Signal processing apparatus capable of correcting high-frequency component of color signal with high precision

A signal processing apparatus processes a signal which has a plurality of spectral sensitivity characteristics and in which the information amount of a signal related to at least one of the spectral sensitivity characteristics is larger than the information amount of any one of signals related to the other spectral sensitivity characteristics. A wavelet transform section resolves the signal of the spectral sensitivity characteristic having a large information amount into high- and low-frequency components. An R- and B-signal correlation coefficient calculating section calculates correlation coefficients between the low-frequency component derived and the signals of the spectral sensitivity characteristics having a small information amount. An R- and B-signal high-frequency creating section creates high-frequency components of the signals of the spectral sensitivity characteristics having a small information amount based on the correlation coefficients derived and the high-frequency component. An R- and B-signal inverse wavelet transform section synthesizes the high-frequency components thus derived and the signals of the spectral sensitivity characteristics having a small information amount to output an output signal with high definition.

BACKGROUND OF THE INVENTION 
This invention relates to a signal processing apparatus, and more 
particularly to a signal processing apparatus for frequency-resolving 
or-decomposing an input signal based on the spectral sensitivity 
characteristic and deriving a high-definition signal by using the 
high-frequency component of a signal of a spectral sensitivity 
characteristic containing a large amount of information to estimate the 
high-frequency component of a signal of another spectral sensitivity 
characteristic containing a less amount of information. 
Recently, image input devices which are inexpensive and light in weight and 
each use a single-plate type imaging device are widely used. In the 
single-plate type imaging device, in order to derive color information of 
a subject from one sheet of imaging device, color filters are arranged in 
a mosaic form on the light receiving surface. FIG. 18 shows the 
arrangement of a complementary color mosaic filter of cyan (Cy), magenta 
(Mg), yellow (Ye) and green (G) which is generally used. 
In FIG. 18, luminance signals and color difference signals for the n-th 
line and (n+1)th line of an even field are respectively denoted by 
Y.sub.o,n, Y.sub.o,n+1 and C.sub.o,n, C.sub.o,n+1. Likewise, luminance 
signals and color difference signals for the n-th line and (n+1)th line of 
an odd field are respectively denoted by Y.sub.e,n, Y.sub.e,n+1 and 
C.sub.e,n, C.sub.e,n+1. In this case, the above signals can be expressed 
by the following equations. 
EQU Y.sub.o,n =Y.sub.o,n+1 =Y.sub.e,n C.sub.e,n+1 =2R+3G+2B (1) 
EQU C.sub.o,n =C.sub.e,n =2R-G (2) 
EQU C.sub.o,n+1 =C.sub.e,n+1 =2B-G (3) 
Cy, Mg and Ye are expressed by the following equations by use of green (G), 
red (R) and blue (B). 
EQU Cy=G+B (4) 
EQU Mg=R+B (5) 
EQU Ye=R+G (6) 
As indicated by the equation (1), the luminance signals are created on all 
of the lines in the even field and odd field. However, as indicated by the 
equations (2) and (3), the two color difference signals are created on 
every other lines, and lines on which color difference signals are not 
created are compensated for by interpolation. After this, three primary 
colors of R, G, B can be derived by performing the matrix operation. In 
the above method, the color signal has an information amount only half 
that of the luminance signal. 
In Jap. Pat. Appln. KOKAI Publication No. 5-56446, there is disclosed a 
method for correcting the color difference signals by use of the luminance 
signal components instead of performing the simple interpolation by use of 
only the color difference signals as described before. That is, the 
luminance signal Y and the color difference signal C are processed by use 
of a low-pass filter to derive low-frequency components Y.sub.low and 
C.sub.low and a color signal C' obtained after correction is represented 
by the low-frequency components as indicated by the following equation. 
EQU C'=Y(C.sub.low /Y.sub.low) (7) 
This means that the color difference signal C' after correction can be 
replaced by a signal obtained by correcting the luminance signal. 
However, first, the above prior art technique only corrects the color 
signal by linear interpolation or by replacing the same by a signal 
obtained by correcting the luminance signal and cannot cope with 
correction of the color signal with high precision. 
Second, the above prior art technique only corrects the color signal by 
interpolating the color signal by use of adjacent color signals or by 
replacing the same by a signal obtained by correcting the luminance signal 
on the same coordinate and cannot cope with a case where the continuity of 
the signal is degraded at the edge portion or the like or where the degree 
of correlation with the luminance signal is low. 
Third, the above prior art technique only corrects the color signal by 
linear interpolation or by replacing the same by a signal obtained by 
correcting the luminance signal and cannot cope with a case where a 
high-frequency component of frequency higher than an input signal is 
created. 
Fourth, the above prior art technique only corrects the color signal by 
linear interpolation or by replacing the same by a signal obtained by 
correcting the luminance signal and cannot cope with optimum correction 
for high- and low-frequency components. 
BRIEF SUMMARY OF THE INVENTION 
Accordingly, a first object of this invention is to provide a signal 
processing apparatus capable of correcting a high-frequency component of a 
color signal with high precision. 
A second object of this invention is to provide a signal processing 
apparatus having a construction in which necessary memory capacity is 
small and capable of correcting a high-frequency component of a color 
signal with high precision. 
A third object of this invention is to provide a signal processing 
apparatus capable of correcting a high-frequency component of a color 
signal even in a case where the continuity of a signal is deteriorated or 
the degree of correlation is low. 
A fourth object of this invention is to provide a signal processing 
apparatus capable of deriving a visually preferable output signal by 
creating a high-frequency component of frequency higher than an input 
signal and enhancing the contrast. 
A fifth object of this invention is to provide a signal processing 
apparatus capable of deriving an output signal with high definition by 
expanding the dynamic range and enhancing the contrast. 
In order to attain the above first object, a signal processing apparatus of 
this invention for processing a signal in which the information amount of 
a signal related to at least one of a plurality of spectral sensitivity 
characteristics is larger than the information amount of any one of 
signals related to the other spectral sensitivity characteristics, 
comprising frequency resolving means for resolving the signal of the 
spectral sensitivity characteristic having a large information amount into 
high- and low-frequency components; correlation coefficient calculating 
means for calculating correlation coefficients between the low-frequency 
component derived from the frequency resolving means and the signals of 
the spectral sensitivity characteristics having a small information 
amount; high-frequency creating means for creating high-frequency 
components of the signals of the spectral sensitivity characteristics 
having a small information amount based on the correlation coefficients 
derived from the correlation coefficient calculating means and the 
high-frequency component derived from the frequency resolving means; and 
frequency synthesizing means for synthesizing the high-frequency 
components derived from the high-frequency creating means and the 
respective signals of the spectral sensitivity characteristics having a 
small information amount to output an output signal with high definition. 
In order to attain the second object, the frequency resolving means and 
frequency synthesizing means use the wavelet transform or, the orthogonal 
transform corresponding to one of the DCT transform, Fourier transform and 
Hadamard transformation for each region of preset size. 
In order to attain the third object, a signal processing apparatus of this 
invention for processing a signal in which the information amount of a 
signal related to at least one of a plurality of spectral sensitivity 
characteristics is larger than the information amount of any one of 
signals related to the other spectral sensitivity characteristics, 
comprising frequency resolving means for resolving a signal into a 
plurality of frequency components by using a function with local 
distribution as a basic function; extraction means for extracting a 
frequency component corresponding to a first preset region of the signal 
of the spectral sensitivity characteristic having a large information 
amount and a frequency component corresponding to a second preset region 
of the signal of the other spectral sensitivity characteristic having a 
small information amount from the coefficients of the plurality of 
frequency components derived from the frequency resolving means; 
similarity calculating means for calculating the degree of similarity 
between the frequency components of the first and second preset regions 
derived from the extraction means; searching means for searching for the 
first preset region having the highest degree of similarity with respect 
to the second preset region based on the degree of similarity derived from 
the similarity calculating means; high-frequency creating means for 
creating a high-frequency component of the second preset region based on 
the degree of similarity according to the high-frequency component related 
to the first preset region derived from the searching means; and frequency 
synthesizing means for synthesizing the high-frequency component derived 
from the high-frequency creating means and the signal of the other 
spectral sensitivity characteristic having a small information amount to 
output an output signal with high definition. 
In order to attain the fourth object, a signal processing apparatus of this 
invention for processing a signal in which the information amount of a 
signal related to at least one of a plurality of spectral sensitivity 
characteristics is larger than the information amount of any one of 
signals related to the other spectral sensitivity characteristics, 
comprising frequency resolving means for resolving the signal of the 
spectral sensitivity characteristic having a large information amount into 
high- and low-frequency components; high-frequency emphasizing means for 
multiplying a coefficient .alpha. larger than 1 by the high-frequency 
component resolved by the frequency resolving means; error calculating 
means for calculating the rate at which a signal obtained by synthesizing 
the high-frequency component emphasized by the high-frequency emphasizing 
means and the low-frequency component is set outside a preset range; and 
control means for controlling the coefficient .alpha. based on the result 
of calculation by the error calculating means. 
In order to attain the fifth object, a signal processing apparatus of this 
invention for processing a signal in which the information amount of a 
signal related to at least one of a plurality of spectral sensitivity 
characteristics is larger than the information amount of any one of 
signals related to the other spectral sensitivity characteristics, 
comprising frequency resolving means for resolving the signal of the 
spectral sensitivity characteristic having a large information amount into 
high- and low-frequency components; reference signal low-frequency 
emphasizing means for emphasizing the low-frequency component resolved by 
the frequency resolving means by raising the normalized signal thereof to 
the .beta.-th power by use of a coefficient .beta.; error calculating 
means for synthesizing the low-frequency component emphasized by the 
reference signal low-frequency emphasizing means and the high-frequency 
component and calculating the rate at which the synthesized signal is set 
outside a preset range; control means for controlling the coefficient 
.beta. based on the result of calculation by the error calculating means; 
reference signal high-frequency emphasizing means for dividing the 
high-frequency component resolved by the frequency resolving means into 
preset regions and multiplying the divided high-frequency component of 
each region by a coefficient .gamma. derived from the coefficient .beta. 
used in the reference signal low-frequency emphasizing means according to 
a preset relational expression; and dependent signal low-frequency 
emphasizing means for emphasizing the signal of the spectral sensitivity 
characteristic having a small information amount by raising the normalized 
signal thereof to the .beta.-th power. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
There will now be described an embodiment of this invention in detail with 
reference to the accompanying drawings. 
