JP4208583B2 - Image processing apparatus and method and program thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing technique for obtaining binary data by performing pseudo gradation processing on multi-valued image data.
[0002]
[Prior art]
Conventionally, an error diffusion method is known as a pseudo halftone process for expressing multilevel data in binary (“An Adaptive Algorithm for Spatial Gray Scale” in society for Information Display 1975 Symposium Digest of Technical Papers, 1975, 36). . In this method, the pixel of interest is P, the density is v, the densities of the peripheral pixels P0, P1, P2, and P3 of the pixel of interest P are v0, v1, v2, and v3, respectively, and the threshold for binarization is T. In this case, the binarization error E in the target pixel P is distributed to the surrounding pixels P0, P1, P2, and P3 according to the weight coefficients W0, W1, W2, and W3 obtained empirically, so that the binary error is obtained macroscopically. In this method, the average density of the converted image is made equal to the density of the original image. At this time, if the output binary data is O,
If v ≧ T, O = 1, E = v−Vmax;
If v <T, O = 0, E = v−Vmin; (1)
(However, Vmax: Maximum density, Vmin: Minimum density)
v0 = v0 + E × W0; (2)
v1 = v1 + E × W1; (3)
v2 = v2 + E × W2; (4)
v3 = v3 + E × W3; (5)
Here, as examples of weighting factors, W0 = 7/16, W1 = 1/16, W2 = 5/16, and W3 = 3/16.
[0003]
When such a method is used to perform pseudo-halftone processing of multiple colors, for example, cyan, magenta, yellow, and black, which are used in color ink jet printers, etc., each color is processed using the above error diffusion method or the like. Had gone. For this reason, when one color is viewed, even if the visual characteristics are excellent, if two or more colors overlap, a good visual characteristic cannot always be obtained.
[0004]
In order to improve such a defect, for example, according to Patent Documents 1 and 2 below, by using an error diffusion method by combining two or more colors, good visual characteristics can be obtained even when two or more colors overlap. The resulting pseudo halftone processing method is disclosed.
[0005]
However, in these methods, when the output corresponding to the input pixel is determined, the output value is determined by a comparator or the like. For example, when the number of output gradations is changed, it is implemented by hardware. If the circuit is implemented by software, or if it is implemented by software, the program must be changed significantly.
[0006]
[Patent Document 1]
JP-A-8-279920
[Patent Document 2]
Japanese Patent Laid-Open No. 11-10918
[Problems to be solved by the invention]
In order to solve such a problem, an image signal of two or more colors obtained by adding error signals from a predetermined number of peripheral pixels as means for performing error diffusion by combining two or more colors and determining the output of the target pixel Has been proposed for determining the output value of an LUT. However, in such a method, when the number of input signal channels increases to 3 or more, the amount of data in the LUT increases. Further, when the number of gradations of multi-value data of each color is increased, or when the number of points per color of the LUT is increased in order to finely control the output characteristics, the data amount of the LUT is increased. Conversely, if the number of points for each color is too small, the output characteristics that can be set in the LUT will be rough.
[0007]
  The present invention has been made in view of the above conventional example.Input an image signal that exceeds color2 for error diffusionUsing two two-dimensional LUTs, obtain pseudo gradation output values of these three colors or moreAccordingly, an object is to reduce the data amount of the LUT.
[0008]
[Means for Solving the Problems]
  In order to achieve the above object, the image processing apparatus of the present invention comprises the following arrangement. That is,
  At least first-color pixel data, second-color pixel data, and third-color pixel data, and first-color error data and second-color data from pixels that have already undergone pseudo-gradation processing Error data of the first color and error data of the third color are input, the error data of the first color is added to the pixel data of the first color, and the pixel data of the first color after the addition is output And adding the error data of the second color to the pixel data of the second color and outputting the pixel data of the second color after the addition, and adding the third error to the pixel data of the third color Adds data and outputs pixel data of third color after additionAdding means;
  A first addition result obtained by adding the pixel data of the first color after addition output from the addition means and the pixel data of the second color after addition, and the addition output from the addition means A first two-dimensional LUT for inputting the subsequent pixel data of the third color and outputting the pseudo gradation output value and the selection signal of the third color; and the pixel data of the first color after the addition And a second two-dimensional LUT for inputting the pixel data of the second color after the addition and outputting the pseudo gradation output candidate value of the first color and the pseudo gradation output candidate value of the second color. The first addition result and the third pixel data after the addition are input to the first two-dimensional LUT, the selection signal is output, and the pseudo gradation output of the third color is output. A value is determined, and the pixel data of the first color after the addition and the previous two-dimensional LUT Based on the pseudo-tone output candidate value of the first color, the pseudo-tone output candidate value of the second color, and the selection signal output by inputting the pixel data of the second color after the addition. Output value determining means for determining the pseudo gradation output value of the first color and the pseudo gradation output value of the second color;
  The first color pseudo gradation output value determined by the output value determination means, the second color pseudo gradation output value, and the third color pseudo gradation output value, and after the addition Error calculating means for calculating an error in the pixel of interest based on the pixel data of the first color of the second color, the pixel data of the second color after the addition, and the pixel data of the third color after the addition. And
  The output value determining means converts the pseudo gradation output candidate value of the first color and the pseudo gradation output candidate value of the second color into the pseudo gradation of the first color according to the selection signal. The output value and the pseudo tone output value of the second color are selected, or the pseudo tone output value of the first color and the pseudo tone output value of the second color are each set to 0. Thus, the pseudo gradation output value of the first color and the pseudo gradation output value of the second color are determined.It is characterized by that.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0010]
[Embodiment 1]
FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to Embodiment 1 of the present invention. In the present embodiment, a case will be described in which 8-bit multi-value image data is input and binary data is output by image processing.
