JPS5941227B2 - Signal interpolation method in memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a correction signal for a memory device that is effectively used for color correction of an image signal in an apparatus that creates color-separated images by photoelectric scanning, such as a color scanner or a color facsimile. Regarding how to interpolate etc.

Traditionally, color correction in photoengraving work for multicolor printing involves
Although methods using photographic masking have been widely used,
This photographic method has a limited ability to correct colors, requires a large number of skilled technicians, produces unstable color separation results, tends to have uneven quality, and has a complicated process. It has many drawbacks.

For this reason, electronic color separation, that is, color separation and color correction (masking) methods using color scanners, has become popular and is now the mainstream.

Most of the color scanners currently in use use a calculation method using analog signals in order to increase the processing speed of color correction calculations.

However, the method using analog signals has limited color calculation functions, it is difficult to introduce free calculation formulas, and there are many operational amplifiers etc. as constituent electrical elements.
It is difficult to avoid the effects of temperature drift and noise, etc.
When the number of adjustment items increases, there are various disadvantages such as a decrease in operability due to the increase in the number of volumes, switches, etc., and a high manufacturing cost.

However, if the analog calculation unit in a current color scanner is simply replaced with a digital calculation device, the speed of color correction calculation will be significantly reduced, and the processing capacity will deteriorate, making it impractical.

On the other hand, in recent years in the printing and plate making industry, the demand for more beautiful and higher quality printed matter has increased, and at the same time, in order to speed up the work, color separation using a color scanner and magnification conversion to the image dimensions of the final printed matter have been implemented. However, so-called direct scanners have appeared that can even perform shading operations.

In this case, unlike the conventional method of separating the colors using a scanner and then converting the magnification and shading using a prepress camera,
Since there are restrictions on the possibility of adding color corrections to the color separations using additional masks and hand retouching, color corrections in color scanners are required to be performed at an even higher level.

In response to these demands, color correction methods have been developed that combine the high-speed color calculation processing capabilities of analog color scanners with the advantages of digital color scanners, such as high reliability, wide color correction variable range, and high operability. In other words, a color scanner photoelectrically scans a color original image and prints R, G, and B.
Obtain three-color separation signals from R, G, and B, and input them into a color calculation circuit to finally generate C (cyan) and M
(magenta), Y (yellow), K (black), and other recording symbols. , C, M, and Y (K is omitted to simplify the explanation), each ink amount must be a certain combination.

That is, once the values of the three color separation signals R, G, and B are determined, the ink amounts of C, M, and Y are uniquely determined.

In other words, as shown in FIG. 1, color correction is the coordinate conversion from the coordinates of the R, G, B system to the coordinates of the C, M, Y system. Therefore, in order to perform color correction by selecting a corresponding combination of C, M, and Y values based on a certain combination of R, G, and B values, each R, G, and B value is stored in the memory device in advance. , color corrected C for the combination of B values,
This means that the combination of M and Y values may be stored and stored, and the combination of R, G, and B values may be used as an addressing signal to read out the C, M, and Y values.

However, for R, G, and B values, if the visual level of each color density is 200, for example, 2003 (=8000000) sets of values must be stored in the memory device by combining the three colors. Naturally, the memory device becomes expensive and impractical.

Therefore, in order to reduce the storage capacity of the memory device, if the number of density levels for each color of R, G, and B is set to 16 levels, the number of combinations of the three colors becomes 163 (-4096), which increases the memory capacity of the memory device. Although the storage capacity can be reduced, in practice the density steps are too coarse and the difference in output density is noticeable, resulting in poor quality of printed matter, so the intermediate value of each density step must be interpolated appropriately.

For example, as shown in Figure 2, consider the case where the output values of C, M, and Y correspond to the input values of R, G, and B. Value (Cl, m,
n, Ml, m, n, Yl, m, n) is also the input value (R1+1, Gm+1, B0.1-
1), the output value (Cl+1, rn+1, n+1F
M1+1ym+? 1yn+1FY1+1jm+1jn+
If 1) corresponds, the interpolated value for the input value can be found as follows.

Let the human power values be (R, G, B), and Rj≦? R1+1,m+
By creating an output signal of 1,n, it is possible to obtain an output value interpolated with respect to the intermediate human power value of 1 at each stage.

However, this interpolation method cannot be used when the minimum interpolation section in the coordinate system of the memory device is a regular cube, rectangular parallelepiped, or parallelogram as shown in FIG. 2, in which opposing sides are parallel. , if the corrected recorded signal value in the memory device changes linearly in response to a change in the addressing signal, no jump will occur in the read out corrected recorded signal value at the boundary of the minimum interpolation section. However, as shown in Figure 3, if the signal value in the memory device changes non-linearly in response to changes in the addressing signal, the readout will occur at the boundary of the minimum interpolation section in the coordinate system of the memory device. This will cause a jump in the corrected recorded signal value.
For example, using points A, B, C, and D in Figure 3 as reference points, (1)
If a point corresponding to point H is found using the interpolation method in the formula, it becomes point H', and a jump of HH' occurs at the boundary between adjacent minimum interpolation sections.

