JPH09261503A - Color image printer and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image printer and its method in which an optional color, especially a black color with a low luminance level is printed out accurately. SOLUTION: A range of dispersion in Y, M, C luminance signals is decided depending on a mean value-of the Y, M, C luminance signals and it is set to a discrimination table 6a. A luminance correction circuit 6 obtains the mean value and the dispersion of the received luminance signals and discriminates whether or not the obtained dispersion is within a range set to the discrimination table 6a. When the dispersion is within a set range, the received luminance signal is decided to be a deteriorated luminance signal and the luminance signal of each of the Y, M, C colors is replaced with a signal denoting the mean value and a color corresponding to the luminance signal after the replacement is printed out. When the dispersion is out of the set range, the received luminance signal is outputted as it is and a corresponding color is printed out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image printing apparatus and method, and more particularly to a color image printing apparatus and method capable of printing an image with high quality.

[0002]

2. Description of the Related Art A thermal transfer color printer is known as a color image printing apparatus. Thermal transfer color printer
The three primary colors Y (yellow), M (magenta), C
An image is printed by the subtractive color method using a color ink ribbon coated with (cyan).

That is, Y, M, and C inks are printed on a recording paper individually or in an overlapping manner, and blue,
Expresses various colors such as red, green, and black. For example, when M and C are overlapped and printed, it becomes blue, when Y and M are overlapped and printed, it becomes red, and when Y and C are overlapped and printed, it becomes green.

When the luminance of Y, M, and C is equal and the level thereof is high, light black is printed, and when the luminance of Y, M, and C is equal and the level thereof is low, dark black is printed. It

FIG. 8 shows the relationship between the overlapping of Y, M and C and the colors expressed by them.

[0006]

In order to print "black" by using this type of printing apparatus, as described above, Y,
The inks of M and C must be overprinted at the same brightness (density).

However, due to the difference between the photoelectric conversion characteristic of the apparatus for obtaining the image to be printed and the sensitivity characteristic of human vision, the error in signal processing, and the like, the colors Y and M of the colors which are recognized as black by human vision are recognized. , C may not be equal in brightness. In such a case, for example, reddish black or bluish black is printed, the print result becomes unnatural, and the quality of the printed image deteriorates.

The human vision feels that something with low luminance is darker. For this reason, the deterioration of the quality of the printed image is particularly noticeable when printing low-luminance black, that is, dark black.

The present invention has been made in view of the above situation, and an object thereof is to provide a color image printing apparatus and method capable of printing an image with high quality. Also,
SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image printing apparatus and method capable of accurately printing any color, for example, dark black.

[0010]

In order to achieve the above-mentioned object, a color image printing apparatus according to a first aspect of the present invention provides a brightness signal representing brightness of a plurality of colors for representing an arbitrary color by color mixture. Receiving means for receiving, discriminating means for discriminating the amount of deviation between the colors represented by the luminance signals of a plurality of colors received by the receiving means and a predetermined color, and the amount of deviation discriminated by the judging means in advance. A determination unit that compares the determined predetermined ranges and determines whether the displacement amount determined by the determination unit is within a predetermined range; and the determination unit determines that the displacement amount is within the predetermined range. Correction means for correcting the luminance signal received by the receiving means to a luminance signal representing the predetermined color when determined.
It is characterized by having.

Also, in the color image printing method according to the second aspect of the present invention, the amount of deviation between the color represented by the brightness signal representing the brightness of a plurality of colors and a predetermined color is judged, and the judged deviation is judged. Comparing the amount and a predetermined value, it is determined whether the determined deviation amount is less than or equal to a predetermined value, when the determined deviation amount is less than or equal to the predetermined value, the luminance signal, It is characterized in that the luminance signal representing the predetermined color is corrected, and the image is printed according to the corrected luminance signal.

According to the color image printing apparatus and method according to the first and second aspects, when the color represented by the luminance signal is close to the predetermined color, the luminance signal is corrected to obtain the predetermined color. To print. Therefore, any color can be printed accurately.

