JP3347411B2 - Image output device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image output device, and more particularly to an image output device for sequentially transferring a plurality of color visible images sequentially formed on an image carrier onto a transfer material.

[0002]

2. Description of the Related Art In recent years, color printers have been used as various means of expression for users. In particular, color page printers have attracted attention due to their quietness, high quality printing, and high speed printing. The feature of the multicolor light beam printer, which is one of the color page printers, is that the light beam is scanned on the photosensitive member in the main scanning direction and the first light beam is scanned.
The first step of performing the first development for the first color and then transferring it to a recording medium such as recording paper on a transfer carrier is a first step, and the second step for the second, third, and fourth colors is continued. The point is that a multicolor image is recorded by the third and fourth steps.

Next, a method of recording a multicolor image in this type of conventional apparatus will be described with reference to FIGS. First, the photosensitive drum 201 rotating at a predetermined constant speed in the direction of the arrow in the drawing has a predetermined polarity by the charger 204.
It is charged to a predetermined voltage. Next, the recording paper P is supplied one by one from the paper supply cassette 215 by the paper supply roller 214 at a predetermined timing. When the leading edge of the paper is detected by the detector 202, the laser light L modulated by the image signal VDO is emitted from the semiconductor laser 205 toward the polygon mirror 207, and is scanned by the polygon mirror 207. After passing through 209, it is guided onto the photosensitive drum 201. A signal (hereinafter, referred to as “TOPSNS”) from the detector 202 disposed at one end of the optical scanning is output as a vertical synchronization signal to an image forming apparatus 250 shown in FIG. Then, the image signal VDO is sequentially transmitted to the laser 205 in synchronization with a BD signal described later that follows the TOPSNS signal.

When the laser beam L is incident on the detector 217, a beam detect (hereinafter, referred to as BD) signal serving as a horizontal synchronizing signal is output. Polygon mirror 2
07 is driven by the scanner motor 206, and the scanner motor 206 is controlled by the motor control circuit 225 so that the scanner motor 206 rotates at a predetermined constant speed in accordance with the signal S2 from the frequency divider 221 for dividing the signal S1 from the reference oscillator 220. Is done.

Then, the photosensitive drum 2 is synchronized with the BD signal.
01 is scanned and exposed, and then the first electrostatic latent image is developed by the developing device 203Y, so that a yellow first toner is formed on the photosensitive drum 201. Also, immediately before the leading edge of the recording paper P fed at a predetermined timing reaches the transfer start position,
A predetermined transfer bias voltage having a polarity opposite to that of the toner is applied to the transfer drum 216, and the first toner image is transferred to the recording paper P, and at the same time, the recording paper P is electrostatically attracted to the surface of the transfer drum 216.

Next, a second electrostatic latent image is formed on the photosensitive drum 201 by scanning with the laser beam L, the second electrostatic latent image is developed by the developing device 3M, and a second magenta latent image is formed on the photosensitive drum 201. The image is adjusted to the position of the two toner images and transferred to the recording paper P. The top end of the image of each color is defined by the TOPSNS signal. Similarly, the third electrostatic latent image is developed, developed by the developing device 3C, and a cyan toner image is formed on the recording paper P.
Then, the fourth electrostatic latent image is developed, developed by the developing device 3K, and the black toner image is transferred to the recording paper P.

As described above, one page of VDO is provided for each process.
The signals are sequentially output to the semiconductor laser 205. Further, the untransferred toner image is scraped off by the cleaner 210 in each transfer step. Thereafter, when the leading end of the recording paper P on which the four color toner images have been transferred approaches the position of the separation claw 212, the separation claw 212 approaches and the leading end of the recording paper P is
16 and separates the recording paper P from the transfer drum 216. The leading end of the separation claw 212 keeps in contact with the transfer drum 216 until the lower end of the recording paper P separates from the transfer drum 216, and then separates and returns to the original position. Then, the charge accumulated on the recording paper P is eliminated by the charger 211, thereby facilitating the separation of the recording paper P by the separation claw 212 and, at the same time, reducing the air discharge during the separation.

