JP2002010079A - Color image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To switch the ink generation starting point depending on the halftoning. SOLUTION: An ink generating section 4 is provided with a table for ground tint screening and a table for diffusing error (delayed behind the ink generation starting point for ground tint screening), a halftoning section 6 is provided with ground tint screening for print sheet and error diffusing for dot print and character and switching is made between the table and halftoning depending on a select signal 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a plurality of pseudo halftone processes including a dot concentration type and a dot distribution type.
The present invention relates to a digital color image processing apparatus that reproduces a color image using M, Y, and K recording color materials.

[0002]

2. Description of the Related Art Conventionally, in a digital color image processing apparatus such as a digital color copying machine, a document R
(Red), G (Green), and B (Blue) signals are read as reflectance data, conversion processing from reflectance data to a density value, color correction processing, black generation processing, under color removal processing (hereinafter, UCR), Pseudo halftone processing is performed, and C (Cy
an), M (Magenta), Y (Yellow),
An image is reproduced and output from the printer using four recording color materials of K (Black).

In the black generation processing, a K signal is generated from the C, M, Y signals, and in the under color removal processing, a K signal is generated from the C, M, Y signals.
Although the amount corresponding to the signal is reduced, the amount of the K toner, that is, how much the so-called black amount is set, is one of the factors that greatly affect the image quality.

The appropriate amount of black greatly depends on the nature of the pseudo halftone processing used. For example, in the error diffusion process,
Due to the quantization error that is propagated, “black” caused by the overlapping of the three CMY toners and “black” due to the K toner appear concentrated at a specific pixel, or conversely, appear at the pixel where the toner is to be attached. In some cases, the toner is not attached at all, and dark black appears sparsely and sparsely in the highlight portion, giving a very noticeable and rough feeling. In a color printer having a large dot diameter and a small number of gradations that can be expressed, black dots are particularly conspicuous. Therefore, in the case of error diffusion processing, it is better not to add black ink from highlights.

On the other hand, such a phenomenon does not occur in multi-value dither processing using a dither matrix having a dot concentration effect, such as screen processing. Therefore, it is possible to aim at improving the color reproducibility of gray highlights and black characters with low contrast by adding black ink from highlights to some extent while taking into account the gradation properties and background stains of the photographic parts. .

[0006]

In recent years, there has been proposed an apparatus having a plurality of halftone processes and selectively switching between them. In general, dot-intensive processing such as a line screen has problems that (1) moire occurs in a halftone dot printing section, and (2) edges are cut off by dither processing. On the other hand, dot dispersion processing represented by error diffusion is considerably more advantageous than the former in terms of resolution and moiré, but has the problem of noticeable graininess noise.

Therefore, there is an image processing apparatus that selects an optimum halftone processing according to the properties of an input image. Further, there has been proposed a method in which other processing is switched in accordance with switching of halftone processing. For example, the image forming apparatus described in Japanese Patent Application Laid-Open No. 9-331450 switches a gamma table and a filter process according to the halftone processing when selecting and outputting halftone processing such as error diffusion processing and screen processing. Things.

The present invention performs processing suitable for each halftone processing, as in the above-mentioned publications. The purpose of the present invention is to focus on the difference in the optimal black generation starting point setting by the halftone processing. Another object of the present invention is to provide a color image processing apparatus that switches the black generation start point in accordance with the halftone processing.

[0009]

According to the present invention, the black generation starting point is switched corresponding to each of a dot concentration type halftone process such as a line screen method and a dot dispersion type halftone process such as an error diffusion method. Thus, the optimum black generation processing is performed for each of the highlight portions.

Further, according to the present invention, in dot-intensive halftone processing such as a line screen method, gray reproducibility of highlight is maintained, and in dot dispersion type halftone processing such as error diffusion, highlight Of the K toner.

Further, in the present invention, an optimum halftone process is performed by selecting a dot concentration type process with less graininess in the photographic paper portion, and a black generation process suitable for the halftone process is performed. Like that.

Further, according to the present invention, in the halftone printing section,
By selecting a dot-dispersion type process in which moire is less likely to occur, an optimal halftone process is performed, and a black generation process suitable for the halftone process is performed.

