Color video still image processing system

The present invention is directed to a method of processing a color video signal in which printing color separation data is formed from a color video signal and a printing original plate is made by using the printing color separation data. This color video signal processing method is comprised of the steps of reading out a reference color test chart by a printing scanner and producing scanner four color separation data of the reference color test chart by the printing scanner, taking a picture of the reference color test chart radiated by a standard light source by a video camera, producing camera four color separation data from a color video signal output from the video camera, comparing the scanner four color separation data with the camera four color separation data and allowing a level difference therebetween to be stored in a memory as correcting data which is used to correct the camera four color separation data, and correcting the four color separation data by the correcting data stored in the memory to thereby produce four color separation data when the four color separation data for making the printing original plate are generated from a color video signal of the video camera. Therefore, a printing original plate having satisfactory color reproducibility can be produced by utilizing the video camera.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to video signal processors for a 
printer and, more particularly is directed to a color video still image 
processing system in which printing color separation data is formed from a 
color video still image. 
2. Description of the Related Art 
As is conventional, a color printing original plate is made by using a 
predetermined one field or one frame of a video signal (i.e., still image 
signal) generated from a video camera or an electronic still camera. In 
this case, the video signal from the video camera or from the electronic 
still camera is converted into digital data of three primary colors R 
(red), G (green) and B (blue). The digital data R, G and B are converted 
into reflection density (i.e.,--log conversion), thereby being produced as 
color separation data of four colors of three primary colors (cyan C, 
magenta M, yellow Y) of subtractive process and black K. Data of black K 
is determined by the minimum values of cyan C, magenta M and yellow Y. 
Then, original plates of four colors of cyan C, magenta M, yellow Y and 
black K are made by using respective color data of color separation data 
of four colors and one color still image is printed by using the original 
plates of four colors. The color still image is printed by using the color 
separation data of four colors in exactly the same way such that a color 
image taken by a halide film is printed. 
The color image printed via the original plates made by the video signal is 
unsatisfactory as compared with the color image printed via the original 
plate made by the halide film. That is, the video still image has poor hue 
and color saturation as compared with those of the color still image of 
the halide film so that the video still image has poor color 
reproducibility. As a consequence, the color video still image becomes 
unsatisfactory as compared of the color still image of the halide film. To 
be more concrete, the color saturation of the color video still image is 
about 60% of that of the halide film still image so that the color image 
is hardly printed by using the original plate made by the video signal in 
the prior art. If the user insists that the color video still image is 
printed by using the original plate made from the video signal, those who 
are engaged in making the original plate must adjust hue and color 
saturation with reference to four color separation data. That is, this 
color adjustment is a manual labor dependent on the visual sense of those 
skilled in the art. 
OBJECTS AND SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide an improved 
color video still image processing system in which the aforesaid 
shortcomings and disadvantages of the prior art can be eliminated. 
More specifically, it is an object of the present invention to provide a 
color video still image processing system in which a color image obtained 
from a video signal of a video camera can demonstrate color reproduction 
similar to that of a color image printed by using a printing scanner. 
Another object of the present invention is to provide a color video still 
image processing system by which video apparatus such as an electronic 
still camera or the like can be utilized to produce a printing original 
plate. 
A further object of the present invention is to provide a color video still 
image processing system by which a printing original plate can be 
manufactured with ease. 
As a first aspect of the present invention, a method of processing a color 
video signal in which printing color separation data is formed from a 
color video signal and a printing original plate is made by using the 
printing color separation data is comprised of the steps of reading out a 
reference color test chart by a printing scanner and producing scanner 
four color separation data of the reference color test chart by the 
printing scanner, taking a picture of the reference color test chart 
radiated by a standard light source by a video camera, producing camera 
four color separation data from a color video signal output from the video 
camera, comparing the scanner four color separation data with the camera 
four color separation data and allowing a level difference therebetween to 
be stored in a memory as correcting data which is used to correct the 
camera four color separation data, and correcting the four color 
separation data by the correcting data stored in the memory to thereby 
produce four color separation data when the four color separation data for 
making the printing original plate are generated from a color video signal 
of the video camera. Therefore, a printing original plate having 
satisfactory color reproduction property can be produced by utilizing the 
video camera. 
