JP2876481B2 - Imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging signal processing device that A / D converts an output signal of a solid-state imaging device and extracts a luminance signal and a color signal.

[Conventional technology]

FIG. 6 is a schematic diagram of an interline type CCD which is a commonly used general solid-state imaging device. In FIG. 1, reference numeral 1 denotes an interline type CCD, 2 denotes a plurality of photodiodes which convert light incident on the photosensitive portion of the CCD 1 into electric charges and accumulates them, and 3 denotes electric charges transferred from the respective photodiodes 2 by 1H (horizontal). V1 to V4 are transfer electrodes of the vertical transfer unit 3, and V1 also serves as a transfer gate for transferring the odd-numbered rows of charges of the photodiode 2 to the vertical transfer unit 3. Similarly, V3 is a transfer gate corresponding to the photodiodes 2 in the even-numbered rows. The vertical transfer unit 3 is driven by four-phase transfer pulses. 4
Is a horizontal scanning unit for horizontally transferring the charges transferred one stage to 1H from the vertical transfer unit 3, and H1 and H2 are transfer electrodes of the horizontal scanning unit 4 and are driven by two-phase pulses. Reference numeral 5 denotes an output amplifier which converts the electric charge into a voltage and outputs the voltage, and VOUT denotes an output terminal.

FIG. 7 is a diagram showing a color filter array provided in the CCD1, and this filter is a stripe in which three colors are repeated in the horizontal direction, such as Ye (yellow), G (green), Cy (cyan),. Has become a filter.

FIG. 8 is a diagram showing a drive timing when electric charges are read out from the CCD1, for example, at the time t1 of the A field.
, The charges of the photodiodes 2 in the upper and lower rows are added when the transfer electrodes V1 and V3 become Hi (high) level. The added charges are transferred to the horizontal scanning unit 4 in the vertical transfer unit 3 one stage at a time in 1H. Also,
The charges transferred to the horizontal scanning unit 4 during the horizontal blanking period are output from the output amplifier 5 in the order of Ye, G, Cy,....

FIG. 9 is a block diagram showing a circuit configuration of a general imaging signal processing device for processing the output signal of the above-described CCD1.
In the figure, reference numeral 6 denotes a CDS circuit for removing noise of CCD1;
7 is a clamp circuit for fixing the output potential of the CDS circuit 6 to a constant value, 8 is an A / D conversion circuit for performing analog / digital conversion, 9 is a frame memory, and 10 is information obtained from the frame memory 9 via the data bus 11. , A digital signal processing unit for generating a luminance signal and a color signal, a D / A conversion circuit 12 for D / A converting the luminance signal output of the digital signal processing unit 10, and 13, 14 A D / A conversion circuit for performing A / A conversion, and 15 is a low-pass filter (LP) for band-limiting the luminance signal
F), 16 and 17 are low-pass filters for band-limiting the color signals, and the luminance signals and color difference signals of Y, RY and BY are obtained as outputs of these low-pass filters 15, 16 and 17, respectively.

FIG. 10 is a diagram showing a detailed configuration of the digital signal processing unit 10, in which 18 is a latch circuit for reading and latching the Ye signal from the frame memory 9, 19 is a G signal latch circuit, and 20 is Similarly, a latch circuit for the Cy signal, a subtraction circuit 21 for subtracting the G signal from the Ye signal to generate an R (red) signal, and a subtraction circuit 22 for subtracting the G signal from the Cy signal to generate a B (blue) signal The circuit 23 is Ye, G, Cy, ... from the frame memory 9.
, A gamma correction circuit for performing gamma correction on the signals read out in the order of and outputting a digital luminance signal Y (D).
A gamma correction circuit for gamma correction to a signal, 25 is a gamma correction circuit for gamma correction to a G signal, 26 is a gamma correction circuit for gamma correction to a B signal, and 27 is a gamma-corrected R, G, B signal matrix operation. Digitized color difference signal R
-Y (D) and a matrix operation circuit for generating BY (D).

In the imaging signal processing device configured as described above,
As described above, the difference between the complementary color signal from the CCD 1 digitized by the A / D conversion circuit 8 from the CCD 1 is obtained by the subtraction circuits 21 and 22 of the digital signal processing unit 10, whereby a primary color signal is generated. And after each signal is gamma corrected,
It is again converted to an analog signal and output to the outside.

