JP2004096777A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the effect caused by a black level correction occurred when an AGC (automatic gain control) gain is high. <P>SOLUTION: In the case of the high AGC gain, a microcomputer 13 inactivates the black level correction for the clamp circuit (29 and 37) of a digital signal processing circuit part 9. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an imaging apparatus, and more particularly to a technique for preventing an adverse effect caused by black level correction during exposure correction or when the gain of an automatic gain control circuit (AGC) is high.

In the conventional video camera, when flare due to irregular reflection on the optical system or the imaging surface occurs, there is a problem that the black level of the video signal increases and the contrast of the image decreases.

Therefore, recently, a flare compensation circuit, a black level correction (hereinafter also referred to as DBS) circuit, and the like have been proposed as countermeasures against a decrease in contrast, and when the contrast is low due to the occurrence of flare or the like, the black level is lowered to improve the contrast. It has become.

However, if the black level correction is always executed by these circuits, the black level is lowered during exposure correction such as backlight correction, and thus there is a disadvantage that a sufficient exposure correction effect cannot be obtained. If the black level is lowered even when the gain is high, there is a disadvantage that the S / N of the dark portion is remarkably deteriorated due to the high gain.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described prior art, and an object thereof is to provide an imaging apparatus capable of preventing adverse effects due to black level correction during exposure correction or when the gain of an automatic gain control circuit (AGC) is high. It is.

An imaging apparatus of the present invention that achieves the above object includes a black level correction unit that corrects a black level of a video signal, a determination unit that determines whether a control value of an automatic gain control unit is a predetermined value or more, And a stopping unit that stops the correction by the black level correcting unit when it is determined that the control value is equal to or greater than the predetermined value.

The imaging apparatus according to the present invention includes a determination unit that determines whether or not the control value of the automatic gain control unit is greater than or equal to a predetermined value, and a black level correction unit that determines that the control value is greater than or equal to the predetermined value. And a stop means for stopping the correction, so that when the AGC gain is high, the black level correction is stopped (off), and the S / N reduction in the dark part of the video signal is prevented. Therefore, when the AGC gain is high It is possible to prevent an adverse effect caused by the black level correction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an imaging system of a video camera to which the present invention is applied. As shown in FIG. 1, an optical image formed by a lens 1 is formed on a light receiving surface of a CCD 3, and an analog imaging signal is output from the CCD 3. This is sampled and held and gain adjusted by the CDS and AGC circuit 5 and further converted into a digital signal by the A / D converter 7 before being input to the digital signal processing circuit unit 9 and simultaneously AE (automatic exposure). And AWB (automatic white balance) digital integration circuit unit 11. In FIG. 1, reference numeral 13 denotes a microcomputer of the camera unit. A hall voltage representing the iris opening is input via the hall element amplifier 15 to detect the iris opening, and a photometric value is obtained from the integrating circuit unit 11. For exposure control, an iris control signal is given to the iris driver 19 via the D / A converter 17 to control the iris opening. Further, the AGC control value is supplied to the CDS / AGC circuit 5 through the D / A converter 21 to adjust the AGC gain. Further, the electronic shutter control value is given to the timing circuit 23, and the electronic shutter of the CCD 3 is controlled by the driver 25. Further, a color temperature detection value is obtained from the integration circuit unit 11 and a control value for AWB is given to the signal processing circuit unit 9. Reference numeral 27 denotes a timing circuit.

As shown in FIG. 2, the digital signal processing circuit unit 9 includes a clamp circuit 29, a γ correction circuit 31, a signal processing circuit 33, and a D / A converter 35 for luminance signals, through which an analog luminance signal Y is output. Is done. Further, there are a clamp circuit 37, a matrix circuit 39, a γ correction circuit 41, a color signal processing circuit 43, and a D / A converter 45 for color signals, through which the analog color signal C is output.

The digital integration circuit unit 11 includes a data comparator 47, an integrator (counter) 49, and an optical black detector 51, as shown in FIG.

The microcomputer 13 determines whether or not the AGC control value is equal to or greater than a predetermined value. If the AGC control value is equal to or greater than the predetermined value, the black level correction value to the clamp circuits 29 and 37 is set to zero and the black level correction is stopped (turned off).

Further, the microcomputer 13 determines whether or not the backlight correction state is in accordance with the information from the integrating circuit unit 11, and even in the backlight correction state, the black level correction value to the clamp circuits 29 and 37 is set to zero and the black level is set. Turn off correction.