Further, in the present invention, an optimal halftone process is performed by selecting a dot dispersion type process that is advantageous in resolution in a character portion, and black generation processing suitable for the halftone process is performed. I have to.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. First, the RGB of the image read by the color scanner 1
The LOG conversion unit 2 performs LOG conversion on the reflectance signal (each color is, for example, an 8-bit digital signal) and converts the signal into a density signal. Next, the color correction unit 3 performs a color correction process on the R′C′B ′ density signal and converts the signal into a CMY signal. The conversion formula of the color correction processing is a color correction parameter group a0 to a3, b
It is expressed as equation (1) using 0 to b3 and c0 to c3.

C = a0 + a1 × R ′ + a2 × G ′ + a3 × B ′ M = b0 + b1 × R ′ + b2 × G ′ + b3 × B ′ Y = c0 + c1 × R ′ + c2 × G ′ + c3 × B ′ Formula (1) Black The generator 4 generates a K signal according to the CMY data. Here, the K signal is generated from the value of Min (C, M, Y) by table conversion, but may be directly calculated by an equation. A plurality of conversion tables from Min (C, M, Y) to K are held, and one of the plurality of conversion tables is selected in response to the selection signal 8. The UCR unit 5 performs an undercolor removal process using the CMY and K signals according to equation (2).

C ′ = C−K M ′ = M−K Y ′ = Y−K Equation (2) The C′M′Y ′ signal and the K signal derived in this way are processed by the halftone processing unit 6. The halftone processing is performed, and the signal C "M" Y "K" after the halftone processing is supplied to the color printer 7.
Output from The halftone processing section 6 is provided with a plurality of halftone processes including both a dot concentration type and a dot dispersion type, and receives a selection signal 8 to determine one of the plurality of halftone processes. Is selected by the above method. Similarly, a plurality of conversion tables in the above-described black generation unit 4 are held, and are selected in response to the selection signal 8. Since the conversion table is set corresponding to the halftone processing, it is uniquely determined when the halftone processing is determined.

FIG. 2 shows an example of a configuration for switching the halftone processing. On the operation panel 11, the photographic paper section 15 and the character section 17 are designated as areas, and the other parts not designated are designated as the halftone dot printing section 16. And the photographic paper section 1
In the area designated as 5, an AM screen process is performed to give priority to smoothness. For example, 2 × 1
Dither processing. If it is a 600 dpi printer, it will be a 300-line line screen type.

On the other hand, error diffusion processes 13 and 14 are performed in the area of the character 17 and the halftone printing 16 in consideration of the priority of resolution and prevention of moiré. FIG. 3 shows a block diagram of the error diffusion process. The error diffusion process is a process of generating an output image by allocating an error between input data and output data to pixels other than the target pixel as shown in FIG. For example, the matrix shown in FIG. 4 may be used as the weighting matrix 24 for determining the distribution weight.

The error diffusion processing 14 for characters and the error diffusion processing 13 for halftone pictures in FIG. 2 may be the same, but the number of quantizations 21 in FIG. If the matrix size in FIG. 4 is made different, for example, more suitable processing can be performed. FIG. 3 shows an example in which binarization is performed with one threshold, but it is also possible to provide a plurality of thresholds and perform binarization. The error diffusion process 13 for halftone printing may place more emphasis on the gradation than the error diffusion process 14 for characters and may increase the number of quantization. Further, in the error diffusion processing 14 for characters, FIG.
If a matrix having a size smaller than the matrix size of is used, the resolution can be further increased.

In the above-described example, the user specifies the area using the operation panel 11, but a method of automatically detecting the type of image may be used. For example, according to the method described in Japanese Patent Application No. 11-182554, the photographic paper and the dot area can be automatically identified.
In addition to switching by area, photographic paper mode,
The mode may be switched according to the mode, such as the character mode or the character / print photo mode.

FIG. 5 is a diagram for explaining an example of switching of the conversion table in the black generator 4. As shown in FIG. 5, the black generation start point of the line screen processing table 31 is a,
Assuming that the black generation start point of the error diffusion table 32 is b,
Set so that a <b.