[Problems to be solved by the invention]

In the conventional image pickup signal processing apparatus as described above, the primary color signal is generated by calculating the difference between the complementary color signals from the digitized solid-state image pickup device.
The problem is that with bit-level quantization, the bit resolution of the chrominance signal is reduced when the difference is taken, and the effects of quantization noise cannot be ignored, thereby deteriorating the S / N ratio of the chrominance signal. was there.

The present invention has been made in view of such a problem, and an imaging signal processing apparatus in which the bit resolution of a color signal is improved, the influence of quantization noise is suppressed, and the S / N ratio of the color signal is improved. The purpose is to get.

[Means for solving the problem]

An imaging apparatus according to the present invention includes an imaging unit that converts an optical image into an electric image signal, a color filter including a complementary color disposed on a front surface of the imaging unit, and an analog primary color signal based on an analog complementary color signal output from the imaging unit. A calculating means for forming a signal or an analog color difference signal, and an A / D converting means for A / D converting an output of the calculating means, wherein the DC potential of the analog signal input to the A / D converting means is The configuration is such that the zero level of the analog signal is at the midpoint of the input range of the A / D conversion means.

The arithmetic means forms an analog color difference signal from the analog complementary color signal output from the imaging means, performs gamma correction on the digital color difference signal output from the A / D conversion means, and adjusts the luminance signal level and the digital color difference signal level. And a gamma correction unit for referring to a correction table for obtaining a digital color difference signal after correction.

[Action]

In the imaging signal processing device of the present invention, since the A / D conversion is performed after performing the subtraction process of extracting the primary color signal or the color difference signal, the bit resolution of the color signal is improved,
Even if an ordinary A / D conversion circuit of about 8 bits is used, quantization noise in the color signal becomes inconspicuous.

〔Example〕

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention, and the same reference numerals as those in FIG. 9 denote the same components. In the figure, 28 is a sample and hold circuit that samples and holds the Ye signal, 29 is a sample and hold circuit that samples and holds the G signal, 30 is a sample and hold circuit that samples and holds the Cy signal, and 31 is a circuit that subtracts the G signal from the Ye signal. A subtraction circuit for generating an R (red) signal, a subtraction circuit for subtracting a G signal from a Cy signal to generate a B (blue) signal, and a 33 for fully utilizing the bit resolution of the subsequent A / D conversion. The gain correction circuit applies a k-fold gain to the G signal, and the gain k is configured to be switched stepwise according to the brightness of the subject. 34 is a white balance circuit that corrects the amplitude of the R signal according to the color temperature of the light source by multiplying the gain-corrected G signal by kxWr times the gain so that the amplitude of the R signal in the white portion of the subject becomes equal. Similarly, 35 is a white balance circuit that corrects the amplitude of the B signal by multiplying the gain by kxWb so that the amplitudes of the G signal and the B signal are equal in the white portion, and 36, 37, and 38 are the R, G, and B signals, respectively. Clamp circuit for fixing the DC (direct current) level of the reference potential to the reference potential, 39, 40, 41 are gamma correction circuits for gamma correction of R, G, B signals, respectively, and 42, 43, 44 are the aforementioned R, G, The A / D conversion circuit performs A / D conversion of the B signal. The digitized signal is stored in the frame memory 9.
Reference numeral 45 denotes a latch circuit for reading and latching the R signal from the frame memory 9; 46, a latch circuit for reading and latching the G signal from the frame memory 9; 47, a latch circuit for reading and latching the B signal from the frame memory 9; A gain correction circuit that applies 1 / Wr times gain to the R signal, 49 is a gain correction circuit that applies 1 / Wb times gain to the B signal, and 50 is a Ye 'signal that adds the R and G signals that have been gain corrected. An addition circuit 51 generates the Cy 'signal by adding the gain-corrected B signal and G signal, and an addition circuit 52 generates the
A switch for switching the signals e ', G, and Cy' in synchronization with a clock having one pixel period. 53 is R, G, B
Color difference signal RY digitized by signal operation
(D), a matrix circuit for obtaining BY (D).