As the predetermined color, for example, black, which human eyes are sensitive to, is desirable. Furthermore, by making the predetermined range wider as the brightness of the color represented by the brightness signal is lower, it is possible to accurately print low brightness black that is sensitive to human vision.

A color image printing apparatus according to a third aspect of the present invention includes receiving means for receiving a luminance signal representing each luminance of a plurality of colors for expressing an arbitrary color by color mixture, and the receiving means. A discriminating unit that discriminates a variation in luminance represented by luminance signals of a plurality of colors, a determining unit that determines whether or not the variation determined by the determining unit is within a predetermined range, and the determining unit determines that the variation is A correction unit that corrects the luminance signals of the plurality of colors so that they match each other when it is determined that the luminance signals are within the predetermined range.

In the color image printing method according to the fourth aspect of the present invention, a receiving step of receiving a brightness signal representing the brightness of a plurality of colors for expressing an arbitrary color by color mixture, and a receiving step received in the receiving step. A step of determining a variation in luminance of a plurality of colors represented by a luminance signal, a determination step of determining whether or not the variation determined in the determining step is within a predetermined correction range, and the variation in the determination step When it is determined that the color image is within the predetermined range, a color image is printed based on a correction step of correcting the luminance signals of the plurality of colors to match each other and the luminance signals of the plurality of colors corrected by the correction step. And a step of performing.

According to the color printing apparatus and the method according to the third and fourth aspects, the luminance signal is corrected and the luminance signals are matched with each other when the variation of the luminance signal is small.
Therefore, it is possible to accurately print the color represented by the same luminance signal.

[0017]

DETAILED DESCRIPTION OF THE INVENTION A color image printing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(First Embodiment) First, the structure of a color image printing apparatus according to a first embodiment of the present invention will be described with reference to FIG.

As shown in the figure, this printing apparatus includes a color image acquisition apparatus 1, a signal processing circuit 2, an analog / digital (A / D) converter 3, an image memory 4, an arithmetic circuit 5, a brightness correction circuit 6, and a color. It is composed of a printer 7.

The color image acquisition device 1 is composed of a video camera or the like, takes in an arbitrary image, and outputs a video signal (composite video signal) defining the taken image. The color image acquisition device 1, like a video tape recorder,
It is also possible to reproduce and output a prerecorded video signal.

The signal processing circuit 2 includes a color image acquisition device 1
Video signals supplied from the three primary colors of light (R (red),
G (green) and B (blue)) are converted into analog signals (R, G, B analog brightness signals) representing the brightness of each color.

The A / D converter 3 converts the R, G, B analog luminance signals supplied from the signal processing circuit 2 into R, G, B signals.
Each is converted into a 4-bit digital luminance signal.

The image memory 4 stores the R, G, B digital luminance signals from the A / D converter 3.

The arithmetic circuit 5 converts the digital luminance signals of R, G and B stored in the image memory 4 into print dots (pixels).
The data is sequentially read in units and converted into 4-bit Y (yellow), M (magenta), and C (cyan) 4-bit digital luminance signals corresponding to the ink colors of the color printer 7. The three primary colors of light (RGB) and the three primary colors of color (YMC) are complementary colors. Therefore, the arithmetic circuit 5, for example, R to C, G
To M and B to Y, respectively.

The brightness correction circuit 6 is provided with the discrimination table 6a shown in FIG. 2, and the digital brightness signals of Y, M, and C colors supplied from the arithmetic circuit 5 are made "black" by the method described later.
Correct so that is printed properly.

The color printer 7 comprises a thermal dot printer using Y, M and C inks. The color printer 7 stores, for example, the Y, M, and C digital luminance signals supplied from the luminance correction circuit 6 in units of one row (printing row), and based on the stored Y, M, and C digital luminance signals, By transferring the Y, M, and C color inks on the ink ribbon onto the recording paper, the colors defined by the Y, M, and C luminance signals are printed.

Next, the contents of the correction executed by the brightness correction circuit 6 will be described with reference to FIGS.