If you make the minimum interpolation section smaller in order to suppress this jup, the storage capacity of the memory device will increase accordingly.For example, if you want to suppress the jup and double the interpolation accuracy, The number of density levels of each color separation density signal must also be doubled.

Therefore, the memory device needs to have a storage capacity 23 (=8) times larger, making it uneconomical considering that the memory device is extremely expensive. Therefore, in order to prevent a large jump-up in the corrected recorded signal value read out at the boundary of the minimum interpolation section in the memory device without increasing the capacity of the expensive memory device, it is necessary to A, B, C, D in Figure 3,
Therefore, it is necessary to perform interpolation calculations taking into account the following points (E, F, G, H, points), and it becomes impossible to obtain a sufficient frequency response for color correction in a scanner that scans at high speed. The present invention improves the conventional interpolation method described above, is relatively simple, and
Another object of the present invention is to provide an interpolation method that suppresses jump-up occurring in corrected recorded signal values read at the boundaries of minimum interpolation sections stored in a memory device.

The turbidity of printing ink, which is the main cause of the need for color correction when reproducing color originals as printed matter, is due to the fact that not all turbidity components in the ink are uniformly large, and particularly large turbidity components are included in magenta ink. They are a yellow component and a magenta component contained in cyan ink.

Therefore, when reading a corrected recorded signal stored in a memory device using a color separation density signal as an addressing signal, the corrected recorded signal is The values also change, but not necessarily all corrected recording signals change to the same extent with respect to changes in individual addressing signals.

This means that the predicted print density, examples of which are shown in Figures 4-A, 4-B, and 4-C (here, the predicted print density is based on the assumption that the print will be the same as the original), This is clear from the halftone dot area table (corresponding to color separation density signals and addressing signals) (a table showing what percentage of halftone dot area must be printed in order to obtain a predetermined printing density).

That is, the predicted print finish densities DR〃,D in Fig. 4-B
When O″, DB″ is DR〃=DO″2DB″=0.8, the halftone dot area of C, M, Y ink is C: 70 (to), M
:57 (to), Y:47 (to), and when only DR7 is changed to make DR''=0.6 and DR〃=1.0, the halftone dot area of C.M.Y ink is: C:55 each
(capital), M: 61 (to), Y: 46 (to) and C: 8
2 (equity), M: 53%, Y: 49 (equity), DG''
The halftone dot areas of C, M, and Y inks when DG〃=0.6 and DG〃=1.0 are respectively changed by C.
:72 (equity), M: 36 (equity), Y: 63 (to) and C: 69%, M: 72 (to), Y: 27 (to),
By changing only DB″, DB〃-0.6 DB″=
The dot areas of C, M, and Y inks when set to 1.0 are C:70 (to) from Figures 4-A and 4-C, respectively.
, M: 58 (to), Y: 14 (to), C: 70 (to), Y: 71 (to). That is, the corrected recording signal of C ink is the color separation density signal DB. which is the address designation signal. When 〃 changes, it changes significantly, and when addressing signal DG'' changes, it changes somewhat, but it hardly changes when addressing signal DB'' changes.

Similarly, the corrected recording signal for M ink changes significantly with changes in DG7, changes to some extent with changes in DR'', but hardly changes with changes in DB''. Furthermore, the corrected recording signal for Y ink changes significantly with changes in DB〃, changes considerably with changes in DG″0), but hardly changes with changes in DR″. In this example, the case of DR''=DG''=DB''=0.8 was considered, but this tendency is not limited to this point but holds true for most combinations of addressing signals.

Therefore, due to changes in the addressing signal that has a three-dimensional coordinate system, that is, the color separation density signal (predicted print density), the corrected recorded signal value changes relatively significantly.Both coordinates determined by two dimensions are one level higher. The present invention was developed as an interpolation method that takes into account the fifth diagonal point corresponding to ! Ru. What is shown in FIG. 5 is an enlarged view of the minimum interpolation section shown in FIG.
l, m, n), P2 (Cl+1Fm2n2M1+17m
2n? Yl+12m'n)) P3(CLm+19n9 {EFm+19ntsu Yl9m+1Fn)) P4(Cl9
Although a corrected recording signal value of P5 (Cl9mpn+1'Ml9mpn+1YM2n+1) is used in the present invention, yet another corrected recording signal value P5 (Cl
+17m+1? n? Ml+1? m+1Fn? Yl+1 la m11+1,n) or P6(Cl,ITl+1,1
+1, M1, 111m'+1・n+1・Yl・m+1・
n+1) to perform interpolation.