[0011]
In the figure, each of I0, I1, and I2 represents pixel data of an input image of color 0 (for example, cyan), color 1 (for example, magenta), and color 2 (for example, black), and each is 8-bit multi-value data. It is. These pixel data are input to adders indicated by 10, 11 and 12, respectively. In these adders 10, 11, and 12, multi-value data I0, I1, and I2 and error data E0, E1, and E2 from pixels that have already undergone pseudo gradation processing are input, respectively, and input pixel data I0. , I1, and I2, the error data E0, E1, and E2 are added and output. The outputs I′0, I′1, and I′2 of the adders 10, 11, and 12 are respectively input to the output determining unit 16, and the output determining unit 16 determines the output values O0, O1, and O2 of the respective colors. The Further, the outputs O0, O1, and O2 of the output determination unit 16 are input to error calculation units 13, 14, and 15, respectively. These error calculators 13, 14, and 15 receive the outputs O0, O1, and O2 of the output determiner 16 and the outputs I'0, I'1, and I'2 of the adders 10, 11, and 12, respectively. Then, errors E0, E1, and E2 are output, respectively.
[0012]
The outputs E0, E1, and E2 of the error calculators 13, 14, and 15 are input to adders 10, 11, and 12, respectively, and added to the pixel data that is input next.
[0013]
In the present embodiment, an example has been described in which the outputs E0, E1, and E2 of the error calculators 13, 14, and 15 are directly fed back to the inputs and input to the adders 10, 11, and 12, respectively. However, as shown in the prior art, the weighting factor may be used to repeat the process for the pixels on the next line.
[0014]
With the above configuration, processing for one input data is performed. Therefore, the above processing is repeated by shifting one pixel at a time in the image direction, one line processing is performed, and then the same processing is repeated by shifting one raster at a time. As a result, pseudo gradation processing can be performed on the entire image.
[0015]
[Output Determination Unit 16]
The output determination unit 16 according to the present embodiment refers to a two-dimensional LUT once or a plurality of times when determining an output value using an LUT for input image data of three or more channels. In this embodiment, the output for the three-dimensional input data is determined by referring to the two-dimensional LUT twice.
[0016]
FIG. 2 is a block diagram for explaining the output determination unit 16 according to the present embodiment.
[0017]
First, when the outputs I′0, I′1, and I′2 from the adders 10, 11, and 12 are input, the one-dimensional LUTs 20, 21, and 22 are referred to, and the LUT grid converted by these LUTs. Signals g0, g1, and g2 corresponding to are respectively output.
[0018]
FIG. 3 is a diagram showing an example of data in each of these one-dimensional LUTs 20, 21, and 22. As shown in FIG.
[0019]
In these LUTs, the input value can take "-128" to "383", and the output signals g0, g1, and g2 are each composed of 3 bits. When the input value is less than that including “36”, the output value is “0”. When the input value is “37” to “73”, the output value is “1” and the input value is “74” to “109”. The output value is “2”, the input values “110” to “146” are the output value “3”, the input values “147” to “182” are the output value “4”, and the input value “ The output value is “5” in the case of “183” to “219”, the output value is “6” in the case of the input value “220” to “254”, and the output value is in the case of the input value “255” to “383”. Each is set to “7”.
