Image forming device and image forming method

An image forming device includes a plurality of holding units that holds data of pixels around a target pixel, a weight generating unit that generates a weight for each holding unit, a plurality of weight applying units that applies a corresponding weight to the data held by each holding unit, and a control unit that determines an exposing energy for the target pixel in accordance with an output of each weight applying unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming device such as a copy machine, a facsimile machine and a printer, and an image forming method.

2. Description of the Related Art

In a conventional laser printer known as an image forming device, when an electrostatic latent image is formed on a photoconductive body by using 100% light energy even on an inner part of a black solid part of the image, a large amount of toner adheres to the photoconductive body. Not only is the toner consumed in a large amount, but there is also a drawback of deterioration in the quality of the image recorded on paper, such as trailing of the toner. In consideration of such a drawback, by using a matrix of pixels, depending on whether surrounding pixels are white or black, a determination can be made as to whether a target pixel is located at a peripheral part or at an inner part of the black solid part. An exposing energy for pixels located in the black solid part is reduced in order to reduce an amount of toner adhered to the photoconductive body. This technology is generally known as “Toner Saving”.

In the above-described technology, by using the matrix of pixels consisting of the target pixel and the surrounding pixels, depending on whether the surrounding pixels are white or black, a determination can be made as to whether or not to reduce the light energy of the target pixel. In fact, a value of the surrounding pixels is arranged in one piece of data and this piece of data is input to a memory as an address. The exposing energy is reduced in accordance with this piece of data output from the memory. That is, the toner is saved for the target pixel.

However, since it becomes necessary to provide a memory, the scale of the circuitry increases. In particular, to improve accuracy for determining whether the target pixel is located at the peripheral part or at the inner part of the black solid part, the size of the matrix increases and a greater capacity of the memory becomes necessary. Meanwhile, when image data becomes multilevel, the number of bits of data as the address increases and a greater capacity of memory becomes necessary.

SUMMARY OF THE INVENTION

An advantage of the present invention is to provide an image forming device and an image forming method which can determine whether or not to save toner for a target pixel by simple circuitry.

According to an aspect of the present invention, the image forming device includes a plurality of holding units that holds data of pixels around a target pixel, a weight generating unit that generates a weight for each holding unit, a plurality of weight applying units that applies a corresponding weight to the data held by each holding unit, and a control unit that determines an exposing energy for the target pixel in accordance with an output of each weight applying unit.

In the present invention, the weight applying unit is a multiplier that multiplies the data and the weight. The control unit includes an adder that adds the output of each weight applying unit. The control unit can compare the output of the adder with one or more reference and determine the exposing energy for the photoconductive body. Depending on how the weight is applied, a sense of direction can be given to saving of an edge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described.FIG. 1shows a configuration of a MFP (including multi-functions such as a copy function, a facsimile function and a scanning function) according to an embodiment of the present invention.

The MFP includes a Micro Processor Unit (MPU)1, a Network Control Unit (NCU)2, a MODEM3, a Read Only Memory (ROM)4, a Random Access Memory (RAM)5, an image memory6, a scanner (image scanning unit)7, an operation unit8, a display9, a Coder and Decoder (CODEC)10, a printer CODEC11, an image processing circuit for a printer12, a page memory13, a Laser Scan Unit (LSU)14, a mechanism controller for a printer15, a system bus16and an image bus17.

The MPU1includes a function for controlling the entire MFP in accordance with a program stored in the ROM4. The NCU2and the MODEM3are connected to the MPU1. The NCU2is controlled by the MPU1. The NCU2controls a connection between a communication line18and the MFP. The NCU2includes a function for transmitting a dial pulse according to a telephone number of another party of a communication, and a function for detecting a ring signal. Further, the communication line18is connected to a Public Switched Telephone Network (PSTN).

The MODEM3modulates transmission data and demodulates received data. Specifically, the MODEM3modulates the transmission data which is a digital signal, into an analog audio frequency signal. Then, the MODEM3transmits the analog audio frequency signal to the communication line18via the NCU2. The MODEM3also demodulates into a digital signal, an analog audio frequency signal received from the communication line18via the NCU2. The ROM4stores in advance, programs or the like for controlling an operation of the entire MFP. For example, the RAM5stores data necessary for the control by the MPU1and data necessary to be stored temporarily. The image memory6stores image data scanned by the scanner7and also stores image data received from a remote device via the communication line18and the MODEM3.

The scanner7scans a shading plate or an image of an original document and converts the scanned data into an electric signal. The scanner7executes various processes on image data scanned by a Charge Coupled Device (CCD) line image sensor.

The operation unit8includes a start key, a mode switching key for switching modes between a copy mode and a facsimile mode or the like, a ten-key numeric pad for inputting numbers such as a telephone number, a speed dial key, and keys for instructing various operations. The display9displays various pieces of information such as a telephone number input from the operation unit8and a remaining amount of toner of the printer.

The CODEC10encodes the image data scanned from the original document and the stored image data in accordance with Modified Huffman (MH), Modified Read (MR) and Modified MR (MMR) schemes or the like for transmitting the image data. The printer CODEC11decodes the encoded image data for printing the received image data and the data scanned from the original document.