FIG. 1 is a diagram showing the construction of a signal processing 
apparatus according to a first embodiment of this invention. In FIG. 1, an 
input section 101 such as a TV camera is connected to an R-signal buffer 
102, B-signal buffer 103 and G-signal buffer 104. An output of the 
G-signal buffer 104 is connected to a G-signal low-frequency buffer 106 
and G-signal high-frequency buffer 107 via a wavelet transform section 
105. An output of the G-signal low-frequency buffer 106 is connected to an 
R-signal correlation coefficient calculating section 108 and B-signal 
correlation coefficient calculating section 109, and an output of the 
G-signal high-frequency buffer 107 is connected to an R-signal 
high-frequency creating section 110 and B-signal high-frequency creating 
section 111. An output of the R-signal buffer 102 is connected to the 
R-signal correlation coefficient calculating section 108 and an R-signal 
inverse wavelet transform section 112 and an output of the B-signal buffer 
103 is connected to the B-signal correlation coefficient calculating 
section 109 and a B-signal inverse wavelet transform section 113. 
The R-signal correlation coefficient calculating section 108 is connected 
to the R-signal high-frequency creating section 110, and the R-signal 
high-frequency creating section 110 is connected to the R-signal inverse 
wavelet transform section 112. The B-signal correlation coefficient 
calculating section 109 is connected to the B-signal high-frequency 
creating section 111, and the B-signal high-frequency creating section 111 
is connected to the B-signal inverse wavelet transform section 113. 
Outputs of the G-signal buffer 104, R-signal inverse wavelet transform 
section 112 and B-signal inverse wavelet transform section 113 are 
connected to an output section 114 such as a magnetic disk. A controller 
115 such as a microcomputer is connected to the input section 101, 
R-signal correlation coefficient calculating section 108, B-signal 
correlation coefficient calculating section 109, R-signal high-frequency 
creating section 110, B-signal high-frequency creating section 111, and 
output section 114. 
The operation of the above construction is explained according to the 
signal flow. Three signals of RGB from the input section 101 are supplied 
to the R-signal buffer 102, B-signal buffer 103 and G-signal buffer 104 
under the control of the controller 115. A G-signal in the G-signal buffer 
104 is supplied to the wavelet transform section 105 and subjected to the 
wavelet transformation by use of a preset basic function, for example, 
Harr function. A low-frequency component after the transformation is 
supplied to the G-signal low-frequency buffer 106 and a high-frequency 
component is supplied to the G-signal high-frequency buffer 107. 
The R-signal correlation coefficient calculating section 108 calculates a 
color correlation coefficient between low-frequency components of an 
R-signal in the R-signal buffer 102 and a G-signal in the G-signal 
low-frequency buffer 106. Likewise, the B-signal correlation coefficient 
calculating section 109 calculates a color correlation coefficient between 
low-frequency components of a B signal in the B-signal buffer 103 and a 
G-signal in the G-signal low-frequency buffer 106. The thus calculated 
color correlation coefficients are respectively supplied to the R-signal 
high-frequency creating section 110 and B-signal high-frequency creating 
section 111 and multiplied by the high-frequency component of the G-signal 
in the G-signal high-frequency buffer 107 so as to synthesize 
high-frequency components of R-and B signals. 
The R-signal inverse wavelet transform section 112 performs the inverse 
wavelet transformation based on the R-signal (low-frequency component) in 
the R-signal buffer 102 and the high-frequency component of the R-signal 
synthesized in the R-signal high-frequency creating section 110 and then 
supplies an R-signal of high definition to the output buffer 114. 
Likewise, the B-signal inverse wavelet transform section 113 performs the 
inverse wavelet transformation based on the B signal (low-frequency 
component) in the B-signal buffer 103 and the high-frequency component of 
the B signal synthesized in the B-signal high-frequency creating section 
111 and then supplies a B signal of high definition to the output buffer 
114. Further, the G-signal in the G-signal buffer 104 is also supplied to 
the output section 114, and as a result, three signals of RGB are output 
from the output section 114. 
FIG. 2 is a diagram showing one example of the concrete construction of the 
input section 101 of FIG. 1. As shown in FIG. 2, a G-signal CCD 201 and 
R-, B-signal CCD 202 are arranged to face an optical system 200. In the 
following description, it is assumed that the number of pixels of the 
G-signal is s.times.s and the number of pixels of each of the R-signal and 
B signal is s/2.times.s/2. An output from the G-signal CCD 201 is stored 
into the G-signal buffer 104 via an A/D 203 and low-pass filter 206 as a 
digital signal GOLL with the size of s.times.s. An output from the R-, 
B-signal CCD 202 is separated by an A/D 204 and R/B separation circuit 205 
and then the R-signal is supplied to the R-signal buffer 102 via a 
low-pass filter 207 as a digital signal R.sub.1LL with the size of 
s/2.times.s/2. The B signal is supplied to the B-signal buffer 103 via a 
low-pass filter 208 as a digital signal B.sub.1LL with the size of 
s/2.times.s/2. The G-signal CCD 201 and R-, B-signal CCD 202 are 
respectively connected to a G-signal CCD driving circuit 210 and R-, 
B-signal CCD driving circuit 211 which are operated by a clock from a 
clock generator 209. 
FIG. 3 is a diagram for illustrating one example of the concrete 
construction of the wavelet transform section 105 of FIG. 1. As shown in 
FIG. 3, in a basic function recording section 303, information of 
general-purpose basic function such as the Harr function is recorded. 
FIGS. 4A, 4B are diagrams for illustrating the Harr function used as the 
basic function. The Harr function can be provided by use of a high-pass 
filter shown in FIG. 4A and a low-pass filter shown in FIG. 4B. The 
filters are defined by the following equations. The filters are commonly 
used in the horizontal and vertical directions. 
EQU Horizontal, Vertical High-Pass Filter={0.5, -0.5} 
EQU Horizontal, Vertical Low-Pass Filter={0.5, 0.5} (8) 
A filter factor reading section 304 reads a filter factor of a preset basic 
function from the basic function recording section 303 under the control 
of the controller 115 and supplies the thus read filter factor to a 
horizontal high-pass filter 305, horizontal low-pass filter 306, vertical 
high-pass filter 309, vertical low-pass filter 310, vertical high-pass 
filter 311, and vertical low-pass filter 312. A data reading section 301 
reads a signal G.sub.0LL in the G-signal buffer 104 and transfers the same 
to a buffer 302 under the control of the controller 115. Data in the 
buffer 302 is subjected to the multi-stage filtering process as shown in 
FIG. 3 and is finally output to the G-signal low-frequency buffer 106 and 
G-signal high-frequency buffer 107 via an output switching section 317. 
Subsamplers 307, 308, 313, 314, 315, 316 have functions of subsampling 
input data to halve the input data number. An output of the subsampler 313 
gives a high-frequency component in both of the horizontal and vertical 
directions, an output of the subsampler 314 gives a high-frequency 
component in the vertical direction, an output of the subsampler 315 gives 
a high-frequency component in the horizontal direction, and an output of 
the subsampler 316 gives a low-frequency component. A data transfer 
control section 318 transfers an output of the subsampler 316 to the 
buffer 302 by a preset number of times under the control of the controller 
115 and subjects the same to the filtering process again. Thus, expansion 
coefficients for respective frequencies can be gradually calculated. In 
this embodiment, since it is assumed that the size of the G-signal is 
s.times.s and the size of the R-signal and B signal is s/2.times.s/2, the 
filtering process is effected once for the G-signal. The number of 
transformation processes is determined such that the low-frequency after 
the transformation comes to have the same size as the R-signal and B 
signal. The output switching section 317 selectively supplies outputs 
G.sub.1HH, G.sub.1HL, G.sub.1LH of the subsamplers 313, 314, 315 to the 
G-signal high-frequency buffer 107 and supplies an output G.sub.1LL of the 
subsampler 316 to the G-signal low-frequency buffer 106 under the control 
of the controller 115. 
FIG. 5 is a diagram for illustrating the above signal processing operation. 
In FIG. 5, the signal processing only relating to the R-signal and 
G-signal is shown, but the signal processing relating to the B signal and 
G-signal is substantially the same. In FIG. 5, (a) and (b) indicate a 
signal G.sub.0LL on the G-signal buffer 104 and a signal R.sub.1LL on the 
R-signal buffer 102. Further, (c) and (d) in FIG. 5 indicate a signal 
G.sub.1LL on the G-signal low-frequency buffer 106 and signals G.sub.1HH, 
G.sub.1HL, G.sub.1LH on the G-signal high-frequency buffer 107 which are 
subjected to the frequency resolving (decomposing) process in the wavelet 
transform section 105. In this case, R.sub.1LL in (b) and G.sub.1LL in (c) 
of FIG. 5 are data of the same size. The R-signal correlation coefficient 
calculating section 108 shown in FIG. 1 calculates a correlation 
coefficient expressed by the following equation between the signal 
G.sub.1LL and the signal R.sub.1LL. 
##EQU1## 
where i indicates the coordinate of data of the signal R.sub.1LL and the 
signal G.sub.1LL. That is, the correlation coefficient .epsilon..sub.G,B 
is calculated between the signal G.sub.1LL and the signal R.sub.1LL on the 
same coordinate for each pixel unit. The correlation coefficient is 
supplied to the R-signal high-frequency creating section 110 and 
multiplied by the signals G.sub.1HH, G.sub.1HL, G.sub.1LH on the G-signal 
high-frequency buffer 107 to create R-signal high-frequency components 
R.sub.1HH, R.sub.1HL, R.sub.1LH shown in (f) of FIG. 5. 
EQU R.sub.1HH (i)=.epsilon..sub.G,R (i)G.sub.1HH (i) 
EQU R.sub.1HL (i)=.epsilon..sub.G,R (i)G.sub.1HL (i) 
EQU R.sub.1LH (i)=.epsilon..sub.G,R (i)G.sub.1LH (i) (10) 
In FIG. 5, (g) indicates an R-signal R.sub.0LL of high definition 
calculated by subjecting the high frequency components R.sub.1HH, 
R.sub.1HL, R.sub.1HL created in the R-signal high-frequency creating 
section 110 and the signal R.sub.1LL on the R-signal buffer 102 to the 
inverse wavelet transform in the R-signal inverse wavelet transform 
section 112. 
FIG. 6 is a diagram showing one example of the concrete construction of the 
R-signal inverse wavelet transform section 112. In FIG. 6, the R-signal 
inverse wavelet transform section 112 is shown but the B-signal inverse 
wavelet transform section 113 can be formed with the same construction as 
that shown in FIG. 6. In a basic function recording section 403, 
information of general-purpose basic function such as the Harr function is 
recorded. Filter information items used in the wavelet transform section 
105 and the R-signal inverse wavelet transform section 112 are the same. 
The high-pass filter in the wavelet transform is set to g(n) and the 
low-pass filter is set to h(n), and the high-pass filter in the inverse 
wavelet transform is set to g'(n) and the low-pass filter is set to h'(n). 