As described above, according to this embodiment, when the dot concentration type line screen processing is selected, the dot dispersion type error diffusion processing is performed using the black generation table 31 whose black generation start point is a. If selected, the black generation start point is b
Since the black generation table 32 of (> a) is used, it is possible to suppress roughness of highlights in the error diffusion processing unit while maintaining gray reproducibility of highlights in the line screen processing unit. Even if the halftone processing is selectively switched in the photographic paper part, the character part, and the halftone dot printing part, since the black starting point is also switched in accordance with the halftone processing, the highlight part is not hindered.

In this embodiment, a line screen is taken as an example of the dot concentration type, and an error diffusion is taken as an example of the dot dispersion type. However, the present invention is not limited to this. For example, as the dot dispersion type, a dither process using a Bayer type matrix having a dot dispersion effect or an FM screen process may be used. In the present embodiment, a scanner and a printer are assumed as input / output devices, but the present invention is not limited to this. Further, the present invention can be applied to a case where image data obtained via a network is input.

[0025]

As described above, according to the first aspect of the present invention, there is provided a device which has a plurality of halftone processes including a dot concentration type and a dot dispersion type and selectively switches between them. Since the black generation start point is switched between the pattern and the dot dispersion type, optimal black generation processing can be performed for each of the highlight portions.

According to the second aspect of the present invention, the dot dispersion type black generation start point b is a dot concentration type black generation start point a.
(A <b), it is possible to maintain the gray reproducibility of highlights of the dot concentration type processing unit and to suppress roughness due to the K toner in highlights of the dot dispersion type processing unit.

According to the third aspect of the invention, in the photographic paper processing section, since the dot concentration type is selected, an image having a small granularity and excellent gray reproducibility in the highlight portion can be obtained.

According to the fourth aspect of the present invention, in the halftone dot printing processing section, since the dot dispersion type processing is selected, an image free from moire and having less roughness due to the K toner in the highlight portion can be obtained. Obtainable.

According to the fifth aspect of the present invention, in the character processing section, since the dot dispersion type processing is selected, it is possible to obtain an image having a high resolution and little roughness due to the K toner in the highlight section. .

[Brief description of the drawings]

FIG. 1 shows a configuration of an embodiment of the present invention.

FIG. 2 shows a configuration example for switching halftone processing.

FIG. 3 shows a configuration example of an error diffusion process.

FIG. 4 shows an example of a weight matrix for performing error diffusion.

FIG. 5 shows characteristics of a black generation table selected according to halftone processing.

[Explanation of symbols]

 Reference Signs List 1 color scanner 2 LOG conversion unit 3 color correction unit 4 black generation unit 5 UCR unit 6 halftone processing unit 7 color printer 8 selection signal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/60 H04N 1/40 D 1/40 F 1/52 1/46 B (72) Inventor Koji Kobayashi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2C262 AA24 AA26 AB13 BA07 BB03 BB06 BB08 BB23 BC17 EA06 5B057 CA01 CB01 CC03 CE13 CE16 CE18 CH07 CH18 5C077 MP02 MP06 MP08 NN08 NN11NNNN PP37 PP38 PQ04 PQ08 PQ23 RR02 RR08 RR09 SS05 5C079 HB01 HB03 HB12 LA21 LA31 LC04 LC09 MA04 NA02 NA04

Claims (5)

[Claims] 1. A color image processing apparatus for performing a pseudo halftone process selected from a plurality of pseudo halftone processes on digital color image data and outputting the same, wherein black is generated from the digital color image data. Wherein the start point of black generation is changed in accordance with the selected pseudo halftone processing. 2. The method according to claim 1, wherein the plurality of pseudo halftone processes include at least a dot concentration type pseudo halftone process and a dot dispersion type pseudo halftone process. 2. The color image processing apparatus according to claim 1, wherein the start point of black generation is delayed later than the dot concentration type pseudo halftone processing. 3. The color image processing apparatus according to claim 1, wherein a dot concentration type pseudo halftone process is selected for a photographic paper portion of the digital color image data. 4. The color image processing apparatus according to claim 1, wherein a dot-dispersion type pseudo halftone process is selected for a halftone printing portion of the digital color image data. 5. The color image processing apparatus according to claim 1, wherein a dot distribution type pseudo halftone process is selected for a character portion of the digital color image data.