FIG. 24 shows the above-mentioned TOPSNS signal and VD
5 is a timing chart showing a relationship between O signals, where A1 is a printing operation of a first color, A2 is a printing operation of a second color,
Reference numeral 3 denotes a third color printing operation, and A4 denotes a fourth color printing operation. The sections A1 to A4 correspond to a one-page color printing operation. Next, the image signal will be described. FIG. 25 shows an overall electrical configuration diagram of a conventional device of this type.
Referring to FIG. 25, a printer 302 includes a control signal and an image signal 30 from an external device such as a host computer 301.
7, the printer controller 303 sends a control signal to the printer control unit 304 and an image signal to the image processing unit 3
05. Then, the semiconductor laser 306 is driven by the output signal of the image processing unit.

FIG. 26 shows an image signal processing unit 30 shown in FIG.
5 is a detailed block diagram of FIG. Receiving RGB 24-bit image signals from the printer controller 303 shown in FIG. 25, the color processing unit of 351 converts the input RGB signals into corresponding YMCK signals sequentially at a predetermined timing. That is, the input RGB signal is converted into the above-described 8-bit VDO signal of the Y signal, the M signal, the C signal, and the K signal. FIG. 27 shows a timing chart of the color signal conversion processing of the color processing unit 351.

[0010] Y, M, C, K from the color processing unit 351
Is subjected to γ correction in the γ correction unit 352, and is output after betting an 8-bit signal. Then, it is input to a pulse width modulation section (hereinafter, referred to as “PWM section”) 353 in the next stage. In the PWM unit 353, the 8-bit image signal is latched in synchronization with the rising edge of the image clock VCLK.
Latch to 4. Then, the latched digital data is
The voltage is converted into a corresponding analog voltage by the / A converter 55 and input to the analog comparator 356.

On the other hand, the image clock VCLK is also input to the triangular wave generator 358, where it is converted to a triangular wave and input to the analog comparator 356. The analog comparator 356 compares the triangular wave signal from the triangular wave generator 358 with the analog signal from the D / A converter 355, and outputs a PWM signal. The PWM signal is inverted by the inverter 357 to obtain a PWM signal. When the 8-bit image data input to the PWM unit 353 is FF [H], the widest PWM signal is output,
At 0 [H], the narrowest PWM signal is output.

[0012]

However, the above conventional example has the following disadvantages. Compared with the toner of the conventional monochrome laser beam printer, the color toner (M,
(C, Y, K colors) are expensive in terms of cost, and since four colors are printed on one sheet, the toner cost is high and the printing cost per sheet is high.

[0013]

SUMMARY OF THE INVENTION The present invention eliminates the above-mentioned drawbacks of the prior art. By thinning out color image signals at a predetermined cycle, it is possible to suppress the consumption of color toner and reduce the cost of printing. It is an object of the present invention to provide an image output device which can determine the density for each pixel and inhibit a thinning process in a low density portion even at a position where an image signal is thinned, thereby preventing a decrease in image quality in the low density portion. . The following configuration is provided as one means for achieving such an object. That is,
Low-density conversion means for performing processing for lowering the density of the input color image signal, mode switching means for selecting whether or not to perform low-density conversion processing by the low-density conversion means, and the magnitude of the density level of the input color image signal Determining means for determining each pixel, and output means for outputting color information according to the color image signal subjected to the low-density conversion processing when the low-density conversion processing is selected by the mode switching means. The low-density conversion means performs low-density conversion processing by thinning out a part of the input color image signal at a predetermined cycle, and the density level of the input color image signal determined for each pixel by the determination means is lower than a predetermined level. When it is determined that the image signal is small, the thinning process is prohibited even at the position where the image signal is thinned.