Then, the relations of g'(n)=g(-n) and h'(n)=h(-n) are set between them in 
the case of orthogonal wavelet and can be derived from the filter 
information of wavelet transform. 
A filter coefficient reading section 404 reads a filter coefficient of a 
preset basic function and supplies the same to a vertical high-pass filter 
409, vertical low-pass filter 410, vertical high-pass filter 411, vertical 
low-pass filter 412, horizontal low-pass filter 415, horizontal high-pass 
filter 416 under the control of the controller 115. A data reading section 
401 and input switching section 402 transfer data from the R-signal buffer 
102 and R-signal high-frequency creating section 110 to the respective 
filters under the control of the controller 115. As shown in FIG. 6, the 
data is subjected to the multi-stage filtering process and the result of 
the filtering process is finally output to the output section 114 or data 
transfer control section 418 via an output switching section 417. 
Up-samplers 405, 406, 407, 408, 413, 414 have a function of up-sampling 
input data to double the input data number. The controller 115 controls 
the data transfer control section 418 to transfer an output of the output 
switching section 417 to the input switching section 402 by a preset 
number of times and subjects the same to the filtering process again. 
Thus, an image is gradually re-constructed. In this embodiment, since it 
is assumed that the size of the G-signal is s.times.s and the size of the 
R-signal and B signal is s/2.times.s/2, the filtering process is effected 
once. In FIG. 5, (g) indicates a reproduced image re-constructed by 
performing the inverse wavelet transform. 
As described above, in the first embodiment, a G-signal having the largest 
number of pixels among the input signals is resolved into a high-frequency 
component and low-frequency component by the wavelet transform, the 
correlation coefficients with the other signals are derived by use of the 
above low-frequency component, and high-frequency components of the other 
signals are derived by multiplying the thus obtained correlation 
coefficients by the high-frequency component of the G-signal. At this 
time, since the original low-frequency component of each signal is used as 
it is and the high-frequency component is added adaptively, that is, it is 
added while controlling a high-frequency component to be created for each 
pixel unit, the high-frequency component of a color signal can be 
corrected with high precision, thereby making it possible to derive an 
output image of high definition with less errors. 
Further, since the wavelet transform shares information of neighboring 
pixels, a reproduced image of high quality which is excellent in the 
continuity can be obtained even if the high-frequency component is 
controlled for each pixel unit. 
Next, a second embodiment of this invention is explained. FIG. 7 is a 
diagram showing the construction of the second embodiment. In FIG. 7, an 
input section 501 such as a TV camera is connected to an input switching 
section 505 via an R-signal buffer 502, G-signal buffer 503 and B-signal 
buffer 504. An output of the input switching section 505 is directly 
connected to an output section 520 and connected to an R-signal frequency 
component buffer 508, G-signal frequency component buffer 509 and B-signal 
frequency component buffer 510 via a DCT transform section 506 and output 
switching section 507. An output of the R-signal frequency component 
buffer 508 is connected to an R-signal correlation coefficient calculating 
section 511 and input switching section 515, an output of the G-signal 
frequency component buffer 509 is connected to the R-signal correlation 
coefficient calculating section 511, B-signal correlation coefficient 
calculating section 512, R-signal high-frequency creating section 513 and 
B-signal high-frequency creating section 514, and an output of the 
B-signal frequency component buffer 510 is connected to a B-signal 
correlation coefficient calculating section 512 and input switching 
section 515. 
Further, outputs of the R-signal high-frequency creating section 513 and 
B-signal high-frequency creating section 514 are connected to a correction 
R-signal buffer 518 and correction B-signal buffer 519 via the input 
switching section 515, inverse DCT transform section 516 and output 
switching section 517. The correction R-signal buffer 518 and correction 
B-signal buffer 519 are connected to the output section 520 such as a 
magnetic disk. Further, a controller 521 such as a microcomputer is 
connected to the input section 501, input switching section 505, output 
switching section 507, R-signal correlation coefficient calculating 
section 511, B-signal correlation coefficient calculating section 512, 
R-signal high-frequency creating section 513, B-signal high-frequency 
creating section 514, input switching section 515, output switching 
section 517 and output section 520. 
The operation of the above construction is explained according to the 
signal flow. In FIG. 7, three signals of RGB from the input section 501 
are supplied to the R-signal buffer 502, G-signal buffer 503 and B-signal 
buffer 504 under the control of the controller 521. Signals in the 
respective buffers are sequentially supplied for each region of preset 
size to the DCT transform section 506 via the input switching section 505 
and subjected to the frequency resolving process. In this embodiment, the 
preset size is set to 8.times.8 as one example. The regions are set so as 
not to overlap each other and signals on the same coordinate are supplied 
to the DCT transform section 506 in the order of RGB. 
In the DCT transform section 506, the DCT transform which is well known in 
the art is performed and an output thereof is sequentially transferred to 
the R-signal frequency component buffer 508, G-signal frequency component 
buffer 509 and B-signal frequency component buffer 510 via the output 
switching section 507 under the control of the controller 521. The 
R-signal correlation coefficient calculating section 511 calculates a 
correlation coefficient between preset low-frequency components, for 
example, low-frequency components of 2.times.2 size of the R-signal 
frequency component buffer 508 and G-signal frequency component buffer 
509. Likewise, the B-signal correlation coefficient calculating section 
512 calculates a correlation coefficient between low-frequency components 
of the B-signal frequency component buffer 510 and G-signal frequency 
component buffer 509. The correlation coefficients are respectively 
supplied to the R-signal high-frequency creating section 513 and B-signal 
high-frequency creating section 514 and multiplied by the high frequency 
component of the G-signal frequency component buffer 509 to synthesize the 
high-frequency components of the R-signal and B-signal. The high-frequency 
components indicate frequency components except the low-frequency 
components of 2.times.2 size. 
The high-frequency components created in the R-signal high-frequency 
creating section 513 and B-signal high-frequency creating section 514 and 
the low-frequency components in the R-signal frequency component buffer 
508 and B-signal frequency component buffer 510 are supplied to the input 
switching section 515. The input switching section 515 transfers the 
high-frequency component and low-frequency component of the R-signal to 
the inverse DCT transform section 516 under the control of the controller 
521 and then transfers the high-frequency component and low-frequency 
component of the B signal to the inverse DCT transform section 516. In the 
inverse DCT transform section 516, the inverse DCT transform which is well 
known in the art is performed and an output signal thereof is transferred 
to the correction R-signal buffer 518 and correction B-signal buffer 519 
via the output switching section 517 under the control of the controller 
521. The input switching section 505 is connected to the output section 
520 and a G-signal of the G-signal buffer 503 is output to the output 
section 520. To the output section 520, the RGB three signals from the 
correction R-signal buffer 518, input switching section 505 and correction 
B-signal buffer 519 are sequentially supplied under the control of the 
controller 521. 
FIG. 8 is a diagram showing an example of the concrete construction of the 
input section 501. A single-plate CCD 601 is arranged to face an optical 
system 600. The single-plate CCD 601 is a complementary color type CCD as 
shown in FIG. 18, for example. An output signal from the single-plate CCD 
601 is separated into a luminance signal and two color difference signals 
indicated by the equations (1), (2) and (3) in a color separation circuit 
603 via an A/D 602. The separated signals are processed in processing 
circuits 604, 605, 606, converted into three signals of RGB via a matrix 
circuit 607 and low-pass filters 608, 609, 610, and stored into the 
R-signal buffer 502, G-signal buffer 503, B-signal buffer 504. Further, a 
CCD driving circuit 615 operated by a clock from a clock generator 614 is 
connected to the CCD 601. The three signals of RGB obtained here have the 
same size, and the G-signal corresponding to the luminance signal is a 
signal having a large number of pixels of the imaging device and 
containing a plenty of high-frequency components. Since the other R-and B 
signals are derived from the color difference signals having a less number 
of pixels of the imaging device, they are obtained as signals having an 
insufficient amount of high-frequency components. 
FIG. 9 is a diagram for illustrating the signal processing operation. In 
FIG. 9, the R-signal and G-signal are shown, but the same processing 
operation is applied to the B signal and G-signal. In FIG. 9, (a) and (b) 
indicate an R-signal on the R-signal buffer 502 and a G-signal on the 
G-signal buffer 503. The signals are divided into regions which have a 
preset size, 8.times.8 size in this embodiment and are not overlapped with 
each other. In FIG. 9, (c), (d), (e), (f) indicate data items obtained by 
frequency-resolving the regions of the R-signal and B signal on the same 
coordinate in the DCT transform section 506. In this embodiment, the 
low-frequency component is arranged on the upper left portion which is the 
origin and the high-frequency component is arranged on the lower right 
portion. In FIG. 9, (c), (e) indicate low-frequency components of 
2.times.2 size and (d), (f) indicate the other high-frequency components. 
The R-signal correlation coefficient calculating section 511 calculates a 
correlation coefficient expressed by the following equation between the 
low-frequency components of (c) and (e) of FIG. 9. 
##EQU2## 
In the above equation, j indicates a region and k indicates a coordinate of 
the low-frequency component. Further, .sigma..sup.j indicates the 
covariance of a j-th region and R.sup.j a, G.sup.j a indicate an average 
value in the j-th region. The correlation coefficient 
.epsilon..sup.j.sub.G,R is transferred to the R-signal high-frequency 
creating section 513 and multiplied by the high-frequency component in the 
G-signal frequency component buffer 509 to create a high-frequency 
component of the R-signal as shown in (g) of FIG. 9. The original 
low-frequency component of the signal on the R-signal buffer 502 and the 
high-frequency component created in the R-signal high-frequency creating 
section 513 are subjected to the inverse transform in the inverse DCT 
transform section 516. In FIG. 9, (h) indicates an R-signal of high 
definition calculated by repeatedly effecting the above-described process 
for all of the regions. 
As described above, in the second embodiment, an input signal is divided 
into regions of preset size and frequency-resolved for each region, the 
low-frequency component of the G-signal having the largest number of 
pixels is used to derive correlation coefficients with the low-frequency 
components of the other signals, and high-frequency components of the 
other signals are created by multiplying the derived correlation 
coefficients by the high-frequency component of the G-signal. At this 
time, since the original low-frequency component of the signal is used as 
it is and only the high-frequency component is adaptively created for each 
region, the high-frequency component of the color signal can be corrected 
with high precision, thereby making it possible to derive an output image 
of high definition with less errors. Further, since the signal processing 
operation is repeatedly effected for each region, the required memory 
capacity can be made small and the apparatus can be constructed at low 
cost. 
