JP3130949B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance component of an input image.
The present invention relates to an image processing apparatus that sets processing conditions of logarithmic conversion means according to a frequency distribution .

[0002]

2. Description of the Related Art Conventionally, as a main apparatus, a copying apparatus equipped with a laser beam printer is well known. Some laser beam printers perform pulse width modulation of an image signal with a reference signal (for example, a triangular wave signal), and reproduce the gradation of the obtained pulse width in accordance with the laser emission time.

In recent years, full-color images have been increased not only in the printing and design fields but also in offices and the like, and color copiers that faithfully read and output color originals have become widespread. In order to faithfully reproduce the above, a laser beam printer using the above-described pulse width modulation is well known. FIG. 2 is a schematic configuration diagram of the image reading unit. In the figure, 41 is a document, 42 is a platen glass on which the document 41 is placed, 43 is a lamp for illuminating the document, 44 an imaging element array, 45 is an infrared cut filter,
1 is a contact type CCD sensor (CCD), 47 is a lamp 4
3 to an optical system unit for integrally holding the CCD 1.

As described above, when a copy key (not shown) is depressed, the lamp 43 irradiates the original 41, and the reflected light from the original 41 is reflected by the imaging element array 44 and the infrared cut filter 45.
To form an image on the CCD 1 through the When the optical system unit 47 is sub-scanned in the direction of the arrow, the main scanning and sub-scanning electric signals from the CCD 1 are sent to the signal processing circuits shown in FIGS.

FIGS. 3-1 and 3-2 are block diagrams showing the configuration of the image forming apparatus. As shown in the figure, a signal from the CCD 1 is amplified by an amplifier 2 and converted into digital image data by an A / D conversion circuit 3. Then, the image data is converted into image (density) data by the LOG conversion circuit 29, subjected to various image processing by the image processing circuit 30, and then input to the D / A converter 14. This digital signal is converted into an analog signal again, and is compared with a signal of a predetermined period generated from the triangular wave generation circuit 15 by the comparator 16 and pulse width modulated. This pulse width modulated binary image signal is input to the laser drive circuit 17,
It is used for an on / off control signal for the light emission of the laser diode 18. The laser beam emitted from the laser diode 18 is scanned in the main scanning direction by a well-known polygon mirror 19, passes through an f / θ lens 20 and a reflection mirror 21, and rotates in the direction of an arrow. Illuminated above to form an electrostatic latent image.

On the other hand, after the photosensitive drum 22 is uniformly discharged by the exposure device 28, it is uniformly negatively charged by the charging device 23. Thereafter, an electrostatic latent image corresponding to the image signal is formed on the surface by receiving the above-mentioned laser beam. Also, as a development method often used in laser beam printers,
Since a so-called image scan method is performed, in which a portion to be developed (black pixel) is exposed, the developing unit 24 uses a well-known reversal developing method to apply a toner having a negative charge characteristic to a portion of the photosensitive drum 22 which has been discharged by the laser. And visualize it.

The visible image (toner image having a negative charge) formed on the photosensitive drum 22 by the above method is transferred onto a transfer material (generally paper) 26 by a transfer charger 25. The transfer toner 26 and the transferred visible toner image are fixed by a fixing device (not shown). The residual toner remaining on the photosensitive drum 22 is thereafter scraped off by the cleaner 27, and the above-described series of processes is repeated again.

Conventionally, in the above-described image forming apparatus, LOG
The conversion circuit 29 performs digital conversion by a Look up Table method. For example, two types of tables are prepared,
Switching between character mode and photo mode was performed.

[0009]

However, in the above-mentioned conventional example, switching of the LOG conversion table for determining the output density has to be performed manually by the user while viewing the original, which is inconvenient. In the case of a photo original, the maximum density greatly differs depending on whether the original is a silver halide photograph or a print.

[0010] Even among silver halide photographs, there are various types of photographs, such as a dark photograph as a whole and a photograph with little brightness and high density, and it is difficult to select a mode each time. Also, the appropriate LOG
If the conversion table is not selected, the following problem occurs. That is, a dark photographic original having many portions with a reflection density of 1.7 to 2.0 or more is LOG1.7 (density 0.05).
If the processing is performed using the table of (up to 1.7 can be reproduced), it is impossible to reproduce the gradation of the portion having the density of 1.7 or more, and the image is crushed. Conversely, if LOG1.7 is selected for a light original having a maximum density of about 1.0, the maximum copy density becomes 1.0.
As a result, the image becomes lighter in density as a whole.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can realize gradation reproduction suitable for an input image .
It is an object of the present invention to provide an image processing apparatus capable of automatically setting logarithmic conversion processing .

[0012]

In order to achieve the above object, an image processing apparatus according to the present invention is represented by a plurality of luminance components.
Input means for inputting color data, and the plurality of brightnesses
The color data represented by the component is represented by multiple density components.
Logarithmic conversion means for converting color data into
Creating means for creating a frequency distribution of the input image corresponding to the luminance component; and an input corresponding to the plurality of created luminance components.
Means for obtaining an average cumulative degree from the frequency distribution of the image;
Processing of the logarithmic conversion means according to the determined average cumulative degree.
Setting means for setting conditions .

