JPH0756461B2 - Color separation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color separation method used for determining a color of a color original in a color scanner, a color facsimile, a color copying machine or the like.

(Prior Art) In a color scanner, a color facsimile, etc., three colors (red, green, and blue) included in the color of a color original are measured by a photo-sensing element (for example, a charge-coupled device), and the color is judged from this photometric amount. Or the tristimulus values of the CIE RGB color system
The color was displayed in R, G, B.

By the way, if the spectral characteristics of the light-sensing element and the light source are different, the photometric amount also changes for the same color original. Conventionally, each time the spectral characteristics differ, it has been necessary to adjust the circuit constants in the color separation device by using standard color targets such as red, green, and blue. Furthermore, even with this adjustment, when fluorescent lamps or light emitting diodes are used as the light source, the spectral characteristics change with temperature, and in the case of fluorescent lamps, the spectral characteristics also change with ambient temperature. , I could not judge the color accurately.

(Object of the Invention) An object of the present invention is to provide a color separation device that can make accurate judgment in color judgment even if the spectral characteristics of a light source or a light sensing element changes.

Further, an object of the present invention is to discriminate the color of an object from an xy chromaticity diagram and output the discriminated color.

By the way, any light color can be equalized by mixing three light colors independent of each other (referred to as primary stimuli). In addition, the color can be displayed as a ratio of the mixture of the three original stimuli. CIE RGB
The color system and the XYZ color system are typical systems that display colors with three primary stimuli, and the XYZ color system is obtained by linear conversion from the RGB color system.

In the RGB color system, the color F is represented by a set of values (R, G, B). Three primary stimuli I, J, K (red with specified wavelength,
The brightness (photometric amount) of the original stimuli I, J, and K when the (green and blue light) is colored with white light having an equal energy spectrum is Lr, Lg, and Lb, respectively. Next, the brightness (photometric amount) of the primary stimuli I, J, and K when the primary stimuli I, J, and K are appropriately mixed and color-matched to the color F is Pr, Pg, and Pb, respectively. To do. At this time, the mixed amount of the original stimulus with respect to the color F (called stimulus value) R,
G and B can be expressed as follows in units of Lr, Lg and Lb.

R = Pr / Lr, G = Pg / Lg, B = Pb / Lb (1) That is, when expressed by a vector, Here, M ₁ = 1 / Lr, M ₂ = 1 / Lg, M ₃ = 1 / Lb (3) If this is rewritten, Therefore, when the tristimulus I, J, K transmitted through this filter is measured using a filter whose tristimulus values R, G, B are known, from the obtained photometric amounts Pr, Pg, Pb ( The conversion vector can be calculated according to the equation (4).

The color separation device according to the present invention comprises three kinds of light sensing elements respectively coated with red, green and blue filters,
It measures the reflected light of a white light source from an object (color original) whose color should be discriminated, or is equipped with a light-sensing element that is not covered with a filter, and sequentially switches between three types of light sources of red, green, and blue. The light reflected from the light source from the above object is measured. When the above-mentioned object is not inserted, the reflected light from the back plate having a uniform high reflectance in the visible light region is incident on the above-mentioned light-sensing element.

Now, based on the above findings, R, G, B filter of which the value is known (colorless filter is preferable) is inserted in the optical path between the back plate and the light sensing element, and the tristimulus value is measured, From the obtained photometric quantities Pr, Pg, Pb and the above R, G, B values, the conversion coefficients M ₁ , M ₂ , M ₃ can be calculated according to the equation (4). Then, when the color of the object is measured, the tristimulus values R, G, B are calculated according to the equation (2).
Is required. If this method is used, variations in the characteristics of the light source and the light-sensing element (including temperature changes and aging changes) are integrated into the conversion vector, so R, G, B
The value of can be accurately determined without changing from device to device.