In the second embodiment, the size of the region is set to 8.times.8 and 
the size of the region of the low frequency is set to 2.times.2, but they 
are not limitative and can be freely set. For example, it is possible to 
set the size of the region to 4.times.4 and set the size of the region of 
the low frequency to 1.times.1. If the size of the region of the low 
frequency is set to 1.times.1, the covariance in the equation (11) is 
always set at 0 and the correlation coefficient cannot be calculated, but 
in this case, the equation (9) in the first embodiment may be used to 
derive the correlation coefficient. Further, in the second embodiment, the 
DCT transform section and the inverse DCT transform section are used as 
one set and are selectively used to process the three signals, but this is 
not limitative. When it is desired to enhance the processing speed, it is 
possible to provide individual transform sections for the three signals. 
As a transform method other than the DCT transform, transformation of 
frequency resolution (frequency decomposition) such as Fourier transform 
and Hadamard transform can be used. 
Further, in the first embodiment, the correlation coefficient of the 
R-signal is calculated based on the equation (9), and in the second 
embodiment, the correlation coefficient of the R-signal is calculated 
based on the equation (11), but it is possible to derive the correlation 
coefficient in the second embodiment by use of the equation (9) and derive 
the correlation coefficient in the first embodiment by use of the equation 
(11). 
A third embodiment of this invention is explained below. FIG. 10 is a 
diagram showing the construction of the third embodiment. In FIG. 10, an 
input section 701 such as a TV camera is connected to an input switching 
section 705 via an R-signal buffer 702, G-signal buffer 703 and B-signal 
buffer 704. An output of the input switching section 705 is directly 
connected to an output section 726 and connected to an R-signal frequency 
component buffer 708, G-signal frequency component buffer 709 and B-signal 
frequency component buffer 710 via a wavelet transform section 706 and 
output switching section 707. 
Outputs of the R-signal frequency component buffer 708, G-signal frequency 
component buffer 709 and B-signal frequency component buffer 710 are 
respectively connected to an R-signal selecting section 711, G-signal 
selecting section 712 and B-signal selecting section 713. The G-signal 
selecting section 712 is connected to an R-signal error calculating 
section 715, B-signal error calculating section 716, R-signal 
high-frequency creating section 719 and B-signal high-frequency creating 
section 720 via a coefficient relocating section 714. Further, the 
R-signal selecting section 711 is connected to the R-signal error 
calculating section 715 and input switching section 721, and the B-signal 
selecting section 713 is connected to the B-signal error calculating 
section 716 and input switching section 721. 
Further, the R-signal error calculating section 715 is connected to the 
input switching section 721 via an R-signal minimum error searching 
section 717 and R-signal high-frequency creating section 719, and the 
B-signal error calculating section 716 is connected to the input switching 
section 721 via an B-signal minimum error searching section 718 and 
B-signal high-frequency creating section 720. An output of the input 
switching section 721 is connected to a correction R-signal buffer 724 and 
correction B-signal buffer 725 via an inverse wavelet transform section 
722 and output switching section 723. The correction R-signal buffer 724 
and correction B-signal buffer 725 are connected to an output section 726. 
Further, a controller 727 such as a microcomputer is connected to the 
input section 701, input switching section 705, output switching section 
707, R-signal selecting section 711, G-signal selecting section 712, 
B-signal selecting section 713, coefficient relocating section 714, 
R-signal minimum error searching section 717, B-signal minimum error 
searching section 718, R-signal high-frequency creating section 719, 
B-signal high-frequency creating section 720, input switching section 721, 
output switching section 723 and output section 726. 
The operation of the above-described construction is explained below. Three 
signals of RGB from the input section 701 are supplied to the R-signal 
buffer 702, G-signal buffer 703 and B-signal buffer 704 under the control 
of the controller 727. Like the second embodiment, in the RGB three 
signals, the G-signal corresponding to the luminance signal contains a 
large number of high-frequency components and the R-and B-signals contain 
a less number of high-frequency components. Signals in the respective 
buffers are sequentially supplied to the wavelet transform section 706 via 
the input switching section 705 and subjected to the frequency-resolving 
process under the control of the controller 727. In the third embodiment, 
a case wherein the resolving process is effected twice is considered, but 
the number of processes to be effected can be adjusted by a difference in 
the high-frequency component between the G-signal and the other signals. 
The input switching section 706 outputs only the G-signal to the output 
section 726. 
In the wavelet transform section 706, the same transform operation as in 
the first embodiment is performed and an output signal thereof is 
sequentially transferred to the R-signal frequency component buffer 708, 
G-signal frequency component buffer 709 and B-signal frequency component 
buffer 710 via the output switching section 707 based on the control of 
the controller 727. The frequency components in the respective buffers are 
input to the R-signal selecting section 711, G-signal selecting section 
712 and B-signal selecting section 713 and, for example, 16 frequency 
components corresponding to a region of preset size of the original 
signal, for example, a region of 4.times.4 size are selected. 
The frequency component selected in the R-signal selecting section 711 is 
supplied to the R-signal error calculating section 715 and input switching 
section 721, and the frequency component selected in the B-signal 
selecting section 713 is supplied to the B-signal error calculating 
section 716 and input switching section 721. Further, the frequency 
component selected in the G-signal selecting section 712 is subjected to a 
preset transform operation in the coefficient relocating section 714 and 
then supplied to the R-signal error calculating section 715, B-signal 
error calculating section 716, R-signal high-frequency creating section 
719 and B-signal high-frequency creating section 720. In the R-signal 
error calculating section 715, the R-signal frequency component from the 
R-signal selecting section 711 and a preset number of low-frequency 
components, for example, three low-frequency components of the G-signal 
frequency component from the coefficient relocating section 714 are used 
to derive an error in the similarity for the configuration thereof. In 
this example, errors in the similarity in all of the regions of the 
G-signal with respect to one region of the R-signal are calculated in the 
R-signal error calculating section 715. 
The R-signal minimum error searching section 717 searches for a region 
which gives a minimum error based on an error calculated by the R-signal 
error calculating section 715 and supplies the degree of similarity as a 
coefficient to the R-signal high-frequency creating section 719. In the 
R-signal high-frequency creating section 719, the high frequency component 
of the G-signal frequency component transferred from the coefficient 
relocating section 714 is multiplied by the coefficient of the similarity 
to create the high frequency component of the R-signal. Likewise, a region 
having a high similarity between the B-signal and the G-signal is searched 
for in the B-signal error calculating section 716, B-signal minimum error 
searching section 718 and B-signal high-frequency creating section 720 and 
the high frequency component of the R-signal is created based on the 
similarity. 
The input switching section 721 selectively transfers the low-frequency 
component of the R-signal from the R-signal selecting section 711 and the 
high-frequency component of the R-signal from the R-signal high-frequency 
creating section 719 to the inverse wavelet transform section 722 under 
the control of the controller 727. Likewise, the input switching section 
721 selectively transfers the low-frequency component of the B signal from 
the B-signal selecting section 713 and the high-frequency component of the 
B signal from the B-signal high-frequency creating section 720 to the 
inverse wavelet transform section 722. 
In the inverse wavelet transform section 722, the inverse transform is 
effected a preset number of times, twice in this embodiment, and the 
result of the inverse transform is transferred to the correction R-signal 
buffer 724 or correction B-signal buffer 725 via the output switching 
section 723. The RGB three signals from the correction R-signal buffer 
724, input switching section 705 and correction B-signal buffer 725 are 
supplied to the output section 726 under the control of the controller 
727. 
FIG. 11 shows a method for searching for a similar region based on the 
similarity between the frequency components of the R-signal and the 
G-signal. FIG. 11A shows a region r.sub.i of 4.times.4 size of the 
R-signal and FIG. 11B shows a region g.sub.j of the G-signal similar to 
the region r.sub.i. In this case, i, j indicate the numbers of the regions 
of the respective signals. FIGS. 11C, 11D show frequency components 
obtained by subjecting images of FIGS. 11A, 11B to the two-stage wavelet 
transform. As shown in FIG. 11C, the region r.sub.i is resolved into 16 
frequency components of r.sub.i,1 to r.sub.i,16. Likewise, as shown in 
FIG. 11D, the region g.sub.j is resolved into 16 frequency components of 
g.sub.j,1 to g.sub.j,16. When the degree of similarity between r.sub.i and 
g.sub.j is checked, the low-frequency components thereof are used. In this 
example, it is assumed that the coefficients of r.sub.i,1 to r.sub.i,4 and 
the coefficients of g.sub.j,1 to g.sub.j,4 are compared. In this case, 
since r.sub.i,1 and g.sub.j,1 indicate the bias which is an average 
density of respective blocks, they are not used. An error Err indicating 
the similarity between r.sub.i and g.sub.j is defined as follows. 
##EQU3## 
In the above equation, s.sub.i is a parameter indicating the scale of 
density. In this example, the regions of the same size are specified 
between the R-signal and the G-signal for searching for the similar 
region, but the sizes of the regions may be made different. 
FIG. 12 is a diagram for illustrating the relocation of the coefficient in 
the coefficient relocating section 714. FIG. 12A indicates the arrangement 
of original expansion coefficients g.sub.j,1 to g.sub.j,16 transferred 
from the G-signal frequency component buffer 709 and arrows indicating the 
directions thereof. For clarifying the explanation, the expansion 
coefficients g.sub.j,1 to g.sub.j,16 are indicated by alphabets of "a" to 
"p". Further, the expansion coefficients are classified into G.sub.1 and 
G.sub.2 according to the expansion level and classified into G.sub.LL, 
G.sub.LH, G.sub.HH and G.sub.HL according to filters used. 
An output of the subsampler 313 shown in FIG. 3 in the first embodiment 
gives a high-frequency component G.sub.HH in both of the horizontal and 
vertical directions, an output of the subsampler 314 gives a vertical 
high-frequency component G.sub.HL, an output of the subsampler 315 gives a 
horizontal high-frequency component G.sub.LH, and an output of the 
subsampler 316 gives a low-frequency component G.sub.LL. The expansion 
coefficients "a" to "p" are assigned such that "a" belongs to G.sub.2LL, 
"b" belongs to G.sub.2LH, "c" belongs to G.sub.2HH, "d" belongs to 
G.sub.2HL, "e", "f", "g", "h" belong to G.sub.1LH, "i", "j", "k", "l" 
belong to G.sub.1HH, and "m", "n", "o", "p" belong to G.sub.1HL. In the 
process of searching the similarity of the configuration, a region of the 
G-signal is not used as it is, but eight patterns including four regions 
obtained by rotating the original region by 0, 90, 180, 270 degrees and 
four regions symmetrically transforming the above four regions are used 
for comparison so that comparison with various types of configurations can 
be attained. 