[0013]

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1-1 and FIG. 1-2
FIG. 3 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment, and a description of the same reference numerals as those in FIGS. 3-1 and 3-2 will be omitted. In the figure, reference numeral 11 denotes a page memory for storing digital data after reading a document. The page memory 11 transfers digital data to the CPU 12 under the control of the CPU 12,
Whether to transfer to the LOG conversion circuit 29 is switched. 1
Reference numeral 3 denotes a RAM, which stores a calculation result of the CPU 12 and allows the CPU 12 to extract data as needed.

In the configuration shown in FIG.
Digital image data corresponding to the original read by D1 is stored in the page memory 11 in image units. Here, when the digital image data for each pixel is, for example, as shown in the schematic diagram of FIG. 4, the image data is sequentially written in 8-bit units in the direction of the arrow in the address corresponding to each pixel on the page memory 11. It is.

Next, the above data is read by the CPU 12, and a histogram of image data as shown in FIG. 5 is created. At this time, the CPU 12 performs arithmetic processing according to the flowchart shown in FIG. 6, and calculates the frequency S (n) of the n-th level of each of the digital data “0 to 255”.
First, in step S1 shown in FIG. 6, the data (n level) of one pixel is read from the page memory 11, and in the following step S2, the frequency of the level is incremented.

Then, in step S3, it is determined whether or not the image data has been completed, and if not, the above processing is repeated. The memory of the RAM 13 is used as needed, and the final frequency distribution S (n) is also stored in the RAM. On the other hand, the LOG conversion circuit 29 converts the CCD sensor output, which is the luminance information of the original image, into density data, as shown in FIG. First, the output of the CCD sensor is amplified through the amplifier 2 and converted into 8-bit (0 to 255) digital data. At this time, data "0" is an output when the original illumination lamp is not turned on (black), and data "255" is an output for paper (white) when the lamp is turned on.

Next, the LOG conversion circuit 29 performs a density conversion for converting the output into data corresponding to the density. Here, a LOG curve is used as the density conversion table. The density Dn can be expressed by the following equation.

[0019]

(Equation 1)

Here, Db and Da are the maximum density and the minimum density to be reproduced, respectively. The density reproduction range can be changed by selecting Db and Da. In the above-described histogram, a portion having a low image data level (for example, data 0 to 7) corresponds to a dark portion of the document, and when the frequency of data in this region is large, there are many high density portions in the document. It can be said that.

Therefore, a method of selecting an optimum LOG conversion table for a document will be described below with reference to a flowchart shown in FIG. The density Dx is given by the following equation. here,
x is image data.

[0022]

(Equation 2)

When x = 1, Dx = 2.4, when x = 4, Dx = 1.8, when x = 7, Dx = 1.6 At this time, the histogram is divided into several groups by the image data. The cumulative frequency for each group is obtained separately (step S11). For example, the cumulative frequency of image data 0 to 4 is n1 and the cumulative frequency of image data 5 to 7 is n
If n 2, n 1 is the frequency of a pixel with a density of 1.8 or more, n 2
Represents the sum of the frequencies of pixels having a density of 1.6 to 1.8.

Next, at step S12, the obtained n1 is compared with a predetermined threshold value m1, and if n1≥m1, the LOG table (1) is selected (step S13). But,
If n1 <m1, the routine proceeds to the next step S13, where the calculated n2 is compared with the threshold value m2.
The table (2) is selected (Step S15). However, if n2 <m2, the LOG table (3) is selected (step S16) and image processing is performed.

The above LOG tables (1) to
(3) is set according to data as shown in FIG. 9 and stored in the ROM 31 in advance. That is, LO
The G table (1) is an image having many portions having a density of 1.8 or more, and is set to Da = 0.1 and Db = 2.0 in the above-described equation (1). The LOG table (2) is an image in which the number of high-density portions of 1.8 or more is small but the density is high of about 1.6 to 1.8. Similarly, Da = 0.1 and Db = 1.8. . The LOG table (3) is a relatively light image having a maximum density of 1.6 or less. In this case, Da = 0.05, D
Let b = 1.5.

Then, the CPU 12 extracts an optimum LOG conversion table from the ROM 31 according to the result of the flowchart shown in FIG. As described above, according to the present embodiment, it is possible to form an image using a LOG conversion table suitable for a document image by using the density information of the document image as an output level and analyzing the frequency distribution. .

That is, for a document having many high-density portions, an image is formed using a LOG conversion table for generating density data capable of reproducing the gradation of the high-density portion, and a relatively light document is formed. On the other hand, by forming an image using a LOG conversion table that generates density data that guarantees gradation reproduction up to the maximum density of the original even if the high-density part cannot be reproduced, a level suitable for the original image is always obtained. Tone reproduction can be realized.