The AE signal output system of the digital integration circuit unit 11 has a configuration as shown in FIG. 3, and the digital luminance signal obtained by the Y / C separation circuit 53 is input to the three gate circuits 55, 57, and 59. The data is input to the three data comparators 47, 63 and 65.

The three gate circuits 55, 57, and 59 are opened in accordance with the AE frame setting information given from the microcomputer 13 via the interface 67, and the respective outputs are photometric frames for 0 frame, 1 frame, and 2 frames. To the integrators 69, 71 and 73. The outputs of the integrators 69, 71, 73 are given to the microcomputer 13 via the interface 87. For example, the photometry frame is set as shown in FIG. 4, and the full-screen average photometry value PMave and the weighted photometry value PMwet are obtained. Therefore, when weighting 2 frames> 1 frame> 0 frame, when PMwet <PMave, it is determined that the backlight is in the backlight state, and the backlight is corrected according to the difference between PMave and PMwet, and this correction amount reaches the predetermined value. Black level correction is turned off when it becomes larger.

The reference value for the comparator is given to the data comparator 47 via the interface 67. The data comparator 47 determines whether or not each digital luminance signal is less than the reference value. When the data comparator 47 is less than the reference value, it outputs one pulse, and the counter (accumulator) 49 outputs 1 V through the gate 75 to 1V. And the number of times S less than the reference value is obtained every predetermined period such as 1H. The reference value is given from the microcomputer 13 through the interface 67 and updated. In FIG. 4, 77 and 99 are gate circuits, and 83 and 85 are counters.

The microcomputer 13 performs black level correction using the number of times obtained from the integrator (counter) 49, that is, the integrated value S. Hereinafter, a description will be given with reference to FIGS. FIG. 5 shows an example algorithm for black level correction. However, in these drawings, K1, K2 and B are fixed set values, R, S, M0, M1, C and T are variable values, and M0 = 1, M0 = 2, M0 = 3, M0. = 4 is a black level correction value, which is defined as follows.
K1: AGC control value (predetermined value) at which black level correction is turned off
K2: Condition count for updating M0 (predetermined number of updates)
B: Set value for black level detection (predetermined number of times)
R: reference value of data comparator 47 S: integrated value (number of times) of integrator 49
M0: Black level correction value being executed M1: Black level correction value obtained from the detection result C: Count number where M0 ≠ M1 continuously T: Initial setting value of the reference value R M0 = 4: Black level correction The quantity is zero M0 = 0 <M0 = 1 <M0 = 2 <M0 = 3

In FIG. 5, when the AGC gain is less than the predetermined value and the backlight correction state is not set (steps 100 and 102), a reference value corresponding to the initial value T is set as R, and the integrated value S is read (steps 104 and 106). ). If the integrated value S is less than the predetermined number of times B and R ≠ 0, R is reduced to R-1 and a corresponding reference value is set (steps 108, 110, 112, 114), and the integrated value at this time If S is less than the predetermined number of times B, R is set to R + 1 (steps 116 and 118). If R = 1 as a result, M1 = 1 is set (steps 120 and 122). If R ≠ 1, and R = 2, M1 = 2 is set (steps 124 and 126). Further, if R ≠ 1, R ≠ 2, and R = 3, M1 = 3, and if R ≠ 3, M1 = 4 (steps 128, 130, 132). If R = 0 in step 110, M1 = 0 is set (step 134), and if B ≦ S in step 116, the process returns to step 110.

If B> S in step 108, if R ≠ 3, R is increased to R + 1 and a corresponding reference value is set (steps 136, 138, 140). If the integrated value S at this time is greater than or equal to the predetermined number of times B, it is determined in step 120 whether R = 1 or not. Conversely, if B> S, the process returns to step 136 (step 142).

When M1 is set in steps 122, 126, 130, and 134, R at that time is set as an initial value T, and it is determined whether or not M1 = M0 (step 140). If M1 = M0, the count number C is set to zero, M0 is left as it is, a black level correction value corresponding to M0 is set, and given to the clamp circuit (steps 148, 150, 152, 154). If M1 ≠ M0 in step 146, the count number C is increased to C + 1, and it is determined whether or not this is K2. If it is K2, the process proceeds to step 148, and if it is not K2, the process ends (step 154). 156).