The image processing circuit for the printer12controls image processing when printing the received image data, the scanned image data or the like. The image processing circuit for the printer12includes a toner saving circuit12a. The page memory13stores the image data to be printed. The LSU14controls a printing operation of a laser printer in accordance with a signal from the image processing circuit for the printer12. The mechanism controller for the printer15controls supplying, transporting, etc. of paper to the printer.

The toner saving circuit12aconsists of an accumulator21that accumulates data of surrounding pixels for the target pixel shown inFIG. 2, and an exposing energy controller22shown inFIG. 3. The data accumulator21shown inFIG. 2is made of the following circuits (i)-(vii):(i) Latches31-11,31-21and31-31which store for each pixel, image data V-Data that is input serially, and a line memory32which stores image data for one line output from the latch31-31,(ii) Latches31-12,31-22and31-32which store for each pixel, the stored data of the line memory32input serially,(iii) A line memory33which stores image data for one line output from the latch31-32, and latches31-13,31-23, . . . and31-33which store for each pixel, the stored data of the line memory33input serially,(iv) Registers34-11,34-21, . . . and34-33which are provided for each of the latches31-11,31-21, . . . and31-33(excluding31-22) respectively, and store a weight coefficient of each of the surrounding pixels,(v) Gate circuits35-11,35-21, . . . and35-33which are provided for each of the latches31-11,31-21, . . . and31-33(excluding31-22) respectively, and when a stored value of the corresponding latch is “1”, derive an output of the corresponding register,(vi) An address decoder36which applies a selection signal to each of the registers34-11,34-21, . . . and34-33, and(vii) An adder37which adds after receiving each output from the gate circuits35-11,35-21, . . . and35-33.

The address decoder36is used when storing the weight coefficient in each of the registers34-11,34-21, . . . and34-33. The MPU1selects one of the registers34-11,34-21, . . . and34-33by outputting an address to the address decoder36, and writes in the weight coefficient to the selected register. This process is normally carried out when power is turned on or when starting a print job.

Suppose that in the pixels of a 3×3 matrix shown inFIG. 4, pixel data of a target pixel I is input to the data accumulator21. Further, the weight coefficient for pixels (b), (d), (e) and (g) that are adjacent vertically and horizontally to the target pixel I is 2, and the weight coefficient for pixels (a), (c), (j) and (h) in a diagonal direction is 1.

For example, when each of pixels Va, Vb, . . . and Vh of the input image data V-Data has a value of “1”, “1” is stored in each of the latches31-11,31-21, . . . and31-33. Therefore, all of the gate circuits35-11,35-21, . . . and35-33are at an opened state. The value “2” is output from each of the registers34-21,34-12,34-32and34-23and the value “1” is output from each of the registers34-11,34-21,34-13and34-33. The outputs are input to the accumulator35, and an additional value of 12 is output.

As another example, among the input image data V-Data, when the pixels Va, Vd, Vf and Vg have a value of “0” and the other pixels Vb, Vc, Ve and Vh have a value of “1”, “1” is stored in the latches31-21,31-31,31-32and31-33. Accordingly, only the gate circuits35-21,35-31,35-32and35-33are opened. The value “2” is output from each of the registers34-21and34-23via the gate circuits35-21and35-23respectively, a value of “1” is output from each of the registers34-31and34-33via the gate circuits35-31and35-33respectively, and an additional value of 6 is output from the adder37.

As another example, among the input image data V-Data, when the pixels Va and Vf have a value of “1” and thus the pixels Vb, Vc, Vd, Ve, Vg and Vh have a value of “0”, “1” is stored in each of the latches31-11and34-13, and only the gate circuits35-11and35-13are opened. The value of “1” is output from each of the registers34-11and34-13respectively and an additional value of 2 is output from the adder37.

As shown inFIG. 3, the exposing energy controller22includes a selector41that receives an input of an additional value output from the adder37and outputs a duty ratio signal according to the additional value, a duty ratio 100% signal generator42, a duty ratio 75% signal generator43, a duty ratio 50% signal generator44and a duty ratio 25% signal generator45. The selector41includes a storage unit41aof a lookup table that associates an output value of the adder37with a duty ratio to be selected (refer toFIG. 5). The selector41selects a duty ratio signal according to the output value (additional value) of the adder37.

When the additional value is 12 as in the above-described example of the output of the data accumulator21, the selector41selects and outputs a signal of the duty ratio 25% signal. The duty ratio 25% signal is applied to a laser diode driver46, and a laser diode47is driven by the signal. In this case, the target pixel corresponds to the black solid region of the image, the toner is saved for the target pixel and the image is printed.

When the additional value of 6 is input to the selector41, the duty ratio 75% signal is selected and output. In this case, the target pixel having a meaning of an edge enhancement is printed. When the additional value of 2 is input to the selector41, the duty ratio 100% signal is selected and output.

Further, in the above-described embodiment, each pixel of the image data is binary data. However, the present invention can be applied even when each pixel is multilevel data. In case the image data is multilevel, a multiplier can be used in place of each of the gates35-11,35-12, . . . and35-33shown inFIG. 2. Furthermore, when the weight coefficient is 2, the multiplier can be exchanged with a bit shift circuit. Even when the image data is binary data, if the weight coefficient can be a fixed value, the weight coefficient can be set by a wired-logic when designing the circuit. As a result, the registers and the address decoder become unnecessary and the circuitry can be simplified even more.