JPS60216350A - Automatic correcting method of gradation conversion table - Google Patents

Abstract

PURPOSE:To easily correct a gradation conversion table by correcting a gray reference conversion curve of each color on the basis of each color input signal to a gray finish point on a final output image so that a value close to a gray finish density signal is obtained, and setting the data in the gradation conversion table. CONSTITUTION:An image of an original on an input drum 1 is color-separated by an input head 3 and input density signal ID(B)-ID(R) are outputted through a photoelectric converter 4, logarithmic converter 5, AD converter 6, and equivalent neutral density converting circuit 7. The original 2 is set previously on a digitizer 18 and the position of a specific point which is to be finished in gray on an output image is inputted to a corrector 17 and stored. The corrector 17 reads the ID signal of the specific point and corrects it so that a reference gradation curve approximates to the specific point, and data on it is set in the gradation conversion table 9. The ID signals from the circuit 7 are inputted to an exposure head 14 through a color processing circuit 8, table 9, light quantity conversion table 10, DA converter 11, and modulator 13 to form a color image on a photosensitive material 16 on an output drum 15.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a tone conversion table automatic correction method for finishing a desired point on a final output image to gray in a color image input/output system.

(Technical Background of the Invention and Prior Art) For example, in a color image input/output system using a color scanner and a laser color printer, each color image from a reading device (color scanner in the above example) that separates the color original In and reads the C color is generally used. Gradation processing is applied to each of the inclusion horn density signals, and each color output density signal after this gradation processing is input to an image output device (a laser color printer in the above example).Then, the final output image (i.e. Correctly select specific points that you want to finish in gray on the direct output image (in the case of a system using the above-mentioned laser color printer, etc., or printed matter printed using a halftone screen in a color plate making system, etc. that uses a color ski A7 screen). It is common practice to modify the gradation conversion table in order to achieve the desired result.

In other words, for example, in a color prepress system using a normal color scanner, the scanner input head is manually moved to the above-mentioned specific point on the document on the scanner drum, and the finished mesh of each color (usually yellow, magenta, cyan) is measured at that specific point. Look at the percentage display, and if it is different from the desired dot percentage, move the tone conversion table correction knob to correct the tone conversion table to the desired finish dot percentage. When using a layout scanner, the document is displayed on a graphic display, the specific point is indicated using a light pen, joystick, etc., and the tone conversion table is then corrected in the same manner as described above.

However, the above-mentioned work is performed manually by the operator relying on his or her intuition, resulting in very low work efficiency. In particular, when there are many specific points and the density of each specific point is different, the gradation conversion table must be modified so that the desired halftone percentage can be obtained at each specific point, so the above work takes a long time and requires a lot of skill. This requires a lot of skill.

(Object of the Invention) The present invention has been made in view of the above-mentioned circumstances, and is intended to provide a color image input/output system as described above.
It is an object of the present invention to provide an automatic gradation conversion table correction method that can easily correct the gradation conversion table for finishing a specific point in gray without requiring any skill.

(Structure of the Invention) The method of automatically correcting a gradation conversion table for a gray finish in a color image input/output system of the present invention is a method for automatically correcting a tone conversion table for a gray finish in a color image input/output system. Each dotted horn 11
From the first signal, a constant output density signal for each color is calculated based on the reference gradation conversion curve for each color, and these constant output density signals for each color are input to an arithmetic unit, and a gray generation function is used to convert the specific point into gray for each color. Calculate the gray finish density signal,
The reference gradation conversion curve for each color is corrected so as to indicate a value near the gray finishing density signal for each color input density signal at the specific point, and the data of this corrected gradation conversion curve is used as the gradation for each color input density signal at the specific point. This is set as a conversion table.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows an example of an image input/output system that automatically corrects a gradation conversion table and performs gray finishing according to an embodiment of the present invention. An original 2 set on the circumferential surface of a rotating input drum 1 is color-separated and scanned by an input optical head 3 equipped with a color separation filter, and blue, green, and red image signals 81G are obtained through a photoelectric converter 4. , R are input to the logarithmic conversion circuit 5 (note that the elements following the photoelectric converter 4 are provided in series for each color, but those not particularly relevant to the present invention are not shown divided into series). The image signals B, G, and R are converted into density signals by the logarithmic conversion circuit 5, converted into digital signals by the AD converter 6, and then inputted to the END (equivalent neutral density) conversion circuit 7. Each digital color input density signal ID (B
), 10 (G), and 10 (R).

Input density signals for each of the above colors 10 (B), ID (G), I
After Q (R) undergoes color correction processing and sharpness enhancement processing in the color processing circuit 8, the gradation conversion table 9 (9B, 9G) is set as described below.

