JP3200093B2 - Color image processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus for converting color image data.

[0002]

2. Description of the Related Art Conventionally, for example, as a color expression method of a color image reading apparatus, the spectral sensitivity of a three-color separation system is represented by R, R in FIG.
The colors of the R, G, and B signals determined by the television standards shown in G and B have been adopted. This has been determined in accordance with the coloring characteristics of R, G, and B fluorescent materials of a cathode ray tube as a light emitting material used in a television receiver. Also, CIE
(International Commission on Illumination) Method of using spectral sensitivity of XYZ color system, Y (yellow), M (magenta), C (cyan) of inks and coloring agents used in originals (transmission or reflection)
A three-color separation system having a spectral sensitivity of a narrow band (narrow bandwidth) has been used to measure the density of.

[0003]

However, in the above-mentioned conventional example, as shown in FIG. 6, the x mark indicating the chromaticity value of each of R, G, B is inside the spectrum locus, FIG. 7 shows that the spectral sensitivity characteristics of a three-color separation system used in a color image reading apparatus for generating R, G, and B signals satisfying the values need to have a theoretically negative region. . However, in reality, it is impossible to realize a spectral sensitivity characteristic having a negative region, so that it is approximated by spectral correction as shown in FIG. 8 (a negative region is removed, or a correction is made as indicated by a dotted line), Alternatively, correction is performed by primary conversion. However, the color characteristics of the target document or object are read with considerable errors. Even if it is read correctly, the chromaticity value of each color of the above-mentioned fluorescent material is made as shown by the color of the mark x in FIG.
Colors outside the square have negative signal values. This has a problem that it is difficult to handle the signal, and if a negative signal is set to 0, the color is not represented.

In the case of using the CIE XYZ color system color expression method, since the color is expressed on the x and y axes of the chromaticity diagram of FIG. 6, the read signal value is not negative. The spectral sensitivity for realizing such an x, y, z color system is shown in FIG.
0 (normalized by the maximum sensitivity value). As is apparent from the figure, since the spectral sensitivity of y for producing the Y signal has a wide half-value width, there is a problem that filters having various spectral transmittances must be combined in order to satisfy the spectral sensitivity. Also, since the digitized XYZ signal values cover a wide area on the chromaticity diagram, the signal values are overwritten even for colors that do not exist,
Valid data is only about 65% of the total data that can be quantized (FIG. 14). FIG. 14 shows the chromaticity when the XYZ signals are quantized to 6 levels. Then you can see that there are quite a few points outside the spectrum locus,
Efficiency is low in terms of effective use of signal values.

In a chromaticity meter using a narrow band spectral filter used in a printing apparatus, an object such as a color photograph is used unless the spectral characteristics of ink or the like used in an original document are known in advance. There is a problem that color separation characteristics are not good for objects.

An object of the present invention is to provide a color image processing apparatus which solves such a problem.

[0007]

In order to achieve the above-mentioned object, a color image processing apparatus according to the present invention comprises: input means for inputting color image data composed of red, green and blue components; Color image data
In the xy chromaticity diagram, red (0.734, 0.26) which is a vertex of a triangle substantially circumscribing the spectrum locus.
5), green (−0.086, 1.086), red (0.095, −0.031) as a primary stimulus,
Converting means for converting into color image data composed of green and blue components.

[0008]

Further, the color image processing apparatus of the present invention is a CIE.
Supply means for supplying color data expressed by a combination of original stimulus data indicated by vertices of a triangle substantially circumscribing the spectrum locus of the chromaticity diagram, and expressing the color data supplied by the supply means in another color Conversion means for converting into color data represented by the method.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Techniques Related to the Present Invention) In the color expression method, three positions of x in FIG. 2 are used as a primary stimulus, for example, in (x, y) coordinates (1.07433, 0.42295) (0.01179, 0.86921) (-0.02358, -0.08679). Thus, the triangle connecting these three points is x
Spectrum locus of y chromaticity diagram, around 505 nm and 525
It is almost in contact with about nm and almost overlaps with a pure purple locus connecting 380 nm and 780 nm.

The spectral sensitivity characteristic for generating the original stimulus is as shown in FIG. 3 (normalized by the maximum sensitivity value).

In FIG. 3, the spectral sensitivity of red has a small peak in the blue region, and the wavelength having the maximum value of the peak is the maximum sensitivity wavelength (around 445 nm) of the spectral sensitivity of blue. And almost match. Also,
In the spectral sensitivity of blue, there is a small peak in the red region, and the wavelength at which the peak of this sensitivity is maximum almost coincides with the maximum sensitivity wavelength (around 600 nm) of the spectral sensitivity of red.

