JP2763305B2 - Digital signal processor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal processing device suitable for a color image pickup device provided with a complementary color filter. Hereinafter, a video color camera will be described as an example, but the present invention can be effectively applied to a still video camera and the like.

[Conventional technology]

Due to recent advances in digital signal processing technology, digital signal processing, which has advantages of high reliability and no adjustment, has become mainstream in signal processing circuits of video color cameras. On the other hand, a color separation filter attached to the sensor often uses a complementary color rather than a pure color. This is because although pure colors have excellent color reproducibility, they have low light utilization and are disadvantageous in terms of S / N and bandwidth of luminance signals.

[Problems to be solved by the invention]

FIG. 2 shows a general configuration example in which a single-chip color camera using a complementary color filter is implemented by digital signal processing in such two tendencies.

In the sensor 201, a complementary color filter as shown in FIG.
It is assumed that the signals of each row are mixed and read, and interlaced scanning is performed for each field.

In this case, (Mg + Cy) in the first horizontal scanning period
And (Gr + ye) signals are repeatedly read, and in the second horizontal scanning period, the (Mg + Ye) and (Gr + Cy) signals are repeatedly read. This read signal is the AGC circuit 2
02, input to the A / D converter 211 via the sample and hold circuit 210. Now, change the full scale of the A / D converter 211 to O to Am
V and the conversion accuracy is 10 bits, (Mg + Cy) and (Gr +
ye), (Mg + Ye), and (Gr + Cy) signals are considered to have 量子 / 2 random quantization noise superimposed thereon.

The luminance signal is basically the read signal (Mg + C
y), (Gr + ye), (Mg + Ye), and (Gr + Cy), the order of the magnitude of the quantization noise in the luminance signal is approximately △ / 2. This luminance signal is subjected to γ correction or the like in a luminance signal processing circuit 205 and then passed through a D / A converter 207 to NTS.
Input to C encoder 209.

On the other hand, for the color signal, the output of the A / D converter 211 is temporarily subtracted by the subtractor 212 into (Mg + Cy)-(Gr + ye) or (Mg + Ye)-(Gr + Cy).
And then color processed by the color signal processing circuit 206. That is, the color signal component is modulated into a luminance signal component, and the ratio of the color signal component to the normal luminance signal component is 20 to 30% or less. This means that the original signal must be multiplied by a factor of 3 to 5 in order to finally obtain a sufficient level of the color signal in the color signal processing circuit 206. Therefore, the magnitude of the quantization noise in the chrominance signal is 3 to 5 times that of the luminance signal and becomes 3Δ to
It is on the order of 5Δ. Thereafter, the color signal processing circuit 206
Are combined with a luminance signal by an NTSC encoder 209 via a D / A converter 208 to form an NTSC signal. Therefore,
In such a configuration, the number of bits of the A / D converter 211 must be at least 12 bits or more in order to secure the final S / N ratio of the color signal, resulting in enormous cost and increased power consumption. Was invited.

As shown in Fig. 3, A / D
Two converters are provided, one of which takes a difference in advance by a differential amplifier 313, adjusts a gain, and performs A / D conversion. The result is used as a color difference signal, and the other is a sample hold circuit 310, 311
At full scale that matches the output sampled and held at
A method of performing A / D conversion in the A / D converter 315 to form a luminance signal is also conceivable. Note that the sample and hold circuits 310 and 311
For example, if the read clock is fc, each cycle is
The phases are inverted at 2 / fc. With this configuration, the deterioration of the S / N ratio of the color signal due to the quantization noise is improved, but two A / D converters are required.

In particular, the A / D converter 315 for a luminance signal requires an accuracy of at least 10 bits or more when the signal is linear, and an accuracy of 8 bits or more even if nonlinear processing such as pleniy is performed immediately before, so that the circuit scale increases and the cost increases. Was invited.

[Means for solving the problem]

In view of the above problems, the present invention has one A / D converter that takes a difference between different color signals, and a decoder that decodes an original signal from the output of the A / D converter, so that the color signal The present invention realizes a digital signal processing device which has little quantization noise and requires only one A / D converter.

[Action]

In addition, by doing so, the quantization noise in the decoded luminance signal is almost the same as the quantization noise in the difference signal. Therefore, for example, only one 8-bit A / D converter is needed to decode the luminance noise. Eight bits or more (usually 9 to 10
bit) accuracy.

