JPS62101179A - Picture information processor - Google Patents

Abstract

PURPOSE:To reduce the chrominance signal difference between black and the other color patches by discriminating whether inputted color picture information is black or not and correcting each chrominance signal in accordance with the discrimination result. CONSTITUTION:The reflected light from an original 2 irradiated by a light source 1 passes a red, green, and blue color separation filters 3, 4, and 5 and is made incident on CCDs 6-8, and photoelectric converted voltage signals are digitized by an A/D converter 9 to obtain digital luminance signals r', g', and b'. Light intensity signals are converted to density signals and CMY signals 16 indicating the quantities of coloring matters of cyan C, magenta M, and yellow Y are obtained by a LOG converter 10. Black is detected by a black detecting circuit 11, and an output signal 17 is supplied to a correcting circuit 12 to switch the conversion coefficient to a value for black originals and a value for the other colors. Thus, the chrominance signal difference between black originals and complementary color originals is eliminated to reproduce colors well.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides for example C-
The present invention relates to an image information processing device that enables correction of color signals from photoelectric conversion elements such as CD line sensors.

[Prior Art J Conventionally, three color filters of red (r), green (g), and blue (b) (hereinafter abbreviated as RGB filters) have been used as color separation filters for color images, and the light obtained through these filters has been used as a color separation filter for color images. C
It is common to convert this into a color signal using a photoelectric conversion element such as an OD. The spectral characteristics of such a photoelectric conversion element with a color separation layer filter are as follows.

As shown in Figure 2, the visible range (approximately 300 nm to 700 nm)
Methods for determining the spectral properties of these typical filters are often designed with overlap to sufficiently cover the range (nm).

There is a method for determining the RGB spectral sensitivity of the NTSC system for color televisions.

When an image signal separated by color using a color separation filter having the characteristics described above is applied to a color printer that reproduces colors by subtractive color mixing, such as an inkjet printer or a laser beam printer, the following problems occur.

Generally, in subtractive color mixing, yellow (Y), cyan (C), and magenta (M) pigments are printed in layers to produce green from yellow and cyan, blue from cyan and magenta, and red from yellow and magenta. Also, black and gray are reproduced by printing equal amounts of three pigments: yellow, cyan, and magenta.Therefore, when reading a black original with the same halftone area ratio, Basically, the level of the color signal and the level of the color signal when reading a monochromatic yellow, magenta, or cyan original must be the same.

However, when the color separation filter is used, a phenomenon occurs in which the magnitude of the color signal differs when a black original is read and a single-color original of yellow, cyan, or magenta is read, depending on the shape of the spectral characteristics of the filter.

FIG. 3 shows the spectral transmittance of a green filter, the spectral reflectance of a black original with the same printing dot area ratio, and the spectral reflectance of a single-color magenta original, which is the complementary color of green, superimposed. The color signal g obtained through the green filter is calculated using equation (1), and is in the form of an integral of the product of the reflectance of the filter and the original.

・φ...Fist...(1) Here, K is a constant, entering 1. Input 2 is the integral range of wavelength, S(
(on) is the light source, 10,000 (on) is the spectral reflectance of the original, Fg (on)
is the spectral characteristic of the green filter, and D (in) is the spectral characteristic of the C00 etc. photoelectric conversion element.

The ratio g/gw of this g signal and the signal gw of the reference white board is calculated using the formula (
The value converted as in 2) becomes a value proportional to the amount of magenta dye for the original in the printer, M=-1og (g/gw) (2) I.

therefore,! As shown in Figure 3, the product of the green filter and the magenta original is also larger than the product of the green filter and the black original, so the magenta color when reading a printed original with the same point area ratio is The dye signal for a monochromatic magenta original tends to be smaller than that for a black original.

FIG. 4(a) shows the relationship between the dot area ratio output signal values before correction.

For this problem, each r before LOG conversion.

Generally, a method is used in which the color signals are corrected using a color separation circuit (not shown) through a primary matrix as shown in equation (3) for each of the g and b signals, but the color separation circuit becomes complicated. Another problem was that it was difficult to adjust the coefficients.

Here, m11 to m33 are coefficients.

[Problems to be Solved by the Invention] The present invention identifies the black component in a document and switches the γ conversion coefficients with those of other colors, thereby reducing the color signal difference between black and other color patches, and An object of the present invention is to provide an image information processing device that enables color reproduction.

[Means for Solving the Problem] As a means for solving this problem, for example, the image information processing apparatus of the embodiment shown in FIG. 12.

[Function] In the configuration shown in FIG. 1, the black detection circuit 11 has CMY
A black signal is detected from the signals and a signal 17 is output. The γ correction circuit 12 adjusts γ according to the signal 17 from the black detection circuit 11.
The conversion is corrected to make the output values of the black signal and other dye signals approximately equal for the same dot area ratio.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

[Description of Image Information Processing Apparatus (FIG. 1) FIG. 1 is a block diagram of an image information processing apparatus according to an embodiment of the present invention.

The reflected light from the document 2 irradiated by the light source 1 is incident on C0D6 to C08 through color separation filters red (r) 3, green (g) 4, and blue (b) 5, respectively. The voltage signals photoelectrically converted by the CCDs 6 to 8 are each digitized by the A/D converter 9, and digital luminance signals r/, r,
It becomes bt. These signals are converted from light intensity signals into density signals by a LOG converter 10 composed of a ROM, etc., and are also converted into cyan (C), magenta CM),
Signals CMY signals 16 representing the amount of yellow (Y) dye are obtained.

