JP3540593B2 - Imaging device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a imaging device, in particular, yellow (Ye), cyan (Cy), Green (Gr), imaging such as with interlaced scanning type CCD element 4 kinds of complementary color filters are arranged magenta (Mg) Equipment related.
[0002]
[Prior art]
The interlace scan type CCD is distinguished from the progressive scan type CCD. The latter has a 1: 1 ratio of the number of vertical pixels to the number of bits of the vertical CCD, whereas the former has a ratio of 2: 1. To obtain an image having a high vertical resolution, for example, as described in “Exposure Control Method for Full-Frame Still Camera”, Annual Conference of the Institute of Television Engineers of Japan, p. It is known to read lines and lines in separate fields. On the other hand, if both CCDs have the same number of pixels, the interlaced scan type has the advantage that the aperture ratio can be increased because the number of bits of the vertical CCD is smaller.
[0003]
FIG. 4 is a diagram showing an arrangement of complementary color filters, and FIG. 5 is a block diagram of signal processing until a luminance signal of a still camera using a conventional interlaced scan type CCD image sensor is created. In FIG. 5, the lens and the mechanical shutter are omitted.
[0004]
The output signal of the CCD element 1 is reduced in noise by a correlated double sampling circuit (hereinafter, referred to as a CDS circuit) 2 and supplied to an AGC amplifier 3. The gain of the AGC amplifier 3 is controlled by a control signal from the exposure control unit 6. The signal from the CCD element 1 amplified by the AGC amplifier 3 is converted into digital data by the A / D converter 4 and then input to the Y creation circuit 5. In the Y creation circuit 5, when the digital data at the address (x, y) is represented as D (x, y), the luminance signal at the address (x, y) is
Y (x, y) = D (x, y) + D (x + 1, y) + D (x, y + 1) + D (x + 1, y + 1)
Is created by adding four adjacent data. At this time, the weights of the four color filters in Y are equal, and are expressed by the following equation.
[0005]
Y = Ye + Cy + Gr + Mg
Next, this Y signal is input to the exposure control unit 6. The exposure control section 6 is constituted by, for example, a microcomputer or the like, and controls an aperture value and a shutter speed applied to frame exposure so that the average value of the Y signal in the screen becomes a predetermined value.
[0006]
The gain of the AGC amplifier 3 is set by the exposure controller 6 such that the minimum value of the saturation level of the CCD element 1 matches the full scale of the A / D converter 4 when sufficient exposure is obtained. In a low illuminance where the exposure is insufficient, the gain of the AGC amplifier 3 is set to be high by the amount of the lack. In any case, the gain is set by the exposure control unit 6 based on the results obtained by several pre-exposures before the frame exposure.
[0007]
If a part of the output signal of the CCD element 1 has reached the saturation level, a step occurs between the saturation levels of the first field and the second field, and the saturation level of the signal read out in the second field is that of the first field. Usually, it is reduced by about 20%.
[0008]
This occurs in principle due to the structure of the CCD element 1. If the electric charge stored in the sensor at the time of exposure has reached the saturation signal amount, the electric charge is transferred to the substrate during the period from the sensor to the vertical CCD. Because it is released to
[0009]
As described above, since the gain of the AGC amplifier 3 is set so that the saturation level of the CCD element 1 in the second field matches the full scale of the A / D converter 4, the gain near the saturation point in the first field is set. The first problem is that the signal is clipped during A / D conversion.
[0010]
This clipping phenomenon will be described with reference to FIGS.
FIGS. 6 and 7 are diagrams showing the output signals of the CCD element 1 after the end of the frame exposure in the case where a vertical gradient waveform is obtained by solid lines. In FIG. Are read out. In FIG. 7, it is assumed that the YeCy line is read in the first field and the MgGr line is read in the second field.
[0011]
Assuming that the saturation levels of the CCD output signals of the first and second fields are VS1 and VS2, the above-described step of the saturation level causes
VS1 ≒ 1.2VS2
It becomes. Since the full scale of the A / D converter 4 is set to VS2 by the gain setting of the AGC amplifier 3 described above, the signal read in the first field is clipped at the position indicated by the dashed line in FIG. That is, the dynamic range of MgGr in the case of FIG. 6 and YeCy in the case of FIG. 7 is lost by about 20%.
[0012]
Next, from the spectral characteristic diagram of the complementary color filter as shown in FIG. 8, the horizontal addition signals Ye + Cy, Mg + Gr in each line have the spectral characteristics shown in FIG. The ratio m of the integral value of the two characteristic curves with respect to the entire visible light region of 400 to 700 nm is approximately represented by the following equation.
