JPS62181573A - Picture processor - Google Patents

Abstract

PURPOSE:To maintain an excellent gradation for each color by providing a color correction processing means that has gamma conversion tables independent for each color. CONSTITUTION:The color correction processing means 102 that comprises a gamma-conversion ROM in which gamma conversion charateristics gammaY, gammaM, gammaC and gammaK corresponding to respective colors Y, M, C, and K, and processes the color-correction of the characteristic of a color picture signal 100, and a correction-characteristic selecting means 103 that selects one color-correction processing characteristic from the said ROM for each color, are provided. The color picture signals in a memory 5 are gamma-converted by a gamma-converting part 6 in the order of picture- sequence or line-sequence. The picture signals after the said conversion, are subjected to binarization processing executed respectively on each color by a binarization processing part 7, and the binarized picture data are reproduced as a picture by an output part 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing device that performs predetermined color correction processing on a color image signal.

[Prior Art] Correcting the gradation of a video signal obtained by digitizing a signal from an image reading element such as a CCD using an analog-to-digital converter (A/D converter) is widely known as γ conversion. . On the other hand, in a color image recording device, for example, Y(
In many cases, a color image is formed from color image signals having four different characteristics: yellow) 1M (magenta), C (cyan), and K (black). However, in image processing for such color recording devices, only one type of γ conversion table is prepared;
Since gradation correction for each color was performed using only that one γ conversion table, the Y, M, and C.

Differences in the characteristics of the four K color developers emerged, and good gradation could not be maintained for each color.

[Problems to be Solved by the Invention] The present invention was proposed in order to eliminate the drawbacks of the above-mentioned conventional example, and performs different color correction processing for each color to obtain a reproduced image of good quality for each color. The present invention provides an image processing device that can perform various functions.

[Means for Solving the Problems] In order to achieve the above-mentioned problems, for example, the image processing apparatus of the embodiment shown in FIG.
As an example of color correction processing, for example, γ conversion, which is gradation correction, is applied to 0. The configuration of such an embodiment is Y, M,
γ conversion characteristics corresponding to each color of C, (γY, γ8.γC
A color correction processing means 10 which has a γ conversion ROM etc. storing 1γK) and performs color correction processing on the characteristics of the color image signal 100.
2, and a correction characteristic selection means 103 for selecting one color correction processing characteristic for each color (for example, γY when correcting a Y image signal) from the γ conversion ROM.

[Operation] Under the above configuration, the color correction processing means 102 having an independent γ conversion table for each color can obtain corrected image processing signals 105 for each color, so that good gradation of each color can be maintained. I can do it.

[Embodiments] Hereinafter, embodiments of the present invention will be described in further detail with reference to the accompanying drawings. In this embodiment, an image processing device is applied to an image recording device. An example of such a recording device is, for example, a color laser beam printer.

A laser beam printer usually forms an electrostatic latent image by controlling irradiation or non-irradiation of a laser beam onto a photosensitive drum, and obtains a visible image by developing the latent image. In this example, the on-time (pulse width) of the laser beam is variably controlled according to the density level of the image signal, so the latent image potential changes depending on the on-time of the laser beam. The relationship has non-linearity. Furthermore, non-linearity also exists between potential and development density. Therefore, in this embodiment, a γ conversion section for the image signal is provided in order to compensate for this nonlinearity. Furthermore, the applicant has discovered that the relationship between potential and development density differs depending on the characteristics of the developing toner of each color. . Therefore, the above-mentioned γ conversion characteristics are made different for each color.

