JPH08212339A - Image processor - Google Patents

Abstract

PURPOSE: To provide an image processor which can reduce the necessary capacity of a storage device and generates corrected density data through simplified operation. CONSTITUTION: An image conversion processing part 200 has a rewritable look-up table inside, refers to the look-up table according to the density of image data inputted by an image input part 100, and outputs density correction data. Here, a ROM 140 stores a basic conversion table. A control part 110 reads the basic table out of the ROM 140, performs address operation according to density and picture quality mode set with panel switches 130, and writes it in the look-up table.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for controlling gradation reproduction characteristics.

[0002]

2. Description of the Related Art Conventionally, in the field of image processing, image conversion is often performed by setting the density characteristics from an input image to an output image non-linearly. Such image conversion is generally performed by storing a desired non-linear characteristic in a lookup table and converting the density data of the input image using this table. At this time, the look-up table is composed of a rewritable memory, and the corrected density data is generated according to the mode of the input image (text, photo, etc.), and is written in the memory, so that the optimum density can be obtained according to the image mode. Conversion can be performed (for example, Japanese Patent Publication No. 6-6
9211).

Here, in order to obtain a desired nonlinear characteristic,
To store all necessary lookup tables in a storage device, or to generate corrected density data, there is a method of limiting the table to be stored and generating it by calculation (see, for example, Japanese Patent Publication No. 6-52931). ).

[0004]

However, with the former,
There is a problem that the capacity for storing the table must be increased, and in the latter case, the calculation for generation becomes complicated and it takes a long time to process it. There is a problem that a storage device for storing the data is also required.

The present invention has been made in view of the above problems, and an object of the present invention is to generate corrected density data by a simplified calculation, which requires a small storage device capacity. It is to provide an image processing device capable of

[0006]

In order to solve the above problems, in the invention described in claim 1, the density data of the input image is used as an address, and the correction density data is stored in advance for each address. On the other hand, it is a conversion unit for converting the density data of the input image into the corrected density data by reading the density data corresponding to the density data of the input image and supplying it as the corrected density data. Data rewritable conversion means, storage means for pre-storing a conversion table in which the density data of the input image is used as an address and correction density data is associated with each address, and an address of the storage means for converting the conversion means The correspondence relationship to the address is changed at least in accordance with the density information indicating the specified density, and each address of the storage means is changed. The corrected density data stored, characterized by comprising a rewriting means for writing each of said converting means at the address changing the correspondence relationship are at.

According to a second aspect of the invention, in the first aspect of the invention, the storage means stores a plurality of conversion tables, and the writing means stores density data of an input image and an image mode. According to the above, one of the conversion tables stored in the storage means is selected, and the corrected density data stored at each address in the conversion table is written into the conversion means.

[0008]

According to the invention described in claim 1, the converting means is:
Convert the density data of the input image to the corrected density data,
The conversion characteristic at this time is determined by the correspondence relationship changed by the writing means, that is, the correspondence relationship from the address of the storage means to the address of the conversion means. Furthermore, since this correspondence relationship changes at least according to the density information indicating the specified density, the conversion characteristic of the conversion means eventually changes according to the density information. Therefore, basically, the desired conversion characteristic is obtained by changing the correspondence relationship between the addresses in the density data of the input image and the corrected density data stored in the storage means, and thus the required storage device capacity is required. Is less,
Further, since no calculation processing is performed on the corrected density data itself, the calculation accompanying this can be extremely simplified.

According to the second aspect of the present invention, the basic conversion table is selected according to the image information of the input image, so that the correspondence relationship need not be changed significantly. This means that the desired conversion characteristic can be obtained more accurately.