By the way, in the RGB color system, one of the tristimulus values R, G, and B may be negative, which is inconvenient for practical use. Therefore, the CIE XYZ color system that displays colors with a set of tristimulus values X, Y, and Z is used. The XYZ color system is a coordinate conversion of the RGB color system, and one set of tristimulus values (R, G, B) is converted to another set of tristimulus values (X, Y, B). Z). Therefore, Where A _ij is a matrix, i, j = 1,2,3.

Where the transformation matrix M _ij is the matrix A _ij with L
It is a combination of r, Lg, and Lb. In the XYZ color system, brightness is represented by Y, and chromaticity is represented by chromaticity coordinates x, y.

Therefore, the colored light is represented by the brightness Y and the chromaticity coordinates x, y. FIG. 1 is a CIE standard chromaticity diagram in which hue is represented by chromaticity coordinates x and y.

Now, let X, Y, and Z values of three filters whose x, y, and Y values are known to be Xp, Yp, and Zp (p = 1, 2, 3), respectively. The value of p indicates these three filters. (This filter does not necessarily have to transmit only the three stimuli I, J, K.) Brightness (photometric amount) Pr, of the original stimuli I, J, K in the transmitted light
It is assumed that the photometric quantities of Pg and Pb are Vrp, Vgp, and Vbp, respectively. Since the formula (3) is established for each filter, when expressed together using a matrix, Therefore, here, In other words, if the brightness of the primary stimuli I, J, and K contained in the transmitted light of white light is measured using three filters, the value of the element M _ij of the transformation matrix can be calculated using equation (9). Can be decided.

Based on the above findings, before reading the color original, the known x,
Three filters having y and Y values are sequentially inserted in the optical path from the light source 3 to the light sensing element, and the brightness Vr of the primary stimuli I, J and K is
Measures p, Vgp, and Vbp. Thus, the conversion coefficient M _ij is
It is determined in advance using the equation (9). Next, when the brightness Pr, Pg, Pb of the color original is measured, from equations (3) and (4),
x, y, Y values can be obtained. From the values of the chromaticity coordinates x and y, the chromaticity of the color original can be determined with reference to FIG. When this method is used, the variation of the characteristics of the light source and the photo-sensing element (including temperature change and aging change) is converted into the conversion matrix (M _ij ).
The color can be accurately determined because it is totally integrated into.

(Structure of the Invention) Red included in the reflected light from the light source of the object whose color is to be determined,
In the color separation method of measuring the colors of three colors, green and blue, by the photo-sensing element and determining the color, the light from the above-mentioned light source can Allow the light to directly or indirectly enter the light-sensing element, and use the CIE X
In the YZ color system, a filter having a known x, y, Y value is inserted for photometry, and from this photometric amount and the X, Y, Z values of each filter whose x, y, Y values are known. , The conversion coefficient for correcting the photometric amount by the object to perform the color judgment of the object is calculated, and the conversion coefficient is stored before the photometry of the object, and the stored conversion coefficient and the photometric value by the object It is characterized in that the X, Y, and Z values are output by calculation with the quantity to perform comprehensive correction of variations in the characteristics of each component.

(Embodiment) FIG. 2 is a schematic diagram showing that light from a color original is measured in an embodiment of the present invention. Color original 1
Is placed on the white original back plate 2. The light source 3 illuminates a portion of the color original 1 on the original back plate 2 as indicated by an arrow in FIG. The reflected light 4 from the color original 1 passes through the aperture of the lens diaphragm 5 and is condensed by the lens 6 to generate the light sensing element 7
Be measured with. The light sensing element 7 is, as shown in FIG.
It is a linear image sensor consisting of a single row of charge-coupled devices (CCDs), which are photosensitive elements. linear·
Red (R), green (G), and blue (B) filters are sequentially covered on the respective elements S1, S2, ... Constituting the image sensor, and a set of elements (for example, S1 and S1 S2 and S3) measure the brightness of red, green, and blue in the reflected light 4 of the color original 1, and from this photometric value, as described above, using the equations (9) and (10), The color can be determined by the processing circuit.