The image recording apparatus of this embodiment will be described in detail below with reference to FIG. In the figure, reference numeral 1 denotes a document image, which is read by a human sensor, such as a full-color CdS sensor 2, and converted into a density signal by a 10g converter 3. The analog density signal is converted into a digital value by the A/D converter 4, and is converted into Y (yellow), 9M (magenta), and C (cyan).
, K (black) are stored in the memory 5 as four color image signals. Note that the digital color image signal has 6 bits for each color. The color image signal in the memory 5 is subjected to gamma conversion by a gamma conversion section 6 in a field-sequential or line-sequential manner. The γ conversion unit 6 may be a γ conversion memory shown in FIG. 1, but it is necessary to prepare γ conversion parameters for each color image signal, which is a feature of this embodiment. The image signal after the γ conversion is subjected to binarization processing for each color by the binarization processing unit 7, and the binarized image data is reproduced as an image by the output unit 8. Incidentally, since the output unit 8 cannot develop each color at the same time, it is necessary to form an image on the recording paper 9 for each color. Therefore, the recording apparatus of the embodiment shown in FIG. 2 receives a signal (step signal 11 to be described later) indicating the printing process for each color from the output unit 8 and performs γ conversion, binarization processing, etc.

A more detailed block diagram of the γ conversion section and the binarization processing section of the color image recording apparatus shown in FIG. 2 is shown in FIG. 3(a), and that of the output section 8 is shown in FIG. 3(b).

<γ Conversion Process> The γ conversion will be explained according to FIG. 3(a). As mentioned above, the memory 5 stores color-separated color image signals (
Y, M, C, K) are stored. The printing process control unit 8 receives a step signal 11 from the output unit 8 indicating which color printing step is being performed, and synchronizes the γ conversion and binarization processing. The print process control section 10 is controlled by a microprocessor (MPU) 20. The MPU 20 sequentially reads out the color image signals in the memory 5 in response to the step signal 11 and sends them to the γ conversion ROM 21.

The memory 5 receives an address signal from the MPU 20, reads an image signal corresponding to the address signal, and outputs the read image signal as an address (AoNA5) of the γ conversion ROM 21.

Next, the ROM 21 for γ conversion will be explained in more detail.

In this example, a ROM with a capacity of 256 bytes is used, but since the digital image signals of each color for Y, M, and C that are manually input are 6 bits, there are 64 (=28) per color.
It is good if you have a byte capacity. Figure 4 shows ROM2 for γ conversion.
1 memory map. As mentioned above, since the present embodiment has a capacity of 256 bytes, it is possible to store four types of conversion tables in Y, M, and C. Addresses (00)H to (3F)u (H represents hexadecimal notation) indicate table 1 for Y, and addresses (40)□ to (
7F) H shows table 2 for M, and address (8
0)□ to (BF)H indicate table 3 for C, and addresses (c O) o to (F F) I+ indicate table 4 for crab. FIG. 5 shows an example of the characteristics of each color input image signal-conversion data signal obtained from the above conversion table in the ROM 21.
~63 levels (6 bits) are converted to levels 0 to 255 (8 bits) according to respective conversion tables.

The γ conversion for each color will be described. In this example, Y, M,
Since there are four conversion tables for C,
Switching of these conversion tables can be realized by changing the upper two bits of the ROM 21 (for example, A6 + A7 in FIG. 2). Therefore, in the embodiment shown in FIG. 2, the MPU 20 applies signals A and B to the latch 8 holding a 2-bit address via an internal output port (not shown) to latch a predetermined address. The MPU 20 converts the signals A and B into a color image forming process, for example Y.

The state of each developing device (36 to 39 in FIG. 3(b)) is input to M, C, as a step signal 11, and A, B signals are outputted according to the state, for example, according to the relationship shown in FIG. 6. do. For example, if the step signal 11 indicates that K is currently being developed, A=A6="1'", B=A7="1"
is output. At this time, the address to ROM21 is (C
○) Indicates any of H to (FF).

<Binarization Process> Returning to FIG. 3(a), the binarization process will be explained. An example of the binarization processing is binarization using pulse width modulation (PWM). That is, a comparator (comparison circuit) 24 compares the analog image signal 22a with a pattern pulse 23a having a predetermined cycle (having a predetermined relationship with the cycle of the image signal) and a predetermined pattern (for example, a triangular wave) to obtain a binary value. It is something that becomes. The timing of the pattern pulse 23a is generated by a timing signal generation circuit 27. FIG. 3(C) shows details of the timing signal generation circuit 27. According to the same figure, reference clock oscillator 2
6 generates a high-speed clock (master clock 50) which serves as a reference timing for binarization processing. The counter 52 controls the master clock 50 by a horizontal synchronizing signal 51 generated for each line from the horizontal synchronizing signal (H3YNC) generating circuit 25.
The master clock 50 is counted down to, for example, 1/24th period in synchronization with . This counted down signal (pixel clock 30) is further divided by a frequency dividing circuit 53 into a screen clock 29 whose frequency is divided by one-third, for example.

