JPH0441551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color density correction device that is capable of converting original density to recording density in accordance with specified characteristics without deteriorating color balance.

[Conventional technology]

As a conventional color density correction device, for example, as shown in FIG.
(red), G (green), and B (blue) density signals D _R , D _G , and D _B are density-converted so as to draw an S-shaped curve shown by a solid line, and the output densities D′ _R , D′ _G , There is one that obtains D′ _B and changes the tone of the original picture.

Through correction based on the tone curve shown in Figure 1, gradation is created in the medium to high density area, and a large output gradation range is given to the intermediate area (the part extending above the dotted diagonal line in the figure). This makes it possible to obtain recorded images that are easier to view. When duplicating a color original, you may want to make a copy with a different brightness.You can change a high-key original that is too bright to a subdued tone, and brighten a low-key original that is too dark to make it easier to see. You can get a copy. As mentioned above, this operation can be performed by arbitrarily providing a conversion curve between input density and output density as the tone curve shown in Figure 1 or a tone curve that draws an inverted S-shaped curve with gradation in the low density area. I can do it.

[Problem that the invention seeks to solve]

However, according to the conventional color density correction device,
The output density that is not emphasized will be too small compared to other output densities, and less ink will be used when recording.
There is a risk that the color balance will be disrupted compared to the original image. For example, if we compare the output densities D' _R , D' _G , D' _B with the input densities D _R , D _G , D _B in Figure 1, D' _B becomes too small compared to the other densities, resulting in less yellow. It is recorded using ink, resulting in a strong bluish color that is out of balance compared to the original.

[Means and actions for solving problems]

The present invention has been made in view of the above, and in order to convert the original density to a recording density according to specified characteristics without deteriorating the color balance, color separation signals (R, G, B) are used. Logarithmic conversion is performed to obtain density signals (D _R , D _G , D _B ), and an input original density signal (D _IN ) is determined based on the luminance signal, that is, the brightness information of the color original. The present invention provides a color density correction device that performs density correction by determining a density correction amount (ΔD) corresponding to a tone curve and adding this correction amount to each density signal.

〔Example〕

Hereinafter, the color density correction device according to the present invention will be explained in detail.

First, logarithmic transformation in color density correction will be explained.

Color separation signals (R, G,
B) is expressed by the amount of light of each color component, that is, the reflectance for each color component. By the way, the amount of ink is generally expressed as density, and the density and reflectance are expressed as density=-Log10 reflectance. In other words, if reflectance is 1.0, density is 0.0,
A reflectance of 0.1 is expressed as a density of 1.0, and a reflectance of 0.01 is expressed as a density of 2.

For printing, cyan is used to reproduce the original painting.
Magenta and yellow inks are used, and the amount of each ink is the density determined from the reflectance of the red component obtained using a red filter for cyan, and the density determined using a green filter for magenta. yellow is expressed by the density determined from the reflectance of the blue component obtained using a blue filter.

Therefore, as a first approximation, R, G, B
The required amounts of cyan, magenta, and yellow ink can be determined by calculating the density (logarithmic conversion) from the reflectance of the ink.

FIG. 2 shows an embodiment of the present invention, in which an input document density signal (optical density signal ) The contents of the density table 1 that outputs D _IN and the density correction table 2 that calculates the density correction amount ΔD based on the input document density signal D _IN determined by the density table 1 are stored in one ROM, for example. a logarithmic conversion means consisting of logarithmic converters 3a to 3c for logarithmically converting the R, G, and B color separation signals and outputting each of the density signals _DR , _DG , _and DB; Concentration signals D _R output from each of the converters 3a to 3c,
Add the density correction amount ΔD to each of D _G and D _B ,
It is comprised of calculation means consisting of adders 4a to 4c that output each of the corrected color separation signals D' _R , D' _G , and D' _B .

In the above configuration, the operation will be explained with reference to the explanatory diagrams of FIGS. 3a and 3b.

By experimentally obtaining a correspondence table between the brightness signal and the original density in advance and storing it in the density table 1, it is possible to output the input original density signal D _IN corresponding to the brightness signal from the density table 1. can. Density table 1 and density correction table 2
can be configured, for example, by storing both in ROM. From the relationship shown in Figure 3a between the input original density signal D _IN and the output density D _OUT , the density correction amount ΔD is calculated as ΔD = D _OUT − D _IN (1), and this is calculated as Ask for _IN .
A table of density correction amounts as shown in FIG. 3b is stored in the density correction table 2 using ΔD obtained by equation (1), and the density correction amount corresponding to the specified tone curve (conversion curve) is stored. Outputs the density correction amount ΔD corresponding to D _IN from the table. On the other hand, R,
The G and B color separation signals are logarithmically converted by logarithmic converters 3a to 3c, respectively, and density signals D _R , _G , D _B are obtained.
are generated. These concentration signals D _E , D _G , D _B
For each of the following, adders 4a to 4c calculate
Concentration signal corrected by calculating equation (2)
Each of D′ _R , D′ _G , and D′ _B is obtained.

D' _R = D _R + ΔD D' _G = D _G + ΔD ...(2) D' _B D _B + ΔD [Effects of the Invention] As explained above, according to the color density correction device of the present invention, RGB can be logarithmically transformed. and the concentration signal D _R ,
In addition to obtaining D _G and D _B , the input document density signal D _IN is determined based on the brightness information of the color document, the density correction amount ΔD corresponding to the tone curve specified by this D _IN is determined, and this ΔD is Concentration signal D _R , D _G , D _B
Since density correction is performed by adding to each of the above, it is possible to convert the original density into a recorded image according to a specified tone curve without disturbing the color balance. Furthermore, density conversion for a plurality of tone curves can be easily performed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional density conversion process, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIGS. 3a and 3b are explanatory diagrams showing the density conversion process of the present invention. Explanation of symbols, 1... Density table, 2... Density correction table, 3a to 3c... Logarithmic converter, 4
a to 4c...Adder.

Claims (1)

[Claims] 1. In a color density correction device that performs density correction by converting the density of a color original into a recording density according to a specified tone curve, a color density correction device that performs density correction by converting the density of a color original into a recorded density according to a specified tone curve, performs color separation after photoelectrically scanning a color original. A logarithmic conversion means for logarithmically converting a color separation signal to obtain a density signal; and a density correction means for inputting brightness information of a color original and outputting a density correction amount based on the input brightness information of the color original. , a color density correction device comprising a calculation means for calculating a density correction amount obtained by the means and each output signal of the logarithmic conversion means to generate a density-corrected color separation signal. .