[0020]
In FIG. 2, gp obtained by adding the signals g0 and g1 by the adder 25 and the signal g2 which is the output of the LUT 22 are input to the LUT 24 to refer to the LUT, and color 2 (in this embodiment) O2 which is an output of black) and a selection signal s are output.
[0021]
4A and 4B are diagrams showing an example of data in the LUT 24. FIG.
[0022]
In FIG. 4A, gp on the horizontal axis indicates the addition result (4 bits) of g0 and g1, and a large amount of data (0-14) is prepared for g2 (0-7) on the vertical axis. Yes. The signal O2 output from the LUT 24 indicates whether or not to generate color 2 dot data for the pixel being processed. Specifically, “1” indicates that there is a dot, and “0” indicates that there is no dot data.
[0023]
If the value of s is “0”, the output of both color 0 and color 1 is set to “0”, that is, there is no dot data for color 0 and color 1. If the value of s is “1”, the output of color 0 and color 1 means that the output determined by the reference result of the LUT 23 is selected as the output. The selection signal s is sent to the AND circuits 26 and 27.
[0024]
In FIG. 2, the LUT 23 receives signals g0 and g1 to refer to the LUT, and outputs 1-bit signals t0 and t1 that are candidates for output of color 0 and color 1, respectively. These t0 and t1 are sent to the AND circuits 26 and 27. If the selection signal s is "1", the output of color 0 and color 1 (t0, t1) is output as O0 (cyan) and O1 (magenta). The If the selection signal s is “0”, the outputs O 0 and O 1 are “0”.
[0025]
5A and 5B are diagrams for explaining data in the LUT 23. FIG.
[0026]
In the present embodiment, it is intended to determine whether or not to generate dot data for at least one of color 0 and color 1 based on the selection signal s obtained by the processing in the LUT 24 described above. . Therefore, in the data used in the LUT 23, either data of color 0 or color 1 is always generated in FIG. 5 (data in FIG. 5A corresponds to “◯” shown in FIG. 5B). Data is not included).
[0027]
In this way, the output determination unit 16 outputs the signals O0, O1, and O2 generated as described above.
[0028]
[Error calculation units 13 to 15]
The outputs O0, O1, and O2 of the output determination unit 16 are input to the error calculation units 13, 14, and 15, respectively.
[0029]
FIG. 6 is a block diagram showing the configuration of each of these error calculators 13, 14, 15.
[0030]
The outputs O 0, O 1 or O 2 of the output determination unit 16 and the outputs I ′ 0, I ′ 1, I ′ 2 of the adders 10, 11, 12 are input, and errors E 0, E 1, E 2 are output respectively. .
[0031]
In the figure, reference numeral 60 denotes a one-dimensional LUT. When the outputs O0, O1, and O2 of the output determining unit 16 are input, the LUT 60 is referred to and O'0, O'1, and O'2 are output. .
[0032]
The data of this LUT 60 is shown in FIG.
[0033]
In FIG. 7, each of O′0, O′1, and O′2 represents each output O0, O1, and O2 of the output determination unit 16 (in the present embodiment, a value of “0” or “1”). This is a value converted to the input signal level (0 to 255).
[0034]
O'0, O'1, and O'2 are subtracted from the outputs I'0, I'1, and I'2 from the adders 10, 11, and 12 by the subtractor 61, and error output E0 is obtained. , E1, E2 are obtained. That is,
E0 = I'0-O'0
E1 = I'1-O'1
E2 = I'2-O'2
It is.
[0035]
The outputs E0, E1, and E2 of the error calculators 13, 14, and 15 are input to adders 10, 11, and 12, respectively, and are added to the next input pixel data (I0, I1, and I2).
[0036]
In FIG. 4, an area where the generated dot is not “0” and the level of the image signal is relatively low, that is, an area having data that is not a black circle or a white circle in FIG. Data for at least one dot of color 1 is generated. For example, if data for color 2 (black) is generated for a certain pixel of interest and dot data for color 0 (cyan) and color 1 (magenta) is not formed, a negative error occurs in color 2, For another pixel close to the target pixel being processed that receives the error, color 2 dot data is less likely to be generated, and color 0 or color 1 dot data is likely to be generated.
[0037]
Thus, it becomes possible to process the input pixel data having a low dot density under the condition that the dot data is difficult to overlap for each color, and it is possible to perform a pseudo gradation process with excellent visual characteristics.
[0038]
In the present embodiment, as described above, by using the two-dimensional LUT data for the three-channel input signal, the necessary data amount can be reduced as compared with the case of using the three-dimensional LUT. I was able to.
