JPH0273779A - Color correction circuit - Google Patents

Abstract

PURPOSE:To save the capacity of a color correction memory by using a sum of an output of a start point address generation memory and other input signal as an address, inputting it as an address and outputting a signal representing the color of the 2nd color system. CONSTITUTION:The circuit is provided with a start point address generating memory 2 inputting two input signals among three input signals representing colors of the 1st color system as addresses and outputting a start point address decided in advance while taking the color reproduction range of an output device into account, an adder 3 obtaining the sum of the output of the start point address generation memory 2 and the other input signal and a color correction memory 1 receiving the output of the adder 3 as the address and outputting a signal representing the color of the 2nd color system. Thus, the start point address is decided in advance so as not to cause waste in a color correction memory while taking the color reproduction range of the color system of the output device into account. Thus, the capacity of the color correction memory is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a color correction circuit for faithfully reproducing the color tone of a document in an apparatus that generates full color including halftones, such as a color copying machine or printer. .

(Prior Art) Many methods have been proposed for color correction in the fields of color printing, color televisions, color copying machines, etc. One of these methods is to use a table memory to
There is a method of directly converting from the GR system to the output YMC system.

However, when the three BGR color signals are individually converted into digital signals with the resolution of the required density level, the amount of information is extremely large, so the number of table memories m becomes enormous, and the cost becomes extremely high.

For example, if 8 bits are allocated to each input BGR color and each output YMCK color is output as 8 bits, 2Z
'X4 bytes of memory is required, which is not practical.

Therefore, as a method for reducing the memory capacity when color correction is performed using a table memory, a method using interpolation has been mainly studied in the past. In other words, this method attempts to reduce the memory capacity by using a color correction memory whose address is the upper bit of the input signal, and to correct the roughness by an interpolation circuit using the lower bit. reduction was not sufficient.

(Problem to be solved by the invention m) The present invention solves the above problems, and is a color correction circuit that performs color correction using a smaller capacity table memory without reducing the accuracy of color correction. The purpose is to provide the following.

In order to achieve the above object, the present invention focuses on the color reproduction range of an output device.

As the input of the color correction device, BGR%L* a* b*
There are several possible options such as HVC, but here L”a1
The case of 1b'' input will be explained as an example.

FIG. 6 shows the color reproduction range of a certain output device [a.

Figure 6 shows the contour of the output device's color reproduction range as a * b on an equal plane with L''=20 to 80 (10 intervals).
*It is shown as a solid line on the chromaticity diagram, and the color reproduction range is inside each closed loose line. What should be noted here is that the outline when cut at each L/equal plane is close to a deformed quadrilateral (and its shape varies depending on the level of L''. Therefore, it is If we assume a rectangular parallelepiped that circumscribes this color reproduction range and has each surface parallel to Ll) am, a m - b 6 planes, and b''-L'' plane, its volume V'' is The volume V of the color reproduction range becomes larger than the volume V of the color reproduction range. A conceptual diagram is shown in FIG.

FIG. 8 shows an example in which the color correction device a1 is not interpolated using a normal table memory.
This means that m data corresponding to outside the output color reproduction range, that is, v'-v, is stored in extra memory.

Furthermore, if the input range is wider than the output color reproduction range, input data corresponding to a larger rectangular parallelepiped (with a volume of ■''>V) than the circumscribed rectangular parallelepiped will be input. Therefore, an amount of data corresponding to v''-v is stored in extra memory.

The present invention focuses on this extra memory and attempts to reduce the capacity of the color correction memory. In the case of the characteristics of the output device shown in Figure 6, even with respect to V'(V' - V)
/V' = 77% reduction in memory capacity 1 is expected, ■"
If we consider this, the reduction rate becomes even greater.

The above was explained in the case of L1180b11 input, but
The same thing can be said for other inputs such as BGR, L"H"C", HVC, etc., although the reduction rate is different. For example, if the BGRiQ degree from a certain input device is directly input, (V'-
The calculation result is V)/V' = 65%.

(Means for Solving Problems) As shown in FIG. 1, the present invention inputs two of three input signals representing colors of a first color system as addresses, and outputs them to an output device. A starting point address generation memory 2 that outputs a starting point address predetermined in consideration of the color reproduction range, an adder 3 that calculates the sum of the output of the starting point address generation memory 2 and one other input signal, and the adder. 3 as an address, and a color correction memory l which outputs a signal representing the color of the second color system.

According to another aspect of the present invention, as shown in FIG. a starting point address generation memory 2 which outputs a predetermined starting point address in consideration of the color reproduction range of the output device; an address adder 3 that calculates the sum of bits; a color correction memory 1 that inputs the output of the address adder 3 as an address and outputs a part of the signal representing the color of the second color system; The remaining lower bits are obtained by removing a certain number m of upper bits from the three input signals representing the color of the color system! and the three outputs of the address adder, h
an interpolation circuit 5 that outputs the correction amount for the 11th interval, and an interpolation circuit 5 that adds the output of the color correction memory 1 and the output of the interpolation circuit 5, and outputs a signal representing the color of the second color system. vessel 6
-1 to 6-4.