From this, the blue region of the red spectral sensitivity can be substituted by the blue spectral sensitivity, and the red region of the blue spectral sensitivity can be substituted by the red spectral sensitivity. That is, the correction can be performed by processing the RGB signals output from the color sensor. Therefore, if the blue region of the red spectral sensitivity is removed and the red region of the blue spectral sensitivity is removed, the result is as shown in FIG.

The spectral sensitivity shown in FIG. 1 is narrower than the spectral characteristic shown in FIG. 8, so that the characteristics can be relatively easily formed with a dye, a pigment, an infrared cut filter of glass, or the like.

Next, FIG. 4 shows a color image reading apparatus having the imaging characteristic of the spectral sensitivity shown in FIG. In FIG.
1 is a document, 2 is a platen glass, 3 is a document illuminating device, 4 is a short focus lens array, 5 is a linear color solid-state image sensor array having the above-mentioned spectral characteristics of FIG. Scan electrically. Reference numeral 6 denotes an optical unit. The optical unit scans the document in the direction of the arrow. The document illuminating device 3 illuminates the document 1 placed on the platen glass 2, and the light reflected from the document is focused on the color solid-state imaging device array 5 by the short-focus lens array 4. The formed original image is converted into RGB images by the color solid-state image sensor array 5.
Is converted into an electric signal.

FIG. 5 is a circuit block diagram of one embodiment for processing signals generated from the color solid-state image sensor array 5 shown in FIG. The RGB image signal is converted from an analog signal to a digital signal by an A / D converter 7, and a shading circuit 8 corrects a variation in sensitivity of the color solid-state imaging device array 5 and a variation in illuminance of the original illumination device 3. Next, calculation is performed by a 3 × 3 matrix calculator 9. The conversion formula is shown below. (In this case, after passing through the shading circuit 8, when R = G = B = 1, R ′ =
It is normalized so that G ′ = B ′ = 1. )

[0017]

[Outside 1] By this calculation, the RGB image signals can be converted into the same RGB signals as if they were read with the spectral sensitivity of FIG. (Embodiment) Instead of, the coefficient of the matrix calculator 9 is calculated as

[0018]

[Outside 2] Then, it can be converted into a source stimulus as shown in the lower diagram of FIG. The color expression method of FIG. 13 is more effective than the XYZ color system.
The signal can be used effectively. FIG. 16 shows such a state.
The valid data can be increased from the XYZ color system up to about 89% of all data that can be quantized. In addition, due to the nature of digital data, R = G, B = 0, G =
Chromaticity points where B, R = 0, R = G, and B = 0 Since (a), (b), and (c) in FIG. 15 have a relatively large amount of data, these chromaticity points correspond to the spectrum locus or pure purple. It is advantageous from the viewpoint of effective use of data if it is located on the trajectory. In the case of FIG. 15, it is on a pure purple locus around 49 nm and around 573 nm. Although the basic stimulus in FIG. 15 has an equal energy spectrum, the positions of (a), (b), and (c) are slightly shifted for other basic stimuli (for example, D ₆₅ and C light sources). It should be near the position in the figure below.

[0019]

[0020] The illumination light source used in the reader of Figure 4 described above, the basic stimulus, such as the observation light source may be an equal energy spectrum, normalized light source at the International Commission on Illumination CIE, for example, even D ₆₅ C It may be D ₅₀ in the light source.

The spectral sensitivity of the filter may be a spectral sensitivity in consideration of the spectral energy distribution of a light source (for example, _D65 or C light source). For this purpose, for example, a characteristic such as a multiplying function obtained by multiplying the spectral energy distribution of the light source by the wavelength and the spectral sensitivity of FIG. 1 described above is changed to the overall spectral sensitivity including the illumination light source of the reading device. I just need.
This is because the may be matched to the overall spectral sensitivity weight value function, the illumination source may other than D ₆₅ and C source.

Further, R obtained by reading with the spectral characteristics of FIG.
The GB signal can be converted into an NTSC or HDTV color signal by a matrix operation. In this case, a matrix for converting the above-mentioned original stimulus and the above-mentioned basic stimulus (for example, an equal energy spectrum) into an NTSC or HDTV original stimulus and a basic stimulus may be used. This is Figure 5
Is performed by the converter 10.

In the case of NTSC (HDTV is omitted because the matrix coefficient can be obtained in the same way except that the primary stimulus and the basic stimulus are different)

[0024]

[Outside 3] The converter 10 can be used for the matrix operation 9 in FIG. 5, but the matrix is multiplied by the above stimulus value conversion matrix,

[0025]

[Outside 4] The above matrix may be used as the coefficient of the matrix operation in FIG.