The CMY signals 16 are input to a black detection circuit 11, which will be described later, to perform black detection, and the output signal 17 is supplied to a γ correction circuit 12, which will be described later. The γ correction circuit 12 switches between the γ conversion coefficient for black originals and the conversion coefficient for other colors.

The γ coefficient of the γ correction circuit in this embodiment is the input data C
This is a coefficient that multiplies the MY signal 16 by a certain constant.If the coefficient is 1 for a black original, it is approximately 1 to 1 for other color signals.
Takes a value between 3. The γ coefficient is determined using the black signal of a black original when halftone surface 8 is 100% in the printing original, and the color original of each complementary color (cyan original for the γ signal, magenta for the g signal). The coefficients are selected so that the CMY signals, which are proportional to the amount of dye in the original (for the b signal, the yellow original) match.

Figure 4(b) shows the relationship between the halftone area ratio and the output signal after correction.Compared to Figure 4(a) before correction, the black original and magenta monochromatic dye signals are almost equal. You can see that

A signal CI M whose signal level has been adjusted by γ correction,
yl is supplied to the color correction circuit 13. Here, the color turbidity in color separation is corrected, and the color turbidity component of the dye used in the printer 15 is corrected. Generally, the formula (4
) is often used.

Here, J1 to a3B are coefficients.

The signals C2, M2 . Y2 is binarized by the binarization circuit 14. This binarization circuit 14 generally uses a dither circuit to reproduce halftones. The binary code C3, M3°Y3 becomes an on/off signal for the printer 15, which is an inkjet printer, and a halftone image of each pigment is formed by this image signal, and the reproduced image is converted into a full color image according to color mixing theory. Become.

[Description of Black Detection Circuit (FIG. 5)] FIG. 885 shows an example of the black detection circuit 11 in a block diagram.

Each color signal of the CMY signal 16 from the LOG converter 10 is
The maximum density (Y, M, C) and minimum density (Y, M, C) are supplied to the maximum detection circuit 50 and the minimum detection circuit 51, respectively.
seek. This difference is obtained by a subtractor 52 and compared with a threshold value 54 by a comparator 53, and if it is smaller than the threshold value 54, the document is identified as a black document. On the contrary, the concentration difference is the threshold (Iiii
If the color is larger than 54, it is identified as a different color original, and a signal 17 corresponding to each color is output.

[Description of γ correction circuit (Fig. 6)] FIG. 6 is a detailed block diagram of the γ correction circuit 12.

The signal 17 from the black detection circuit causes the γ conversion ROM 60 to
By switching the address 62, the γ coefficients for the black original and the other color originals are switched, and the densities of the black original and the other color originals are made almost the same.

In this embodiment, black original detection is performed using color signals Y, M, and C.
Although we have explained that the difference between the maximum and minimum density values of the three signals is calculated, it is also possible to calculate the ratio between the minimum value and the maximum value, and to identify a black original when the ratio is close to 1. Also good.

[Effects of the Invention] As described above, according to the present invention, the colors of the black original and the complementary color original are adjusted by identifying the black component in the original and switching the γ correction coefficient between the black component and other colors. It has become possible to eliminate signal differences and perform good color reproduction.

[Brief explanation of drawings]

Figure 1 is a block diagram of an image information processing device that is an embodiment of the present invention. Figure 2 is a diagram showing the spectral characteristics of a general RGB filter. Figure 3 is a diagram showing the spectral sensitivity of a COD with a green filter and a magenta original. , a diagram showing the spectral characteristics of a black original, Figure 4(a) is a diagram showing the relationship between the output and the halftone area ratio of the read original of a black original and a magenta original after LOG conversion, Figure 4(b) 5 is a diagram showing the relationship between the output and the dot area ratio of a black original and a magenta original after correction by the γ correction circuit, and FIG. 5 is a block diagram of the black original detection circuit. FIG. 6 is a block diagram of the γ correction circuit. In the figure, 2... original, 3... red (r) filter, 4...
...Green (g) filter, 5...W (b) filter, 6
~B...CCD, 9...A/D converter, 10...
LOG converter, 11... Black detection circuit, 12... γ correction circuit, 13... Color correction circuit, 14... Binarization circuit, 15... Printer, 50... Maximum detection circuit , 51
. . . Minimum detection circuit, 52 . . . Subtractor, 53 . . . Comparator, 60 to 62 . Patent applicant: Canon Co., Ltd. Figure 4 (O) 4 @ (b) Hihara's jealousy, zozakubei ('/,)

Claims (3)

[Claims] (1) Image information characterized by comprising a determining means for inputting color image information and determining whether the color image information is black, and a correcting means for correcting each pigment signal in accordance with the determination result. Processing equipment. (2) The image information processing apparatus according to claim 1, wherein the determining means determines black based on density signals of three colors: yellow, magenta, and cyan. (3) The image information processing device according to claim 1 or 2, characterized in that the correction means performs γ correction to make the γ conversion coefficient of the non-black dye signal larger than that of the black signal. .