Even if an image is recognized as black by human vision, photoelectric conversion characteristics and A / D in the color image acquisition device 1 are obtained.
Values of digital luminance signals of Y, M, and C colors supplied to the luminance correction circuit 6 due to a conversion error in the converter 3 and an arithmetic error in the arithmetic circuit 5 (that is, the luminance represented by these signals).
May not be equal. Even in such a case, since the appropriate “black” is printed, the brightness correction circuit 6
The digital luminance signals of Y, M, and C that indicate colors near black are corrected so that their values are equal, and the color printer 7 is made to print accurate black.

The correction process of the brightness correction circuit 6 will be specifically described. Note that, here, it is assumed that the Y, M, and C color digital luminance signals have 4 bits, and the luminance is expressed in 16 levels from 0 to 15.

FIG. 2 shows the contents of the discrimination table 6a stored in the brightness correction circuit 6.

The discrimination table 6a shows the relationship between the average value of the luminance of Y, M, and C and the range (predetermined range) of the variation of the luminance (difference between the maximum value and the minimum value) that requires correction.

The predetermined range is set wider as the average value of the brightness of Y, M and C is smaller. That is, the average value is 0
In the range of to 4, the predetermined range is set to 0 to 2,
The average value is set to 0 or 1 in the range of 5 to 10, and is set to 0 in the range of 11 to 15.

The brightness correction circuit 6 has an average value and a variation of the brightness of Y, M and C represented by the digital brightness signals of Y, M and C supplied from the arithmetic circuit 5 (difference between the maximum value and the minimum value of the brightness).
And determines whether the variation is within a predetermined range corresponding to the average value. When the variation is within a predetermined range, that is, when the color represented by the Y, M, and C digital luminance signals approximates to black, the luminance of each of the Y, M, and C colors is corrected to their average value. Note that when the variation is 0, the luminance of each color of Y, M, and C is originally equal to each other, and thus no correction is performed.

FIG. 3 shows an example of correction when the average of the luminances of Y, M and C is high. FIG. 3A shows Y, M, and C before correction.
Of luminance, and Y = 10, M = 12, and C = 11.
In this case, the average value of the luminance of Y, M, and C is 11 (= (10
+ 12 + 11) / 3), and the variation is 2 (= 12−).
10). Since the correction range is 0 when the average value is 11 from the discrimination table 6a, the variation is outside the correction range. Therefore, the brightness correction circuit 6 does not correct the brightness signal, and as shown in FIG.
Output to In this case, slightly reddish black is printed.

On the other hand, FIG. 4 shows a correction example in the case where the average luminance of Y, M and C is low. FIG. 4A shows Y before correction,
The brightness of M and C is shown, and Y = 2, M = 0, and C = 1.
In this case, the average value of the brightness of Y, M, and C is 1 (= (2 + 0
+1) / 3), and the variation is 2. From the discrimination table 6a, the predetermined range when the average value is 1 is 0 to 2, and the variation is within the predetermined range. Therefore, FIG.
As shown in, the brightness of each of the Y, M, and C brightness signals is given by Y = M
= C = 1 = corrected to an average value and output to the color printer 7. In this case, black is printed correctly.

In the discrimination table 6a of FIG. 2, the predetermined range referred to when correcting the luminance signal is set so as to become smaller as the average value of the luminances of Y, M and C becomes higher. That is, as described with reference to FIGS. 3 and 4, the correction is set to be easier as the average value of the luminance of Y, M, and C is lower. As described above, human vision has the characteristic of making dark objects appear blacker. Therefore, with this correction method, it is possible to perform printing that matches the characteristics of human color (black) recognition.

Next, the operation of the printing apparatus shown in FIG. 1 from capturing an image to printing will be described with reference to FIGS.

First, the color image acquisition apparatus 1 is driven to
An image is captured (step S1), the captured image is converted into a video signal, and the video signal is sequentially supplied to the signal processing circuit 2. The signal processing circuit 2 converts the video signals sequentially supplied from the color image acquisition device 1 into R, G, B analog luminance signals and outputs them (step S2). The A / D converter 3 converts the R, G, B analog luminance signals supplied from the signal processing circuit 2 into R, G, and B of 4 bits for each pixel.
The digital luminance signals of G and B are converted and sequentially output (step S3). R, G supplied from the A / D converter 3,
The B digital luminance signal is sequentially stored in the image memory 4 on a pixel-by-pixel basis (step S4).