As mentioned above, this corrected recording signal value P5 or P6 is determined in two dimensions in which the signal value changes relatively largely due to changes in the addressing signal having a three-dimensional coordinate system.For example, cyan ink and When performing interpolation calculations on the corrected recording signal for magenta ink, use P5.
In the case of yellow, P6 is used, and when compared with Fig. 3, P,, P2, P3, P4 are A, B, P4, respectively.
They correspond to points C and D, P5 corresponds to F, and point P6 corresponds to point F, respectively. According to the interpolation method according to the present invention, (-ΔGIn), o − in equation (1). If (-ΔBO) are respectively X, y, z (0≦X, y, z≦1), then the quantities corresponding to, for example, the C version of formula I are as follows.

By the way, regarding the C version, when B, that is, z, changes, the amount of change in the C version is small, and the deviation from the linearity of the change is even smaller, so the quadratic correction term including the Z change, that is, {...} The terms expressed by x−z and {...}y・z can be ignored.

However, when R, that is, X1, and G, that is, y change, the amount of change in the C plate is not only large to some extent, but also the amount of deviation from linearity when both of them change becomes so large that it cannot be ignored. Therefore, correction is necessary, but in the present invention, this is solved by introducing a quadratic correction term.
The number of second-order correction terms is also kept to the minimum necessary.

By the way, if we consider that when at least one of X and y is small, the answer needs to be almost the same as the formula (when at least one of X and y is zero, it is the same as formula I), then the added quadratic correction term is {・...} has the form of X, y.

The biggest problem when adding this type of quadratic correction term is:
Since this is the time of x-y-1, it is sufficient to introduce a quadratic correction term so that the j-up becomes zero at the position P5 in FIG.

The present invention has found that this requirement is met by a new interpolation formula.

Considering this, the new interpolation formula is as follows.

In this formula, the position of P, for example x-y
-1, under the conditions of z=O.

Similarly, for the M version, when B or z changes, the amount of change in the M version is small, and for the Y version, when R or x changes, the amount of change in the Y version is small. Corrected recording signal values for each color CX, 2,
MX, 2, YX, 7. becomes as follows.

(As shown in the formula, the interpolation method according to the present invention is (1)
The corrected recording signal value C2M. obtained from the formula. In Y, respectively {Ct4-1, m→1, n{t+1, m, n) one (
Ct, nl・1. .

-Ct. m, n)}Xy. {(Mノ+1, m+1, n-
Mt+1, mtn) one (M7lm+HlMt!M.n)
}Xy? {(Yt, m+1, n+l−Yt, m, n ten,
)-(Yt, m+1, n-Yt, m,.)}Yz becomes 2
The following term has been added, thereby making it possible to suppress to a small extent the jump that occurs in the read corrected recorded signal value at the boundary of the minimum interpolation section in the memory device. For example, in equation (), if x-0sy=z=l, the fifth
When calculating the corrected recorded signal value for yellow ink at P6 in the figure, it is found that the interpolation method according to the present invention has a value of 1
.

▲ ▲! ! ! In contrast, in the conventional method shown in equation (1), the result is FA, and there is a possibility that a jump may occur in the corrected recorded signal value.

In order to examine this result in more detail, by assuming and comparing the coordinates of the addressing signal as shown in FIG. 6, the difference from the conventional method shown in equation (1) will become clear.

That is, by the interpolation method according to the present invention, the addressing signals DR''=0.8, DG''1 are set based on the addressing signals DR''=0.8, DO''=0.8, DB7O,8.
．． 0. Corrected recording signal Y of yellow ink for DB″=1.0.

8,,. O, l. When O is determined from the print finish predicted density per halftone dot area table shown in FIG. 4, it is 59 (f).

On the other hand, in the conventional interpolation method shown in equation (1), YO. 8, l
．． Otsu0.8+YOJ3yO. 8 rivers. O-YO. 8P.O.
．． 8y prefecture 227 + 71 - 47 = 51ca, which means that there is an increase of 8 (to).

Also, address designation signals DR#, DO″, DB〃 are DR
Corrected signal value Y when 72DG''-DB''=1.0
,.

，! ．． 0,,. . , same as above, DR″-DG〃D
Using B″=068 as a reference, the conventional method and the interpolation method according to the present invention are used to find that in the conventional method of equation (1))Yl.O》1.0)1.02Y1.0》0.820 [
i0. or 1.0, 0.8+YO. 8, O. 8, O. 8-
49+27+71-2×4753 (to), (H)
In the method of the present invention shown in the formula, Yl. OFl. Ola 1.0:
:YO. 82l. O river. 0+Yl. O2O. 8?0.8
One YO. 8, O. 8, O. 8259+49-47261
? Become. On the other hand, the true corrected signal value is Yl. O, l. O, l. Since O=60 (to), the interpolation method according to the present invention can suppress the amount of jump-up of H to that of the conventional method.