[0014]

In the above arrangement, the toner consumption can be reduced by lowering the density without changing the color tone by selection.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is an overall view of an image recording apparatus according to a first embodiment of the present invention. Referring to FIG.
1 is gripped by the gripper 1
03f, and is held on the outer periphery of the transfer drum 103. A latent image formed for each color by the optical unit 107 on the photosensitive drum 100 as an image carrier is developed by each color developing unit Dy, Dc, Dm, Db, and is transferred to a sheet around the transfer drum a plurality of times. A multicolor image is formed. Thereafter, the paper 102 is separated from the transfer drum 103, fixed by the fixing unit 104, and
5 is discharged to the discharge tray unit 106. Here, each color developing device has a rotation support shaft at both ends thereof, and each is held by the developing device selection mechanism 108 so as to be rotatable about the shaft, and each developing device has its posture as shown in FIG. The rotation for selecting the developing device is performed while the constant is maintained. After the selected developing device moves to the developing position, the developing device selecting mechanism 108 moves and positions the selecting mechanism holding frame 109 in the direction of the image carrier 100 by the solenoid 109a around the fulcrum 109b integrally with the developing device.

Next, the operation of the color laser beam printer of the present embodiment having the above configuration will be described. First, the photoconductor drum 100 is uniformly charged to a predetermined polarity (for example, a negative polarity) by the charger 111. Thereafter, the photosensitive drum 10 is exposed by the laser beam light L.
On 0, for example, a first magenta latent image is formed.
Next, in this case, a required developing bias voltage is applied only to the magenta developing device Dm to develop a magenta latent image, and a first toner image of magenta M is formed on the photosensitive drum 100.

On the other hand, immediately before the transfer paper P is fed at a predetermined timing and its leading end reaches the above-described transfer start position,
A transfer bias voltage (+1.8 KV) of the opposite polarity (for example, plus polarity) to the toner is applied to the transfer drum 103,
When the first toner image on the photosensitive drum 100 is the transfer paper P
Is transferred to At the same time, the transfer paper P is transferred to the transfer drum 10
3 is electrostatically adsorbed on the surface of the substrate. Then, the photosensitive drum 10
In the case of 0, the remaining magenta toner is removed by the cleaner 112, and a preparation is made for a latent image forming and developing process of the next color.

Next, a second latent image of cyan is formed on the photosensitive drum 100 by the laser beam L, and then the second latent image on the photosensitive drum 1 is formed by the cyan developing unit Dc.
Is developed to form a second toner image of cyan C. Then, the second toner image of cyan C is transferred to the transfer sheet P in accordance with the position of the first toner image of magenta M previously transferred to the transfer sheet P.

In the transfer of the second color toner image,
Immediately before the transfer paper reaches the transfer portion, the transfer drum 103
A bias voltage of 2.1 KV is applied. Similarly,
The third and fourth latent images of yellow and black are sequentially formed on the photosensitive drum 100, and the developing units Dy and D are respectively formed.
b, and the third and fourth toner images of yellow and black are sequentially transferred in alignment with the toner images previously transferred to the transfer paper P. Thus, the transfer paper P
The four color toner images are formed on top of each other.

In the transfer of the third and fourth color toner images, the transfer drum 1 is moved immediately before the transfer paper reaches the transfer portion.
6 are applied with bias voltages of +2.5 KV and +3.0 KV, respectively. The reason why the transfer bias voltage is increased each time the transfer of the toner image of each color is performed is to prevent a decrease in transfer efficiency. The main cause of the decrease in transfer efficiency is that when the transfer paper separates from the photosensitive drum 100 after the transfer, the surface of the transfer paper is charged to a polarity opposite to the transfer bias voltage by air discharge (the transfer paper is carried). The surface of the transfer drum is also slightly charged), and this charge is accumulated for each transfer, and if the transfer bias voltage is constant, the transfer electric field decreases every time the transfer is performed.

In the transfer of the fourth color, when the leading edge of the transfer paper reaches the transfer start position (including immediately before and immediately after), the AC voltage is 5.5 KV (effective value (the same applies hereinafter). Is 500 Hz.) And a DC bias voltage +3.0 KV of the same polarity and the same potential as the transfer bias voltage applied at the time of transfer of the fourth toner image is superimposed thereon.
Apply to 1.