An example of the above processing results is shown in FIG. In FIG. 6A, when the initial setting of the reference value is R = 0, the black level is detected for the third time as R = 0 → R = 1 → R = 2, and the initial setting is R = 2 of the previous result. In this case, the black level can be detected for the second time as R = 2 → R = 1. In FIG. 6B, when the initial setting is R = 0, the detection can be performed at the fourth time as R = 0 → R = 1 → R = 2 → R = 3, and when the initial setting is R = 3 of the previous result, 1 Can be detected at a time. In FIG. 6C, it can be detected immediately when the initial setting is R = 0.

The initial value T may be 0 or 3. If the reference value is updated a predetermined number of times, the black level correction value may be set to zero and correction may be turned off, or correction may be performed with a black level correction value corresponding to the latest reference value. Further, the data comparator 63, the gate circuit 77, and the counter 83 shown in FIG. 4 are additionally used, and different reference values are given to the two data comparators 47 and 63, thereby performing parallel processing and shortening the black level. Can be detected in time.

In the embodiment of the invention described above, the control value of the black level correction means for correcting the black level of the video signal, the determination means for determining whether or not the backlight correction state is in effect, and the control value of the automatic gain control means are not less than a predetermined value. The determination means for determining whether or not there is, and the determination result of one of the determination means is affirmative (determination that the backlight correction state is present, or determination that the control value of the automatic gain control means is greater than or equal to a predetermined value) In this case, the image pickup apparatus including the stop unit that stops the correction by the black level correction unit has been described. Thereby, if it is a backlight correction state, black level correction | amendment is stopped (off), and sufficient exposure correction effect can be exhibited, without reducing a black level. Even when the gain of AGC is high, the black level correction is stopped (turned off) to prevent the S / N drop in the dark part of the video signal. That is, it is possible to prevent an adverse effect due to the black level correction during exposure correction or when the AGC gain is high.

In addition to this, in the above-described embodiment of the invention, A / D conversion means for converting the analog video signal obtained from the image sensor into a digital video signal, and the black level of the digital video signal are clamped to the black level correction value. Clamping means, sampling means for sampling the digital video signal, comparison means for comparing the sampled signal with a reference value every predetermined period, and the number of times the sampled signal is less than the reference value is predetermined in the predetermined period A determination unit that determines whether the number is greater than or less than a predetermined number, a reference value update unit that updates the reference value of the comparison unit by a predetermined amount when it is determined that the number is less than the predetermined number, An image pickup apparatus including a black level correction value setting unit that sets a black level correction value according to a reference value and supplies the black level correction value to the clamp unit when it is determined that the number of times is greater than or equal to the number of times. And Akira. This imaging apparatus performs black level correction by digital processing. The reference value is updated from a small value to a large value from the pedestal side, and the number of times the sampled video signal becomes smaller than the reference value is set to a predetermined value such as 1V or 1H. Counting every period, if the number of times is equal to or greater than the predetermined number, the dark level of the video signal is detected, and by setting and clamping the black level correction value according to the reference value at that time, the video signal Correct the black level. As a result, compared with the case where the average value of the video signal is detected and the black level is changed in proportion to the average value, the black level is not corrected excessively or insufficiently, and the contrast is sufficiently improved. Therefore, highly reliable black level correction by digital processing can be performed.
In this case, since it is meaningless to keep updating the reference value too much, it is further provided with an update continuation determining means for determining whether or not the reference value has been updated a predetermined number of times in order to solve this. However, the apparatus has been described in which the black level correction value setting means does not set the black level correction value when the number of times that the sampled signal is less than the reference value is less than the predetermined number even if the predetermined update number is continued. In this apparatus, even if the reference value is updated a predetermined number of times, the black level is not corrected if the sampled video signal is not less than the predetermined value and less than the reference value. In addition, by providing the same update continuation determining means, the apparatus in which the black level correction value setting means gives the black level correction value according to the latest reference value to the clamp means when the predetermined number of updates has been continued. did. In this apparatus, the video signal is clamped with a black level correction value corresponding to the reference value at that time.