[0039]
In this embodiment, an example in which the number of grids of the LUT is relatively small has been described for ease of explanation. However, as the grid interval is narrower than the input signal range, that is, as the number of grids increases, each input is increased. The output characteristics for the level can be set smoothly or finely. As the number of grids increases, the amount of data required for a three-dimensional or more LUT increases dramatically. Therefore, the data reduction effect according to this embodiment is also increased.
[0040]
Although the binary example has been described in the present embodiment, the present invention is not limited to the above-described configuration. If the LUT data is changed, pseudo gradation processing with three or more values or pseudo gradation processing with different maximum levels for each color can be performed.
[0041]
The gist of this embodiment is to perform pseudo gradation processing that reflects the relationship of each input signal by using a two-dimensional LUT once or more than once for input signals of three or more channels. It is possible to provide a highly versatile image processing apparatus that can cope with processing under different conditions by changing LUT data.
[0042]
[Embodiment 2]
In the first embodiment, the output determination unit 16 determines the output data value by referring to the 2-channel input LUT (two-dimensional LUT) twice.
[0043]
On the other hand, in the second embodiment, the algorithm for determining the output value is basically the same as in the first embodiment, but an example in which the processing flow is slightly different will be shown.
[0044]
FIG. 8 is a flowchart showing the flow of processing in the output determination unit 16 according to Embodiment 2 of the present invention. In the second embodiment, the configuration other than the output determination unit 16 is the same as that of the first embodiment described above, and the parts common to the first embodiment are indicated by the same symbols.
[0045]
Also in the second embodiment, as in the first embodiment, first, in step S1, the input signals (I0, I1, I2) of the respective colors to the output determining unit 16 are changed to the respective colors corresponding to the LUT grid. Convert to signals g0, g1, and g2. In step S2, the signal g0 and g1 are summed to obtain a signal gp (adder 25). Thereafter, the signals gp and g2 are input to the LUT 24, and an output O2 of color 2 and a selection signal s are obtained.
[0046]
In the second embodiment, in the subsequent step S4, it is determined whether or not the LUT 23 is referred to determine the output of the color 0 and the color 1 based on the selection signal s. That is, if the selection signal s is “1”, the LUT 23 is referred to determine the output values O 0 and O 1 for the color 0 and color 1 (step S5). Otherwise, the LUT 23 is not referred to and the output value O 0, O1 is set to “0” (step S6).
[0047]
In this example, in order to perform pseudo gradation processing that reflects the relationship between the input levels for three-channel inputs, the number of times a two-dimensional LUT is referenced for one pixel may be one time depending on the combination of input data. Shows good things.
[0048]
[Embodiment 3]
In the third embodiment, an example in which a condition for referring to an LUT for determining an output value is changed by a combination of input data will be described. The third embodiment is the same as the first embodiment except for the output determining unit 16.
[0049]
FIG. 9 is a block diagram for explaining the output determination unit 16a according to Embodiment 3 of the present invention.
[0050]
The third embodiment shows an example in which cyan image data is handled as color 0, magenta image data as color 1, and black image data as color 2. First, when I′0, I′1, and I′2 are input from the adders 10, 11, and 12 (FIG. 1), these are respectively input to the one-dimensional LUTs 70 to 72, and the LUT converted by these LUTs. Input signals g0, g1, and g2 corresponding to the grid are output from the respective LUTs. These are the same as those in the first embodiment described above, and the same applies to LUT data used in the one-dimensional LUTs 70, 71, 72 (FIG. 3).
[0051]
Thereafter, the input signals g0, g1, and g2 corresponding to the grid of the LUT are sent to the output determination units 100, 101, and 102 and the unit selection information acquisition unit 73, respectively. These three output determining units 100, 101, and 102 receive input signals g0, g1, and g2 and output information of output candidates for each color. The information is sent to the output selection unit 80, the output selection unit 81, and the output selection unit 82 for each color. Each of these output determination units 80 to 82 will be described in detail later.
[0052]
The unit selection information acquisition unit 73 receives the input signals g0, g1, and g2 and outputs unit selection signals s0, s1, and s2, respectively. The configuration of the unit selection information acquisition unit 73 will be described in detail later.
[0053]
FIG. 10 is a block diagram showing the configuration of each of the output selection units 80-82.