The reason why the charger 111 is operated when the leading edge of the transfer paper reaches the transfer start position during the transfer of the fourth color is to prevent transfer unevenness. Particularly, in the transfer of a full-color image, even if slight transfer unevenness occurs, it is easy to notice as a color difference. Therefore, as described above, a required bias voltage is applied to the charger 111 to perform a discharging operation. It is necessary.

Thereafter, when the leading end of the transfer paper P on which the toner images of four colors are superimposedly transferred approaches the separation position, the separation claw 113 is moved.
Approach, the leading end thereof comes into contact with the surface of the transfer drum 103, and the transfer paper P is separated from the transfer drum 103. The leading end of the separation claw 113 keeps contact with the surface of the transfer drum 103 until the rear end of the transfer paper P leaves the transfer drum 103, and then separates from the transfer drum 103 and returns to the original position.

The charger 111 operates from the time when the leading end of the transfer paper reaches the transfer start position of the final color as described above until the rear end of the transfer paper leaves the transfer drum 111, and stores the accumulated charge (toner) on the transfer paper. The opposite polarity) and the separation claw 113
Facilitates separation of the transfer paper, and reduces air discharge during separation. When the rear end of the transfer paper reaches the transfer end position (the exit of the nip formed by the photosensitive drum 100 and the transfer drum 103), the transfer bias voltage applied to the transfer drum 103 is turned off (installation potential). To
At the same time, the bias voltage applied to the charger 111 is turned off.

Next, the separated transfer paper P is applied to the fixing device 104.
, Where the toner image on the transfer paper is fixed and discharged onto the discharge tray 115. FIG. 2 is a block diagram focusing on the electric circuit of the present embodiment. In FIG. 2, the printer 2 is roughly classified into a printer controller 3 for developing image information in a predetermined description language sent from the host computer 1 and a printer engine 4. In addition, RGB data read from the host computer 1 by an image reader or the like is used.
, Etc. are also transmitted.

FIG. 3 shows a detailed block diagram of the printer engine 4. In FIG. 3, the reference clock from the reference oscillator 10 is frequency-divided by the frequency divider 11 and the scanner motor 13 controls the motor so that the phase difference between the frequency-divided clock and the feedback signal from the scanner motor 13 becomes a predetermined phase difference. Circuit 12 (Built-in known phase control circuit not shown)
Is rotated at a constant speed.

On the other hand, the transfer drum 103 (FIG. 1) is rotated at a constant speed by a drive motor (not shown).
The leading end of the upper recording paper P is detected by the detector 8 (FIG. 3), and the vertical synchronization signal VSYNC is output to the image processing unit 7 (FIG. 3). The vertical synchronizing signal VSYNC defines the leading edge of each color image. The image signal VDO is sequentially sent to the laser 5 in synchronization with the beam detect signal BD after the VSYNC signal.

Vertical sync signal VSYNC, horizontal sync signal B
D and the timing of the image signal VDO are shown in FIG.
Next, the operation of the laser beam scanning device will be described with reference to FIGS. An optical unit 107 in FIG.
It comprises a semiconductor laser 120, a polygon mirror 121, a scanner motor 122, a lens 123, and a mirror 125.

When the leading edge of the recording paper P is fed, an image signal VDO for one page is output to the semiconductor laser 120 in synchronism therewith, and the light beam L modulated by the image signal VDO is output by the scanner motor 122. The light is emitted toward the rotating polygon mirror 121. The emitted light beam L is guided to the photosensitive drum 100 by the lens 123 and the mirror 125.

When the light beam L is emitted, the light beam L is detected by the detector 9 shown in FIG. 2 arranged on the scanning axis, and a beam detection signal BD serving as a horizontal synchronizing signal is detected.
Is output. As a result, the photosensitive drum 100 is scanned and exposed by the light beam L in synchronization with the BD signal, and an electrostatic latent image is formed. FIG. 5 shows an internal block diagram of the image processing unit 7. 5, reference numeral 30 denotes a FIFO circuit, 31 denotes an invalid data mask unit, 32 denotes a toner-saving image conversion unit, 33 denotes a full dot detection unit, 34 denotes a selector, 35 denotes a γ correction unit, and 36 denotes a selector.
Is a PWM (pulse modulation) unit, and 38 is a CPU.

