Television – Camera – system and detail – With single image scanning device supplying plural color...
Reexamination Certificate
1997-03-26
2001-11-27
Eisenzopf, Reinhard J. (Department: 2612)
Television
Camera, system and detail
With single image scanning device supplying plural color...
C348S277000
Reexamination Certificate
active
06323901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to color cameras, and more particularly to a single CCD type color camera having a color separation circuit for processing a signal from a solid state imaging device which includes photoelectric conversion elements arranged in an array corresponding to color filters arranged in a color differentially ordered array, and a method of separating color signals using such a circuit.
2. Description of the Background Art
A CCD (Charge Coupled Device) which is widely used today as an imaging device in a color camera simply changes the amplitude of a signal to output in response to the brightness of light which it receives, and the output signal does not include any color information. Therefore, in order to obtain color information, some optical means must be employed for example for filtering light incident to the CCD.
For home use, a so-called single CCD type color camera which extracts three primary color signals from a single CCD is employed, and a color filter array is used on the side of the light receiving surface of the CCD according to a so-called simultaneous color imaging method.
Structure of Inter-line Transfer CCD
FIG. 16
is a block diagram schematically showing the structure of an inter-line transfer CCD
10
generally used in a color camera for home use.
Inter-line transfer CCD
10
includes a photosensitive portion
12
formed of p-n junction type photodiodes arranged in an array, a transfer portion
14
including an analog shift register formed of a CCD, and a horizontal transfer register
16
for transferring signals formed by converting signal charges sequentially transferred from transfer portion
14
into voltage in the horizontal direction for output.
FIG. 16
includes p-n junction type photodiodes corresponding to three pixels arranged each in the vertical and horizontal direction for ease of illustration. In an actual CCD for use in a color camera, photodiodes corresponding to 500 pixels in the vertical direction and 500 to 800 pixels in the horizontal direction for example are arranged in an array.
The operation will be briefly described.
When light comes into the photodiodes, charges are generated and accumulated within the diodes. Then, application of a prescribed voltage to a shift gate causes the accumulated charges to be simultaneously transferred to the analog shift register. The CCD analog shift register sequentially transfers charges toward horizontal transfer register
16
in response to applied clock pulse voltages &phgr;V
1
, &phgr;V
2
, and &phgr;V
3
. Horizontal transfer register
16
converts thus transferred received signal charges into voltages, and is then driven by externally applied horizontal driving signals &phgr;H
1
, &phgr;H
2
, and &phgr;H
3
to externally sequentially output the voltages as imaging signal outputs.
Driving Method of Inter-line Transfer CCD
The inter-line transfer CCD is generally driven in two modes, i.e., frame accumulation and field accumulation. The field accumulation mode used corresponding to a color differentially ordered color filter array will be detailed.
FIGS. 17A and 17B
are schematic diagrams for use in illustration of how signal charges are read out form inter-line transfer CCD
10
according to the field accumulation mode,
FIG. 17A
shows a method of reading out a signal charge in an odd-numbered field, and
FIG. 17B
a method of reading out a signal charge in an even-numbered field.
As shown in
FIG. 17A
, in an odd-numbered field, signals from an odd-numbered pixel and an even-numbered pixel in the vertical direction are simultaneously transferred from the photosensitive portion to the transfer portion, where the signals are added.
In an even-numbered field as shown in
FIG. 17B
, signals from an even-numbered pixel and an odd-numbered pixel in a different combination from the above are simultaneously transferred to transfer portion
14
, where they are added.
If the color filter array is color differentially ordered, color differential signals are separated using such a method of transferring in inter-line transfer CCD
10
.
Method of Separating Color Differential Signals
FIG. 18
is a diagram schematically showing the flow of processing a signal output from inter-line transfer CCD
10
when the color filter array is color differentially ordered.
As shown in
FIG. 18
, in the color differentially ordered color filter array, color filters of magenta (hereinafter Mg), green (hereinafter G), cyan (hereinafter Cy), and yellow (hereinafter Ye) are arranged in a mosaic.
Now, since so-called additive color process is possible in mixing colors in light, between three primary colors red (R), green (G) and blue (B) and the complementary colors Mg, Ye and Cy, the following relation is established:
Mg=R+B
(1)
Ye=R+G
(2)
Cy=B+G
(3)
Therefore, using Mg, G, Ye and Cy described above as the colors of color filters permits the intensity of a G signal weighing the most in a luminance signal among three primary colors R, G and B to be higher than that of a B signal.
In the example shown in
FIG. 18
, an array portion of four rows and four columns is extracted from the color differentially ordered color filter array for illustration. In odd-numbered rows (y-direction), color filters of Mg and color filters of G are alternately arranged in the horizontal direction (x-direction).
In even-numbered rows, color filters of Ye and color filters of Cy are alternately arranged in the horizontal direction. The method of reading out from inter-line transfer CCD
10
having the color filter array arrangement is on the basis of 2-pixel addition reading in the vertical direction (y-direction).
In an odd-numbered field, an odd-numbered pixel and an even-numbered pixel in the vertical direction are added, and in the following even-numbered field, a different combination of an even-numbered pixel and an odd-numbered pixel are added. Thus, in the even-numbered field for example signals are output in the order of G+Cy, Mg+Ye, . . . in the n-th scanning line and in the order of Mg+Cy, G+Ye, . . . in the n+1-th scanning line.
These signals are pulse amplitude modulated signals as shown in FIG.
18
. In
FIG. 18
, based on the above expressions (1) to (3), the complementary color signals are replaced by three primary color signals and indicated as the amplitude modulated waveforms of the three primary color signals.
A direct current component and a fundamental wave component excluding a harmonic component are shown as follows.
Signal So in the n-th scanning line in the even-numbered field is as follows:
So=
(
Mg+Ye
)+(
G+Cy
)+½·{(
Mg+Ye
)−(
G+Cy
)}sin(2&pgr;
fnt
)=2
R+
3
G+
2
B+
½·(2
R−G
)sin(2&pgr;
fnt
) (4)
Signal Se in the n+1-th scanning line is as follows:
Se
=(
Mg+Cy
)+(
G+Ye
)+½·{(
Mg+Cy
)−
G+Ye
)}sin(2&pgr;
fnt
)=2
R+
3
G+
2
B+
½·(2
B−G
)sin(2&pgr;
fnt
) (5)
where fn indicates a Nyquist frequency, i.e. a sampling frequency.
A luminance signal is obtained by filtering only the direct current component in the above expressions (4) and (5) through a low-pass filter (hereinafter LPF).
The luminance signal and two color differential signals 2R−G and 2B−G can be readily separated if passed through a band-pass filter (hereinafter BPF) having a center frequency fn and detected.
More specifically, the luminance signal and color differential signals can be line-sequentially obtained.
However, in view of a single scanning line, only the color differential signals obtained are 2R−G and 2B−G, and the color signals corresponding to the scanning line cannot be reproduced.
The luminance signal and color signals are actually reproduced as follows:
A luminance signal CL is produced by the sum of adjacent pixels in each ro
Eisenzopf Reinhard J.
Michaelson Peter L.
Michaelson & Wallace
Moe Aung S.
Sanyo Electric Co,. Ltd.
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