[0054]
Each of these output selection units includes signals t0-0 to t0-2, t1-0 to t1-2, t2-0 to t2-2 sent from the three output determination units 100, 101, 102, respectively. AND units 90 to 92 take the logical product of the unit selection signals s0, s1, and s2 sent from the unit selection information acquisition unit 73, and select information from one of the output determination units as an output. That is, if the selection signal s0 is “1” and the signals s1 and s2 are both “0”, the signal O0 from the output determination unit 80 is selected as an output. The adder 93 inputs the outputs of the AND circuits 90 and 91 and outputs the addition result to the adder 94. The other input of the adder 94 receives the logical product of the selection signal s2 from the AND circuit 92 and outputs the addition result as output signals O0, O1, and O2.
[0055]
[Description of Output Determination Units 100 to 102]
The three output determination units 100 to 102 have different combinations of signals used as input signals for the two LUTs referred to for output determination. Specifically, the output determination unit 100 acquires the output signal of color 2 (for example, black) and the selection signal s by referring to the first LUT, whereas the output determination unit 101 has the color of 0 (for example, cyan). The output determination unit 102 determines the output signal and selection signal s for the color 1 (for example, magenta) by referring to the first LUT.
[0056]
Block diagrams of the output determination unit 100, the output determination unit 101, and the output determination unit 102 are shown in FIGS. 11, 12, and 13, respectively.
[0057]
FIG. 11 is a block diagram illustrating the configuration of the output determination unit 100.
[0058]
Of the input signals g0, g1, and g2 of each color converted to correspond to the grid of the LUT, the adder 114 calculates the sum of the signals g0 and g1 to obtain gp. The gp and g2 are input to the LUT 110 for reference, and an output signal t0-2 for color 2 and a selection signal us are obtained. On the other hand, the LUT 111 receives and references the signals g0 and g1, and obtains output signals ut0 and ut1 of the color 0 and color 1 output candidates. These are sent to the AND circuits 112 and 113. The AND circuits 112 and 113 calculate the logical product of the output candidate signals ut0 and ut1 of color 0 and color 1 and the selection signal us, and output the outputs t0-0 and t0-1 of color 0 and color 1. That is, if the selection signal us is “1”, ut0 and ut1 output from the LUT 111 are the outputs t0-0 and t0-1 of color 0 and color 1, respectively. On the other hand, if the selection signal us is “0”, the outputs t0-0 and t0-1 of the colors 0 and 1 are both “0”.
[0059]
In the third embodiment, the same data is used in the output determination units 100 to 102 as the LUT data of the output determination unit.
[0060]
Examples of data used in the LUT 110 of the output determination unit 100, the LUT 120 of the output determination unit 101, and the LUT 130 of the output determination unit 102 are shown in FIGS.
[0061]
In FIG. 14A, the horizontal axis and the vertical axis use different signals as inputs depending on the respective output determination units, and are indicated by input1 and input2 (gp). Of the three input signals g0, g1, and g2, a signal (gp) obtained by summing two signals is used for the horizontal axis (input1), and a signal of a color that is not summed among the three signals is represented by the vertical axis (input2). use. This data is the same as the data used for the LUT 24 in the first embodiment.
[0062]
15A and 15B show data examples used in the LUT 111 of the output determination unit 100, the LUT 121 of the output determination unit 101, and the LUT 131 of the output determination unit 102.
[0063]
In FIG. 15A, two inputs are assigned to the horizontal axis and the vertical axis. This data is different from that used in the LUT 23 in the first embodiment, and when the sum of the input signals to the two LUTs is “3” or less, the output is “0” for both colors. Become. The output determination unit 101 and the output determination unit 102 are different from each other in the combination of color data used for each LUT of the output determination unit 100.
[0064]
(Effect of switching output decision unit)
In the third embodiment, as described above, the LUT data shown in FIG. 14 is the same as that in the first embodiment, but the LUT data shown in FIG. 15 is an input signal to two LUTs. When “3” or less is added, the output is “0” for both colors, which is different from the first embodiment.
[0065]
When such data is used, when both the input levels to the LUT in FIG. 15 are small, the dot data of the color corresponding to input1 and input2 is not generated. When both input1 and input2 are small, there is an advantage that the data of dots of these two kinds of colors can be arranged more orderly for the colors of input1 and input2 than the processing of the first embodiment. On the other hand, when data with another color (the color whose output is determined by the LUT 110, LUT 120, and LUT 130) coexists, the dot arrangement is somewhat disturbed.
[0066]
That is, when the output determination unit 100 is used, the LUT is referred to by inputting the signal obtained by adding the signals g0 and g1 and the signal g2, and the signals g0 and g1 are input to refer to the LUT data in FIG. Therefore, the result of pseudo gradation processing of dot arrangement with better visual characteristics can be obtained for data mixture of color 0 and color 1 dots. However, the mixing of dot data of color 2 and other colors results in a relatively poor result.