In this way, in the conventional interpolation method shown in equation (1), an interpolation error occurs in the interpolated signal value, and a jump occurs in the corrected recorded signal value read at the boundary of the minimum interpolation section in the memory device. Although the interpolation method according to the invention is simply a simple quadratic term added to the conventional interpolation method as shown in equation (), the corrected tracking signal read at the boundary of the minimum interpolation section It is possible to significantly suppress the rise in the value.

Therefore, in some cases, such as when the corresponding corrected recorded signal does not change linearly with a change in address designation information, this method may be more effective than increasing the number of address stages. .

As described above, if color correction is performed by applying the interpolation method according to the present invention, in order to reduce the storage capacity of the memory device, even if the number of address stages in the memory device is reduced to an appropriate number, each This has various effects, such as suppressing the jump that occurs in the interpolated signal value between the minimum interpolation sections and allowing the reproduction of color original images to be performed sufficiently smoothly.

FIG. 7 shows an example of a specific arithmetic circuit that performs the arithmetic operation of equation (4) according to the present invention.

The R, G, and B color separation signals are processed by logarithmic converters 1R and 1, respectively.
G, 1B (!:.A/D (analog digitizer (c)
After each is converted into an 8-bit digital signal via converters 2R, 2G, and 2B, the digital R, G
, B color separation signals are respectively J, m,
It is sent to the color-corrected table memory 3 as a signal of n,
The lower 4 bits each serve as X, y, and z signals, respectively.
It is sent to multipliers 4xy, 4x, 4y, 4z, and
The output signal of multiplier 4xy, which multiplies two of the signals X and y, is sent to multiplier 5xy. In the color corrected table memory 3, the interpolation formulas for C, M, and Y are determined, so the values are predetermined based on the interpolation formulas, for example, for the C version, the C to calculate Cxyz of the formula
l, m, n la cl + 1ym evening NyC otsu m + 1'N2cl
Five color-corrected signals of ym, n+1, cl+, , n+1, and n are read out by addressing each of the 4-bit signals of 1, m, and n.

The five signals read here are sent to subtracters 6x, 6y, 6z, and 6xy that calculate each part (d) of the equation.
The signals calculated by the subtractors 5xy and 5y are sent to the subtractor 7xy, which calculates the inside of {}, where it is calculated.

The multipliers 4x, 4y, 4z as well as 4xy multiply the calculated values in each (d) and the calculated values in {}, respectively, by
Then, the second to fifth terms are calculated by multiplying x-y, and the symbol of each term is sent to the force H multiplier 8.

The signal of the first term is inputted to the force n calculator 8 from the color correction table memory 3, so that the color calculator 8 inputs the signal of the first term.
The signals of terms 1 to 5 are summed to output the calculated value of Cxyz. The above description and drawings are based on Cx for C version.
This is to find yz, and the M version and Y version of the formula Mxyz
, Yxyz can be found in the same way.

In the above explanation, the signal stored in the memory device is referred to as a corrected recorded signal, but the present invention is not limited to this, and the signal stored in the memory device is not limited to this. The interpolation method according to the present invention can also be applied to the case of a correction signal that is applied H to a color separation density signal serving as an addressing signal to perform color correction.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing the principle of color correction using a memory device, FIG. 3 is a three-dimensional diagram showing an example of the minimum interpolation division of an actual memory device, and 4-A, B, Diagram C is
A portion of a table showing an example of the relationship between predicted print density and halftone dot area, FIG. 5 is an enlarged view of the minimum interpolation section of the memory device shown in FIG. 2, and FIG. 6 is a diagram showing the coordinates of the addressing signal. FIG. 7, which is a three-dimensional diagram showing an example of the system, is a block diagram of an arithmetic circuit showing a specific example of calculating the equation.

Claims (1)

[Claims] 1 The primary color values of red (R), green (G), and blue (B) obtained by photoelectrically scanning a color original using a photoelectric color separation scanning device are used as the values of the three-dimensional addressing first signal system, A memory device including values of secondary colors of cyan (C), magenta (M), and yellow (Y) corresponding to the values of the primary color as values of a second signal system corresponding to the values of the first signal system. When calculating the corresponding value of the second signal system from the value of the given first signal system using , only for the two coordinate axes for which the change in the signal stored in the memory device is relatively large with respect to the change in the addressing signal, the corrected stored signal at the diagonal position is included in the coefficient, and the quadratic correction by the addressing signal is performed. A signal interpolation method in a memory device, characterized in that a term is added.