JPH08111778A - Image processor - Google Patents

Abstract

PURPOSE: To provide an image processor which can give the optimum correction of density to various input images by generating the correction density data in response to the type of the input image that is acquired based on the mode set by a control panel means. CONSTITUTION: A scanner 1 scans an original, applies the photoelectric conversion to the reflected light of the original via a three-color filter, and then applies the A/D conversion to the reflected light undergone the photoelectric conversion to acquire a digital image signal Si'. The signal Si' is normalized into a color signal Si through a shading correction circuit 2. The signal Si is inputted to a matrix circuit 3 and separated into a luminance signal I and the color difference signals C1 and C2. The signal I undergoes the conversion of density and the texture processing through a gamma conversion circuit 4. The contents of the data stored in a ROM 5 are processed by a CPU 7 based on the input received from a control panel 6 so that the correction density data can be obtained. The panel 6 includes a mode setting switch, a density setting switch and a texture density setting lever.

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 used for a digital copying apparatus, a television camera, an electronic still camera, etc., and more particularly to an optimum correction density for input density data regardless of the properties of an input image. The present invention relates to an image processing device capable of obtaining data.

[0002]

2. Description of the Related Art In the field dealing with the prior art, various density corrections are often performed, such as gamma correction when the density characteristic of input versus output is non-linear. In particular, in a digital copying apparatus for obtaining a color copy, it is necessary to correct input density information based on a curve corresponding to human visual characteristics.

Therefore, in a digital copying apparatus which processes density information of an image with digital data, an RO in which corrected density data is written in order to speed up the correction process.
A technique has been proposed in which M (read-only memory) is prepared as a density conversion table, a luminance signal is given as an address of the ROM, and correction density data corresponding to this is output to a printer (Japanese Patent Publication No. 60-23541). ).

[0004]

However, in such a copying apparatus, since only one type of correction density data is given, when copying various original papers having different background densities or the original papers are not stained. In some cases, the background (fog) stains occur, or conversely, the necessary parts are not copied. To avoid this, it is necessary to give an appropriate correction amount according to each original.

However, in consideration of all cases, in order to store each correction data in the memory in advance, a very large memory capacity had to be required.
The present invention has been made in consideration of the above circumstances, and provides an image output device capable of obtaining an output image with optimum density for various types of input images without increasing the memory capacity. The purpose is to do.

[0006]

According to the present invention, there is provided an image processing apparatus having a density conversion table for converting density data of an input image into corrected density data of an output image, wherein the density conversion table is constituted by a rewritable memory. Along with
Operation panel means for allowing the user to set a mode including at least a character mode and a photograph mode, and the corrected density data is generated according to the type of the input image obtained based on the mode set by the operation panel means. And generating means for writing in the memory.

Preferably, the image signal of the input image is separated into a luminance signal and a color difference signal, the luminance signal is given as density data to the density conversion table, and the color difference signal is corrected in correspondence with the corrected density data. It is characterized by doing.

[0008] Preferably, the value of the color difference signal is expanded both when the density characteristic of the luminance signal is reduced and when the density characteristic is increased. (Operation) In the present invention, the user sets a mode such as a character mode or a photo mode on the operation panel means. The generation unit generates the optimum corrected density data according to the type of the input image obtained based on the mode set by the user. Then, by writing this in a rewritable memory constituting the density conversion table, optimal correction corresponding to the type of the input image can be performed.

According to the present invention, since the density conversion table is a rewritable memory, the corrected density data can be freely rewritten, and the corrected density data is generated according to the type of the input image. A capacity that can store one type of corrected density data is sufficient.

Further, according to the present invention, the user does not have to perform a difficult operation such as adjustment of the correction density data, but simply performs a simple operation of setting a mode with the operation panel means, and the input image is displayed on the apparatus. Optimal correction can be executed according to the type.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a digital color copying machine according to an embodiment of the present invention.

The scanner 1 scans an original document (not shown), photoelectrically converts the reflected light from the original document through three color filters, and further A / D-converts these signals to generate a digital image signal Si '. I will get it. In addition,
Here, i represents the color of the color filter, and i = {red (r), green (g), blue (b)}, {yellow (y), green (g), cyan (c)}, etc. Is usually used. This digital image signal Si ′ is input to the shading correction circuit 2. The shading correction circuit 2 normalizes the signal value obtained by scanning the white reference plate to, for example, “1”, and the signal value obtained by scanning the black reference plate to be output, for example, “0”. When the reflectance of the white reference plate is Rwi and the reflectance of the black reference plate is Rbi, the signal value Si when the reflectance of the document is Ri is expressed by the following equation.