[0067]
Similarly, when the output determination unit 100 is used, a dot arrangement with relatively good visual characteristics can be obtained for a mixture of dot data of color 2 and color 0, and a comparison of dot data of color 1 and other colors can be obtained. The result is not good. Furthermore, when the output determination unit 101 is used, a dot arrangement with relatively good visual characteristics can be obtained for the mixing of dot data of color 1 and color 0, but the mixing of dot data of color 2 and other colors can be comparatively comparative. The result is not good.
[0068]
For each output determination unit having such characteristics, it is possible to select and use an output determination unit that can obtain a pseudo gradation processing result with excellent visual characteristics by combining input signals of each color. It is the purpose of the form.
[0069]
[Unit selection information acquisition unit 73]
FIGS. 16A and 16B are diagrams illustrating an example of data of a lookup table used by the unit selection information acquisition unit 73 according to the present embodiment.
[0070]
According to the block diagram (FIG. 9) of the output determination unit 16 according to the present embodiment described above, the unit selection information acquisition unit 73 receives signals g0, g1, and g2 corresponding to the LUT grid for all three colors. ing. However, in the fourth embodiment, the unit selection signals s0, s1, and s2 are selected by referring to the two-dimensional LUT that receives the signals g0 and g1.
[0071]
In the data of FIGS. 16A and 16B, when the sum of g0 and g1 is “3” or less, the selection signal s0 is set to “1” and the selection signals s1 and s2 are both set to “0”. It is set as follows. In other cases, that is, when the sum of g0 and g1 is greater than “3” and g0 is greater than or equal to g1, the selection signal s1 becomes “1”, and the selection signals s0 and s2 both become “0”. Become. When the sum of g0 and g1 is larger than “3” and g0 is smaller than g1, the selection signal s2 is “1”, and the selection signals s0 and s1 are both “0”.
[0072]
The setting of this condition assumes the following case. When an image is formed by a recording apparatus or printing, black is conspicuous, and light gray is formed by dots of cyan, magenta, and yellow (this method is hereinafter referred to as process black). Then, with process black, after increasing the gray density to some extent, black dots are used. This recording method makes black dots relatively inconspicuous.
[0073]
The black dots are conspicuous and the image quality of the pseudo gradation processing result may be lowered when the black dot data is generated at a low frequency. Therefore, in order to make black dots inconspicuous, low-frequency black data is used simultaneously with a certain amount of cyan, magenta, and yellow data.
[0074]
In this embodiment, when the input of cyan and magenta is below a certain level, that is, when the sum of g0 and g1 is “3” or less, the black data is always “0”. Assuming that the output of the output determining unit 100 having excellent cyan and magenta dot arrangement characteristics is adopted. In other cases, that is, when there is a black signal, if cyan data (color 0) is larger than magenta data (color 1), priority is given to the arrangement of magenta dot data and black dot data. Since the experimental result that black dot data is less conspicuous is obtained, the output of the output determination unit 101 is used. Further, when there is a black signal and magenta data (color 1) is larger than cyan data (color 0), the output determination unit 102 gives priority to the arrangement of cyan dot data and black dot data. To use the output of.
[0075]
[Other Embodiments]
Although the embodiment has been described in detail above, the present invention may be applied to a system constituted by a plurality of devices, or may be applied to an apparatus constituted by one device.
[0076]
In the present invention, a software program that realizes the functions of the above-described embodiments is directly or remotely supplied to a system or apparatus, and the computer of the system or apparatus reads and executes the supplied program code. Including the case where it is also achieved by. In that case, as long as it has the function of a program, the form does not need to be a program.
[0077]
Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the function processing.
[0078]
In this case, the program may be in any form as long as it has a program function, such as an object code, a program executed by an interpreter, or script data supplied to the OS.
[0079]
As a recording medium for supplying the program, for example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card ROM, DVD (DVD-ROM, DVD-R) and the like.
[0080]
As another program supply method, a client computer browser is used to connect to an Internet homepage, and the computer program of the present invention itself or a compressed file including an automatic installation function is downloaded from the homepage to a recording medium such as a hard disk. Can also be supplied. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.
[0081]
In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to execute the encrypted program by using the key information and install the program on a computer.
[0082]
In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer based on the instruction of the program is a part of the actual processing. Alternatively, the functions of the above-described embodiment can be realized by performing all of them and performing the processing.
[0083]
Furthermore, after the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board or The CPU or the like provided in the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.