In the embodiment of the invention described above, the A / D conversion means for converting the analog video signal obtained from the image sensor into the digital video signal, and the clamping means for clamping the black level of the digital video signal to the black level correction value. A sampling means for sampling the digital video signal; a comparing means for comparing the sampled signal with a reference value every predetermined period; and the number of times that the sampled signal is less than the reference value is a predetermined number of times or more in the predetermined period. A determination means for determining whether or not less than a predetermined number of times, a reference value updating means for reducing the reference value of the comparison means by a predetermined amount and updating it to be the next reference value if it is determined to be greater than or equal to the predetermined number of times, and less than the predetermined number of times An image pickup apparatus including a black level correction value setting unit that sets a black level correction value according to a reference value and supplies the black level correction value to a clamp unit when it is determined has been described. This imaging device also corrects the black level by digital processing. In this case, the reference value is updated from a larger value to a smaller value from the pedestal side, and the sampled video signal is smaller than the reference value. Is counted for each predetermined period such as 1V or 1H, and if the number is less than the predetermined number, the dark level of the video signal is detected, and a black level correction value corresponding to the reference value at that time is set. To correct the black level of the video signal. This also prevents the black level from being excessively or insufficiently corrected and sufficiently improves the contrast as compared with the case where the average value of the video signal is detected and the black level is changed in proportion to the average value. Therefore, highly reliable black level correction by digital processing can be performed.
Also in this case, it is meaningless to keep updating the reference value too much, so in order to solve this, an update continuation determining means for determining whether or not the reference value has been updated a predetermined number of times is provided. However, the apparatus has been described in which the black level correction value setting means does not set the black level correction value when the number of times that the sampled signal is less than the reference value is equal to or greater than the predetermined number even if the predetermined number of update times continues. In this apparatus, even if the update of the reference value continues for a predetermined number of times, if the sampled video signal becomes less than the reference value for a predetermined number of times or more, the black level is not corrected.

Further, in the above-described embodiments of the invention, the description has been given of any imaging apparatus having a plurality of comparison means so that different comparison values are given to each comparison means to perform comparison processing in parallel. . Thus, by performing the comparison process in parallel, the black level correction can be performed in a short time.

Furthermore, in the above-described embodiment of the invention, any imaging apparatus includes a determination unit that determines whether or not the backlight is in the backlight correction state, so that if it is determined that the backlight is in the backlight correction state, the black level correction is performed. The value setting means has been described so as not to output the black level correction value. As described above, in the case of the reverse correction state, the black level correction is not performed, and the black level correction is turned off. Thus, in addition to performing the reliable black level correction by the digital processing described above, a sufficient exposure correction effect can be obtained. It can be demonstrated.

In the above-described embodiment of the present invention, in any of the imaging apparatuses, the automatic gain control unit is controlled by including a determination unit that determines whether or not the control value of the automatic gain control unit is equal to or greater than a predetermined value. In the above description, the black level correction value setting unit does not output the black level correction value when it is determined that the value is equal to or greater than the predetermined value. As described above, when the gain of AGC is high, the black level correction is not performed, and the black level correction is turned off to thereby perform the black level correction with high reliability by the digital processing described above, in addition to the dark portion of the video signal. S / N reduction can be prevented.

In the embodiment of the invention described above, in any imaging apparatus, when the black level correction value setting unit once sets the black level correction value and starts the next black level correction process, the reference value updating unit In the above description, the last reference value in the black level correction process is set as the initial value. As described above, when the black level correction is performed once, when the next black level correction processing is started, the black level correction with high reliability by the digital processing described above is started by starting from the last reference value of the previous time. In addition to this, black level correction can be performed in a short time.

1 is a circuit diagram showing an imaging system of a video camera according to an embodiment of the present invention. The circuit diagram which shows the structural example of a digital signal processing circuit part and a digital integration circuit part. The figure which shows the example of a photometry frame. The circuit diagram which shows the structural example of the AE processing system of a digital integration circuit part. The figure which shows the example of an algorithm of black level correction | amendment. The figure which shows the black level correction example.

Explanation of symbols

3 CCD
DESCRIPTION OF SYMBOLS 5 AGC circuit 7 A / D converter 9 Digital signal processing circuit part 11 AE, AWB digital integration circuit part 13 Camera part microcomputer 29, 37 Clamp circuit 47, 63 Data comparator 49, 83 Accumulator

Claims (1)

A black level correction means for correcting the black level of the video signal; a determination means for determining whether or not a control value of the automatic gain control means is equal to or greater than a predetermined value; and the control value is determined to be equal to or greater than a predetermined value. An image pickup apparatus comprising stop means for stopping correction by the black level correction means.

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