It is considered to previously form the above eight patterns and subject 
them to the wavelet transform, but in this case, there occurs a problem 
from the viewpoint of the amount of calculations and memory capacity. In 
this example, the effect equivalent to that of the eight patterns is 
attained by relocation of the expansion coefficients and inversion of the 
signs. FIG. 12B is an example obtained by rotating FIG. 12A by 90 degrees 
in the counterclockwise direction. The difference therebetween is that the 
locations of G.sub.2LH and G.sub.2HL and the locations of G.sub.1LH and 
G.sub.1HL are replaced and the signs of G.sub.2HH, G.sub.2HL, G.sub.1HH 
and G.sub.1HL are inverted. This can be summarized as follows. 
EQU G.sub.mLH .rarw..fwdarw.-G.sub.mHL, -G.sub.mHH (13) 
In the above equation, m indicates the expansion level of the wavelet 
transform and, in this embodiment, m=1.2. FIGS. 12C to 12H indicate 
conversion of coefficients obtained by rotation and symmetric 
transformation. FIG. 12 shows a case of two-stage wavelet transform, but 
the above regularity applies in the wavelet transform of any desired 
stage. 
An error Err is calculated for each of the eight patterns obtained based on 
the above regularity in the coefficient relocating section 714 according 
to the equation (12) in the R-signal error calculating section 715. The 
G-signal selecting section 712 and coefficient relocating section 714 
transfer data relating to all of the regions obtained derived from the 
G-signal for one region of the R-signal under the control of the 
controller 727. The R-signal minimum error searching section 717 searches 
for a region which gives the minimum error based on all of the errors 
calculated in the R-signal error calculating section 715 and transfers a 
scale parameter s.sub.i relating to the searched region and a coefficient 
p.sub.i indicating the eight types of patterns to the R-signal 
high-frequency creating section 719. 
FIG. 13 is a flowchart for illustrating the similarity searching process. 
In this case, a variable i indicates the number of a region of the 
R-signal, j indicates the number of a region of the G-signal, k indicates 
eight types of rotation patterns relating to the region of the G-signal, 
R() indicates the array in which the frequency components of the region of 
the R-signal are stored, G() indicates the array in which the frequency 
components of the region of the G-signal are stored, a variable Err 
indicates an error of the equation (12), and a variable Scale indicates a 
Scale parameter s.sub.i of the equation (12). Further, the number of 
regions contained in the R-signal and G-signal is indicated by Image. 
First, i is set to 0 in S1. 
Next, in S2, the frequency component of the i-th region of the R-signal is 
substituted into the array R(), and the frequency component of the 0-th 
rotation pattern of the 0-th region of the G-signal is substituted into G( 
). 
In S3, an error and scale parameter are calculated between R() and G() 
according to the equation (12), the error is substituted into a variable 
Best.sub.-- Err and the scale parameter is substituted into a variable 
Best.sub.-- Scale. 
At this time, 0 is substituted into a variable Best.sub.-- G-and a variable 
Best.sub.-- Pi. In S4, S5, j, k are set to 0. 
In S6, the frequency component of an i-th region of the R-signal is 
substituted into the array R(), and the frequency component of the k-th 
rotation pattern of the j-th region of the G-signal is substituted into G( 
). 
In S7, an error and scale parameter are calculated between R() and G() 
according to the equation (12), and the error and the scale parameter are 
substituted into Err and Scale. 
In S8, Err and Best.sub.-- Err are compared with each other, and the step 
S9 is effected when Best-Err is larger and the step S10 is effected when 
Best.sub.-- Err is smaller. 
In S9, Scale is substituted into Best.sub.-- Scale, Err is substituted into 
Best.sub.-- Err, j is substituted into Best.sub.-- G, and k is substituted 
into Best.sub.-- Pi. 
In S10 to S13, "1" is added to j, k, and the above process is repeatedly 
effected until k exceeds 8 and j exceeds Image. 
In S14, Best.sub.-- Scale, Best.sub.-- G, Best.sub.-- Pi are output. 
In S15, S16, "1" is added to i, and the above process is repeatedly 
effected until i exceeds Image. 
Based on the above process, a region included in all of the regions derived 
from the G-signal and having the highest similarity to one region of the 
R-signal can be obtained. 
FIG. 14 is a diagram showing the above signal processing operation. In FIG. 
14, the signal processing only relating to the R-signal and G-signal is 
shown, but the signal processing relating to the B-signal and G-signal is 
substantially the same. In FIG. 14, (a) and (b) indicate an R-signal 
R.sub.0LL in the R-signal buffer 702 and a G-signal G.sub.0LL in the 
G-signal buffer 703. The above signals are divided into regions which have 
a preset size, 4.times.4 size in this embodiment, and are not overlapped 
with each other. In FIG. 14, (c), (d), (e), (f) indicate R.sub.2LL, 
R.sub.2HH, R.sub.2LH, R.sub.1HH, R.sub.1HL, R.sub.1LH in the R-signal 
frequency component buffer 708 which are frequency-resolved in the wavelet 
transform section 706 and G.sub.2LL, G.sub.2HH, G.sub.2LH, G.sub.1HH, 
G.sub.1HL, G.sub.1LH in the G-signal frequency component buffer 709. The 
R-signal error calculating section 715 and R-signal minimum error 
searching section 717 calculate the scale parameter s.sub.i and the 
coefficient p.sub.i indicating eight types of patterns between R.sub.2HH, 
R.sub.2HL, R.sub.2LH of (c) in FIG. 14 and G.sub.2HH, G.sub.2HL, G.sub.2LH 
of (e) in FIG. 14. The coefficient is supplied to the R-signal 
high-frequency creating section 719, the relocation of the coefficient 
shown in FIG. 12 is performed for G.sub.1HH, G.sub.1HL, G.sub.1LH based on 
the coefficient p.sub.i, and then G.sub.1HH, G.sub.1HL, G.sub.1LH are 
multiplied by the scale parameter s.sub.i. Components of the respective 
regions shown in FIGS. 11C and 11D are subjected to the process expressed 
by the following equation. 
EQU r.sub.i,k =S.sub.i g.sub.j,k (14) 
In the above equation, k is a coefficient shown in FIGS. 11C, 11D and k=5 
to 16. In FIG. 14, (g) indicates created high-frequency components 
R.sub.1HH, R.sub.1HL, R.sub.1LH of the R-signal. In FIG. 14, (h) indicates 
an R-signal R.sub.0LL of high definition calculated by subjecting the 
created high-frequency components R.sub.1HH, R.sub.1HL, R.sub.1LH and 
R.sub.2LL, R.sub.2HH, R.sub.2HL, R.sub.2LH in the R-signal frequency 
component buffer 708 to the inverse wavelet transform in the inverse 
wavelet transform section 722. 
As described above, in the third embodiment, an input signal is divided 
into regions of preset size so as to be frequency-resolved, a region in 
which the low-frequency component of a signal other than the G-signal 
containing a largest number of pixels is similar in configuration to the 
low-frequency component of the G-signal is derived, and the high-frequency 
component of the other signal is created based on the high-frequency 
component of the G-signal in the derived region. At this time, since the 
original low-frequency component of the signal is used as it is and only 
the high-frequency component thereof is adaptively created for each 
region, the high-frequency component of the color signal can be corrected 
with high precision and an output image of high definition with less error 
can be obtained. Further, since the high-frequency component is derived 
based on the similarity in configuration, the high-frequency component can 
be derived even in a case where the continuity of the signal is degraded 
in the edge portion or the like or the degree of correlation with the 
G-signal is low, and thus a preferable output image can be obtained for 
various types of images. 
In the third embodiment, the size of the region is set to 4.times.4, but 
this is not limitative and can be freely set. Further, in the third 
embodiment, the wavelet transform section and the inverse wavelet 
transform section are used as one set and are selectively used to process 
the three signals, but this is not limitative. When it is desired to 
enhance the processing speed, it is possible to provide individual 
transform sections for the three signals. 
Next, a fourth embodiment of this invention is explained. FIG. 15 is a 
diagram showing the construction of the fourth embodiment. The 
construction is basically the same as that of the first embodiment, but in 
the fourth embodiment, the construction of the stage which follows the 
G-signal high-frequency buffer 107 in the first embodiment is modified by 
adding a high frequency emphasizing section 801, G-signal inverse wavelet 
transform section 802 and error calculating section 803. 
An output of the G-signal high-frequency buffer 107 is connected to the 
R-signal high-frequency creating section 110, B-signal high-frequency 
creating section 111 and G-signal inverse wavelet transform section 802 
via the high frequency emphasizing section 801. The G-signal inverse 
wavelet transform section 802 receives inputs from the high frequency 
emphasizing section 801 and G-signal low-frequency buffer 106 and is 
connected to the output section 114 and error calculating section 803. The 
error calculating section 803 is connected to the high frequency 
emphasizing section 801 and the controller 115 is connected to the 
R-signal correlation coefficient calculating section 108, R-signal 
high-frequency creating section 110, B-signal correlation coefficient 
calculating section 109, B-signal high-frequency creating section 111, 
high frequency emphasizing section 801 and error calculating section 803. 
Next, the operation of the above construction is explained. Three signals 
of RGB from the input section 101 are supplied to the R-signal buffer 102, 
B-signal buffer 103 and G-signal buffer 104 under the control of the 
controller 115. A G-signal in the G-signal buffer 104 is supplied to the 
wavelet transform section 105 and subjected to the wavelet transformation. 
A low-frequency component after the wavelet transformation is supplied to 
the G-signal low-frequency buffer 106 and a high-frequency component is 
supplied to the G-signal high-frequency buffer 107. The high-frequency 
component in the G-signal high-frequency buffer 107 is transferred to the 
high frequency emphasizing section 801 and multiplied by a preset 
coefficient .alpha.. 
FIGS. 16A and 16B are diagrams for illustrating a method for determining 
the coefficient .alpha. in the high frequency emphasizing section 801. An 
initial value of the coefficient .alpha. is set to 1.5, for example. A 
G-signal is re-constructed in the G-signal inverse wavelet transform 
section 802 based on the high frequency component of the G-signal 
subjected to the emphasizing process and the low-frequency component from 
the G-signal low-frequency buffer 106. The density range of the 
re-constructed G-signal is checked in the error calculating section 803, 
and the rate of the number of pixels which is set outside a preset range, 
for example, a range of 0 to 255 in the case of 8-bit density level, is 
checked. As shown in FIG. 16A, if the rate does not exceed a preset 
threshold value, for example, 1%, the high frequency emphasizing section 
801 increases the coefficient .alpha. and then effects the emphasizing 
process again. If the rate exceeds the preset threshold value as shown in 
FIG. 16B, the high frequency emphasizing section 801 decreases the 
coefficient .alpha. and then effects the emphasizing process again. When 
the rate of error changes from a smaller value to a larger value than the 
threshold value or changes from a larger value to a smaller value than the 
threshold value, the emphasizing process is completed. 