Si = (Ri−Rbi) / (Rwi−Rbi) (1) The color signal Si standardized by the white and black reference plates is
The signal is a signal in which unevenness in sensitivity of the sensor, illumination unevenness, and optical unevenness such as a color filter are corrected. Also, when the sensor is a CCD sensor having a plurality of chips, a signal in which unevenness such as variation in gain of a plurality of amplifiers connected to each sensor chip is corrected can be obtained.

The color signal Si is supplied to a matrix circuit 3
And is separated into a luminance signal I and color difference signals C1 and C2. At this time, the magnitudes of the color difference signals C1 and C2 change according to the operation switch for controlling the density characteristic. Details of this circuit will be described later.

The luminance signal I is subjected to density conversion and background processing in a gamma conversion circuit 4. The correction density data at the time of correction is obtained by processing the content of the data stored in the ROM 5 by the CPU 7 based on an input from the operation panel 6 as described later.

Luminance signal I after density conversion and background processing
'And the color difference signals C1 and C2 are input to the color conversion circuit 8. The color conversion circuit 8 is constituted by, for example, a ROM, and converts a color represented by a combination of the values of the luminance signal I 'and the color difference signals C1 and C2 into an amount of ink necessary for outputting the color by a printer. It is a table. When the signals I ', C1, and C2 are input to the color conversion circuit 8, an output converted to the amount of ink necessary for printing is obtained. This color conversion table may be created by a method described by a masking equation, a Neugebauer equation, or the like. Each signal converted into the amount of ink, for example, a signal for yellow, magenta, cyan, and black in a four-color printer is input to the dither circuit 9. The dither circuit 9 is a circuit that performs binarization by dithering so that halftone printing is possible even in a color printer that can only perform binary printing. The signal binarized by the dither circuit 9 is output to the printer 10. Printer 1
0 prints the ink of each color in accordance with the input signal and generates a color copy.

Next, the details of the density correction centering on the gamma conversion circuit 4 will be described. Originals have different density and saturation characteristics depending on the type. Therefore, when trying to obtain various copies, it is desirable to be able to change the correction value according to the original. It is also necessary that the output value can be freely changed depending on the purpose of copying. The former case is a case where it is necessary to set the mode separately for each document such as a normal document or a document such as a photograph which is required to have high density and high saturation. The latter is a case where it is desired to change the density of an output image depending on the purpose, such as when it is desired to copy a picture particularly beautifully or to copy both a picture and text normally even with a normal original. Also, when the background of the document is dark, or when a part of the document is dirty and it is desired to remove it, a certain threshold value is set, and a saturation level is uniformly applied to a luminance signal exceeding the threshold value. Is also required. In order to meet such requirements, the operation panel 6 of FIG. 1 is configured as shown in FIG. 2 in this embodiment. That is,
The operation panel 6 has a mode setting switch 11 for selecting one of five modes, that is, an automatic mode, a picture mode, a character mode, a photograph mode, and an illustration mode, and density adjustment for each of these modes. As described above, the density setting switch 12 for setting the density characteristic switching in, for example, five steps, and the background density setting lever 13 capable of independently performing nine levels of background processing for each density characteristic are provided. is there.

FIG. 3 shows how 25 kinds of density characteristics can be set by combining the mode setting switch 11 and the density setting switch 12. However, in this case, since the automatic mode, the picture mode, and the character mode are all modes for ordinary documents, the same density characteristics are given. As an example of the density characteristics described here, I
FIG. 4 shows 00 to I04. This density characteristic is expressed by the following equation.

[0019]

[Equation 1]

Here, I indicates density data, that is, a luminance signal value input to the gamma correction circuit 4, and I 'indicates corrected density data, that is, a luminance signal value output from the gamma correction circuit 4, respectively. Indicates an appropriate positive real value. (2) is used for the following reason. That is, it is necessary for the density conversion to ensure natural correctness for the human eye, but as described above, the human sense is said to be approximately proportional to the logarithm of the strength of the stimulus. Then, taking the logarithm on both sides of equation (2), the following equation is obtained.

[0021]

[Equation 2]

That is, the luminance signal I 'obtained by raising the luminance signal I to the power of α looks like α times the original luminance signal I. The luminance signals I and I ′ appear to change while maintaining this relationship.