Further, even when a copy is made again based on the copy of the original, there is an effect that the density difference between the original and the copy of the second generation can be made as small as possible. It is clear from the gist of the present invention.

[0029]

Next, another embodiment according to the present invention will be described with reference to FIG.
This will be described below with reference to the block diagrams shown in FIG. In the figure, reference numeral 32 denotes a counter circuit, and the other configuration is the same as that of FIGS.

In the above-described embodiment, the frequencies of all levels of the digital data are stored. In this embodiment, for example, frequencies of two groups of 0 to 3 levels and 4 to 7 levels are accumulated. Accordingly, the counter circuit 32 is as shown in FIG. In the figure, first, image data sent in 8 bits is judged by the comparator 321, and data corresponding to 0 to 3 sends an ON signal to the counter 1 to
Data corresponding to .about.7 sends an ON signal to the counter 2. Then, in response to the ON signal, two counters 3
22 performs addition.

As described above, the C / C of the density information of the original image
Data corresponding to the high density portion for the CD output (for example,
0 to 3, 4 to 7) (results are denoted as n1 and n2), and after reading of the document is completed, the counter circuit 32 controls the CPU 12 to accumulate the frequency n1 under the control of the CPU 12.
, N2. The following processing is the same as the processing in the above-described embodiment.

In this embodiment, an expensive page memory is not used as in the above-described embodiment, so that there is an effect of cost reduction, and it is possible to obtain an image equivalent effect as in the above-described embodiment. it can. <Modification> Next, a case where the present invention is applied to a color image forming apparatus will be described.

The configuration of the image forming apparatus is not directly related to the essence of the present invention, and is therefore omitted. As in the above-described embodiment, the original is read by the CCD, but the color components of the original are read by providing a color separation filter in front of the CCD. At this time, the frequency distribution of the CCD output corresponding to red, green, and blue is created in the same manner as in the above-described embodiment. FIGS. 12A to 12C are diagrams showing the luminance data level and the frequency distribution in this embodiment.

Next, as in the two embodiments described above, the cumulative frequency of each group corresponding to the high density portion is obtained for each color. Then, the calculation result of the cumulative frequency of red is represented by n1R, n
2R, green and blue calculation results are respectively n1G and n2
G, n1B, and n2B, and the average cumulative degree in each group is obtained, and n1 and n2.

[0035]

(Equation 3)

The following processing is the same as that of the above-described embodiment, and the CPU 12 draws an optimum LOG conversion table for a document and forms an image.

[0037]

As described above, according to the present invention,
Input for inputting color data represented by multiple luminance components
Means, and color data represented by the plurality of luminance components.
Logarithm to convert to color data represented by multiple density components
Conversion means, and generating means for generating <br/> frequency distribution of the input image corresponding to the plurality of luminance components, a plurality of the created
Average cumulative degree from frequency distribution of input image corresponding to luminance component
Means, and according to the determined average cumulative degree,
Setting means for setting processing conditions of the logarithmic conversion means.
By doing so, it is possible to realize gradation reproduction suitable for the input image.
Color data represented by multiple luminance components
It is possible to automatically set the logarithmic conversion process to be performed.

[Brief description of the drawings]

FIG. 1-1,

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment.

FIG. 2 is a diagram illustrating a configuration of an image reading unit.

FIG. 3-1

FIG. 3-2 is a diagram illustrating a configuration of an image forming apparatus in a conventional example.

FIG. 4 is a schematic diagram illustrating a density distribution of a document in pixel units.

FIG. 5 is a diagram showing a relationship between a CCD output level and a frequency.

FIG. 6 is a flowchart illustrating a processing procedure for creating a frequency distribution.

FIG. 7 is a diagram showing a luminance-density conversion table (LOG conversion table).

FIG. 8 is a flowchart illustrating a processing procedure for selecting a LOG conversion table.

FIG. 9 is a diagram showing a LOG conversion table.

FIG.

FIG. 10-2 is a diagram illustrating a configuration of an image forming apparatus according to another embodiment.

FIG. 11 is a diagram showing a counter circuit.

FIG.

FIG. 12-2,

FIG. 12-3 shows R, G, and R when reading a color original;
This is a frequency for the CCD output level of each color B.

[Explanation of symbols]

 1 CCD 11 page memory 12 CPU 13 RAM 29 LOG conversion circuit 30 image processing circuit 31 ROM 32 counter

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-24690 (JP, A) JP-A-61-45676 (JP, A) JP-A-63-139481 (JP, A) JP-A-2- 294163 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46-1/62

Claims (1)

(57) [Claims] 1. Color data represented by a plurality of luminance components
Input means for inputting the color data represented by the plurality of luminance components,
Logarithmic conversion means for converting to color data represented by degree components
When a generating means for generating a frequency distribution of the input image corresponding to the plurality of luminance component, every input image corresponding to a plurality of luminance component the created
Means for calculating an average cumulative degree from a number distribution, and the logarithmic conversion means according to the determined average cumulative degree
The image processing apparatus characterized by having setting means for setting the processing conditions.