After the process for the high-frequency component of the G-signal is 
completed, the R-signal correlation coefficient calculating section 108 
calculates a color correlation coefficient between the R-signal in the 
R-signal buffer 102 and the low-frequency component of the G-signal in the 
G-signal low-frequency buffer 106. Likewise, the B-signal correlation 
coefficient calculating section 109 calculates a color correlation 
coefficient between the B signal in the B-signal buffer 103 and the 
low-frequency component of the G-signal in the G-signal low-frequency 
buffer 106. The above color correlation coefficients are supplied to the 
R-signal high-frequency creating section 110 and B-signal high-frequency 
creating section 111 and multiplied by the high-frequency component of the 
G-signal subjected to the emphasizing process in the high frequency 
emphasizing section 801 so as to create the high-frequency components of 
the R-signal and B-signal. 
The R-signal inverse wavelet transform section 112 performs the inverse 
wavelet transform based on the R-signal (low-frequency component) in the 
R-signal buffer 102 and the high-frequency component of the R-signal 
created in the R-signal high-frequency creating section 110 and supplies 
the R-signal of high definition to the output section 114. Likewise, the 
B-signal inverse wavelet transform section 113 performs the inverse 
wavelet transform based on the B-signal (low-frequency component) in the 
B-signal buffer 103 and the high-frequency component of the B-signal 
created in the B-signal high-frequency creating section 111 and supplies 
the B-signal of high definition to the output section 114. Further, the 
G-signal of the G-signal inverse wavelet transform section 802 is also 
supplied to the output section 114 and thus three signals of RGB are 
output from the output section 114. 
As described above, in the fourth embodiment, the G-signal having the 
largest number of pixels among an input signal is divided into low- and 
high-frequency components by the wavelet transform and the high-frequency 
component is subjected to the emphasizing process. Then, correlation 
coefficients with the other signals are derived by use of the 
low-frequency component thereof, and the high-frequency components of the 
other signals are derived by multiplying the derived correlation 
coefficients by the high-frequency component of the G-signal subjected to 
the emphasizing process. At this time, since the original low-frequency 
component of the signal is used as it is and the high-frequency component 
is adaptively created for each pixel unit, the high-frequency component of 
the color signal can be corrected with high precision, thereby making it 
possible to derive an output image of high definition with less errors. 
Further, since the high-frequency component is subjected to the 
emphasizing process with the error rate kept less than a preset threshold 
value, it becomes possible to derive an output signal of high visual 
quality with enhanced contrast. 
In the fourth embodiment, the coefficient .alpha. used for the emphasizing 
process is automatically adjusted to prevent the error rate from exceeding 
the preset threshold value, but this is not limitative. The coefficient 
.alpha. can be manually derived, and in this case, the error calculating 
section 803 can be omitted. 
Next, a fifth embodiment of this invention is explained. FIG. 17 is a 
diagram showing the construction of the fifth embodiment. The construction 
of the fifth embodiment is basically the same as that of the first 
embodiment, but in the fifth embodiment, an R-signal low-frequency 
emphasizing section 901, B-signal low-frequency emphasizing section 902, 
G-signal low-frequency emphasizing section 903, G-signal high-frequency 
emphasizing section 904, G-signal inverse wavelet transform section 905 
and error calculating section 906 are added to the construction of the 
first embodiment. The R-signal low-frequency emphasizing section 901 
connected to the output of the R-signal buffer 102 is connected to the 
R-signal inverse wavelet transform section 112. The B-signal low-frequency 
emphasizing section 902 connected to the output of the B-signal buffer 103 
is connected to the B-signal inverse wavelet transform section 113. The 
G-signal low-frequency emphasizing section 903 connected to the output of 
the G-signal low-frequency buffer 106 is connected to the G-signal inverse 
wavelet transform section 905. The G-signal high-frequency buffer 107 is 
connected to the R-signal high-frequency creating section 110, B-signal 
high-frequency creating section 111 and G-signal inverse wavelet transform 
section 905 via the G-signal high-frequency emphasizing section 904. The 
G-signal inverse wavelet transform section 905 is connected to the outputs 
of the G-signal high-frequency emphasizing section 904 and G-signal 
low-frequency emphasizing section 903 and connected to the output section 
114 and error calculating section 906. The error calculating section 906 
is connected to the G-signal high-frequency emphasizing section 904 and 
the controller 115 is connected to the R-signal correlation coefficient 
calculating section 108, R-signal high-frequency creating section 110, 
R-signal low-frequency emphasizing section 901, B-signal correlation 
coefficient calculating section 109, B-signal high-frequency creating 
section 111, B-signal low-frequency emphasizng section 902, G-signal 
low-frequency emphasizing section 903, G-signal high-frequency emphasizing 
section 904 and error calculating section 906. 
The operation of the above construction is explained below. Three signals 
of RGB from the input section 101 are supplied to the R-signal buffer 102, 
B-signal buffer 103 and G-signal buffer 104 under the control of the 
controller 115. A G-signal in the G-signal buffer 104 is subjected to the 
wavelet transformation by the wavelet transform section 105. A 
low-frequency component after the wavelet transformation is supplied to 
the G-signal low-frequency buffer 106 and a high-frequency component is 
supplied to the G-signal high-frequency buffer 107. The low-frequency 
component G.sub.1LL of the G-signal low-frequency buffer 106 is normalized 
by the maximum value M.sub.max of density based on the following equation 
in the G-signal low-frequency emphasizing section 903 and then raised to 
the .beta.-th power by use of a coefficient .beta.. In the fifth 
embodiment, since it is assumed that an 8-bit density range is used, 
M.sub.max is equal to 255. 
##EQU4## 
The coefficient .beta. expands the range of a dark portion when .beta.&lt;1 
and expands the range of a bright portion when .beta.&gt;1. Therefore, the 
G-signal low-frequency emphasizing section 903 determines the bright 
portion or dark portion based on the average density value of the 
low-frequency components of the G-signal and sets the initial value of the 
coefficient .beta.. As one example, since a range of 0 to 255 is set in 
the case of 8-bit density level, a portion whose average density value of 
the low-frequency components is 128 or less is determined as a dark 
portion and a portion whose average density value is larger than 128 is 
determined as a bright portion. The initial value of the coefficient 
.beta. is set to 0.5 in the dark portion and 1.5 in the bright portion. As 
the coefficient .beta., the same value is used for all of the 
low-frequency components. 
The low-frequency component subjected to the emphasizing process and the 
normal high-frequency component are supplied to the G-signal inverse 
wavelet transform section 905 under the control of the controller 115 and 
G-signal is re-constructed. In the error calculating section 906, the 
density range of the re-constructed G-signal is checked and the rate of 
the number of pixels which is set outside a preset range is checked. Like 
the fourth embodiment, an optimum coefficient .beta. can be thus obtained. 
The coefficient .beta. is supplied to the R-signal low-frequency 
emphasizing section 901 and B-signal low-frequency emphasizing section 902 
via the controller 115 and the range of the low-frequency component is 
expanded as in the case of equation (16). 
Next, the controller 115 triggers the G-signal high-frequency emphasizing 
section 904. In the G-signal high-frequency emphasizing section 904 as 
shown in FIG. 11D, the high-frequency components G.sub.1HH, G.sub.1HL, 
G.sub.1LH of the G-signal are divided into regions of 4.times.4, for 
example, and the components g.sub.j,5 to g.sub.j,16 thereof are extracted. 
Then, a coefficient .gamma..sub.j used for emphasis is calculated for each 
region according to the following equation. 
##EQU5## 
In the above equation, j indicates the number of a region of the 
high-frequency component, k indicates a factor of 5 to 16, and 
g.sub.j.sup.a indicates the average density of a j-th region. The equation 
(17) indicates a condition that the density range of each region does not 
depart from a preset range for a given coefficient .beta.. The 
high-frequency component of the G-signal high-frequency buffer 107 is 
multiplied by the coefficient .gamma. in the high frequency emphasizing 
section 904. After this, the R-signal correlation coefficient calculating 
section 108 calculates a color correlation coefficient between the 
R-signal in the R-signal buffer 102 and the low-frequency component of the 
G-signal in the G-signal low-frequency buffer 106. Likewise, the B-signal 
correlation coefficient calculating section 109 calculates a color 
correlation coefficient between the B signal in the B-signal buffer 103 
and the low-frequency component of the G-signal in the G-signal 
low-frequency buffer 106. The above color correlation coefficients are 
supplied to the R-signal high-frequency creating section 110 and B-signal 
high-frequency creating section 111 and multiplied by the high-frequency 
component of the emphasized G-signal in the G-signal high-frequency 
emphasizing section 904 so as to create the high-frequency components of 
the R-signal and B signal. The R-signal inverse wavelet transform section 
112 performs the inverse wavelet transform based on the emphasized 
low-frequency component in the R-signal low-frequency emphasizing section 
901 and the high-frequency component of the R-signal created in the 
R-signal high-frequency creating section 110 and supplies an R-signal of 
high definition to the output section 114. Likewise, the B-signal inverse 
wavelet transform section 113 performs the inverse wavelet transform based 
on the emphasized low-frequency component in the B-signal low-frequency 
emphasizing section 902 and the high-frequency component of the B signal 
created in the B-signal high-frequency creating section 111 and supplies a 
B-signal of high definition to the output section 114. Further, the 
G-signal in the G-signal inverse wavelet transform section 905 is also 
supplied to the output section 114 and thus the RGB three signals are 
output from the output section 114. 
As described above, in the fifth embodiment, the G-signal having the 
largest number of pixels among an input signal is divided into high- and 
low-frequency components by the wavelet transform and the high- and 
low-frequency components are subjected to the emphasizing process. Then, 
correlation coefficients between the original low-frequency component of 
the G-signal and the other signals are derived and the high-frequency 
components of the other signals are derived by multiplying the derived 
correlation coefficients by the high-frequency component of the G-signal 
subjected to the emphasizing process. The same emphasizing process as that 
for the low-frequency component of the G-signal is effected for the other 
signals. Since the high- and low-frequency components are subjected to the 
optimum emphasizing process and then the high-frequency component is 
adaptively created for each region, an output signal with expanded dynamic 
range and enhanced contrast can be obtained. Further, since parameters are 
controlled by previously checking occurrence of error caused by the 
expanding process, and at the same time, parameters for the emphasizing 
process are controlled, unnatural emphasis will not tend to occur. 