Note that the horizontal synchronization signal 51 may be generated internally,
Although it may be given from the outside, since this embodiment is an example of a signal applied to a laser beam printer, the horizontal synchronization signal corresponds to a well-known beam detect (BD) signal.

To explain with reference to FIG. 3(a), the 8-bit image data converted by the γ conversion ROM 21 is converted into an analog quantity by the digital-to-analog converter (D/A converter) 22. The two picture elements are sequentially connected to the comparator 24.
is input to one terminal of On the other hand, the pattern signal generator 23 generates a pattern signal 23a having a predetermined shape, for example a triangular wave, according to the period of the screen clock 29, and inputs it to the other terminal of the comparator 24. Further, the pixel clock 30 from the timing generation circuit 27 mentioned above is used for locking the transfer of digital data and latch timing of the D/A converter 22. Comparator 2
4, the analog-converted image signal 22a and the signal level of the triangular wave 23a from the pattern signal generator 23 are compared, and pulse width modulated binary image data of each color is output. This pulse width modulated image signal is then inputted to, for example, a modulation circuit (laser oscillator 41 in FIG. 3(b)) for modulating a laser beam. Then, the laser beam is turned on/off according to the pulse width, Y, M, C.

Halftone images are formed on the recording medium (for example, the photosensitive drum 31 in FIG. 3(b)) in the order of K.

FIG. 7 is a diagram for explaining signal waveforms at each part in FIG. 3(b). The 8-bit color image signals of each color before DA conversion are expressed as digital data, and the ones after DA conversion are expressed as analog image signals, which are synchronized with the pixel clock 30. Here, it is assumed that the higher the level, the blacker it becomes.

On the other hand, the output 23a of the pattern signal generator 23, which is one of the inputs to the comparator 24, is shown by a solid line in the figure. The stair-like broken line is analogized image data, and the triangular wave 23 from the pattern signal generator 23 is generated by the comparator 24.
The image data that is compared with a and converted into an analog signal becomes a pulse width modulation signal.

In this way, in the binarization process used in this example, Y
, M, C, digital image data, which is once converted to analog image data and then compared with a triangular wave of a predetermined period, enables almost continuous pulse width modulation and provides high gradation image output. It is. In addition, the pattern signal (
For example, since the screen clock synchronized with the horizontal synchronization signal is formed using a reference clock (master clock) with a higher frequency than the frequency of the synchronization signal for generating a triangular wave, the fluctuation of the pattern signal generated from the pattern signal generation circuit 23 (For example, the difference between the pattern signal of the first line and the second line) is 12 of the pattern signal period in this embodiment.
It becomes 1/1.

Therefore, since the gradation information is pulse-width modulated almost steplessly using a pattern signal with little fluctuation, a high-quality reproduced image can be obtained. Although a triangular wave is used in the above example as the pattern signal 23a used for pulse width modulation, a sawtooth wave or a sine wave can also be used to obtain the same effect.

<Output Unit> FIG. 3(b) shows an output unit 8 for recording an image as a visible image, using a laser beam printer as an example. The pulse width modulation signal in FIG. 3(a) is generated by the laser oscillator 41.
, and becomes laser light 43. The laser beam 43 is horizontally scanned on the photosensitive drum 31 by the polygon rotating mirror 42 . The photosensitive drum 31 is charged by a primary charger 40, and when the laser beam 43 is irradiated onto the photosensitive drum 31, it is exposed. The exposed portion is developed with toner by the Y developing device 39, and is transferred to the recording paper 33 in close contact with the transfer drum 32 by the transfer charger 34. In this way, Y (yellow) development is first performed. Thereafter, magenta development, cyan development, and black development are repeated in the same manner. By the way, 35 is a step signal generator that rotates together with the photosensitive drum.
1, a step signal 11 is generated and sent to the MPU 20 of the printing process control section 10, and the MPU 20 determines the development timing for each color. This will be explained next with reference to the flowchart of FIG.