By the way, the original back plate 2 has a uniform high reflectance in the visible light region, and when the color original 1 is not inserted, the reflected light from the original back plate 2 is detected by light. It is arranged to reach on the element 7. When the color separation device is turned on or when no color original is inserted, three filters of red, green and blue having known x, y, Y values are provided.
Are sequentially inserted in the optical path of the reflected light, and the brightness of the transmitted light Vrp, Vg
Photometry of p, Vbp (p = 1,2,3). FIG. 4 is a graph of the transmittance of each filter 8. Using the processing circuit below,
_{Find the} transformation matrix (M _ij ).

FIG. 5 is a circuit diagram of a processing circuit that _obtains a conversion matrix (M _ij ) from the photometric amount and determines a hue. The brightness Pr, Pg, Pb of red, green and blue measured by the photo-sensing element is
The AD converters 11r, 11g, 11b respectively convert the digital values into a digital value having a bit number of 6 bits or more, and then input to the matrix calculation circuits 12X, 12Y, 12Z and the input memory 13. On the other hand, the output memory 14 includes M ₁₁ , M ₁₂ , M ₁₃ for the matrix calculation circuit 12X, M ₂₁ , M ₂₂ , M ₂₃ for the matrix calculation circuit 12Y, and M ₃₁ , M ₃₂ , M ₃₃ for the matrix calculation circuit. It outputs to 12Z. The matrix calculation circuits 12X, 12Y, 12Z are
It is composed of a well-known multiplier circuit and an adder circuit, and the matrix calculation of the right side of the formula (8) is performed in real time from the input values Pr, Pg, Pb and the matrix element M _ij, and the calculated values X, Y, Output Z. Conversion circuit 15
Is a circuit including a look-up table of a large-capacity ROM. Input values X, X from the matrix calculation circuits 12X, 12Y, 12Z
Y and Z are converted into x and y values by the expression (7) and output. The color determination circuit is also a circuit including a look-up table of a large-capacity ROM, which outputs a Y value representing brightness and determines a color from the correspondence between a predetermined m color and an x, y value.
The voltage of the color judgment output of the judged color in the color judgment outputs C ₁ , C ₂ , ..., Cm corresponding to the individual colors is set to a high level.

The matrix calculation circuit 17 is composed of a well-known adder circuit, a subtractor circuit, a multiplier circuit and a divider circuit, and the nine photometric quantities stored in the input memory 13 and the matrix calculation circuit 17 From the X, Y, Z values of the filter stored therein, the result is output to the output memory 14 according to the equation (9). In addition,
The memories 13 and 14 can be composed of a RAM, a shift register and the like. Further, since the calculation of the conversion matrix does not have to be performed in real time, it may be performed by software using a microprocessor or the like.

The control circuit 18 controls the calculation of the transformation matrix. FIG. 6 is a flowchart of this control. First, the control circuit 18 drives the pulse motor 20 with the driver circuit 19. The above three filters 8 are connected to the shaft of the pulse motor 20, and one of them is inserted into the optical path between the original back plate 2 and the light sensing element 7 (step P1). . The brightness Pr, Pg, Pb measured by the light sensing element is
After being respectively converted into digital values by the AD converters 11r, 11g, 11b, they are stored in the input memory 13 (step P2). Next, this filter 8 is evacuated and another filter 8 is inserted into the above optical path (step P3). Then, similarly, the photometric amounts Pr, Pg, Pb by the light sensing element 7 are stored in the input memory 13 (step P4), and the filters 8 to 8 (step 6). Next, the matrix calculation circuit 17
Is the above nine photometric quantities and the above three filters 8,8,
From the X, Y, and Z values of 8, the matrix element M _ij is calculated according to equations (9) and (10) (step P7). And
Output to the output memory 14 (step P8). Finally, the filter 8 is saved (step P9).

When the color separation device is turned on or before a color original is inserted, the conversion matrix (M
_{If ij} ) is obtained, it is possible to comprehensively correct variations in the characteristics of the light source, the light sensing element, and the like.