〔Example〕

FIG. 1 is a block diagram showing the signal processing of a video camera to which the present invention is applied. The sensor 101 is, for example, a CCD image sensor, on which a complementary color filter as shown in FIG. 4, for example, is formed.
As shown in FIG. 3, mixed readout is performed in the vertical direction by the same interlaced scanning as in the conventional example.

The gain of the read signal is adjusted by the AGC circuit 102, and the read signal is input to the two sample and hold circuits 110 and 111. Pulses P1 and P2 are supplied from the timing generation circuit 104 to the sample and hold circuits 110 and 111, respectively. As shown by the circles in FIGS. 8B and 8C, P1 and P2 are synchronized with the readout clock fc of the sensor at a period twice as long as the readout clock fc, and have mutually inverted phases.

FIGS. 8 (a), (b), (c) and (d) are schematic diagrams showing the output of the AGC circuit 102 and the output of the output differential amplifier 112 of the sample and hold circuits 110 and 111, respectively. One scale is T at time T
= 1 / fc. Also, in FIG.
The timing of P2 is shown, and (e) shows the A / D converter
The timing of the pulse at which 114 operates is shown.

Thus, for example, in the first horizontal scanning period, the outputs of the sample and hold circuits 110 and 111 are (Mg + C
y), (Gr + Ye), and (Mg + Ye), (Gr + Cy) in the second horizontal scanning period, respectively. Therefore, the output of the differential amplifier 112 connected to the sample and hold circuits 110 and 111 is given by Becomes

The A / D converter 114 is an 8-bit A / D converter with a conversion range of -A / 2mW
~ A / 2mV, and input in the range of -A / 2 to -A / 2 + Δ is 0, (A
/ 2−Δ) to (A / 2) mV is converted to 1023.

 However, Δ = A / 256 mV.

Needless to say, a level shifter or the like may be provided before the A / D converter to set the input range from 0 to AmV.

Now, let the maximum value of the output of S / H110 and S / H111 be Vmax.
Possible values of the output of the differential amplifier 112 are in the range of −KV to KV mV.

However, when actually examining the histogram of the output at point A, although the colors are different, the difference between horizontally adjacent signals has a horizontal correlation of luminance, so that almost -αKV to αKV m
V range. α is smaller than 1 and approximately 1/5.

Therefore, if α, K, V, A satisfy the relationship αKV = A / 2, the full scale of the A / D converter 114 is effectively used. However, although the frequency is very low, the output of the point A may rarely be smaller than -αKV or larger than αKV. Therefore, the output is clipped by the clipping circuit 113 in the range of -αKV to αKV. The closer α is to 1, the smaller the error in the decoder 115 described later, but the larger the color quantization error, so it is desirable to set it to an appropriate value. If no accuracy is required, the clip circuit 113 is unnecessary.

The output of the A / D converter 114 is input to the color signal processing circuit 106 having the structure shown in FIG.
Converted to Y.

Next, a configuration example of the color signal processing circuit 106 will be described with reference to FIG.

The output of the A / D converter 114 is input to the 1H memory 501 and the constant multiplier 503. For example, when the input of the 1H memory 501 is a signal corresponding to P, the input of the 1H memory 502 is Q and the output is a signal corresponding to P.

Therefore, if the constants of the constant multipliers 503 and 505 are set to 1/2 and the constant of the constant multiplier 504 is set to 1, the outputs of the adders 506 and 504 have P and Q alternately every 1H and different from each other. Appears in phase. Therefore, these are input to the switch 507, and
By switching every H, the output of P is always obtained and the output of Q is always obtained, so that P and Q are synchronized.

In the case of a color filter arrangement as shown in FIG. 4, it can be considered that P = [(Mg + Cy)-(Gr + Ye)] = 2B-GB-Y Q = [(Mg + Ye)-(Gr + Cy)] = 2B-GR-Y Constant multiplier 508,509,511,512, adder 51
There is no need for a dye matrix circuit composed of 0,513, but in order to obtain better color reproduction, it is desirable to determine the constants set in 509 to 512 according to the spectral characteristics of the color filter. Further, the gain of the color difference may be adjusted with these constants. Next, the color difference signals RY, B-
Y is D / A converted by a D / A converter 108 and input to a standard television signal generator 109.

 Next, the operation of the decoder 115 will be described.

Now, consider a horizontal scanning period in which Mg + Cy Gr + Ye is repeatedly scanned by the filter arrangement shown in FIG.