The arithmetic circuit 5 reads out the R, G, B digital luminance signals to be printed from the image memory 4 on a pixel-by-pixel basis. The arithmetic circuit 5 converts the read digital brightness signals of R, G, B into digital brightness signals of 4 bits for each color of Y, M, C corresponding to the colors of ink used in the color printer 7, and the brightness correction circuit 6 Sequential supply (step S
5).

The brightness correction circuit 6 obtains the average value and variation of the brightness represented by the Y, M, and C digital brightness signals sequentially supplied from the arithmetic circuit 5 in pixel units (step S6).

Based on the obtained average value, the discrimination table 6a shown in FIG. 2 is referred to, and it is discriminated whether or not the luminance variation is within a predetermined range (step S7). If it is within a predetermined range, that is, if the variation in the brightness of Y, M, and C of each pixel is relatively small and black or a color close to black is to be printed, the brightness of the received Y, M, and C is displayed. The signal values are replaced with their average value (step S8). The brightness correction circuit 6 sends the corrected Y, M, and C digital brightness signals to the color printer 7.

In accordance with this luminance signal, the color printer 7 sequentially prints Y, M, and C inks on the corresponding pixels in the same luminance (darkness), and finally prints black (step S9). .

If it is determined in step S7 that the variation is not within the predetermined range, that is, if the variation is large, the values of the supplied Y, M, and C luminance signals are not corrected and the color printer is not corrected. Send to 7 as is. The color printer 7 prints the colors represented by the supplied Y, M, and C luminance signals (step S9).

The arithmetic circuit 5, the brightness correction circuit 6, and the color printer 7 in FIG. 1 sequentially repeat the processing from step S5 to step S9 until the printing is completed.

In this way, the color represented by the luminance signal, which is close to black, in particular, the dark color is corrected to black and printed, and high quality printing that matches the human visual characteristics is performed.

In the discrimination table 6a of FIG. 2, Y,
Although the predetermined range is changed in three steps according to the average value of the brightness of M and C, the average value and the predetermined range (range of brightness variation) corresponding thereto can be arbitrarily set. For example, when the average value is 0 to 4, the predetermined range is 0 to 4, and when the average value is 5 to 8, the predetermined range is 0 to 3, and so on.

Further, in the discrimination table 6a of FIG. 2, the range of the variation to be corrected is set, but the maximum value of the variation to be corrected is set, and when the variation is smaller than this maximum value, Y , M, and C may be set to average values.

In this embodiment, the amount of deviation (difference, distance) between the color represented by the Y, M, and C luminance signals and black is Y,
Although it is determined by the variation in the brightness of M and C, Y, M, and C
The difference (distance) between the color represented by the luminance signal and the black color (distance) may be determined using another method. For example, whether or not to perform the correction may be determined based on the difference (distance) on the chromaticity diagram between the color represented by the Y, M, and C luminance signals and black.

Further, the number of bits of the R, G and B luminance signals,
The number of bits of the Y, M, and C luminance signals can be set arbitrarily.

The processing procedure shown in FIG. 5 is an example.
It can be changed arbitrarily. Further, in the first embodiment, Y,
Although the correction range is set according to the average value of the brightness represented by the M and C brightness signals, any other reference may be adopted.

In the above description, the case where a thermal dot printer using Y, M, and C ink ribbons is used as the color printer 7 has been described. However, the present invention is not limited to this.
The present invention can be similarly applied to a color printer that prints an image using Y, M, and C toners.

(Second Embodiment) In the first embodiment, an apparatus and method for accurately printing black, which is the most important color for human color recognition, has been described, but the present invention is optional. It is also applicable to an apparatus and method for printing colors accurately.