In accordance with a second aspect of the present invention, a system for 
processing a color video signal in which printing color separation data is 
formed from a color video signal and a printing original plate is made by 
using the printing color separation data is comprised of a printing 
scanner for reading out a reference color test chart and outputting four 
color separation data which are used to make a printing original plate, a 
video camera for taking a picture of the reference color test chart 
radiated by a standard light source to thereby output a color video 
signal, a four color separation data generating circuit for generating 
four color separation data from the color video signal output from the 
video camera, a comparing circuit for comparing the four color separation 
data from the printing scanner with the four color separation data 
generated from the color video signal, and a correcting data generating 
circuit for generating correcting data on the basis of a difference 
information obtained from the comparing circuit, wherein the color video 
signal from the color video camera is corrected by using the correcting 
data to thereby produce four-color color separation data when the four 
color separation data for making the printing original plate are generated 
from a color video signal of the video camera.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the present invention will now be described with reference 
to the drawings. 
FIG. 1 of the accompanying drawings shows the entire arrangement of the 
color video still image processing system according to an embodiment of 
the present invention. In FIG. 1, reference numeral 1 depicts a video 
camera and 2 an electronic still camera. The video camera 1 can 
continuously take a picture of an object, record a video signal thereof on 
a video tape and reproduce a recorded video signal from the video tape 
continuously. The electronic still camera 2 can record one field of or one 
frame of a video signal (still image signal) of an object taken at a 
predetermined timing on a magnetic disk and reproduce a recorded video 
signal from the magnetic disk. The video signal recorded and reproduced in 
that case is an analog composite video signal according to the broadcast 
standards such as the NTSC system or the like. When a printing original 
plate is made by using one predetermined field or frame of the video 
signal taken and recorded on the video tape by the video camera 1, that 
one field or frame is reproduced from the video tape and then supplied to 
an image data converting apparatus 10. Also, when a printing original 
plate is made by using one predetermined field or frame of the video 
signal taken and recorded on the magnetic disk by the electronic still 
camera 2, that one field or frame is reproduced from the magnetic disk and 
then supplied to the image data converting apparatus 10. The video camera 
1 and the electronic still camera 2 will hereinafter be generally referred 
to as a video camera for simplicity. 
In the image data converting apparatus 10, one field or one frame of the 
analog composite video signal from the video camera is supplied to an 
analog-to-digital (A/D) converter 11, in which it is converted into 
digital video signals of three primary colors (R, G, B). The digital video 
signals of three primary colors R, G and B are supplied to and converted 
into a reflection density by a four color separation data converter 12 and 
are thereby produced as data (four color separation data) of four colors 
of three primary colors (cyan C, magenta M and yellow Y) according to the 
subtractive process and black K. In this embodiment, when the digital 
video signals of three primary colors R, G and B are converted into the 
four color separation data C, M, Y and K, the four color separation data 
C, M, Y and K are corrected on the basis of correcting data stored in a 
conversion table 15 which will be described later. 
Then, the four color separation data C, M, Y and K thus produced by the 
four color separation data converter 12 are supplied to an original plate 
producing apparatus 3 as an output of the image data converting apparatus 
10 and the original plate producing apparatus 3 produces original plates 
of four colors (four original plates) of cyan C, magenta M, yellow Y and 
black K by utilizing respective color data supplied thereto. The four 
color original plates thus made are utilized to print a color still image 
by a predetermined printing apparatus. 
An arrangement in which the four color separation data are corrected by 
utilizing the conversion table 15 in the image data converting apparatus 
10 will be described below. 
The correcting data stored in the conversion table 15 are obtained by 
utilizing a transparent-type color test chart 4. More specifically, the 
color test chart 4 on which a plurality of colors having various gray 
levels are provided is illuminated by the radiation of a standard lighting 
apparatus 5 at color temperature of 5000.degree. K. and a picture of the 
transparent type color test chart 4 thus radiated is taken by the video 
camera (video camera 1 or electronic still camera 2) utilized when the 
original plate is made. Then, one field or one frame of video signal, 
which results from shooting the color test chart 4 by the video camera, is 
supplied to the image data converting apparatus 10, in which it is 
converted into the digital video signals of three primary color signals R, 
G and B by the A/D converter 11 and then converted into the four color 
separation data C, M, Y and K by the four color separation data converter 
12. When the digital video signals of three primary colors R, G and B are 
converted into the four color separation data, at this time the four color 
separation data are not corrected by the correcting data stored in the 
conversion table 15. 
Then, the four color separation data C, M, Y and K based on the still image 
of the color test chart 4 are supplied to a comparing means 13. 
The same color test chart 4 is, on the other hand, read by a printing 
scanner 6 that is utilized to make the ordinary printing original plate. 
Still image data on the color test chart 4 read by the printing scanner 6 
is supplied to a four color separation data detector 7, in which it is 
converted into electrical four color separation data C, M, Y and K. The 
four color separation data C, M, Y and K from the detector 7 are supplied 
to the comparing means 13 in the image data converting apparatus 10. 