In consideration of the gamma characteristic of the monitor, it is sufficient to multiply by 0.45.

The conversion of the CIE XYZ stimulus values can also be determined by the above stimulus value conversion matrix. Further, if XYZ is obtained, both xyY and L ^* A ^* B ^* can be obtained by performing the processing according to the mathematical formula in the converter 10 of FIG.

FIG. 11 shows another example of the image processing apparatus of the present invention. 11, the same elements as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 11, reference numeral 100 denotes the CR of this embodiment.
A complementary color converter 110 converts a GB signal into Y, M, and C (yellow, magenta, and cyan) signals of complementary colors.
A masking circuit UCR for correcting a signal according to a turbid component of a color material used in the color printer 120, removing undercolor, and inking. Reference numeral 120 denotes the above-described color printer, which may be an electrophotographic system, an inkjet system, or another system.

According to the embodiment shown in FIG. 11, since accurate color data is given, the color reproducibility of a color printer can be improved.

In the above embodiment, the image reading apparatus of the flat bed shown in FIG. 4 is taken as an example, but it goes without saying that the present invention can be applied to an image input apparatus such as a video camera or a still video camera.

In the above-described embodiment, the color is expressed by the combination of the original stimulus data indicating the vertices of the triangle shown in FIG. 2. However, the present invention is not limited to this embodiment and is shown in FIGS. A color may be represented by a combination of original stimulus data indicating the vertices of a triangle. The chromaticity diagram is CI
Although the color matching function of the 2-degree visual field of E is used, it may be a 10-degree visual field, an RGB color-matching function of Guild or Wright, or a chromaticity diagram obtained from other color-matching functions.

FIGS. 12A and 13A are diagrams showing spectral sensitivity characteristics for obtaining the original stimuli of FIGS. 12B and 13B, respectively.

As described above, according to the present embodiment, the image pickup characteristic is such that the original stimulus is provided at the apex of the triangle in contact with the spectrum locus of the chromaticity diagram and the spectral sensitivity is realized, and the signal value is effectively set. By using a usable color expression method, there is an effect that the color reproduction is improved, the signal value can be used efficiently, and the signal value does not become negative.

[0035]

According to the present invention, the input color image data is converted into red (0.734, vertices) of a triangle substantially circumscribing the spectrum locus in the xy chromaticity diagram.
0.265), green (-0.086, 1.08)
6), since it is converted into color image data composed of red, green, and blue components with blue (0.095, -0.031) as a primary stimulus, signal values can be used efficiently; The signal value can be prevented from becoming negative. Therefore, color reproducibility can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the spectral sensitivity of one embodiment of the present invention.

FIG. 2 is a chromaticity diagram showing a primary stimulus according to one embodiment of the present invention.

FIG. 3 is a diagram showing the spectral sensitivity of a filter used in the image reading apparatus according to one embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 5 is a circuit block diagram of an embodiment of the present invention.

FIG. 6 is a chromaticity diagram illustrating a conventional example.

FIG. 7 is a diagram showing spectral sensitivity for explaining a conventional example.

FIG. 8 is a diagram showing spectral sensitivity used in an image reading device used in a conventional device.

FIG. 9 is a chromaticity diagram for explaining FIG. 6;

FIG. 10 is a spectral sensitivity illustrating a conventional example.

FIG. 11 is a diagram showing an image processing apparatus according to an embodiment of the present invention.

FIG. 12 is a view showing another example of FIG. 2;

FIG. 13 is a view showing another example of FIG. 2;

FIG. 14 is a diagram showing a case in which conventional color expression is represented by X, Y, and Z.

FIG. 15 is a diagram showing another example of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 original 2 original platen glass 3 original illuminating device 4 short focal length lens array 5 color solid-state image sensor array having characteristics of FIG. 1 of the embodiment of the present invention 6 optical unit 7 A / D converter 8 shading circuit 9 3 × 3 matrix Arithmetic unit 10 Converter

Claims (4)

(57) [Claims] 1. An input means for inputting color image data composed of red, green, and blue color components, and the input color image data substantially circumscribing a spectrum locus in an xy chromaticity diagram. Red (0.734, 0.265), green (-
0.086, 1.086), blue (0.095,-
0.031) as a primary stimulus, and a conversion means for converting the image data into color image data composed of red, green, and blue color components. 2. The color image processing apparatus according to claim 1, wherein said conversion means performs a 3 × 3 matrix operation. 3. The apparatus according to claim 1, further comprising: a color image reading unit that reads a color image and generates color image data; and a shading correction unit that performs shading correction on the color image data. Color image processing device. 4. The color image processing apparatus according to claim 1, further comprising a color printer unit that forms a color image based on the color image data converted by said conversion unit.