In the above, the reflected light of the white light source 3 from the color original 1 is transmitted by the filter 8, and the transmitted light is measured by the three kinds of photo-sensing elements respectively covered with the red, green and blue filters, and the light is measured. The quantities Vrp, Vgp, Vbp are measured. However, the three types of light sources of red, green and blue are sequentially switched to illuminate the color original 1, the reflected light is transmitted by the filter 8, and the transmitted light is measured by the photo-sensing element not covered by the filter. Also in the method, the photometric quantities Vrp, Vgp, and Vbp can be measured as in the above method. Therefore, just change the input of the photometric quantity appropriately,
The above embodiments can be applied.

In addition, when determining the color with the RGB display system, as in the above case, a filter with a known RGB value (a colorless filter is preferable) is inserted in the optical path between the back plate and the light sensing element. , When the tristimulus values are measured, the obtained photometric amounts Pr, Pg, Pb
From the above R, G, and B values, the conversion coefficient M ₁ ,
M ₂ and M ₃ can be calculated. Then, when the color of the object is measured,
The tristimulus values R, G, B are obtained according to the equation (2). When this method is used, variations in the characteristics of the light source and the light-sensing element (including temperature changes and aging changes) are integrated into the conversion vector, so the values of R, G, and B vary from device to device. Can be accurately determined without changing to.

(Effect of the Invention) According to the color separation method of the present invention, the conversion coefficient for correction is obtained in advance by the photometric amount obtained through each filter before the photometric measurement with the color original, and the color By correcting the photometric amount from the original, it is possible to obtain accurate X, Y, and Z values regardless of variations in the spectral characteristics of the light source and photodetector, temperature changes, and changes over time. Accurate color judgment can be performed by the CIE XYZ color system.

[Brief description of drawings]

FIG. 1 is a chromaticity diagram in the x, y coordinate system in the XYZ color system. FIG. 2 is a schematic diagram showing photometry for color determination from a color original. FIG. 3 is a diagram showing a linear image sensor of a charge coupled device. FIG. 4 is a graph of transmittance curves of three types of filters. FIG. 5 is a circuit diagram of a processing circuit for determining a color from the photometric amount. FIG. 6 is a control flowchart for obtaining the conversion matrix. 1 ... color original, 2 ... original back plate, 3 ... light source, 4 ...
Reflected light, 5 ... Lens aperture, 6 ... Lens, 7 ... Photosensitive element, 8 ... Filter, 11r, 11g, 11b ... AD converter, 12X, 12Y, 12Z ... Matrix calculation circuit, 13, 14 ......
Memory, 20 ... Pulse motor, Pr, Pg, Pb ... Photometric quantities of red, green, and blue by photo-sensing elements.

Claims (1)

[Claims] 1. An object whose color is to be determined is irradiated with light from a light source, and three colors of red, green, and blue contained in reflected light from the object are measured by a light-sensing element, and the light is measured according to the amount of light measured. In the color separation method for determining the color by the CIE XYZ color system in the optical path where the light from the light source is directly or indirectly incident while the light from the object is not incident on the light sensing element. In the first step of sequentially inserting three filters whose values of x, y and Y are known, in the second step of storing the photometric amount measured by the photo-sensing element, and in the first of the three filters The step and the second step are repeated, and the photometric amount by the object is corrected from the stored photometric amount and the X, Y, Z values of each filter whose x, y, Y values are known. The third step of calculating the conversion coefficient and storing the conversion coefficient, the reflected light from the object is The fourth step of performing the calculation of the photometric amount measured while the light is incident on the light sensing element and the stored conversion coefficient to output the X, Y, Z values in the CIE XYZ color system, and the above output The fifth step of outputting x, y values for judging the color based on the determined X, Y, Z values, and X, which is accurate by the reflected light from the object by the conversion coefficient A color separation method characterized by being able to obtain Y and Z values.