Hereinafter, the operation of the image processing section 7 of the present embodiment having the above-described components will be described. Multivalued image data 6 (consisting of an 8-bit density signal and a 1-bit image designation signal) is transmitted from a printer controller 3 (not shown) in synchronization with the transfer clock VCLK. Image designation signal I
MG is a signal for switching between printing 200 lines when "H" and printing 600 lines when "L".

The FIFO circuit 30 writes the 9 bits of the image data with the transfer clock VCLK and reads the 9 bits with the printer clock PCLK. The FIFO circuit reads and writes one line of data, and has a data width of 9 bits and 51 lines.
The storage amount is set to 20 dots. The write clock is 16 MHz and the read clock is 22 KHz.
(PCR-) is a main scanning synchronization signal, and the FIFO circuit 3
0 is cleared by (PCR-). Fifo
The image signal 39 output from the circuit 30 is sent to the invalid data mask unit 31 at the next stage, where the area other than the print area is masked. (DE-) is a signal in which the print area of the main scanning line is "L" and the non-print area is "H".

FIG. 6 shows a circuit example of the invalid data mask section 31. The output signal from the invalid data mask unit 31 is input to the toner-saving image conversion unit 32 at the next stage. The toner-saving image conversion unit 32 converts an image signal based on the toner-saving print mode designation signal A from the CPU 38. The toner-saving print mode is a mode in which the toner consumption is reduced by extracting and printing image data every other dot in the normal print mode. At that time, the printing density is lowered but the color tone is not changed.

FIG. 7 shows a circuit example of the toner-saving image conversion unit 32. In the circuit example of the toner-saving image conversion unit 32 shown in FIG. 7, the image data is extracted in a staggered manner by one dot in both the main scanning direction and the sub-scanning direction, and the extraction of the outline of the image is prohibited. It is. In FIG. 7, a flip-flop 53 generates a toggle signal of “H” or “L” every other dot of PCLK, and inputs a normal rotation and an inverted output to the selector 55, respectively. On the other hand, the selector 55 switches between the A input and the B input every other line in accordance with the output signal 57 of the flip-flop 54 and outputs it.

The selector 56 inhibits tooth removal at the edge of the image. The selector 56 selects the "H" of the A input by the image edge detection signal 58 to inhibit the tooth removal. The image edge detection signal 58 is generated by eight-circuit flip-flops 48 and 49 and comparators 50 and 51. The output signals from the flip-flops 48 and 49 (the center pixel 60 and the adjacent pixels 59 and 61) are compared by the next-stage comparator, and if the density difference between the center pixel and the adjacent pixels is 128 or more, it is determined that the image is an edge. , Image edge detection signal 5
8 is set to "H".

A desired data mask signal 74 is output from the selector 56, and the extracted image signals VDOC0 to VDOC0 are extracted.
7, IMGC is obtained. FIG. 8 shows a toner-saving image conversion unit 3.
2 shows an operation timing chart. In the present embodiment, this tooth removal process is performed for all four colors of Y, M, C, and K. The output image signal from the toner-saving image conversion unit 32 in FIG.
After adding 0 and COL1, the signal is input to the full dot detection unit 33 of the next stage as a signal of 11 bits in total. In the full dot detection unit 33, the image data is designated by 600 lines and
In the case of [H], the signal FDOT is set to "H", and in the case of specifying 600 lines and 00 [H], the signal ODOT is set to "H". FIG. 9 shows a detailed circuit example of the full dot detection unit 33.

In FIG. 5, reference numeral 35 denotes a gamma correction unit, which is a look-up table composed of a RAM. FIG. 10 shows an example of the contents of the look-up table of the gamma correction unit 35. As shown in FIG. 10, a γ table of 200 lines and 600 lines is provided for each of the colors M, C, Y, and K, respectively.
The contents of the γ correction table are written from the CPU 38 when the power of the printer is turned on, for example.