Furthermore, according to another aspect of the present invention, as shown in FIGS. 4 and 5, in the color correction circuit of the above two aspects,
When there is an input signal corresponding to a color outside the color reproduction range of the output device connected to the output of the color correction circuit, means is provided for converting this into a signal corresponding to a color within the color reproduction range of the output device.

The conversion means converts the starting point address generation memory 2 into a color outside the color reproduction range in response to two input signals representing colors in the first color system that correspond to colors outside the color reproduction range of the output device. The configuration is such that a color within the color reproduction range is substituted, and the other one is configured in response to the two input signals representing the colors of the first color system.
A maximum/minimum memory 7 is provided that outputs a signal that determines the upper and lower limits that can be taken by one input signal, and another input signal is compared with the output of the upper and lower limits of the maximum/minimum memory 7, and the other one is This is realized by providing comparators 8 and 9 which substitute a value within the range when the two input signals are outside the range of the upper and lower limits.

(Function) The operating principle of the present invention will be explained using FIG. 2 and Table 1.

FIGS. 2(a) to 2(d) show the color reproduction range of an output device assumed for detailed explanation of the present invention, and Table 1', S(,3) U, It shows the address assigned by. In the figure, the shaded area is the color reproduction range for each L'' level, and the numbers therein indicate the allocated addresses. In this case, 2 bits each for L ``a'' and ``b'' are I assumed. Therefore, in the case of the conventional method shown in FIG. 8, the number of input addresses of the color correction memory is 22×3=64. This situation is shown on the left side of Table 1.

Next, in the case of the present invention, the starting point address of L9 is generated from the table memory with "a fist" as input, and L months are added, resulting in the result shown on the right side of Table 1.

Of the numbers on the right side of Table 1, the parts shown in parentheses will be used later when explaining the examples, so they will be described here. 1 (You can watch it.

To explain step by step, first, (a"b") = (0
, O) and (a” b”) = (0, 1) is the output device a
Since the color is outside the color reproduction range, it is assumed that the corresponding signal will not be input, and a color correction memory address is not required. The first thing you need is (all b*L”)= (0,2
, 2). In this case, in order to set the address of the color correction memory to O, it is sufficient to store -2 in the memory that generates the L'' starting point address.The reason is that color correction memory address = L'' starting point address + L8 value. This is because they are in a relationship.

Next, we need (a and b” L”): (0,
3, 2), and L at this time! The starting address is −
If it is set to 1, the address of the color correction memory will be l.

In this manner, the LI starting point address may be determined by sequentially checking the color reproduction range of the output device and incrementing the address of the color correction memory only for the necessary portion by ■.

In this case, while the conventional example required 64 addresses for color correction memory, the number can be reduced to 26 in the present invention. If the number of addresses required for the color correction memory is reduced, the capacity of the color correction memory is reduced accordingly, resulting in a significant reduction in memory space. The memory for generating the L* starting point address increases, but even in this case, it is a memory of at most 16 addresses, and if the number of input bits increases, this will not be a problem compared to the amount of reduction in color correction memory.

Furthermore, the present invention is configured such that the color correction memory is configured to output only the upper part and part of the second color system, and the lower bits can be applied to a color correction circuit that generates by interpolation.
In this case, the reduction in memory capacity due to interpolation and the reduction in memory capacity due to address starting point generation combine to make it possible to reduce the number of memories in the − layer by eight.

Further, according to the present invention, part of the function of saturating within the color reproduction range of the output device can be used as the starting point address generation memory, and circuit drawing can be simplified accordingly.

(Embodiment) FIG. 3 shows a first embodiment of the present invention. Each m bit of input all b* is stored in address generation memory 2.
The output L'' starting point address and the L'' m-bit input are added by an adder 3, and the result is input as an address of the color correction memory l.

In the case of L * a m b umbrella , the input range of L * is
Since it is narrow compared to the input range of the all b umbrella, there is no problem even if L'' is reduced by 1 bit from the others.As mentioned earlier, the compression ratio is about 23% or less, so the address of color correction memory 1 is at least 2 bits can be reduced.Also, the output of color correction memory is normally YMCK%, but
There is no problem even if only YMC% is output and K% is generated by another method.

Since the operation of this embodiment is almost the same as the operating principle described above, the explanation will be omitted here, and only the differences will be described.