Conveniently, the conversion according to the equation (2) is performed when the luminance signals I and I 'are 8-bit numbers, for example, when I = 0, I' = 0 and I = 255. At this time, since I '= 255, crushing occurs in the high density area, the density does not reach the maximum density level, a portion that is not printed in the low density area occurs, and the fog density which causes background stain is generated. Does not occur. As the value of α, for example, 0.5, 0.67, 0.8, 1.0,
1.25, 1.5, etc. can be used. By varying α in this way, various density characteristics as shown in FIG. 4 can be obtained. When there are only a few α values of the density characteristic selected in the ROM 5 as in this embodiment, Iij (here, i = 0 to 4,
j = 1 to 2) are stored, and each density data is stored in the ROM 5.
Obtained directly from However, if α can take a value of several tens to several hundreds, the ROM 5 stores, for example, a typical density characteristic I 02 (α = 1). Each corrected density data can be obtained by processing the data.

Further, in this embodiment, the threshold value can be adjusted by the background adjustment lever so that the background contamination of the original and the background contamination of the copy due to the background density of the paper itself do not occur. When the threshold value is Th, the concentration characteristic obtained by this processing is as shown in the following equation.

[0025]

(Equation 3)

That is, as shown in FIG. 4, when the input density data I exceeds the threshold value Th, the output corrected density data I 'is output as a white level, thereby cutting off the background stain. I have to.

The corrected density data I 'is stored in the CPU.
Processed at 7. RAM from correction data generation
FIG. 5 shows the flow of processing up to writing to (gamma conversion circuit 4). First, when a mode and a density characteristic are input (21, 22), the CPU 7 selects a combination of correction data (23). A threshold value Th for background processing is input (24). I is cleared (25). If I is smaller than Th (26), the corrected density data I'of the selected density characteristic is processed, or the correction data is read from the ROM (27), and the data I'is written in the RAM (28). ). If I is equal to or greater than Th, the correction data is set to the saturation level data (29) and written to the RAM (28). Count up I by one (30),
This is repeated until I reaches 255 (31). As a result, the corrected density data is stored inside the RAM.

The gamma correction circuit 4 can be composed of, for example, four buffers and a rewritable memory (RAM) as shown in FIG. The luminance signal I obtained from the matrix circuit 3 is stored in the buffer 40. On the other hand, writing of correction data is performed as follows. The 8-bit data 0-255 generated by the CPU 7 is stored as it is in the buffer 41 as an address, and the corrected density data I ′ corresponding to 0-255 is stored.
Are stored in the buffer 42. The corrected density data I ', which is a power value of the address corresponding to the address, is RA
Written to M43. At this time, the buffer 41
43 is separated. The luminance signal I stored in the buffer 40 is given as an address to the RAM 43 as an address, and the corrected density data stored at the location given by the address is stored in the buffer 45 as a corrected luminance signal I '. To go. The correction of the density is performed in this manner.

By the way, when such density conversion is performed, the chromatic color may become pale or muddy, and the saturation may be reduced. For this reason, it is necessary to increase the saturation by the amount by which the density is moved. The correction of the saturation is performed by enlarging the value of the color difference signal. Assuming that the enlargement ratio of the color difference signal is P, the signal Si input to the matrix circuit 3 is
Is converted into a luminance signal I and color difference signals C1 and C2 output from the matrix circuit 3 by the following equation.

I a11 a12 a13 S1 C1 = Pa21 Pa22 Pa23 S2 ... (5) C2 Pa31 Pa32 Pa33 S3 Here, when P = 1, the 3 × 3 matrix (hereinafter, referred to as M) of the equation (5) is This is a basic matrix when the degree is not changed. In order to adjust the saturation according to each mode and each density in this manner, a plurality of types of matrices M are set as shown in FIG. This combination of matrices corresponds to the combination of FIG. According to experiments by the present inventors, the range in which the enlargement ratio P of the color difference signal values C1 and C2 is moved is suitably in the range of 1.0 to 1.3. This is because when P is 1.3, the saturation of the chromatic color reaches the saturation level, and the saturation does not increase even if the value of P is further increased. Explaining with an experimental example, for example, when α = 0.8 in the density conversion equation, the density becomes lighter as a whole. At this time, if the saturation is kept in the standard state at P = 1.0, the apparent saturation decreases by an amount corresponding to the lighter chromatic color. Therefore, by making P larger than 1, the value of the color difference signal is enlarged to increase the apparent saturation. Here, the image looked more natural when P = 1.1. By performing such density conversion, background processing, and saturation correction, density conversion is performed to make the image look natural to the human eye. And it is possible to obtain a preferable copy by preventing an apparent decrease in saturation, which is likely to occur as a result of density conversion.

Thus, according to this embodiment, 2
Combining 9 types of thresholds with 5 types of density characteristics,
A total of 225 density corrections can be performed, and the required memory amount is 1/225 of that required when all data is stored in the ROM.