9R), each color output density signal 00
(B), OD (G), and OD (R). These color output density signals 0D (B), OD (G)
, 00 (R) is the light amount control signal conversion table 101D
The analog light control signal B' is passed through the A converter 11,
It is converted into G' and R'. These light amount control signals B', G
', R' are exposure light W! These signals B', G', R'
Recording light modulated in accordance with the above is emitted from the exposure head 14, and a color image is formed on the photosensitive material 16 on the rotating output drum 15.

Here, the tone conversion table 9 (9B, 9G, 9
The settings for R) will be explained. Prior to the main scan for outputting a color image as described above, the document 2 is subjected to a relatively rough pre-scan.

Each color input density signal IO(B), ID(G), ID after equivalent neutral density conversion obtained by this pre-scanning
(R) is not sent to the color processing circuit 8 mentioned above, but is sent to the gradation conversion table generation and correction unit 17 (17B).

17G, 17R). This gradation conversion table generator and corrector 17 (178117G).

17R) is each color input density signal ID (B), 10 (G),
10(R), calculates the cumulative density histogram of original 2, etc., and outputs the input density signal using them as judgment criteria.
Calculate a standard gradation conversion curve for each color that appropriately converts the variable magnification signal (this standard gradation conversion curve can be used, for example, in Japanese Patent Application No. 1983-
(It can be calculated by the method of No. 145491, etc.)

However, the data of the reference gradation conversion curve for each color set as described above is used as is in the gradation conversion table 9 (9
B, 9G, 9R), the balance of each color may be disturbed and points that should originally be finished in gray on the output image may become colored.

Hereinafter, a method according to an embodiment of the present invention for automatically correcting the gradation conversion table 9 (9B, 9G, 9R) so as not to cause such a problem will be described in detail.

Before setting the original 2 on the input drum 1, the operator places it on the digitizer 18, and specifies on the digitizer 18 the position of a specific point (N points) that he wants to make gray on the output image of the photosensitive material 16. Then, it is input to the gradation conversion table generation and correction unit 17 (17B, 17G117R) and stored.

Of course, there is a one-to-one correspondence between the coordinates of the digitizer 18 and the input drum 1, and each gradation conversion table generation and correction unit 17 (178, 17G,
17R) is each color input density signal ID (
B)ノ, ID(G), j, ID(R)ノ ()=1.
2,...N) is read.

Then, each gradation conversion table generation and correction unit 17 (17
B, 17G, 17R) are each Shirayuki constant output density signal 0 from the reference gradation conversion curve determined as described above.
Find 0'(B), OD'(G), OD'<R), and z. That is, OD'(B), /: =fa (ID(B)ノ)
OD'(G),=fcr(10(G)ノ)OD'(R
), z = fa (I D (R), j ) fBlf
cT, fR are the reference gradation conversion curves for each color, where the above N=3
, that is, the above relationships when three specific points are specified are shown in FIGS. 2, 3, and 4 for each color, respectively. As mentioned above, each color input density signal ID (B), ID (G)
, ID(R) are equivalent neutral density signals, the gray finishing density signals of each color at a specific point are respectively D(B).
i , D (G) ノ, D (R) i, then D (B
)ノ =D (G)i =D (R), : If so, the specific point will always be finished in gray.

Therefore, D(B)ノ = 1/3 X (OD'(B), -+O
D'(G)・+OD'(R), ) = D (G)i=, D (R)j By performing the calculation using the gray generation function, D(B), :=D
(G) = D(R) (Figures 2.3 and 4 show the above relationship only for the specific point 1.t-1). Of course said input m degree signal and these gray finish! !
Coordinate points (1 (B) no, D (B
), i, ), (ID(G,)ノ.

D(G)), (ID(R)), D(R)() often deviate from the respective reference gradation conversion curves fB1fcT1fR.

Therefore, next, each of the above reference gradation conversion curves fB, fcT1fR
As shown by the broken lines in Figures 2.3 and 4, the coordinate points (ID(B)ノ, D(B)ノ) and (ID(
G)ノ, D(G)ノ), (ID(R)zu.

D(R) ノ) is corrected so that it passes through D(R), and the data of f and - is set to this corrected gradation conversion curve as the gradation conversion table 9 (9B, 9G, 9R), respectively. As a result, each color input density signal ID is
(B), ID (G), and ID (R) are subjected to gradation processing by passing through gradation conversion table 9 (9B, 9G, 9R) so that a gray finish is always achieved at the specific point. It turns out.

The modified gradation conversion curves, r/B, -r5, respectively, are the coordinate points (ID(B)) as described above.

D (B)ノ), (ID (G), /: , D (Gaf
f), (ID(R)ノ, D(R)ノ), but even if it is corrected to pass as close to these coordinate points as possible, it is better to prevent the specific point from being colored. Achieves a finish close to gray.