The color tone of each color is determined by the ratio of the luminances of Y, M and C. Therefore, in the case of printing an arbitrary color accurately, it is necessary to correct a luminance signal representing a color that approximates the color to be accurately printed into a luminance signal of Y, M, C corresponding to the color to be accurately printed. Good.

Here, the luminance ratio is Y: M: C = Ay:
A procedure for accurately printing a color of Am: Ac will be described.

Now, the colors represented by the Y, M, and C digital luminance signals supplied from the arithmetic circuit 5 to the luminance correction circuit 6 are as shown in FIG.
It is assumed that it is located at the point X in the three-dimensional space of Y, M, and C shown in. When this point X is located in the vicinity of the straight line represented by Y: M: C = Ay: Am: Ac, that is, when the color represented by the luminance signal from the arithmetic circuit 5 is accurately approximate to the color to be printed. Therefore, it is necessary to correct the luminance of Y, M, and C. Therefore, a perpendicular is drawn from the point X to a straight line represented by Y: M: C = Ay: Am: Ac, and a point Z and a point X where the straight line and the perpendicular intersect.
Find the distance to. Then, this distance is set as a shift amount that represents a measure of how far the color represented by the luminance signal is accurately separated from the color to be printed.

When the amount of deviation is within a predetermined range of the shaded portion in FIG. 6 which is set in advance, the digital luminance signals of Y, M and C are replaced with the luminance signal of the point Z. The brightness correction circuit 6 sends the replaced brightness signal to the color printer 7.

On the other hand, like the color represented by the point Q in FIG.
If the amount of deviation is outside the predetermined range, the Y, M, and C digital luminance signals are not corrected and are directly transmitted to the color printer 7.

With such a configuration, it is possible to print an arbitrary color in a color that human eyes can perceive without being affected by photoelectric conversion characteristics, errors due to signal processing, and the like.

In FIG. 6, the lower the luminance of an arbitrary color is, the narrower the predetermined range is. The reason why such a predetermined range is adopted is that black having low brightness, which is important for human color recognition, is not changed to a color of Y: M: C = Ay: Am: Ac. However, the present invention is not limited to this, and the correction range of any pattern can be set.

In the first and second embodiments, the color to be accurately printed is one color, but it is also possible to accurately print a plurality of colors by preparing a predetermined range for a plurality of colors. Is.

(Third Embodiment) In the first embodiment, the contents of the judgment table are fixed, but for example, the user may arbitrarily set / change the contents of the judgment table. For example, as shown in FIG.
Therefore, the contents of the discrimination table 6a may be arbitrarily set. With such a configuration, the predetermined range can be arbitrarily set / changed by the control device 8, so that the print color is corrected according to the user's preference, or the degree of correction is changed according to the characteristics of the color printer. , The correction process can be optimized.

Further, the control device 8 may be allowed to set different determination tables for each of a plurality of areas of the image to be printed. With such a configuration,
It is possible to perform various types of image processing, such as preventing black color shift in only a specific area of the image.

The present invention is not limited to the first to third embodiments described above, and various modifications and applications are possible.
For example, the circuit configuration of FIG. 1 can be arbitrarily changed. For example, without providing an image acquisition device or the like, the brightness correction circuit 6 may be directly supplied with Y, M, and C brightness signals from the outside. . Further, the color printer 7 and other circuits may be separately arranged.

[0064]

As described above, according to the present invention, it is possible to correct a color close to a predetermined color to a predetermined color before printing. For example, a color close to black represented by the luminance signal can be printed in black. Therefore, it is possible to suppress a color shift that occurs during image acquisition or signal processing, and to print a high-quality image that matches human vision. Further, by expanding the correction range for a color having low luminance, it is possible to print an image having a natural impression close to the human visual sense of a dark color that is darker.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a printing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a determination table shown in FIG.

FIG. 3 is a diagram illustrating a correction example of a digital luminance signal when Y, M, and C have high luminance.

FIG. 4 is a diagram showing a correction example of a digital luminance signal when the luminance of Y, M, and C is low.

FIG. 5 is a flowchart illustrating a procedure from image capture to printing in the printing apparatus according to the first embodiment of the present invention.

