition at time of the real imaging and then executes imaging by preliminary irradiation at a light quantity of 1/n of that of the real irradiation (Step S4). Further, in this image pickup, the inflection point changing unit 25 minimizes the voltage VL impressed to the image pickup device 4, thereby may always make the image pickup device 4 perform the linear conversion operation, and may put the image pickup device 4 into the state capable of performing both linear conversion operation and logarithmic conversion operation.
Then, in the predetermined areas A to E, the line sensor 5 detects a sensor received light quantity (i) of reflected light of a photographic subject in imaging when the strobo device is not used and a sensor received light quantity (ii) of reflected light of a photographic subject in imaging when preliminarily irradiated and transmits the respective received light quantities to the system control unit 8 (Step S5).
Next, the system control unit 8 obtains the difference between the sensor received light quantity (i) and the sensor received light quantity (ii), thereby calculates a reflected light quantity X according to the distance of the photographic subject in the respective areas A to E (Step S6). And, among the areas existing within the range where the strobo light reaches appropriately, the area where the reflected light quantity X is largest, that is, in this embodiment, the photographic subject of the area D is decided as a main photographic subject (Step S7).
Furthermore, the system control unit 8 sets the irradiation quantity of the irradiation unit so as to make the exposure quantity of the decided main photographic subject appropriate.
Next, the inflection point changing unit 25, in image pickup of the main photographic subject, changes the inflection point so as to use the linear area of the output signal of the image pickup device 4 (Step S8). In this embodiment, the inflection point changing unit 25 changes the inflection point so as to position the brightness distribution of the area D in the linear area of the output signal of the image pickup device 4. Namely, the inflection point a in the graph (a) shown in
Next, the inflection point changing unit 25, to change the inflection point of the image pickup device 4, calculates a voltage VL to be set in the image pickup device 4.
Next, the process moves to the real imaging and the system control unit 8 performs real irradiation by the strobo device and also performs real imaging. Namely, the system control unit 8 performs the real irradiation after start of exposure of the real imaging and ends the exposure after a lapse of predetermined time. Then, the pixels G11 to Gmn of the image pickup device 4 switches the linear conversion operation and logarithmic conversion operation at the inflection point changed by the inflection point changing unit 25, thereby converts photoelectrically the incident light. And, the concerned pixels output the electric signal obtained by photoelectric conversion to the signal processing unit 9.
And, the signal processing unit 9 performs a predetermined image process for the electric signal obtained by photoelectric conversion. Namely, when the amplifier 30 amplifies the electric signal outputted from the image pickup device 4 to a predetermined specified level, the A-D converter 31 converts the amplified electric signal to a digital signal.
Next, the black reference correction unit 32 corrects the black level which is a lowest brightness value to the reference value. Further, the AE evaluation calculation unit 33 detects an evaluation value necessary for automatic exposure (AE) from an electric signal after black reference correction and transmits it to the system control unit 8. On the other hand, the WB processing unit 34 calculates a correction coefficient from the electric signal after black reference correction, thereby adjusts the gain values of the color components of R, G, and B of the picked-up image, and correctly displays the white.
Further, the color interpolation unit 35 performs a color interpolation process of interpolating missing color components for each pixel. And, the color correction unit 36 corrects the color component values for each pixel and generates an image emphasizing the color tone of each pixel. Further, when the gradation conversion unit 37 performs a gamma correction process of correcting the gradation response characteristic of the image to an optimum curve according to the gamma value of the image pickup apparatus 1, the color space conversion unit 38 converts the color space from R, G, and B to Y, U, and V.
And, the recording unit 11 records image data outputted from the signal processing unit 9.
Further, in this embodiment, a constitution that a user designates a main photographic subject on the preview screen of the monitor 12 is used, though a constitution that the image pickup apparatus 1 decides automatically a main photographic subject can be used.
The image pickup apparatus of the embodiment of the present invention includes an image pickup device having a plurality of pixels for switching a linear conversion operation for linearly converting incident light to an electric signal and a logarithmic conversion operation for logarithmically converting it according to an incident light quantity, an irradiation unit for irradiating light at time of picking up an image of a photographic subject, and an inflection point changing unit, when imaging using the irradiation unit, for changing an inflection point which is a boundary between the linear area and the logarithmic area so as to position the brightness distribution of the main photographic subject in the linear area of the output signal of the image pickup device.
Therefore, when imaging using the irradiation unit such as the strobo device, the inflection point of the output signal of the image pickup device is moved, and the brightness distribution of the main photographic subject is positioned in the linear area, thus data represented in a predetermined brightness distribution in the image pickup ready area can be avoided from getting fewer. By doing this, sufficient data is obtained in the predetermined brightness distribution, thus the contrast of the photographic subject can be improved.
According to another aspect of the embodiment of the present invention, the image pickup apparatus has a control unit, for photographic subjects within the arrival distance of irradiation light by the irradiation unit, from the difference between the reflection light quantity when preliminarily imaged using the irradiation unit and the reflection light quantity when preliminarily imaged not using the irradiation unit, for obtaining a reflection light quantity according to the distance from the image pickup apparatus and deciding the photographic subject having the largest reflection light quantity as the aforementioned main photographic subject.
Therefore, within the arrival distance of the irradiation light of the irradiation unit, the difference between the reflected light quantity when imaged using the irradiation unit and the reflected light when imaged without using the irradiation unit becomes the reflected light quantity according to the distance of the photographic subject, so that the photographic subject having a largest reflected light quantity is assumed as a main photographic subject, thus the photographic subject positioned at a shortest distance from the image pickup apparatus can be decided as a main photographic subject.
According to still another aspect of the embodiment of the present invention, in the image pickup apparatus, the control unit aforementioned sets the irradiation quantity of the irradiation unit so as to make the exposure quantity of the main photographic subject appropriate.
Therefore, the exposure quantity of the main photographic subject closest to the image pickup apparatus is made appropriate and then the brightness value of the main photographic subject is positioned in the linear area, thus the contrast can be improved.
According to a further aspect of the embodiment of the present invention, in the image pickup apparatus, the inflection point changing unit changes the voltage set in the pixels of the image pickup device, thereby changes the inflection point.
Therefore, the inflection point of the output signal of the image pickup device can be changed.
As mentioned above, according to the image pickup apparatus of the present invention, at time of imaging using the irradiation unit such as the strobo device, the linear area is used to image the main photographic subject, and sufficient data is obtained in a predetermined brightness distribution, thus the contrast of the photographic subject can be improved.
Further, the main photographic subject at a closest distance from the image pickup apparatus can be decided as a main photographic subject.
Further, the exposure quantity of the main photographic subject is made appropriate and the contrast of the main photographic subject can be improved.
Further, while the present invention has been described by reference to specific embodiments, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2005-152082 | May 2005 | JP | national |