In the fifth embodiment, the coefficient .beta. used for the emphasizing 
process is automatically adjusted so that the rate of error will not 
exceed a threshold value, but this is not limitative. It is possible to 
manually determine the coefficient .beta., and in this case, the error 
calculating section 906 can be omitted. 
The above-described embodiments include the following constructions 1 to 9 
of this invention. 
1. A signal processing apparatus for processing a signal in which the 
information amount of a signal related to at least one of a plurality of 
spectral sensitivity characteristics is larger than the information amount 
of any one of signals related to the other spectral sensitivity 
characteristics, comprising: 
frequency resolving means for resolving the signal of the spectral 
sensitivity characteristic having a large information amount into high- 
and low-frequency components; 
correlation coefficient calculating means for calculating correlation 
coefficients between the low-frequency component derived from the 
frequency resolving means and the signals of the spectral sensitivity 
characteristics having a small information amount; 
high-frequency creating means for creating high-frequency components of the 
signals of the spectral sensitivity characteristics having a small 
information amount based on the correlation coefficients derived from the 
correlation coefficient calculating means and the high-frequency component 
derived from the frequency resolving means; and 
frequency synthesizing means for synthesizing the high-frequency component 
derived from the high-frequency creating means and the signal of the 
spectral sensitivity characteristic having a small information amount to 
output an output signal with high definition. 
2. A signal processing apparatus described in the item 1, wherein the 
signal of the spectral sensitivity characteristic having a large 
information amount corresponds to a luminance signal and a signal other 
than the above signal having a large information amount corresponds to a 
color signal. 
3. A signal processing apparatus described in the item 1, wherein the 
frequency resolving means and frequency synthesizing means use the Harr 
function or Daubechies function as the basic function to perform the 
orthogonal wavelet transform or bi-orthogonal wavelet transform. 
4. A signal processing apparatus described in the item 1, wherein the 
correlation coefficient calculating means calculates a correlation 
coefficient based on the color correlation between signals of a plurality 
of spectral sensitivity characteristics. 
5. A signal processing apparatus described in the item 1, wherein the 
frequency resolving means and frequency synthesizing means use the 
orthogonal transform corresponding to one of the DCT transform, Fourier 
transform and Hadamard transformation for each region of preset size. 
6. A signal processing apparatus for processing a signal in which the 
information amount of a signal related to at least one of a plurality of 
spectral sensitivity characteristics is larger than the information amount 
of any one of signals related to the other spectral sensitivity 
characteristics, comprising: 
frequency resolving means for resolving a signal into a plurality of 
frequency components by using a function of local distribution as a basic 
function; 
extraction means for extracting a frequency component corresponding to a 
first preset region of the signal of the spectral 
sensitivity-characteristic having a large information amount and a 
frequency component corresponding to a second preset region of the signal 
of the other spectral sensitivity characteristic having a small 
information amount from the coefficients of the plurality of frequency 
components derived from the frequency resolving means; 
similarity calculating means for calculating the degree of similarity 
between the frequency components of the first and second preset regions 
derived from the extraction means; 
searching means for searching for the first preset region having the 
highest degree of similarity with respect to the second preset region 
based on the degree of similarity derived from the similarity calculating 
means; 
high-frequency creation means for creating a high-frequency component of 
the second preset region based on the degree of similarity according to 
the high-frequency component related to the first preset region derived 
from the searching means; and 
frequency synthesizing means for synthesizing the high-frequency component 
derived from the high-frequency creating means and the signal of the 
spectral sensitivity characteristic having a small information amount to 
output an output signal with high definition. 
7. A signal processing apparatus described in the item 6, wherein the 
frequency resolving means and frequency synthesizing means use the Harr 
function or Daubechies function as the basic function to perform the 
orthogonal wavelet transform or bi-orthogonal wavelet transform. 
8. A signal processing apparatus for processing a signal in which the 
information amount of a signal related to at least one of a plurality of 
spectral sensitivity characteristics is larger than the information amount 
of any one of signals related to the other spectral sensitivity 
characteristics, comprising: 
frequency resolving means for resolving the signal of the spectral 
sensitivity characteristic having a large information amount into high- 
and low-frequency components; 
high-frequency emphasizing means for multiplying a coefficient .alpha. 
larger than 1 by the high-frequency component resolved by the frequency 
resolving means; 
error calculating means for calculating the rate at which a signal obtained 
by synthesizing the high-frequency component emphasized by the 
high-frequency emphasizing means and the low-frequency component is set 
outside a preset range; and 
control means for controlling the value of the coefficient .alpha. based on 
the result of calculation by the error calculating means. 
9. A signal processing apparatus for processing a signal in which the 
information amount of a signal related to at least one of a plurality of 
spectral sensitivity characteristics is larger than the information amount 
of any one of signals related to the other spectral sensitivity 
characteristics, comprising: 
frequency resolving means for resolving the signal of the spectral 
sensitivity characteristic having a large information amount into high- 
and low-frequency components; 
reference signal low-frequency emphasizing means for emphasizing the 
low-frequency component resolved by the frequency resolving means by 
raising the normalized signal thereof to the .beta.-th power by use of a 
coefficient .beta.; 
error calculating means for synthesizing the low-frequency component 
emphasized by the reference signal low-frequency emphasizing means and the 
high-frequency component and calculating the rate at which the synthesized 
signal is set outside a preset range; 
control means for controlling the coefficient .beta. based on the result of 
calculation by the error calculating means; 
reference signal high-frequency emphasizing means for dividing the 
high-frequency component resolved by the frequency resolving means into 
preset regions and multiplying the divided high-frequency component of 
each region by a coefficient .gamma. derived from the coefficient .beta. 
used in the reference signal low-frequency emphasizing means according to 
a preset relational expression; and 
dependent signal low-frequency emphasizing means for emphasizing the signal 
of the spectral sensitivity characteristic having a small information 
amount by raising the normalized signal thereof to the .beta.-th power. 
The embodiments, operations and effects corresponding to the constructions 
1 to 9 of this invention are as follows. 
(Constructions 1 to 4) 
(Corresponding Embodiments) 
The embodiments of this invention correspond to the first embodiment 
described before. The frequency resolving means in the above construction 
corresponds to the wavelet transform section 105 shown in FIGS. 1 and 3. 
The basic function of the wavelet transform corresponds to the Harr 
function shown in FIG. 4, but it includes an orthogonal wavelet function 
such as a Daubechies function or bi-orthogonal wavelet function. The 
correlation coefficient calculating means in the above construction 
corresponds to the R-signal correlation coefficient calculating section 
108 and B-signal correlation coefficient calculating section 109 in FIG. 
1. The correlation coefficient calculating means also has a function of 
calculating a correlation coefficient based on the color correlation 
between output signals of a plurality of spectral sensitivity 
characteristics. The high-frequency creating means in the above 
construction corresponds to the R-signal high-frequency creating section 
110 and B-signal high-frequency creating section 111 of FIG. 1. The 
frequency synthesizing means in the above construction corresponds to the 
R-signal inverse wavelet transform section 112 and B-signal inverse 
wavelet transform section 113 shown in FIGS. 1 and 6. 
A preferable example of the signal processing apparatus according to this 
invention is as follows. An image signal from the input section. 101 is 
stored in the R-signal buffer 102, B-signal buffer 103 and G-signal buffer 
104, and the G-signal having the largest number of pixels and stored in 
the G-signal buffer 104 is transferred to the wavelet transform section 
105 and is frequency-resolved into high- and low-frequency components. 
Then, correlation coefficients between the low-frequency component and the 
R-signal and B signal are respectively calculated by the R-signal 
correlation coefficient calculating section 108 and B-signal correlation 
coefficient calculating section 109 and the high-frequency components of 
the R-signal and B signal are created by multiplying the calculated 
correlation coefficients by the high-frequency component of the G-signal 
in the R-signal high-frequency creating section 110 and B-signal 
high-frequency creating section 111. The thus created high-frequency 
components and the original R-signal and B-signal are synthesized in the 
R-signal inverse wavelet transform section 112 and B-signal inverse 
wavelet transform section 113. 
(Operation) 
A signal related to the spectral sensitivity characteristic having a large 
information amount (in this example, a G-signal having the largest number 
of pixels) among an input signal is subjected to the frequency-resolving 
process such as the wavelet transform to be resolved into high- and 
low-frequency components. The thus obtained low-frequency component is 
used to derive correlation coefficients with signals of other spectral 
sensitivity characteristics having a less information amount (in this 
example, R- and B-signals) and the correlation coefficients are multiplied 
by the high-frequency component of the G-signal to create the 
high-frequency components of the R-and B-signals as the other signals. 
(Effect) 
Since the original low-frequency component of the signal is used as it is 
and the high-frequency component is adaptively created for each pixel unit 
and added, the high-frequency component of the color signal can be 
corrected with high precision and an output image of high definition with 
less error can be obtained. Further, in a case where wavelet transform 
means is used as the frequency-resolving means, information of neighboring 
pixels can be commonly used so that the satisfactory continuity can be 
obtained even if the high-frequency component is controlled for each pixel 
unit and a reproduced image of high quality can be obtained. Further, 
since the frequency information and position information can be 
simultaneously obtained, the high-frequency component can be adaptively 
created by calculating a correlation coefficient for each pixel unit. 
(Construction 5) 
(Corresponding Embodiment) 
The embodiment of this invention corresponds to the second embodiment 
described before. The frequency resolving means in the above construction 
corresponds to the input switching section 505, DCT transform section 506 
and output switching section 507 shown in FIG. 7. The frequency 
synthesizing means in the above construction corresponds to the input 
switching section 515, inverse DCT transform section 516 and output 
switching section 517. 
A preferable example of the signal processing apparatus according to this 
invention is as follows. An image signal from the input section 501 shown 
in FIG. 7 is stored in the R-signal buffer 502, G-signal buffer 503 and 
B-signal buffer 504 and is then frequency-resolved into high- and 
low-frequency components for each region of preset size in the DCT 
transform section 506. Then, correlation coefficients between the 
low-frequency component of the G-signal having the largest number of 
pixels and the low-frequency components of the R-signal and B signal are 
respectively calculated by the R-signal correlation coefficient 
calculating section 511 and B-signal correlation coefficient calculating 
section 512 and the high-frequency components of the R-signal and B signal 
are created by multiplying the calculated correlation coefficients by the 
high-frequency component of the G-signal in the R-signal high-frequency 
creating section 513 and B-signal high-frequency creating section 514. The 
thus created high-frequency components and the original low-frequency 
components of the R-signal and B-signal are synthesized in the inverse DCT 
transform section 516. 