FIG. 6 is a diagram for explaining color correction according to the second embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a printing apparatus according to a third embodiment of the present invention.

FIG. 8 is a diagram illustrating a printing method of a subtractive color method.

[Explanation of symbols]

1 ... Color image acquisition device, 2 ... Signal processing circuit,
3 ... A / D converter, 4 ... Image memory, 5 ...
Calculation circuit, 6 ... Luminance correction circuit, 6a ... Discrimination table, 7 ... Color printer

Claims (12)

[Claims] 1. A receiving means for receiving a luminance signal representing luminance of a plurality of colors for expressing an arbitrary color by color mixture, a color represented by a luminance signal of a plurality of colors received by the receiving means, and a predetermined color. A discriminating unit for discriminating the amount of deviation from the color is compared with a discriminating amount discriminated by the discriminating unit and a predetermined range, and whether or not the discriminating amount discriminated by the discriminating unit is within a predetermined range. And a brightness signal representing the predetermined color, the brightness signal being received by the receiving means when the displacement amount is determined to be within the predetermined range by the determining means. A color image printing apparatus comprising: 2. The color image printing apparatus according to claim 1, wherein the correction means outputs a brightness signal representing black by color mixing by matching the brightness signals of the plurality of colors. 3. The discriminating means comprises means for discriminating variations in luminance represented by the luminance signals of the plurality of colors, and the judging means determines whether or not the deviation amount is within the predetermined range. The color image printing apparatus according to claim 1 or 2, comprising a means. 4. The color image printing apparatus according to claim 1, wherein the brightness signal is composed of signals indicating the brightness of each color of yellow, magenta, and cyan. 5. The predetermined range is set to a different range according to the brightness of the color represented by the brightness signals of the plurality of colors, according to claim 1, 2, 3 or 4. Color image printing device. 6. The predetermined range is set to different ranges according to an average value of the brightness represented by the brightness signals of the plurality of colors, according to claim 1, 2, 3 or 4. The described color image printing device. 7. The color according to claim 2, wherein the predetermined range is set to become narrower as the average value of the brightness represented by the brightness signals of the plurality of colors becomes higher. Image printing device. 8. A printing means for printing the color represented by the brightness signal by printing inks of a plurality of colors in an overlapping manner based on the brightness signals of the plurality of colors corrected by the correction means. The color image printing apparatus according to claim 1, wherein the color image printing apparatus is a color image printing apparatus. 9. A color represented by a luminance signal representing luminance of a plurality of colors,
The amount of deviation from a predetermined color is determined, the determined amount of deviation is compared with a predetermined value, and it is determined whether the determined amount of deviation is less than or equal to a predetermined value. When it is determined that the brightness signal is equal to or less than a predetermined value, the brightness signal is corrected to a brightness signal representing the predetermined color, and an image is printed according to the corrected brightness signal. Method. 10. The luminance signals are yellow, magenta,
10. A signal indicating the brightness of each color of cyan, wherein the correction step outputs a brightness signal representing black by matching the brightness of each color of yellow, magenta, and cyan. The described color image printing method. 11. A receiving unit that receives a luminance signal representing each luminance of a plurality of colors for expressing an arbitrary color by color mixture, and a variation in luminance represented by the luminance signals of the plurality of colors received by the receiving unit are determined. A determining unit, a determining unit that determines whether the variation determined by the determining unit is within a predetermined range, and the determining unit determines that the variation is within a predetermined range. A color image printing apparatus comprising: a correction unit that corrects luminance signals of a plurality of colors so as to match each other. 12. A receiving step of receiving a luminance signal representing luminances of a plurality of colors for expressing an arbitrary color by color mixture, and a variation of luminances of a plurality of colors represented by the luminance signal received in the receiving step. A step, a determination step of determining whether or not the variation determined in the determination step is within a predetermined range, and a plurality of values when the variation is determined to be within a predetermined range by the determination step. A color image printing method, comprising: a correction step of correcting the color luminance signals to match each other; and a step of printing a color image based on the luminance signals of a plurality of colors corrected by the correction step. Method.