The writing process will be described. CPU38
Calculates the optimum gamma correction data according to the environment around the printer, and controls the selector 34 to select and output the address bus 43. Then, the write position address of the RAM of the γ correction unit 35 is output to the address bus 43, the calculated γ correction data is output to the data bus 44, and the γ on the data bus 44 is stored in a predetermined area of the RAM via the bus transceiver 37. Write the correction data.

The data γ-corrected by the γ-correction unit 35 is input to the PWM unit 36 at the next stage. The PWM unit 36 generates a digital signal having a pulse width corresponding to the image data and sends it to a laser driver (not shown). FIG. 11 shows a detailed circuit example of the PWM unit 36, and FIG. 12 shows its operation timing. In FIG. 11, 79 is an 8-bit input D / A converter, 82 and 83 are triangular wave generators, 84 and 85 are comparators, 86 and 87 are selectors, and 80 is PCLK99.
A multi-phase dividing circuit 3 for generating a clock having eight phase differences at the same time as the dividing, 81 is a selector.

The PWM unit 3 of this embodiment having the above configuration
Operation 6 will be described below with reference to the timing chart of FIG. PCLK is 600 dots / inch, 1
This is a clock in dot units. The triangular wave generator 82 outputs P
The triangular wave generator 83 generates a triangular wave 91 for performing 600-line PWM based on the CLK, and the triangular wave generator 83 generates a triangular wave 92 for performing 200-line PWM combining three PCLKs.
The 200-line PWM selects one of the clock signals 89 having six phase differences from the selector 81 to control the screen angle.
To select.

FIG. 13 shows an output signal from the multi-phase dividing circuit 80. For example, to represent a screen angle of 45 ^° , a 0 ^° phase clock and 180 ^{°
o The} phase clock may be selected by the selector 81. That is, (SCR2, SCR1, SCR0) = (0, 0,
0) and (0, 1, 1) are output for each line. FIG.
FIG. 15 schematically shows a printing state in the normal mode in this embodiment, and FIG. 15 schematically shows a printing state in the toner saving mode in this embodiment.

In FIGS. 14 and 15, A is γ
The correction unit input image data B is in a printing state. Note that the toner-saving mode can be selected from a method of designating from the display unit of the printer and a method of designating with a command from an external device.
In a printer to which a 1-bit binary image signal is input, the configuration is such that binary data is extracted. Further, in this embodiment, the extracted image is set to 00 [H], but the image may be converted to, for example, 1/4 density without complete extraction.

As described above, according to this embodiment, if necessary, the image data of M, C, Y, and K colors are removed by a predetermined amount, the density is reduced without changing the color tone much, and the toner consumption is reduced. Can be lowered. Also in this case, the edge does not become unclear. Second Embodiment Next, a second embodiment according to the present invention will be described. FIG. 16 is a block diagram illustrating a detailed configuration of the toner-saving image conversion unit according to the second embodiment of the present invention. In the second embodiment, the basic configuration is the same as that of the above-described first embodiment. In the first embodiment, the toner-saving image conversion unit 32 shown in FIG. 7 has the configuration shown in FIG. The other configurations and operations are the same as those in the first embodiment, and thus detailed description is omitted.
In FIG. 16, the same components as those in FIG. 7 described above are denoted by the same reference numerals, and detailed description is omitted.

In the second embodiment, the divide-by-3 circuit 160 is a PC
The LK signal is divided by three and input to the flip-flop 142. The switching of the selector 55 is performed by the counter 143.
Is controlled by In this manner, image data is extracted in units of three dots in the main scanning direction, and tooth extraction positions in the main scanning direction are staggered in units of two lines in the sub-scanning direction. Further, in order to prohibit the extraction of the image in the low-density part of the image data, the comparator 141 compares the image data with 40 [H], and only when the image data has a density higher than 40 [H]. Tooth extraction.