[0010]

【Example】

1: Configuration of Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of this embodiment. In the figure, reference numeral 100 is an image input unit for reading in image data, which corresponds to, for example, an image scanner or an MO (magneto-optical disk). Reference numeral 110 is a control unit, which is configured by a CPU or the like, and controls each unit. Reference numeral 200 denotes an image conversion unit having a rewritable look-up table therein, which converts the density data of the input image data into corrected density data by referring to the look-up table, and the gradation characteristics of the input image. Change. Reference numeral 120 is an image output unit that outputs the converted image data to the outside, and corresponds to, for example, an image forming apparatus or an MO.

On the other hand, reference numeral 130 is a panel switch, which is a switch for designating a desired density, a switch for selecting a mode of an input image, and a switch for designating the start of image conversion (none of which are shown). ) And the like, and supplies the setting information of these switches to the control unit 110. Reference numeral 140 is a ROM, which stores 12 types of tables having basic characteristics among gradation (conversion) characteristics. Note that, among these tables, the table actually used is selected by setting the panel switch 130, as described below.

1-1: Relationship between Panel Switch Setting and Table Conversion Characteristic Here, the setting by the panel switch 130 and the ROM 1
The relationship with the conversion characteristic of the table selected in 40 will be described. In this embodiment, as shown in FIG.
The density can be set in 5 levels, dark ← normal → light, and the image mode can be set to text, photo,
Also, it can be set in a three-stage mode of mixing these. Further, in the mixed mode, the character or photograph mode is automatically determined by analyzing the input image data, and there are substantially four modes. After all, the combination of the designated density and the designated / determined image quality mode is 5 × 4 in total.
It becomes a street. Of these, 12 types of designated densities of “normal” or more are assigned as shown in FIG. 2, and the conversion tables A to L having the optimum conversion characteristics are assigned to each of them. Now, regarding one conversion table, the correction density data is stored at the addresses "0" to "255", and if the input density data is supplied as the read address, the correction density data is obtained. The characteristics of the inputted density data versus the corrected density data are set to be optimum according to the setting state. Further, as to the eight different density ranges from “normal”, as will be described later, the conversion tables A to D corresponding to the “normal” density are calculated based on the ones in which the image quality modes match. Has become.

1-2: Structure of Image Converting Unit Next, the structure of the image converting unit 200 will be described separately for the case where the image quality mode is the mixed mode and the case where it is the character or photograph mode.

1-2-1: Mixed Mode First, the configuration in the mixed mode will be described. FIG.
FIG. 7A is a block diagram showing the configuration of the image conversion unit 200 in this case. As shown in this figure, the input image data is supplied to the lookup tables LUT (1) and LUT (2), respectively. The density data of this image data is composed of, for example, 8 bits (per pixel) and has 256 gradations of "0" to "255". Here, the lookup table LUT (1), LU
Two T (2) are provided in parallel so that they are separately converted for characters and pictures. These lookup tables LUT (1) and LUT (2) are each "0".
The corrected density data corresponding to the density data of "-255" is stored, and the corrected density data corresponding to the density data of the input image is read and converted. More specifically, the correction density data is stored in each of the addresses "0" to "255", and the correction density data can be obtained by supplying the input density data as a read address. The lookup table LUT
The conversion characteristic of the density data to the corrected density data in (1) is the conversion table B corresponding to the density and the image quality mode.
It is set to either F or J, or one obtained by calculation. Similarly, the lookup table LUT
The characteristic in (2) is set to one of the conversion tables C, G, and K, or one obtained by calculation.

On the other hand, the error coefficient is information indicating the character-likeness or the photograph-likeness of the pixel of interest, and can be obtained by comparing the relationship of the pixel of interest with the front, rear, left and right pixels. . This error coefficient is converted into the mixing coefficient p by the coefficient converter 201, and is multiplied by the corrected density data by the look-up table LUT (1) in the multiplier 204. In addition, the arithmetic unit 202 is
The mixing coefficient p is subtracted from "1", and the subtraction result (1-
p) is multiplied in the multiplier 203 by the corrected density data obtained by the lookup table LUT (2). Then, the multiplication results of the multipliers 203 and 204 are added in the adder 205, and the image data having the addition result as density data is output. As a result, even if the character area and the photograph area are mixed in the image data, the mixing ratio of the look-up table output is controlled according to the character-likeness or the photograph-likeness of the pixel of interest, and the character area to the photograph area are continuously controlled. It can be changed.