[0084]
[Embodiment 1] A color multilevel image signal of 3 channels or more is input, and for each color, an error signal from a pixel for which pseudo gradation processing has been completed is added to the input color multilevel image signal for each color. A plurality of adding means to
An output determining means for inputting each addition result of the plurality of adding means and determining a pseudo gradation output for each color;
Error calculation means for calculating an error in the pixel of interest based on the pseudo gradation output for each color determined by the output determination means and the addition result for each color of the plurality of addition means;
The image processing apparatus, wherein the output determining means determines the pseudo gradation output by referring to a two-dimensional LUT having two-channel inputs a plurality of times.
[0085]
[Embodiment 2] The sum of color multi-value image signals of two channels among the three or more channels is input to one channel of the two-dimensional LUT, and the two-dimensional LUT is referred to at least once. The image processing apparatus according to the first embodiment.
[0086]
[Embodiment 3] An implementation characterized by further comprising selection means for selecting and outputting a pseudo gradation output for each color output from the output determination means in accordance with the addition results of the plurality of addition means. The image processing apparatus according to aspect 1 or 2.
[0087]
[Embodiment 4] A color multilevel image signal of 3 channels or more is input, and for each color, an error signal from a pixel for which pseudo gradation processing has been completed is added to the input color multilevel image signal for each color. An adding step to
An output determination step of inputting each addition result added in the addition step and determining a pseudo gradation output for each color;
An error calculation step of calculating an error in the pixel of interest based on the pseudo gradation output for each color determined in the output determination step and the addition result for each color in the addition step,
In the output determination step, the pseudo gradation output is determined by referring to a two-dimensional LUT having two-channel inputs a plurality of times.
[0088]
[Embodiment 5] The sum of two or more color multilevel image signals of the three or more channels is input to one channel of the two-dimensional LUT and the two-dimensional LUT is referred to at least once. The image processing method according to the fourth embodiment.
[0089]
[Embodiment 6] Embodiment 4 further comprising a selection step of selecting and outputting a pseudo gradation output for each color output in the output determination step according to each addition result in the addition step. Or the image processing method of 5.
[0090]
As described above, according to the present embodiment, when performing pseudo gradation processing for determining output using an LUT for three-channel input, the two-channel input LUT (two-dimensional LUT) is referred to a plurality of times. To determine the output. As a result, the data amount of the LUT can be reduced as compared with the case where the output is determined using the LUT having three or more channels.
[0091]
As a result, pseudo gradation processing that reflects the relationship of each input signal can be performed for inputs of three or more channels with a smaller amount of LUT data. Furthermore, even when three or more colors overlap, it is possible to obtain an output result of pseudo gradation processing that provides good visual characteristics. Furthermore, by changing the LUT data, the output characteristics for image input can be easily changed, and an image processing apparatus with high versatility can be realized.
[0092]
【The invention's effect】
  As described above, according to the present invention, 3Input an image signal that exceeds color2 for error diffusionUsing two two-dimensional LUTs, obtain pseudo gradation output values of these three colors or moreThe amount of data in the LUTTheSharpeningWith a decreaseThere is an effect that can.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image processing (error diffusion processing) apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an output determination unit according to Embodiment 1 of the present invention.
FIG. 3 is a diagram showing an example of LUT data in the one-dimensional LUT according to the present embodiment.
4 is a diagram for explaining an example of LUT data of the LUT 24 in FIG. 2; FIG.
FIG. 5 is a diagram for explaining an example of LUT data of the LUT 23 in FIG. 2;
FIG. 6 is a block diagram showing a configuration of an error calculation unit according to the first embodiment of the present invention.
FIG. 7 is a diagram showing an example of LUT data used in the error calculation unit according to the first embodiment of the present invention.
FIG. 8 is a flowchart showing a flow of processing in an output determining unit according to Embodiment 2 of the present invention.
FIG. 9 is a block diagram showing a configuration of an output determining unit according to Embodiment 3 of the present invention.
FIG. 10 is a block diagram showing a configuration of an output selection unit according to Embodiment 3 of the present invention.
FIG. 11 is a block diagram showing a configuration of an output determination unit 1 (100) according to Embodiment 3 of the present invention.
FIG. 12 is a block diagram showing a configuration of an output determination unit 2 (101) according to Embodiment 3 of the present invention.
FIG. 13 is a block diagram showing a configuration of an output determination unit 3 (102) according to the third embodiment of the present invention.
FIG. 14 is a diagram illustrating an example of LUT data of LUTs 110, 120, and 130 of the output determination units 100, 101, and 102.
15 is a diagram illustrating an example of LUT data of LUTs 111, 121, and 131 of output determination units 100, 101, and 102. FIG.