The difference is that in the explanation of the operating principle, when the address of the color correction memory was small, the starting address for l and 11 had a negative sign, but here, it only has a positive sign. It is a point. With a negative sign,
The number of output bits of the starting point address generation memory increases by 1 bit, the capacity of the starting point address generation memory increases, and an adder capable of calculating a correspondingly large number of bits is required.

Therefore, we will set the first L'' starting point address to 0.As a result, the input address of the first color correction memory will not start from 0, but
If the number of input bits increases, for example, if m≧4th place,
This waste is at most about Max2' compared to the total address of about 2+o of the color correction memory, so it is a negligible amount and no problem occurs.

FIG. 3 is a block diagram showing a second embodiment of the invention. The difference from the first embodiment shown in FIG. 1 is that Lma
Of the *b* input, the memory capacity saving technique by generating the starting point address of the first embodiment is applied only to each of the upper m bits, and the lower 1 bit is finally processed by the interpolation circuit 5 to convert the correction amount into YMC(K). The point is that it is added to the percentage. That is, the address generation memory 2 is configured as a look-up table for extracting 3m-2 bits of the L umbrella starting point address using the upper m bits of am and the upper m bits of b'', and the L'' starting point address obtained by the address generating memory 2 and The adder 3 adds the upper m bits of the L11 address to obtain the address for the color correction memory 1. Color correction memory 1 is YMC
The upper bits of (K)% are stored, and the corresponding value is read out based on the address output from the adder 3. The interpolation circuit 5 outputs a correction amount for interpolation using each lower l bit of aob"L" and the output of the adder 3, and
The positive 1 is added to the output of the color correction memory 1 by adders 6-1 to 6-4 to obtain interpolated YMC(K)%.

In this case, since the manner between R1i is affected by the upper bits, the same signal as the input of the color correction memory l is applied as an input to the interpolation circuit 3.

As mentioned earlier, this signal has already decreased by at least 2 bits, so if the interpolation circuit 3 is also configured with a table memory, the interpolation memory capacity will also be reduced by at least 1/4. .

Therefore, regardless of the presence or absence of interpolation, the advantage of reducing the total memory capacity by at least 1/4 remains the same.

In addition, both the embodiments in FIGS. 1 and 3 are a11b
Although we have shown the case of generating the starting address of “L” from @,
The combination of L"a"b" is not limited to this, and may be any combination. For example, the starting address of fist b may be generated from inside L umbrella a (in this case, L" may be If the number of bits is reduced by one bit, there is also the advantage that the capacity of the address generation memory will be halved.

Furthermore, the input is not limited to the set of (, *a*b umbrellas), but may also be three variables representing other colors, such as L"H"C", BGR, HVC, etc. This is obvious from the principle of the present invention.

FIG. 4 shows still another embodiment (third embodiment) of the present invention. This is because the first and second embodiments shown in FIGS. 1 and 3 assume that the input data contains only data within the output color reproduction range. On the other hand, the embodiment shown in FIG. 4 is different in that data outside the output color reproduction range can be included. In other words, a function has been added that allows any input data to be converted to within the color reproduction range of the output device. The principle of this operation will be explained again based on FIGS. 2(a) to 2(d) and Table 1.

First, regarding input data within the color reproduction range, the results in FIG. 5 and FIG. 3 are completely the same. For example, in Table 1, (
If a umbrella b fist L umbrella) = (0, 2, 2), the L$ starting address that is the output of address generation memory 2 is -2
is output. Along with this, from the minimum/maximum generation memory 7, M of L'' corresponding to (ae b・)=(0,2)
ax and Min, that is, L”M 1n=2, L”Max=2 are outputted and compared by the comparator 8.9, and M + n and M
The corrected * that is saturated between the values of ax is output, but for data within the color reproduction range, the input * and the corrected L'' are naturally equal, so correct the L fist address and add #. The result is the same as the embodiment shown in FIG.

Next, input data outside the color reproduction range, for example in Table 1, (
7. First, from the starting point address generation memory 2,
The same data within the color gamut that you want to output (a” b◆
)=(1,0), so we set it to -1. Along with this, from the minimum and maximum generation memory 7, the minimum and maximum L of (811b") = (1, 0)
11. In this case, L”Min = 3, L”Max
=3 is output. Then, comparator 8 calculates L”Min and L
* is compared and outputs the larger value 3, and the output is compared with L9Max by comparator 9, and 3 is output as corrected L''=3.

In this way, for inputs outside the color reproduction range, first
It is possible to realize the function of saturating L1′ within the color reproduction range and then saturating L1′ within the color reproduction range.Normally, the function of saturating L1′ within the color reproduction range is achieved by color correction. Although it is provided separately from the circuit, by applying the present invention, it is possible to make a part of the circuit, that is, the function of saturating a 11 b * within the color reproduction range, to the starting point address generation memory 2. This means that the circuit can be simplified.