1-2-2: Character or Photo Mode Next, the configuration in the character or photo mode will be described. FIG. 3B is a block diagram showing the configuration of the image conversion unit 200 in this case. As shown in this figure, the input image data is the lookup table LUT.
(1), and the subtraction result (1-
p) is multiplied by the multiplier 207, and image data having the multiplication result as density data is output. Here, in the case where the character mode is selected, the coefficient converter 201 is supplied with an error coefficient corresponding to the character mode, and this is supplied as a mixing coefficient, while the photographic mode is selected. In some cases, the error coefficient corresponding to the photo mode is supplied, and this is supplied as the mixing coefficient. In this figure, the case where the character mode is selected is shown, and when the photo mode is selected, the mixing coefficient by the coefficient converter 201 is directly supplied to the multiplier 206.

2: Operation of the Embodiment Next, the operation of the embodiment will be described. First, the control unit 1
When a switch for instructing the start of image processing is operated on the panel switch 130, the controller 10 determines whether the set density is "normal" or higher, or whether it is lighter than "normal". Hereinafter, for convenience of description, the two cases will be described separately.

2-1: When a Density of "Normal" or Higher is Specified When it is determined that the density set by the panel switch 130 is "normal" or higher, the control unit 110 further controls the panel switch 130. The set image quality mode is also discriminated, the combination of the specified density and the image quality mode is recognized, and the table A to table corresponding to the combination shown in FIG.
L is read from the ROM 140. Then, the control unit 110
Writes it into the look-up table LUT (1) or LUT (2) of the image quality conversion unit 200 as it is.
Here, "as is" means to write the corrected density data read from the ROM 140 into the lookup table LUT (1) or LUT (2) at the read address. Further, if the image quality mode is the mixed mode, the control unit 110 converts the conversion table B into LUT (1),
One of F and J and one of the conversion tables C, G, and K are selected and written in the LUT (2) corresponding to the designated densities.

As a result, as shown in FIG.
The conversion table itself selected by the OM 140 is the lookup table LUT (1) or LUT.
As a result of being written in (2), it is possible to convert the density of the input image data with the optimum gradation characteristic for the specified density and image quality mode.

2-2: When the density which is less than "normal" is designated On the other hand, when it is determined that the density set by the panel switch 130 is less than "normal", the control section 110 The correction coefficient a is set according to the specified density, and the correction density data of the conversion table corresponding to the set image quality mode among the conversion tables A to D is set to
The address is manipulated to write in the lookup table LUT (1) or LUT (2) of the image quality conversion unit 200. Here, the "address operation" means a write address in which the corrected density data read from the conversion table has a fixed relationship with the read address, and specifically, the following. Will be done. Here, the read address of the conversion table is n and the write address m of the lookup table is m. In this embodiment, since the density data is described as 8 bits,
n and m are integers of "0" to "255", respectively.

First, m is set to “0”. Next, the minimum n that satisfies the equation (1) in m is obtained, the corrected density data stored at this address n is read from the conversion table, and this is read at the address m in the look-up table LUT (1) or look-up table LUT (1). Write to the up table LUT (1). (255-n) * a / 64 <= 255-m ... Formula (1) However, if n <0, it will be set as n = 0. Next, m is incremented by "1". If m is larger than "255", the process ends, and otherwise, and are executed again. As a result, "0" to "25" in the lookup table
The density correction data read from the conversion table is written in all the addresses "5".