FIG. 17 shows a printing example when printing is performed in the toner saving mode of the second embodiment. In FIG. 17, A is a γ-correction input image signal, and B is a printing state. As described above, according to the second embodiment, the image data of the colors M, C, Y, and K are removed by a predetermined amount as necessary, the density is reduced without changing the color tone much, and the toner consumption is reduced. be able to. Also in this case, in the low-density part of the image data, the extraction of the image is prohibited, and the quality of the formed image in the low-density part does not deteriorate.

Third Embodiment FIG. 18 shows a third embodiment according to the present invention.
3 shows a detailed configuration of the image processing unit of the embodiment. The basic configuration of the third embodiment is the same as that of the first embodiment described above, and the third embodiment is different from the first embodiment in the configuration of the image processing unit 7 shown in FIG. Are different. In addition,
In FIG. 18, the same components as those of the first embodiment shown in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the third embodiment, the first embodiment shown in FIG.
As compared with the embodiment, the toner saving mode is executed by the γ correction unit 164, and the entire image is converted to low density, and this mode is executed.
In FIG. 18, when the execution of the toner saving mode is instructed from the CPU 165, the toner saving designation signal EC becomes “valid” and is output. The CPU 165 writes the γ correction data in the γ correction unit 164 at the same timing as in the first embodiment before printing, but in the third embodiment, the γ correction data in the normal mode printing and the Is written.

FIG. 19 shows the γ correction section 16 in the third embodiment.
4 shows an example of the γ correction table. And when printing, CP
The gamma correction data for the toner saving mode is selected from the gamma correction look-up table in accordance with the toner saving designation signal EC output from U165, and the image density is converted to lower.
When the toner saving designation signal EC is not output from the CPU 165, the normal mode gamma correction data in the gamma correction look-up table is selected, and the gamma correction data is changed without changing the image density.
to correct.

FIG. 20 shows the relationship between the multi-value image data output from the controller and the print density in the normal mode of the third embodiment. FIG. 21 shows the relationship between the multi-valued image data output from the controller and the print density in the toner saving mode of the third embodiment. As shown in FIG. 21, in the third embodiment, the low-density conversion is reduced in the highlight part, and the low-density conversion is increased in the dark part. This is because, in general, in the case of printing by the electrophotographic method, the density becomes unstable in the highlight portion, so that the conversion in the low density portion is small, and the conversion in the high density portion, which greatly affects the toner consumption, is performed. They do a lot of conversion.

As described above, according to the third embodiment, the density can be reduced without changing the color tone and the toner consumption can be easily changed by simply switching the γ correction table without having to perform any special circuit or operation. The amount can be reduced.
The present invention may be applied to a system including a plurality of devices or to an apparatus including a single device.

It is needless to say that the present invention can be applied to a case where the present invention is achieved by supplying a program to a system or an apparatus.

[0052]

As described above, according to the present invention, by thinning out color image signals at a predetermined cycle, the consumption of color toner can be suppressed, and the printing cost can be reduced.
It is possible to provide an image output apparatus that can determine the density for each pixel and prohibit the thinning process in the low-density portion even at the position where the image signal is thinned, thereby preventing the image quality from being reduced in the low-density portion.

[Brief description of the drawings]

FIG. 1 is an overall view of an image recording apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a control-related configuration according to the first embodiment.

FIG. 3 is a block diagram illustrating a detailed configuration of a printer engine illustrated in FIG. 2;

FIG. 4 is a diagram illustrating timings of a vertical synchronization signal VSYNC, a horizontal synchronization signal BD, and an image signal VDO according to the first embodiment.

FIG. 5 is an internal block diagram of the image processing unit shown in FIG. 3;

FIG. 6 is a diagram illustrating a circuit example of an invalid data mask unit illustrated in FIG. 5;

FIG. 7 is a diagram illustrating a circuit example of a toner-saving image conversion unit illustrated in FIG. 5;

8 is an operation timing chart of the toner-saving image conversion unit shown in FIG.