As a method for correcting the reference gradation conversion curves f, fcr, fR, etc., as described above, a known interpolation smoothing process may be used, and for example, a method such as that shown in Japanese Patent Application No. 1454C10/1988 may also be used. In other words, taking the standard gradation conversion curve t'B as an example, several coordinate points (10(B)
D(B)l) and some coordinate points on this curve fB are two-dimensional discrete data with variations, and the sum of squares of the amount of change in the two-dimensional discrete data before and after the smoothing process is smaller than the reference value. The smoothing process is repeated until the smooth two-dimensional discrete data with little variation is obtained, and the slope of the straight line connecting each adjacent discrete data is calculated to check the magnitude of the low-frequency waviness. The discrete data is collected again until it becomes smaller than the value, and when the waviness becomes smaller than the predetermined value, the smooth two-dimensional discrete data is subjected to interpolation processing such as Lagrange interpolation, quasi-Hermite interpolation, B-spline interpolation, etc. Then, the modified gradation conversion curve f
'B can be obtained.

In addition, the standard tone conversion curves fB, f(:T, f) are obtained by correcting the tone conversion curve t'B, into an r-elephant using the method shown in Japanese Patent Application No. 122164/1982. is also possible.

In the embodiment described above, since each white person) j moisture level signal ID (B), TO (G), 10 (R) is an equivalent neutral density signal, the gray finishing density D(B)l゛=D
(G) A, -D (R) When χ, the specific point goes up by 1 to gray J: It is, but each color input density signal I
D (B), ID (G), 10 (R) are not equivalent neutral concentration signals, ID (B): ID (G): 10 (R) B Φ
When the final output image is gray, each gray finish density signal is converted to D(B)(α
B/(α8+αq+α, ) ) X, TD(G)=
(αke / (α8 + chant + αR)) XTD (R)
, = (α8 / (αB + α9 + αR))
'(R)l.

Furthermore, in the embodiment described above, pre-scanning is performed every time an image is input to determine the reference tone conversion curves fB and fCtlfR, but in this way, there is no need to determine the reference tone conversion curves each time an image is input. In other words, for example, when the quality of the input manuscript is high, OD'(B),, = ID(B) no OD'(G)! -)D(G)ノOD'(R)ノ -ID(R)j (i.e. fB(ID(B)ノ)=ID(B)ノ, f
, (ID(G)ノ)=ID(G)ノ , fR(ID(R
))=ID(R)(R)).

Above, an example in which the present invention is applied to a color image input/output system equipped with a color printer as an image output device has been described. However, the gradation conversion table automatic correction method of the present invention
In a general color plate making system using Color Skillena etc., each color output* controls the halftone percentage of each color plate.
It is also possible to apply Jζ to the gradation conversion of the i signal, thereby correctly finishing a specific point on a printed matter in gray.

(Effects of the Invention) As explained above in detail, according to the method for automatically correcting the tone conversion table of the present invention, the tone conversion table is automatically corrected without the need for troublesome operations. In a short time, it becomes possible to set the gradation conversion table so that desired points on the final output image are correctly finished in gray.

[Brief explanation of the drawing]

FIG. 1 shows an example of an image input/output system to which an embodiment method of the present invention is applied.
The figure is an explanatory diagram for explaining the tone conversion curve correction in the above embodiment method. 2... Original 3... Input optical head 4... Photoelectric converter 9... Gradation conversion table 12... Light source for exposure 13... Modulator 14... Exposure head 16...
Sensitive material 17...Tone conversion curve generation and correction device 18...
- Digitizer ID (B), ID (G), ID (R)...Input density signal OD (B), OD (G), OD (R)...Output density signal OD' (B), OD' (G), OD (R)... Provisional output density signal D (B), D (G), D (R)... Gray finishing density signal f, , fj, fR... Reference gradation conversion curve f',
f', f'...Modified l@key conversion curve CrR 15- Fig. 1

Claims (1)

[Claims] Gradation processing is performed on each inclusion level signal from an image input device that separates and reads a color original based on a gradation conversion table for each color, and each color output 811 signal after this gradation processing is converted into an image. In the color image input/output system that inputs the input to the output device, each package fixed horn density signal is calculated based on the reference gradation conversion curve of each color from the input density signal of each color at a specific point where a gray finish is desired on the final output image. , these packaging constant output density signals are input to an arithmetic unit, and each color gray finishing density signal for finishing the specific point in gray is calculated using a gray generation function, and the reference gradation conversion curve for each color is converted to The horn density signal is corrected so as to indicate a value near the gray finish density signal, and the data of this corrected gradation conversion curve is converted into the data of the above-mentioned 11! ! A method for automatically correcting a gradation conversion table, characterized in that it is set as an isl conversion table.