Here, the signals {V _n } to be demodulated are: V ₁ = Mg ₁ + Cy ₁ , V ₂ = Gr ₁ + Ye ₁ , V ₃ = Mg ₂ + Cy ₂ ,.

Now, considering a signal {U _n } determined by U _n = V _{n + 1} −V _n (2), U ₁ = (Gr ₁ + Ye ₁ ) − (Mg ₁ + Cy ₁ ) U ₂ = (Mg ₂ + Cy ₂₎ ) − (Gr ₁ + Ye ₁ ) U ₃ = (Gr ₂ + Ye ₂ ) − (Mg ₂ + Cy ₂ ) (3)

On the other hand, the output {P _n } of the A / D converter 114 is P ₁ = (Mg ₁ + Cy ₁ ) − (Gr ₁ + Ye ₁ ) P ₂ = (Mg ₂ + Cy ₂ ) − (Gr ₁ + Ye ₁ ) P ₃ = (Mg ₂ + Cy ₂ ) − (Gr ₂ + Ye ₂ ) (4) Therefore, U _n = (− 1) ⁿ P _n (5).

From (2) Because Becomes

Accordingly, from (6), V _k −V _k−1 = (− 1) ^k P _k ... (7), so that V _k = (− 1) ^k P _k + V _k−1 . Decoding is performed according to equation (8).

FIG. 6 shows a configuration example of the decoder. The output of the A / D converter 114 is input to a switch 602 and a sign inverter 601. Switch
At 602, an inverted output and a non-inverted output are selected according to a clock φ synchronized with a pixel output clock supplied from the timing generation circuit 104. The output of the switch 602 is an adder 603, which adds the output of the switch 602 to the output of one pixel. The operation accuracy of the adder 603 is desirably set to 10 to 12 bits, which is higher than the bit accuracy of the A / D converter by about 2 to 4 bits, so that overflow and underflow do not occur.

The output of 603 is 1 / the maximum value of the output of A / D converter 114.
Although it is multiplied by α (α is the above-mentioned constant), it is sufficient for the luminance signal circuit at the subsequent stage to have 10 bits or more, so that the shift circuit 605 may uniformly shift the bit to the right by 0 to 2 bits.
By doing so, although the luminance of the A / D converter is 8 bits, the same effect can be obtained as if the luminance signal were equivalently quantized with an accuracy of 10 bits or more.

The luminance signal processing circuit 105 performs non-linear conversion such as Knee conversion and γ conversion, and filtering processing such as low-pass filtering and aperture compensation. The output is D / A converted by the D / A converter 107. In the standard television signal generator 109, a luminance signal, two color difference signals, and a timing generation circuit 104
Supplies a required pulse from the controller to generate and output a standard television signal.

[Other embodiments]

 FIG. 7 shows a second embodiment of the present invention.

The first embodiment has a simple structure, but has a clip circuit.
If the conversion error in the A / D converter 114 and the A / D converter 114 is large, the influence may propagate in a certain range. Therefore, when aiming at high image quality in this way, it is preferable to form a decoder with a portion 713 surrounded by a dotted line as shown in FIG. 7 and put it in a feedback loop.

The output from the AGC circuit 702 is sampled and held by the sample and hold circuit 720 at the same cycle as the read clock fc of the sensor. The differential amplifier 710 amplifies the difference between the output from the sample hold circuit 720 and the output from the D / A converter 717 provided in the feedback system with an appropriate gain.

This output is clipped by the clip circuit 711, and A
Input to the / D converter 712. The setting of the gain, the clip level, and the range of the A / D converter may be the same as in the previous embodiment.

Next, the output of the A / D converter 712 is delayed by a delay circuit 714 and then input to a decoder including a delay circuit 716 and an adder 715. The output of adder 715 is D / A by D / A converter 717
Is converted.

 This behavior will be analyzed below.

The signal from the S / H 710 is {V _n }, the output from the differential amplifier 710 is {y _n }, the output from the A / D converter 712 is {U _n }, and the adder
出力 x _n出力 output from 715 and ｛X output from D / A converter 717
_{Let n} ′｝. The A / D converter 712 operates in synchronization with the read clock fc, {U _n }, {x _n } are digital data for each clock, and {V _n }, {Y _n }, {X _n ′} Is the analog data value at the corresponding time.