For example, the designated concentration is the most "thin"
If the image quality mode is the character mode, RO
The conversion table A is selected in M140, and the corrected density data corresponding to the address n is sequentially written in the lookup table LUT (1) in FIG. 3B at the address m. If the specified density is the most "light" and the image quality mode is the mixed mode, the ROM
In 140, the conversion tables B and C are selected. For the conversion table B, the correction density data corresponding to the address n is the lookup table LU in FIG.
T (1) is sequentially written at address m, and similarly, for the conversion table C, corrected density data corresponding to address n is sequentially written at lookup table LUT (2) at address m.

As a result, as shown in FIG.
The conversion table selected in OM140 is compressed
It is decompressed and written in the lookup table LUT (1) or LUT (2). In this figure, the correction coefficient a is "63". As a result, the density of the input image data is converted with the gradation characteristics obtained based on the "normal" density conversion characteristics for the specified density and image quality mode.

According to this embodiment, since it is not necessary to store the conversion characteristic corresponding to the density in advance, RO
The storage capacity of the M140 can be saved accordingly. Further, when writing from the conversion table of the ROM 140 to the look-up table, the density correction data itself is not subjected to any calculation, and only the correspondence relationship of the addresses is stored. Therefore, the calculation itself is extremely simplified. can do.

The concentration of "thin" or "normal" has a large sensory ratio, so that "normal" on the one hand may correspond to "thin" on the other hand, and vice versa. It can happen. Therefore, in the above-described embodiment, even if the "normal" density is specified, the conversion characteristic of "normal" is actually calculated, and "slightly thin" is calculated.
The image conversion processing may be performed by designating the density of.

Further, in the above-mentioned embodiment, the ROM 1
The relationship between the read address n of the conversion table and the write address m to the lookup table in 40 is expressed by the formula (1).
However, the present application is not limited to this. For example, the density correction data of the read address n may be written in the lookup table at consecutive addresses, or may be written in a thinned form. By such a comparatively simple address operation, various conversion characteristics can be obtained based on the conversion characteristics CHR as shown in FIG. 5, for example.

[0027]

As described above, according to the present invention, the capacity of the storage device required is small, and the correction density data can be generated by a simplified calculation. 1). It is also possible to more accurately obtain the desired conversion characteristic (claim 2).

[Brief description of drawings]

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

FIG. 2 is a diagram showing designation of density and image quality mode in the embodiment.

3A is a block diagram showing a configuration of an image quality conversion unit in the same embodiment when the image quality mode is a mixed mode, and FIG. 3B is a block diagram showing a case where the image quality mode is a character / photo mode. It is a block diagram which shows the structure of an image quality conversion part.

FIG. 4A is a diagram for explaining a writing operation in the same embodiment when the designated density is “normal” or more, and FIG. 4B is a diagram illustrating the designated density is “normal”. It is a figure for demonstrating the address operation in the same Example in the case of more "thin".

FIG. 5 is a diagram showing a change in conversion characteristic according to the embodiment.

[Explanation of symbols]

LUT (1), LUT (2) ... Look-up table (conversion means), 110 ... Control unit (rewriting means), 140 ... ROM (storage means)

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area H04N 1/40 B

Claims (2)

[Claims] 1. The address is density data of an input image,
A conversion unit that converts the density data of the input image into the corrected density data by storing the corrected density data for each address in advance and reading the density data corresponding to the density data of the input image and supplying the read density data as the corrected density data. And a conversion means capable of rewriting the correction density data corresponding to each address, and a storage means for pre-storing a conversion table in which the density data of the input image is used as an address and the correction density data is associated with each address. The correspondence relationship from the address of the storage means to the address of the conversion means is changed at least according to the density information indicating the specified density, and the correction density data stored at each address of the storage means is changed to Rewriting means for respectively writing to the conversion means with the address whose correspondence has been changed. The image processing apparatus according to symptoms. 2. The storage means stores a plurality of conversion tables, and the writing means selects one of the conversion tables stored in the storage means according to density data of an input image and an image mode. The image processing apparatus according to claim 1, wherein the corrected density data stored in each address in the conversion table is written in each of the conversion means.