FIG. 5 shows yet another embodiment (fourth embodiment) of the present invention,
! -1, an example will be shown in which the present invention is applied to a color correction circuit that can handle input data outside the color reproduction range and has interpolation. Its operation corresponds to a combination of both the embodiments shown in FIGS. 3 and 4, and its operation is also the same as the combination of the operations of both embodiments. Its characteristics are (a"b")
This point has a generation memory 10 for the lower bits of . When data outside the color gamut is input, (aebI
This is necessary because the lower bits of I) also change.

As mentioned above, the embodiments shown in FIGS. 4 and 5 have shown examples in which the starting point address of L8 is generated from (a"b"), but the input is not limited to this, and L"H"C ``The same can be said for HV C, etc. In this case, the combination is
If you use H''C* or He instead of as b, you can saturate the saturation first and then saturate the brightness, which is almost the same way as shown in Figures 4 and 5. ″b
If you use L" H reference or V, H instead of fist, and C fist or C instead of L", you can achieve a different method of saturation, which saturates the brightness and then saturates the saturation. can be easily inferred.

(Effects of the Invention) The present invention provides a starting point that inputs two of the three input signals representing colors or the upper bits of the two input signals as an address, and outputs the starting point address of the other one input signal. It has an address generation memory and an adder that obtains the address of the color correction memory by adding the generated starting point address and one other input signal or the upper bits of that signal, and outputs the starting point address. Since the color HLR can be predetermined in consideration of the color reproduction range of the color system so as not to cause waste, the capacity of the color correction memory can be significantly reduced compared to the conventional method.

Furthermore, the present invention can be implemented in such a manner that the memory is reduced by generating an address starting point using the upper bits, and the memory is reduced by using interpolation using the lower bits, making it possible to reduce the memory capacity. .

Furthermore, the present invention has the effect that part of the function of saturating within the color reproduction range of the output device can be implemented in such a manner that the starting point address generation memory is also used, and the circuit configuration can be simplified accordingly. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is a diagram showing an example of the color reproduction range and address assignment of a hypothetical output bag for detailed explanation of the present invention. FIG. 3 is a block diagram showing a second embodiment of the invention. FIG. 4 is a block diagram showing a third embodiment of the present invention. FIG. 5 is a block diagram showing a fourth embodiment of the present invention. FIG. 6 is a diagram showing an example of the color reproduction range of a certain output device, and FIG. 7 is a schematic three-dimensional representation thereof. FIG. 8 is a diagram showing the (1° configuration) of the color corrector memory in the conventional example. 1...Color correction memory, 2...Starting point address generation memory, 3...Address adder, 5 ...interpolation circuit, 6
-1 to 6-4... Interpolation signal adder, 7... Maximum and minimum memory, 8.9... Comparator, IO... Lower bit generation memory. Figure 2

Claims (3)

[Claims] (1) Starting point address generation that inputs two of the three input signals representing the colors of the first color system as addresses and outputs a starting point address predetermined in consideration of the color reproduction range of the output device. a memory; an address adder for calculating the sum of the output of the starting point address generation memory and one other input signal; and inputting the output of the address adder as an address and generating a signal representing a color of a second color system. 1. A color correction circuit, comprising: a color correction memory for outputting. (2) A certain number of high-order bits of two input signals out of the three input signals representing the colors of the first color system are input as addresses, and a predetermined address is set in consideration of the color reproduction range of the output device. a starting point address generation memory that outputs a starting point address; an address adder that calculates the sum of a fixed number of upper bits of the output of the starting point address generating memory and one other input signal; and an address adder that inputs the output of the address adder as an address. a color correction memory that outputs a part of the signal representing the color of the second color system; and a color correction memory that outputs a part of the signal representing the color of the second color system, and the remainder after removing the predetermined number of upper bits from the three input signals representing the color of the first color system. an interpolation circuit that inputs the lower bits of the color correction memory and the output of the address adder and outputs an interpolation signal representing a correction amount for interpolation; and a second 1. A color correction circuit comprising: an interpolation signal adder that outputs a signal representing a color in a color system. (3) When there is an input signal corresponding to a color outside the color reproduction range of the output device, there is a means for converting this into a signal corresponding to a color within the color reproduction range of the output device; For two input signals representing colors of the first color system that correspond to colors outside the color reproduction range of the output device, the starting point address generation memory is configured to convert the colors outside the color reproduction range to within the color reproduction range. and corresponding to the two input signals representing the colors of the first color system,
A maximum/minimum memory is provided that outputs a signal that determines the upper and lower limits that one other input signal can take, and the other input signal is compared with the output of the upper and lower limits of the maximum/minimum memory, and the output of the other input signal is 3. The color correction circuit according to claim 1, further comprising a comparator that substitutes a value within the range when the signal is outside the upper and lower limits.