[0013]
m = {(Ye + Cy) dλ / {(Mg + Gr) dλ} 1.2
Therefore, the Y signal is modulated by about 20% in a two-line cycle, and aliasing distortion is generated. As a result, the vertical resolution is degraded, and a jagged line appears in an actual photographed image.
[0014]
FIG. 10 is a block diagram showing another example of the conventional example. The example shown in FIG. 10 is an example published in Ohm's "Electronics", January 1998, p29. That is, a multiplying circuit 8 is arranged between the A / D converter 4 and the Y creating circuit 5 shown in FIG. 5 described above, and the selector 7 switches between different coefficients of YeCy gain and GrMg gain for each line. The multiplier and the output of the A / D converter 4 are multiplied by a multiplier 8.
[0015]
[Problems to be solved by the invention]
In the example shown in FIG. 10, it is necessary to use a digital multiplier as the multiplier 8, and there remains a problem in a trade-off relationship that the calculation accuracy or the gate scale or power of the LSI increases. Also in this example, there remains a problem that the signal near the saturation point of the first field is clipped when the A / D converter 4 performs A / D conversion.
[0016]
Therefore, a main object of the present invention is to solve the above two problems and to provide an imaging apparatus which does not increase the calculation accuracy, the gate scale and the power of the LSI.
[0017]
[Means for Solving the Problems]
According to the first aspect of the present invention, a high-sensitivity color filter is arranged in each pixel of one line, and a low-sensitivity color filter is arranged in each pixel of the other line. An imaging apparatus for operating a light-shielding unit that blocks light from passing through to an image sensor, reading a signal, amplifying the read signal by an amplifying unit, and converting the signal into a digital signal by an A / D converter, comprising: After the light is shielded, the signal charge of the line with high sensitivity is read out in the first field period, the signal charge of the line with low sensitivity is read out in the second field period, and the gain of the amplifying means in the first field period is changed in the second field period. The control means is provided so as to set the gain to be lower than the gain at the step (1).
[0018]
In the invention according to claim 2, the control means according to claim 1 integrates a signal based on the output of the image pickup device in each of the first and second field periods, and performs the integration on the integrated value in the first field period. It is characterized in that the ratio of the integral value in the two-field period is calculated, and the gain in the first field period is set lower than the gain in the second field period by the ratio.
[0019]
According to the third aspect of the present invention, in the first field period of the first or second aspect, the signal charges of the line on which the Ye and Cy color filters are arranged are read, and in the second field period, the Gr and Mg color filters are read. It is characterized by reading out signal charges of the arranged lines.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram of one embodiment of the present invention. 1, the configuration of the CCD elements 1 to Y creation circuit 5 is the same as that of FIG. 5 described above, and only the exposure control unit 10 for controlling the AGC amplifier 3 is different. Further, in the conventional example shown in FIG. 10, the YeCy line and the MgGr line are multiplied by different coefficients for the Y signal generation in the multiplier 8 at the subsequent stage of the A / D converter 4, but in this example, for example, The AGC amplifier 3 is multiplied by different coefficients by an exposure control section 10 constituted by a microcomputer.
[0021]
FIG. 2 is a diagram showing an output signal of the CCD element 1 after frame exposure according to an embodiment of the present invention. Assuming a vertical gradient waveform as in FIG. 7, a YeCy line is set in a first field, It is assumed that the MgGr line is read out in the second field. Here, the output signal of the CCD element 1 is shown by a solid line.
[0022]
Suppose now that the saturation level ratio S (= VS1 / VS2) between the fields and the sensitivity ratio m are S = m = 1.2.
Think on the assumption that.
[0023]
The exposure controller 10 switches the gain of the AGC amplifier 3 depending on the field in synchronization with the illustrated first field pulse. That is, the gain is set to 1 / 1.2 in the first field and 1 in the second field. As a result, the output signal of the AGC amplifier 3 can completely match the slope and the saturation level of the first field with those of the second field as shown by the dashed line in FIG. The two problems of range loss and aliasing can be solved 100%.
[0024]
Since S and m of the actual CCD element 1 vary respectively, there is a method of actually measuring S or m at the time of manufacturing a still camera in order to accurately correct without excess or deficiency regardless of the variation. For example, m is calculated based on the unsaturated output data obtained by imaging the light box with the proper exposure. S is calculated based on full-screen saturated data obtained by imaging the light box with the maximum exposure. The method of setting the inter-field gain ratio of the AGC amplifier 3 from the actually measured S and m, that is, the AGC modulation degree, may be set in consideration of the dynamic range, the priority of aliasing removal, and the like.