In the imaging signal processing device configured as described above, the complementary color signal obtained from the CCD 1 is separated into R, G, B pure color signals, and each signal is input to each of the A / D conversion circuits 42 to 44. In this case, since the gain is corrected and then digitized to make the best use of the signal input range, the complementary color signal is directly converted from analog to digital and then subtracted to obtain a pure color signal. The effect of quantization noise on the color signal is remarkably suppressed as compared with. For this reason,
The S / N ratio of the color signal can be greatly improved.
Since a complementary color signal is reproduced from the pure color signal read out from the frame memory 9 by digital operation and a luminance signal is generated by the complementary color signal, a high-quality luminance signal with little aliasing noise, which is an advantage of the complementary color filter, is obtained. be able to.

FIG. 2 is a block diagram showing a circuit configuration of another embodiment of the present invention. In this embodiment, the complementary color mosaic filter shown in FIG. 3 is provided in the CCD 1, and a color signal having a high S / N ratio is obtained from the output of the CCD 1.

The complementary color mosaic filter shown in FIG. 3 has a color arrangement as shown in FIG.
From the output signal, a luminance signal and a line-sequential color difference signal are obtained by the following arithmetic expression. At this time, as shown in FIG. 3, the charges of two lines shifted one line up and down are added and read out in the form shown in FIG. 8 according to the drive timing shown in FIG. By doing so, a luminance signal and a color difference signal are obtained.

A field: n lines: Luminance signal: Ye (n) + Mg (n) + Cy (n) + G (n) = (R + G) + (R + B) + (G + B) + (G) = 2R + 3G + 2B color signal: Ye (n) + Mg (n)-{Cy (n) + G (n)} = {(R + G) + (R + B)}-{(B + G ) + G} = 2R-G n + 1 line: Luminance signal: Ye (n + 1) + G (n + 1) + Cy (n + 1) + Mg (n + 1) = 2R + 3G + 2B Color signal: Cy (n + 1) + Mg (n + 1)-{Ye (n + 1) + G (n + 1)} = 2B-G B field: n 'line: Luminance signal: Mg (n') + Ye (n ′) + G (n ′) + Cy (n ′) = 2R + 3G + 2B Color signal: Mg (n ′) + Ye (n ′) − {G (n ′) + Cy (n ′)｝ = 2R-G n + 1 'line: Luminance signal: G (n + 1') + Ye (n + 1 ') + Mg (n + 1') + Cy (n + 1 ') = 2R + 3G + 2B color signal : Mg (n + 1 ') + Cy (n + 1')-{G (n + 1 ') + Ye (n + 1')} = 2B-G In FIG. 2, 54 is G + Cy on the nth line. A sample and hold circuit that samples and holds the G + Ye signal on the n + 1 line, a sample and hold circuit 55 that samples and holds the Ye + Mg signal on the n line, a Mg + Cy signal on the n + 1 line, and 56 is the output of the sample and hold circuits 54 and 55. Take the difference Subtraction circuits for generating color difference signals 2R-G and 2B-G for each horizontal scanning period. 57 and 58 are gains at the time of subtraction such that the color difference signal of a white object becomes zero (zero) according to the color temperature of the light source. Is a white balance circuit that corrects the error, 59 is a switch that switches every horizontal scanning cycle to obtain 2R-G and 2B-G in line sequence, and 60 is a switch that makes effective use of the bit resolution of the subsequent A / D conversion. Gain correction circuits for correcting the amplitude of the color difference signals, 61, 62 and 63 are sample and hold circuits 54 and 5, respectively.
5 and a clamp circuit for fixing the DC level of the output signal of the gain correction circuit 60; 64, a reference potential 1 source that is the reference potential of the clamp circuits 61 and 62; 65, a reference potential 2 that is the reference potential of the clamp circuit 63 Source, 66, 67 are gamma correction circuits, 68, 6
A / D conversion circuits 9 and 70 store the A / D converted signals in the frame memory 9. 71 is G + Ye signal or G + Cy
A latch circuit for reading and latching a signal from the frame memory 9, a latch circuit 72 for reading and latching an Mg + Cy signal or an Mg + Ye signal from the frame memory 9, and a reference numeral 73 for 2R-G
A latch circuit for reading and latching signals from the frame memory 9; 74, a latch circuit for reading and latching 2B-G signals from the frame memory 9; The output is a digitized luminance signal Y (D). 76,7
Reference numeral 7 denotes a gamma correction circuit whose output is digitized color difference signals RY (D) and BY (D).