The comparing means 13 compares the four color separation data C, M, Y, K 
obtained by the video camera with the four color separation data C, M, Y, 
K obtained by the read-out by the printing scanner 6 to thereby detect 
gray level difference of respective colors at respective points 
(respective pixels). The gray level difference data thus detected by the 
comparing means 13 is supplied to a correcting value determining means 14, 
and the gray level difference data is stored (memorized) in the conversion 
table 15 as the correcting value under the control of the correcting value 
determining means 14. 
The conversion table 15 includes a memory (not shown) which stores the 
correcting value supplied from the correcting value determining means 14. 
The conversion table 15 is supplied with the four color separation data C, 
M, Y and K converted by the four color separation data converter 12 and 
reads out and supplies the converter 12 with correcting values 
corresponding to the four-color separation data C, M, Y and K supplied 
from the converter 12. At that time, if proper correcting values 
corresponding to the four color separation data C, M, Y, K supplied from 
the converter 12 are not stored in the conversion table 15, then data of 
other gray level than those stored therein are interpolated within the 
conversion table 15 to generate correcting values, which are then fed to 
the converter 12. Since the gray level of black K is determined by the 
minimum values of data of other colors as described above, a correcting 
value of the black K need not be stored in the conversion table 15. 
Since the image data converting apparatus 10 is constructed as described 
above, the color printing original plates of four colors of cyan C, 
magenta M, yellow Y and black K are satisfactorily made from the video 
signal of the video camera by the original plate producing apparatus 3. 
More specifically, let it be assumed that, when the video signal from the 
video camera, for example, is converted into the four color separation 
data C, M, Y and K by the four color separation converter 12 within the 
image data converting apparatus 10, gray levels of the four-color color 
separation data C, M, Y and K at a certain portion before being corrected 
are 5% for cyan C, 30% for magenta M, 35% for yellow Y and 5% for black K, 
respectively, as shown in FIG. 2. At that time, if correcting values 
corresponding to the four color separation data C, M, Y and K of the 
above-mentioned respective gray levels are read out from the conversion 
table 15 and these correcting values are adapted to increase gray levels 
of cyan C, yellow Y and black K by 5%, 15% and 5%, respectively, then the 
respective gray levels are increased by the correction in the four color 
separation data converter 12 as shown by broken lines in FIG. 2. Then, 
four color separation data thus corrected are supplied to the original 
plate producing apparatus 3. The correcting values stored in the 
conversion table 15 are provided on the basis of the four-color color 
separation data similar to those read out from the color test chart 4 by 
the scanner 6 so that, when the four color separation data C, M, Y and K 
of the video signal supplied from the video camera are set in the 
conditions shown in FIG. 2, then gray levels added with the correcting 
values as shown in FIG. 3 become similar four color separation data read 
out by the printing scanner 6. Accordingly, by correcting the gray levels 
to those illustrated in FIG. 3, the four color separation data from the 
video camera are allowed to have gray levels similar to those of the four 
color separation data read out from the color test chart 4 by the printing 
scanner 6. Therefore, a color image original plate whose quality (color 
reproducibility) is the same as that of color image provided when the 
color separation data are read out by the printing scanner 6, which can 
compensate for a low color saturation of a video signal utilized in the 
ordinary video camera. In this case, since this correcting work is carried 
out automatically, those who are engaged in making the original plate need 
not adjust the colors in a manual fashion while checking colored 
conditions of respective colors. Thus, a printing original plate for 
satisfactory colors can be produced with ease and a uniform color 
adjustment can be carried out constantly unlike the manual color 
adjustment. 
Incidentally, since the read-out work for reading out color separation data 
from the color test chart 4 by the printing scanner 6 is carried out once 
in the first stage, the printing scanner 6 and the four color separation 
data detector 7 are required only in the initialization. Therefore, in the 
succeeding stages during which the original plate is made, it is 
sufficient that the image data converting apparatus 10 is provided between 
the video signal source such as the video camera or the like and the 
original plate producing apparatus 3. Thus, the original plate can be made 
readily with ease. 
According to the present invention, since the color image printed by means 
of the original plate made by utilizing the video camera can be printed 
with a color reproducibility similar to that of the color image printed by 
means of the original plate made in the ordinary printing process 
utilizing the printing scanner or the like, instead of the halide film 
camera, the video apparatus such as the electronic still camera or the 
like can be utilized to produce the printing original plate and therefore 
the printing original plate can be produced with ease. 
Having described the preferred embodiment of the invention with reference 
to the accompanying drawings, it is to be understood that the invention is 
not limited to that precise embodiment and that various changes and 
modifications thereof could be effected by one skilled in the art without 
departing from the spirit or scope of the invention as defined in the 
appended claims.