[0025]
FIG. 3 is a block diagram of another embodiment of the present invention. In this embodiment, the sensitivity ratio m between lines is not calculated at the design stage as shown in FIG. 10, but the sensitivity ratio m between lines and the saturation level ratio S are set by the AGC when the user actually uses it. This is set to the amplifier 3. For this purpose, an AE integration circuit 11 is provided at the output of the A / D converter 4. The AE integration circuit 11 generates a luminance signal based on the output of the A / D converter 4 and, when a signal corresponding to each of the first field and the second field is input, performs an integration operation for each field. The exposure control unit 6 calculates the sensitivity ratio m and the saturation level ratio S between the lines, and sets the sensitivity ratio m and the saturation level ratio S in the AGC amplifier 3. This setting operation may be set when the power switch is turned on or when a calibration key is provided and the key is operated.
[0026]
【The invention's effect】
As described above, according to the present invention, when reading out signal charges on a line with high sensitivity in the first field period and reading out signal charges on a line with low sensitivity in the second field period, the AGC in the first field period is used. Since the gain of the amplifier is set to be lower than that of the second field period by a certain ratio, the dynamic range can be increased and the aliasing distortion can be eliminated without increasing the calculation accuracy, the gate size and the power of the LSI. .
[Brief description of the drawings]
FIG. 1 is a signal processing block diagram according to an embodiment of the present invention.
FIG. 2 is a diagram showing output signals of a CCD element 1 after frame exposure according to an embodiment of the present invention.
FIG. 3 is a block diagram of another embodiment of the present invention.
FIG. 4 is a diagram showing an arrangement of complementary color filters.
FIG. 5 is a block diagram of signal processing until a luminance signal of a still camera using a conventional interlaced scan CCD image sensor is created.
FIG. 6 is a diagram showing output signals of the CCD element 1 when MgGr lines are read in a first field and YeCy lines are read in a second field after exposure of a frame is completed when a vertical gradient waveform is obtained.
FIG. 7 is a diagram showing output signals of the CCD element 1 when a YeCy line is read in a first field and an MgGr line is read in a second field.
8 is a spectral characteristic diagram of the complementary color filter shown in FIG.
FIG. 9 is a spectral characteristic diagram of a horizontal addition signal obtained from each line.
FIG. 10 is a block diagram showing another example of the conventional example.
[Explanation of symbols]
Reference Signs List 1 CCD element 2 CDS circuit 3 AGC amplifier 4 A / D converter 6, 10 Exposure control unit 11 AE integration circuit

Claims (3)

High sensitivity color filters are arranged in each pixel of one line, and low sensitivity color filters are arranged in each pixel of the other line. to block the Rukoto is opening and closing the mechanical shutter, the second field period where the first field period and the other signal charges of the line low sensitivity sensitive said one signal charge line is read out is read in alternate fields, the imaging means to read out the signal (1),
An automatic gain control (AGC) amplifier (3) for amplifying a signal read from the imaging means with a controllable variable gain;
A / D conversion means (4) for converting the signal amplified by the automatic gain control amplifier into a digital signal;
A luminance signal generation unit (5) for generating a luminance signal based on the digital signal output from the A / D conversion unit;
An exposure control unit (10) for controlling an optical system of the image pickup unit based on the luminance signal created by the luminance signal creation unit so that the luminance signal level becomes a predetermined value; 10) Further, the imaging apparatus performs switching control for each field such that the variable gain of the automatic gain control amplifier is lower in the first field period than in the second field period . High sensitivity color filters are arranged in each pixel of one line, and low sensitivity color filters are arranged in each pixel of the other line. By opening and closing a mechanical shutter that shuts off the signal, a first field period in which the signal charge of the one line with high sensitivity is read out and a second field period in which the signal charge of the other line with low sensitivity is read out Imaging means (1) for reading out signals in the field of
An automatic gain control (AGC) amplifier (3) for amplifying a signal read from the imaging means with a controllable variable gain;
A / D conversion means (4) for converting the signal amplified by the automatic gain control amplifier into a digital signal;
Integrating means (11) for creating a luminance signal by integrating the digital signal output from the A / D conversion means, wherein the integrating means further comprises an integrating means for each of the first field period and the second field period And calculating the ratio of the integral value of the second field period to the integral value of the first field period,
An exposure control unit configured to control an optical system of the imaging unit based on the luminance signal generated by the integration unit so that the luminance signal level becomes a predetermined value; and the exposure control unit. Further, the imaging apparatus performs switching control for each field such that the variable gain of the automatic gain control amplifier is lower by the ratio in the first field period than in the second field period . In the first field period, the signal charges of the line on which the Ye and Cy color filters are arranged are read, and in the second field period, the signal charges of the line on which the Gr and Mg color filters are arranged are read. The imaging device according to claim 1 or 2, wherein

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