_{Thus, Y n = V n -X n} 'U n = Y n -Q n (9) is _{X n = U n -X n-} 1. However, Q _n is the error of the clip circuit 711 and the A / D converter 712. Now, the error of the D / A converter 717 is extremely small since _{X n = X n ', Y} n = V n -X n U n = Y n + Q n (10) X n = U n-1 + X If the _n-1 (10) equation is Z-transform, Y (Z) = V ( Z) -X (Z) U (Z) = Y (Z) -Q (Z) (11) X (Z) = Z - ^When Y (Z) and V (Z) are deleted from ¹ U (Z) + Z ^-1 X (Z) (11), X (Z) = Z ^-1 (V (Z) + Q (Z)) (12) When Y (Z) and X (Z) are deleted from (11), U (Z) = (1−Z ⁻¹ ) (V (Z) + Q (Z)) (13) Y (Z) = (1−Z ⁻¹ ) V (Z) −Z ⁻¹ Q (Z) (14)

That is, X (Z) is obtained by adding the quantization noise {Q _n } to the original signal {V _n } and delaying it by one delay, so that this signal is directly input to the luminance signal processing circuit 705. The rest may be the same as in the previous embodiment. From (14), {y _n } is the difference between two different color signals. Therefore, also in the present embodiment, the difference between color signals adjacent in the horizontal direction is A / A
It will be D-converted. The resulting {U _n } is the same as the {U _n } shown in equation (3) of the previous embodiment. However, in order to match the phase with the luminance signal, the output of the delay circuit 714 is considered as {U _n }, and this is input to the switch 719 and the inverter 718. Switch 719 is the output of 714 per clock fc
By selecting the output of 718, the output of 719 becomes {P _n } shown in Expression (4). Therefore, this signal is directly input to the color signal processing circuit 706, and the subsequent processing is performed in the same manner as in the previous embodiment.

In addition, the D / A converter 717 is used to make _Xn and _Xn 'equivalent, and the adder 715 is used to avoid overflow or underflow by 2 to 3 bits from the number of bits of the A / D converter 712.
It is desirable to use one with higher accuracy.

That is, in the present embodiment, similarly to the previous embodiment, A / D conversion is performed on a signal corresponding to a difference between different color signals, and a color signal is formed based on the A / D conversion. The S / N of the luminance and chrominance signals is improved by decoding the luminance signal using a decoder.

In the above description, the color filter array is described as an example in FIG. 4, but any other so-called complementary color mosaic filter can be applied. Also, of course, Cy,
Even for complementary color stripes in which G, Ye, etc. are arranged in a stripe pattern, any type of color signal processing that performs color signal processing from the difference or modulation component of the color signal and forms a luminance signal for the baseband can be used. The invention is valid.

〔The invention's effect〕

According to the present invention, A / D conversion is performed after the difference between different color signals is once obtained in an analog state, so that quantization noise in the color signal can be reduced. Is decoded to form a luminance signal, so that only one A / D converter is required, the quantization noise of the luminance signal can be reduced, and the circuit scale and cost can be reduced.

[Brief description of the drawings]

 FIG. 1 is a diagram showing an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing a conventional example, FIG. 4 is a diagram showing an arrangement of color filters, and FIG. FIG. 6 is a diagram showing a configuration example of a decoder, FIG. 7 is a diagram showing another embodiment of the present invention, and FIG. 8 is a diagram for explaining the operation of the first embodiment. 112,710 …… Differential amplifier, 113,711 …… Clip circuit, 114,712 …… A / D converter, 611,718 …… Inverter, 602,719 …… Switch, 603,715 …… Adder, 604,716 …… Delay, 605 …… Shift 717 …… D / A converter.

Claims (3)

(57) [Claims] 1. A color imaging means using a complementary color filter,
A / D converter for A / D converting a signal corresponding to a difference between different color signals from the color imaging unit, and a color signal processing unit for forming a color signal using an output of the A / D converter, A digital signal processing device, comprising: a decoder for decoding an original color signal from the output of the A / D converter; and a luminance signal processing device for forming a luminance signal using the output of the decoder. . 2. A differential circuit having a signal corresponding to the difference between the color signals, which has a period twice as long as the readout clock of the color image pickup means and outputs from two sample-and-hold circuits which operate so that phases are inverted with respect to each other. The digital signal processing device according to claim 1, wherein the digital signal processing device is formed using an amplifier. 3. A digital signal obtained by decoding a signal corresponding to the difference between the color signals from an output of a sample-and-hold circuit having the same period as a readout clock of a color imaging means and an output of the A / D converter using a decoder. The digital signal processing device according to claim 1, wherein the digital signal processing device is formed using a differential amplifier having an input of a D / A converter and an output of the D / A converter.