(Operation) 
An input signal is subjected to the DCT transform, for example, for each 
region of preset size so as to be resolved into high- and low-frequency 
components. The thus obtained low-frequency component is used to derive 
correlation coefficients between the G-signal having the largest number of 
pixels and the R- and B-signals as the other signals and the thus derived 
correlation coefficients are multiplied by the high-frequency component of 
the G-signal to create the high-frequency components of the R-and B 
signals. 
(Effect) 
Since the frequency-resolving process and synthesizing process are effected 
for each region of small size, the apparatus construction in which 
necessary memory capacity is reduced can be attained. Further, since the 
original low-frequency component of the signal is used as it is and the 
high-frequency component is adaptively created for each pixel unit and 
added, the high-frequency component of the color signal can be corrected 
with high precision and an output image of high definition with less error 
can be obtained. 
(Constructions 6 and 7) 
(Corresponding Embodiments) 
The embodiment of this invention corresponds to the third embodiment 
described before. The frequency resolving means in the above construction 
corresponds to the wavelet transform section 706 shown in FIG. 10. As the 
basic function of the wavelet transform, the Harr function shown in FIG. 4 
can be used, but an orthogonal wavelet function such as the Daubechies 
function and a bi-orthogonal wavelet function can also be used. The 
extracting means in the above construction corresponds to the R-signal 
selecting section 711, G-signal selecting section 712, and B-signal 
selecting section 713 of FIG. 10. The similarity calculating means in the 
above construction corresponds to the R-signal error calculating section 
715 and B-signal error calculating section 716 of FIG. 10. The searching 
means in the above construction corresponds to the R-signal minimum error 
searching section 717 and B-signal minimum error searching section 718 of 
FIG. 10. The high-frequency creating means in the above construction 
corresponds to the R-signal high-frequency creating section 719 and 
B-signal high-frequency creating section 720 of FIG. 10. The frequency 
synthesizing means in the above construction corresponds to the inverse 
wavelet transform section 722 of FIG. 10. 
A preferable example of the signal processing apparatus according to this 
invention is as follows. An image signal from the input section 701 shown 
in FIG. 10 is stored in the R-signal buffer 702, G-signal buffer 703 and 
B-signal buffer 704 and the signals in the respective buffers are 
transferred to the wavelet transform section 706 and then 
frequency-resolved into high- and low-frequency components. Next, the 
degrees of similarity in configuration between the low-frequency component 
of the G-signal having the largest number of pixels and the low-frequency 
components of the R-signal and B signal are respectively calculated for 
each region of preset size by the R-signal error calculating section 715 
and B-signal error calculating section 716, and a region having the 
highest similarity is derived by the R-signal minimum error searching 
section 717 and B-signal minimum error searching section 718. Next, the 
high-frequency component of the G-signal corresponding to the thus derived 
region is corrected according to the degree of similarity by the R-signal 
high-frequency creating section 719 and B-signal high-frequency creating 
section 720 and the corrected high-frequency component and the original 
low-frequency components of the R-signal and B signal are synthesized in 
the inverse wavelet transform section 722. 
(Operation) 
An input signal is resolved into a plurality of frequency components by 
effecting the frequency-resolving process, for example, wavelet transform 
using a function with local distribution as the basic function. Next, a 
region of similarity in configuration between the low-frequency component 
of a signal of the spectral sensitivity characteristic having a large 
information amount (in this example, a G-signal having the largest number 
of pixels) among an input signal and the low-frequency components of 
signals of other spectral sensitivity characteristics having a less 
information amount (in this example, R- and B-signals) is searched for and 
the high-frequency component of the G-signal in this region is corrected 
according to the degree of similarity so as to create the high-frequency 
components of the R- and B-signals. 
(Effect) 
Since the high-frequency component is created based on the similarity in 
configuration, the high-frequency component can be obtained even when the 
continuity of the signal at the edge portion or the like is degraded or 
the correlation with the G-signal is low, and a satisfactory output image 
for variety of images can be obtained. 
(Construction 8) 
(Corresponding Embodiment) 
The embodiment of this invention corresponds to the fourth embodiment 
described before. The high-frequency emphasizing means in the above 
construction corresponds to the high-frequency emphasizing section 801 
shown in FIG. 15. The error calculating means in the above construction 
corresponds to the G-signal inverse wavelet transform section 802 and 
error calculating section 803 shown in FIG. 15. The control means in the 
above construction corresponds to the controller 115 shown in FIG. 15. 
A preferable example of the signal processing apparatus according to this 
invention is as follows. A G-signal in the G-signal buffer 104 shown n 
FIG. 15 is supplied to the wavelet transform section 105 and 
frequency-resolved into high- and low-frequency components and the 
high-frequency component is multiplied by a coefficient .alpha. for 
emphasis in the high-frequency emphasizing section 801. Next, the 
emphasized high-frequency component and the low-frequency component are 
re-constructed by the G-signal inverse wavelet transform section 802 and 
the rate at which the re-constructed image is set outside a specified 
density range is calculated in the error calculating section 803. Then, 
the coefficient .beta. is controlled by the controller 115 so that the 
error will not exceed a preset threshold value, the emphasized 
high-frequency component is used to create the emphasized high-frequency 
components of the R-signal and B-signal, and three signals of R, G, B are 
re-constructed based on the emphasized high-frequency components and the 
low-frequency components. 
(Operation) 
A signal of the spectral sensitivity characteristic having a large 
information amount (in this example, a G-signal having the largest number 
of pixels) among an input signal is resolved into high- and low-frequency 
components by the frequency-resolving means, for example, wavelet 
transform or DCT transform section. The high-frequency component is 
multiplied by a coefficient .alpha. and emphasized, the emphasized 
high-frequency component is used to re-construct an original signal and 
the coefficient .alpha. is controlled according to the magnitude of error. 
After this, correlation coefficients between the low-frequency component 
of the G-signal and the low-frequency components of signals of other 
spectral sensitivity characteristics having a less information amount (in 
this example, R- and B-signals) are derived and multiplied by the 
emphasized high-frequency component of the G-signal so as to create the 
emphasized high-frequency components of the R- and B-signals. 
(Effect) 
An output signal of high visual quality with enhanced contrast can be 
obtained. Since occurrence of error caused by the emphasizing process is 
previously checked, unnatural emphasis will not tend to occur. Further, 
when the wavelet transform is used as the frequency-resolving means, 
information of neighboring pixels can be commonly used so that a 
reproduced image which is excellent in the continuity and high in the 
image quality can be obtained. When the DCT transform is used as the 
frequency-resolving means, the memory capacity can be reduced. 
(Construction 9) 
(Corresponding Embodiment) 
The embodiment of this invention corresponds to the fifth embodiment 
described before. The reference signal low-frequency emphasizing means in 
the above construction corresponds to the G-signal low-frequency 
emphasizing section 903 shown in FIG. 17. The error calculating means in 
the above construction corresponds to the G-signal inverse wavelet 
transform section 905 and error calculating section 906 shown in FIG. 17. 
The control means in the above construction corresponds to the controller 
115 shown in FIG. 17. The reference signal high-frequency emphasizing 
means in the above construction corresponds to the G-signal high-frequency 
emphasizing section 904 shown in FIG. 17. The dependent signal 
low-frequency emphasizing means in the above construction corresponds to 
the R-signal low-frequency emphasizing section 901 and B-signal 
low-frequency emphasizing section 902 shown in FIG. 17. 
A preferable example of the signal processing apparatus according to this 
invention is as follows. A G-signal in the G-signal buffer 104 shown n 
FIG. 17 is supplied to the wavelet transform section 105 and 
frequency-resolved into high- and low-frequency components. Next, the 
normalized low-frequency component is raised to the .beta.-th power by use 
of a coefficient .beta. in the G-signal low-frequency emphasizing section 
903 to expand the dynamic range and the expanded low-frequency component 
and the high-frequency component are re-constructed in the G-signal 
inverse wavelet transform section 905. Then, the rate at which the 
re-constructed image is set outside a specified density range is 
calculated in the error calculating section 906 and the value of the 
coefficient .beta. is controlled by the controller 115 so that the error 
will not exceed a preset threshold value. Next, the high-frequency 
component is multiplied by a coefficient .gamma. which is derived from the 
coefficient .beta. according to a preset relational equation for each 
region of preset size for the adequately expanded low-frequency component 
and thus the high-frequency component is emphasized. Then, the normalized 
low-frequency components of the R-signal and B signal are raised to the 
.beta.-th power in the R-signal low-frequency emphasizing section 901 and 
B-signal low-frequency emphasizing section 902 and thus the emphasized 
high-frequency components of the R-signal and B-signal are created by use 
of the emphasized high-frequency component of the G-signal. After this, 
three signals of R, G, B are re-constructed based on the emphasized 
high-frequency components and the low-frequency components whose dynamic 
range is expanded. 
(Operation) 
A signal of the spectral sensitivity characteristic having a large 
information amount (in this example, a G-signal having the largest number 
of pixels) among an input signal is resolved into high- and low-frequency 
components by the frequency-resolving means, for example, wavelet 
transform or DCT transform section. The low-frequency component is 
normalized and raised to the .beta.-th power to expand the dynamic range, 
the expanded low-frequency component is used to reconstruct an original 
signal, and the value of the coefficient .beta. is controlled according to 
the magnitude of error. After this, the high-frequency component of the 
G-signal is multiplied by a coefficient .gamma. derived from the 
coefficient .beta. according to a preset relational equation and 
emphasized. Then, correlation coefficients between the low-frequency 
component of the G-signal and the low-frequency components of signals of 
other spectral sensitivity characteristics having a less information 
amount (in this example, R- and B-signals) are derived and multiplied by 
the emphasized high-frequency component of the G-signal so as to create 
the emphasized high-frequency components of the R- and B-signals. Further, 
the coefficient .beta. adequately controlled for the low-frequency 
component of the G-signal is used to expand the dynamic range of the 
low-frequency components of the R- and B-signals. Finally, three signals 
of R, G, B are re-constructed by the emphasized high-frequency components 
and the low-frequency components whose dynamic range is expanded. 
(Effect) 
An output signal of high definition with expanded dynamic range and 
enhanced contrast can be obtained. Since occurrence of error caused by the 
emphasizing process is previously checked to control the parameter and 
control the parameter for emphasizing process, unnatural emphasis will not 
tend to occur. Further, when the wavelet transform is used as the 
frequency-resolving means, information of neighboring pixels can be 
commonly used so that a reproduced image which is excellent in the 
continuity and high in the image quality can be obtained. When the DCT 
transform is used as the frequency-resolving means, the memory capacity 
can be reduced. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details and representative embodiments, shown and 
described herein. Accordingly, various modifications may be made without 
departing from the spirit or scope of the general inventive concept as 
defined by the appended claims and their equivalents.