FIG. 16 is a diagram showing an example of LUT data used in the output determination unit according to the third embodiment of the present invention.

Claims (4)

At least first-color pixel data, second-color pixel data, and third-color pixel data, and first-color error data and second-color data from pixels that have already undergone pseudo-gradation processing Error data of the first color and error data of the third color are input, the error data of the first color is added to the pixel data of the first color, and the pixel data of the first color after the addition is output And adding the error data of the second color to the pixel data of the second color and outputting the pixel data of the second color after the addition, and adding the third error to the pixel data of the third color Adding means for adding data and outputting pixel data of the third color after the addition;
A first addition result obtained by adding the pixel data of the first color after addition output from the addition means and the pixel data of the second color after addition, and the addition output from the addition means A first two-dimensional LUT for inputting the subsequent pixel data of the third color and outputting the pseudo gradation output value and the selection signal of the third color; and the pixel data of the first color after the addition And a second two-dimensional LUT for inputting the pixel data of the second color after the addition and outputting the pseudo gradation output candidate value of the first color and the pseudo gradation output candidate value of the second color. The first addition result and the third pixel data after the addition are input to the first two-dimensional LUT, the selection signal is output, and the pseudo gradation output of the third color is output. A value is determined, and the pixel data of the first color after the addition and the previous two-dimensional LUT Based on the pseudo-tone output candidate value of the first color, the pseudo-tone output candidate value of the second color, and the selection signal output by inputting the pixel data of the second color after the addition. Output value determining means for determining the pseudo gradation output value of the first color and the pseudo gradation output value of the second color;
The first color pseudo gradation output value determined by the output value determination means, the second color pseudo gradation output value, and the third color pseudo gradation output value, and after the addition Error calculating means for calculating an error in the pixel of interest based on the pixel data of the first color of the second color, the pixel data of the second color after the addition, and the pixel data of the third color after the addition. And
The output value determining means converts the pseudo gradation output candidate value of the first color and the pseudo gradation output candidate value of the second color into the pseudo gradation of the first color according to the selection signal. The output value and the pseudo tone output value of the second color are selected, or the pseudo tone output value of the first color and the pseudo tone output value of the second color are each set to 0. Thus, the pseudo gradation output value of the first color and the pseudo gradation output value of the second color are determined . The image processing apparatus according to claim 1, wherein the first color is cyan, the second color is magenta, and the third color is black . At least first-color pixel data, second-color pixel data, and third-color pixel data, and first-color error data and second-color data from pixels that have already undergone pseudo-gradation processing Error data of the first color and error data of the third color are input, the error data of the first color is added to the pixel data of the first color, and the pixel data of the first color after the addition is output And adding the error data of the second color to the pixel data of the second color and outputting the pixel data of the second color after the addition, and adding the third error to the pixel data of the third color An adding step of adding data and outputting pixel data of the third color after the addition;
The first addition result obtained by adding the pixel data of the first color after the addition output in the addition step and the pixel data of the second color after the addition, and the addition output in the addition step The first addition result and the post-addition second data are input to a first two-dimensional LUT that inputs pixel data of the third color after that and outputs a pseudo gradation output value and a selection signal of the third color. 3 pixel data is input and the selection signal is output, and the pseudo gradation output value of the third color is determined.
The first color pixel data after the addition and the pixel data of the second color after the addition are input, and the pseudo gradation output candidate value of the first color and the pseudo gradation output of the second color are input. The pseudo color of the first color that is output by inputting the pixel data of the first color after the addition and the pixel data of the second color after the addition to the second two-dimensional LUT that outputs the candidate value. Based on the tone output candidate value, the pseudo tone output candidate value of the second color, and the selection signal, the pseudo tone output value of the first color and the pseudo tone output value of the second color are obtained. An output value determination step to be determined;
The first color pseudo gradation output value determined in the output value determination step, the second color pseudo gradation output value, and the third color pseudo gradation output value, and after the addition An error calculating step of calculating an error in the pixel of interest based on the pixel data of the first color, the pixel data of the second color after the addition, and the pixel data of the third color after the addition. And
In the output value determining step, the pseudo gradation output candidate value of the first color and the pseudo gradation output candidate value of the second color are respectively converted into the pseudo gradation of the first color according to the selection signal. The output value and the pseudo tone output value of the second color are selected, or the pseudo tone output value of the first color and the pseudo tone output value of the second color are each set to 0. Thus, the pseudo gradation output value of the first color and the pseudo gradation output value of the second color are determined . A program causing a computer to function as the image processing apparatus according to claim 1 .

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