FIG. 4 is a diagram for explaining how to determine the DC reference potential 1 and the reference potential 2 in FIG. The reference potential 1 is a signal of G + Ye, G + Cy, Mg + Cy, Mg + Ye for generating a luminance signal,
This is a reference potential for determining the potential at the time of D conversion. Therefore, in order to use the resolution of the A / D conversion circuits 68 and 69 to the maximum, the black level must be set as shown in FIG. A /
The reference potential 1 must be set so as to be at the 0 level of the D input window. However, for the reference potential 2, since the color difference signal originally fluctuates in both positive and negative directions, it is preferable to set the 0 level of the color difference signal to the middle point of the A / D input window as shown in FIG. That is, the color difference signal 0
It is preferable that the level be at the midpoint of the input range of the A / D conversion circuit.

FIG. 5 shows the gamma correction circuits 76 and 77 in FIG.
Is a diagram for explaining the operation of the gamma correction circuit 76.
Is shown. By generating a color difference signal by operation of the purely gamma-corrected pure color signals, a correctly gamma-corrected color difference signal can be obtained. However, since a pure color signal cannot be obtained here, an approximate color difference signal is obtained. Gamma correction is applied. That is, since the correction value of the gamma correction cannot be obtained directly from the level of the color difference signal, the level of the luminance signal is detected by the continuous two-pixel average value detection circuit 78 for detecting the average value of two consecutive pixels, and the level of the luminance signal is detected. By referring to a gamma correction table (two-dimensional table) 79 for obtaining the value of the color difference signal gamma-corrected from the level and the level of the color difference signal, the gamma of the color difference signal is approximated as it is without returning the color signal to a pure color signal. Correction has been performed.

Also in this embodiment, a subtraction process for generating a color difference signal is performed before A / D conversion.
Prevents the phenomenon that the bit resolution of the color difference signal deteriorates due to the subtraction processing after D conversion, and has no effect of quantization noise
A color difference signal with a good S / N ratio can be obtained.

〔The invention's effect〕

As described above, according to the present invention, since the A / D conversion is performed after performing the subtraction processing for extracting the primary color signal or the color difference signal, the bit resolution of the color signal is improved, and the influence of quantization noise is reduced. Suppressed in color signals
This has the effect of improving the S / N ratio.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of one embodiment of the present invention, FIG. 2 is a block diagram showing a circuit configuration of another embodiment of the present invention, and FIG. 3 is a complementary color provided in the CCD of FIG. FIG. 4 is an explanatory diagram showing the color arrangement of the mosaic filter, FIG. 4 is an explanatory diagram showing how to determine the reference potential 1 and the reference potential 2 of the clamp circuit in FIG. 2, and FIG. 5 shows the operation of the gamma correction circuit in FIG. FIG. 6 is a schematic view of an interline type CCD which is a general solid-state imaging device, FIG. 7 is an explanatory view showing a color filter array of the CCD of FIG. 6, and FIG. 8 is a CCD of FIG. FIG. 9 is a timing chart showing a drive timing when electric charges are read from the memory, FIG. 9 is a block diagram showing a circuit configuration of a general image pickup signal processing device, and FIG. 10 is a block diagram showing a detailed configuration of a digital signal processing unit in FIG. FIG. 1 Interline CCD 10 Signal processing circuit 31, 32 Subtraction circuit 39-41 Gamma correction circuit 42-44 A / D conversion circuit 38-70 A / D conversion circuit

Claims (2)

(57) [Claims] An imaging unit for converting an optical image into an electric image signal; a color filter including a complementary color disposed in front of the imaging unit; an analog primary color signal or an analog primary color signal from an analog complementary color signal output from the imaging unit; Calculating means for forming an analog color difference signal; and A / D converting means for A / D converting the output of the calculating means. The DC potential of the analog signal input to the A / D converting means An imaging apparatus, wherein a zero level of a signal is set to a middle point of an input range of an A / D converter. 2. The arithmetic means forms an analog color difference signal from an analog complementary color signal output from an image pickup means, and performs gamma correction to be applied to a digital color difference signal output from an A / D converter to a luminance signal level and the digital signal. 2. The image pickup apparatus according to claim 1, further comprising a gamma correction unit that performs a correction by referring to a correction table for obtaining a corrected digital color difference signal from the color difference signal level.