<Control Procedure> Explaining according to the flowchart of FIG. 8, in step S2, it is determined from the state of the step signal 11 which color development process is to be executed next. This is easily done by inputting the step signal 11 to a counter (not shown). Once the next process to be executed is known, the process proceeds to step S4 for Y development, step S8 for M development, step S12 for C development, and step S16 for K development. .

In these steps, signals A and B according to FIG. 6 are set. Next, step S6. SlO, S14. S18
Then, image signals of each color are read out from the memory 5, respectively. The read image signal is subjected to color correction (γ conversion) in step S20. This γ conversion is as described above. The image signal after the γ conversion is binarized in step S22. This binarization process is also as explained in connection with FIGS. 3(a) and 7. In step S24, the binarized pulse width modulation signal is printed by a laser. Above steps S2 to S24
Repeat the above cycle for each color.

<Effects of the Embodiment> As explained above, when obtaining a full-color copy by binarizing the image signal of an original containing a halftone image such as a photograph, Y, M
,C, prepares multiple gradation correction γ conversion tables for each color image signal and performs optimal correction processing for each color,
For example, it is possible to correct differences in the characteristics of each color developer and obtain a full-color copy in which each color maintains good gradation. Although the above embodiments have been described using an example of γ conversion as an example of color correction, the present invention is not limited to γ conversion and can be similarly applied to masking adjustment, UCR (color removal), and the like.

Furthermore, in the image processing apparatus shown in the second diagram, four γ conversion tables for each color, Y, M, and C, are prepared in the ROM 21, but it is possible to use these in the RAM and rewrite the γ conversion tables for each color developer. You can also do it. Also, the binarization process is also PWM.
It is clear that the present invention can be applied not only to binarization processing using pulse width modulation, but also to binarization processing using a threshold matrix such as a dither matrix.

[Effects of the Invention] As explained above, according to the present invention, for color correction of a color image signal, it is possible to select the most suitable correction amount for each color and then perform color correction, resulting in high image quality. It becomes possible to obtain full-color reproduced images.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of an embodiment according to the present invention, FIG. 2 is a block diagram of the embodiment applied to a printing device, and FIGS. 3(a) and (c) are γ conversion in the embodiment, A block diagram for binarization processing, Fig. 3(b) is a configuration block diagram when the embodiment is applied to a laser beam printer, and Fig. 4 is a γ conversion ROM.
FIG. 5 is a memory map diagram of each color in the γ conversion. Figure 6 is a truth table of signals used to select and access the γ conversion ROM for each color in γ conversion, Figure 7 is a timing chart of binarization processing using pulse width modulation, and Figure 8 is It is a flowchart of control in the process from γ conversion to printing. In the figure, 5...memory, 6...γ conversion unit, 21...
γ conversion ROM, 7... Binarization unit, 10... Printing process control unit, 11... Step signal, 20... MP
U, 23...Pattern signal generator, 26...Oscillator, 31 Photosensitive drum, 32...Transfer drum, 9,3
3...Recording paper, 36-39...Developer, 40...
-Next 1F electric appliances, 42...polygon mirror, 41...
Laser oscillator, 52... counter, 53... frequency divider. Patent applicant: Canon Co., Ltd. Figure 4 Figure 5 Figure 6

Claims (4)

[Claims] (1) a color correction processing means for color-correcting a color-separated color image signal for each color according to predetermined color correction characteristics prepared for each color; and a color correction processing means for performing color correction processing for each color; and correction characteristic selection means for selecting the color correction processing means to perform color correction processing. (2) The image processing apparatus according to claim 1, wherein the color correction process is γ conversion. (3) A pulse width modulation binarization means is further provided, and the pulse width modulation binarization means pulse width modulates the image signal after color correction processing. image processing device. (4) further comprising an image forming means for forming an image from the color image signal after color correction, the selection of correction processing characteristics by the correction characteristic selection means, color correction processing and image formation of each color by the image forming means; The image processing apparatus according to claim 3, characterized in that the image processing apparatus performs the processing in association with the process.