In the embodiment described above, the correction parameters for the density characteristic, the background processing, and the saturation are manually given by using the operation switches. However, it is also possible to do this automatically. In this case, obtain the degree of saturation correction from the density distribution of the document obtained by the scanner, estimate the threshold value for background processing from the density and dirt of the paper itself, and process the signal. Good. By doing so, it is possible to save the user from having to select an operation switch.

In the above-described embodiment, both the density correction and the background processing are performed by the gamma correction circuit 4. However, as shown in FIG. 8, the gamma correction circuit 51 and the background processing circuit 52 are connected to each other. They may be provided separately and the two processes may be performed separately. In this case, the gamma correction circuit 5
1, the density conversion is performed using the curve (Equation (2 ′)) as shown in FIG. 9A, and the background processing circuit 52 performs the conversion as shown in FIG. What is necessary is just to perform a process.

[0034]

[Equation 4]

In this case, there is an advantage that the setting change of only the threshold value can be easily performed. It is also possible to set two thresholds, Th1 and Th2, to remove the background in a low density range and to adjust the saturation density in a high density range. The threshold values Th1 and Th2 may be freely changed by a switch. of course,
The processing using these two thresholds is also possible in the embodiment described above.

In the above-described embodiment, the saturation is corrected by the matrix circuit. However, the saturation can be corrected by correcting the gamma characteristic of the color difference signal. In this case, a color difference correction circuit 53 may be provided as shown in FIG. The color difference correction circuit 53 shown in FIG.
By giving a characteristic having a high gamma value as shown in FIG. 1 to the color difference signal, it is possible to increase the apparent saturation.
Further, when the input value of the color difference signal is Ci and the output value is Ci ′, it is possible to increase the saturation by using the following conversion formula.

[0037]

(Equation 5)

Here, i = 1, 2 and β are real numbers of 1 or more. As described in the case of the luminance signal correction, since the intensity is proportional to the logarithm of the intensity of the human stimulus, this relationship also holds for the saturation. Therefore, according to the equation (6), the apparent saturation becomes β times. In addition, the correction by the expression (6) does not cause the solid-colored image to have all colors having a saturation of a certain level or more, as in the case where the gamma of the color difference signals C1 and C2 are changed. It is possible to copy with high saturation while maintaining the image quality, which is convenient.

In the above, an example in which the image processing apparatus of the present invention is mainly applied to a digital copying machine has been described, but the present invention is not limited to the copying machine, and a color television camera, an electronic still camera, or the like. Needless to say, it can be applied to various uses.

[0040]

As described above, according to the present invention, it is possible to obtain the optimum value according to the type of the input image without increasing the memory capacity required for the density conversion table and by the simple mode setting operation by the user. It is possible to perform various density corrections.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an operation panel of the digital copying machine.

FIG. 3 is a diagram showing density correction determined by mode selection and density selection.

FIG. 4 is a diagram showing an example of a corrected density data curve.

FIG. 5 is a flowchart for explaining the operation of the digital copying machine;

FIG. 6 is a block diagram showing an example of an internal configuration of a gamma correction circuit of the digital copying machine.

FIG. 7 is a diagram showing a matrix determined by mode selection and density selection.

FIG. 8 is a block diagram showing a digital copying machine according to another embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of a characteristic curve when gamma correction and background processing are performed separately.

FIG. 10 is a block diagram showing a digital copying machine according to still another embodiment of the present invention.

FIG. 11 is a diagram illustrating an example of a characteristic curve when correcting a gamma characteristic of a color difference signal.

[Explanation of symbols]

1 ... Scanner, 2 ... Shading correction circuit, 3 ... Matrix circuit, 4, 51 ... Gamma conversion circuit, 5 ... ROM,
Reference numeral 6: operation panel, 7: CPU, 8: color conversion circuit, 9: dither circuit, 10: printer, 52: background processing circuit, 53
… Color difference correction circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H04N 7/18 K 9/77

Claims (3)

[Claims] 1. An image processing apparatus provided with a density conversion table for converting density data of an input image into corrected density data of an output image, wherein the density conversion table is composed of a rewritable memory, and at least a character mode and a photograph. Operation panel means for allowing the user to set a mode including a mode, and the corrected density data is generated according to the type of the input image obtained based on the mode set by the operation panel means and written in the memory. An image processing apparatus comprising: 2. An image signal of the input image is separated into a luminance signal and a color difference signal, the luminance signal is supplied to the density conversion table as density data, and the color difference signal is corrected in accordance with the corrected density data. The image processing apparatus according to claim 1, wherein: 3. The image processing apparatus according to claim 2, wherein the value of the color difference signal is expanded both when the density characteristic of the luminance signal is reduced and when the density characteristic is increased.