FIG. 9 is a diagram illustrating a detailed circuit example of a full dot detection unit illustrated in FIG. 5;

FIG. 10 is a diagram showing an example of the contents of a look-up table of the γ correction unit shown in FIG. 5;

11 is a diagram illustrating a detailed circuit example of a PWM unit illustrated in FIG. 5;

FIG. 12 is an operation timing chart of the PWM unit of the present embodiment.

FIG. 13 is a diagram showing an output signal from the multi-phase frequency dividing circuit shown in FIG. 11;

FIG. 14 is a diagram schematically illustrating a printing state in a normal mode according to the present embodiment.

FIG. 15 is a diagram schematically illustrating a printing state in a toner saving mode according to the present exemplary embodiment.

FIG. 16 is a diagram illustrating a circuit example of a toner-saving image conversion unit according to a second embodiment of the present invention.

FIG. 17 is a diagram illustrating a print example when printing is performed in the toner saving mode according to the second embodiment.

FIG. 18 is a diagram illustrating a detailed configuration of an image processing unit according to a third embodiment of the present invention.

FIG. 19 is a diagram illustrating an example of a γ correction table of a γ correction unit according to the third embodiment.

FIG. 20 is a diagram illustrating a relationship between multi-value image data output from a controller and a print density in a normal mode according to the third embodiment.

FIG. 21 is a diagram illustrating a relationship between multivalued image data output from a controller and a print density in a toner saving mode according to a third embodiment.

And FIG. 22 is a diagram illustrating a configuration of a conventional multicolor image recording apparatus.

FIG. 23 is a diagram illustrating a configuration of a conventional multicolor image recording apparatus.

FIG. 24 shows a TOPSNS signal and VD in a conventional device.
6 is a timing chart illustrating a relationship between O signals.

FIG. 25 is an overall electrical configuration diagram of a conventional device of this type.

26 is a detailed block diagram of the image signal processing unit shown in FIG.

FIG. 27 is a timing chart showing a color signal conversion process of the color processing unit shown in FIG. 26;

DESCRIPTION OF SYMBOLS 1, 30 Host computer 2, 302 Printer 3, 303 Printer controller 4 Printer engine 7, 305 Image processor 8, 202, 217 Detector 10, 220 Reference oscillator 11 Divider 12, 225 Motor control circuit 13, 122, 206 Scanner motor 30 Fifo circuit 31 Invalid data mask section 32 Toner image conversion section 33 Full dot detection section 34 Selector 35, 164 γ correction section 36 PWM (pulse modulation) section 37 Bus transceiver 38, 165 CPU 48, 49, 53, 142 Flip-flops 50, 51, 84, 85, 141 Comparators 55, 56, 81, 86, 87 Selectors 79 D / A converters 80 Multi-phase divide-by-3 circuit 82, 83 Triangular wave generator 80 Multi-phase 3 Dividing circuit 100,201 feeling Body drum 101 Paper feed section 102, 201 Paper 103, 216 Transfer drum 104 Fixing unit 105 Paper discharge section 106 Paper discharge tray section 107 Optical unit 108 Developing device selection mechanism section 111 Charger 115 Paper discharge tray 120 Semiconductor laser 121, 207 Polygon Mirror 123 lens 125 mirror 143 counter 160 frequency dividing circuit 304 printer controller 306 semiconductor laser

Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/23-1/31 H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (1)

(57) [Claims] A low-density conversion means for performing processing for lowering the density of an input color image signal; a mode switching means for selecting whether to perform low-density conversion processing by the low-density conversion means; Determining means for determining the magnitude of the density level for each pixel; and when the mode switching means selects low-density conversion processing, color information is obtained according to the low-density conversion color image signal. and output means for outputting said low density conversion means own the part of the input color image signal
A low-density conversion process is performed by thinning out at a fixed cycle. If the density level of the input color image signal determined for each pixel by the determination means is determined to be smaller than a predetermined level, the position of the image signal is determined. an image output apparatus characterized by prohibiting the thinning process be.