JPH10150549A - Image forming device and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple image-forming device by which a compressed image with high image quality is generated at high speed. SOLUTION: A read pointer for a head address of an expansion buffer for interleave purpose and a write pointer for an address to store compressed image data after the interleaving are initialized (S6000), bit map data by 4-pixels consecutive in each adjacent line are read according to the read pointer, a reference address to access a conversion table based on the data and errors R0, R1 of adjacent pixels to the data having already been compressed is generated (S6040), and data are read from the conversion table based on the reference address). The compressed image data being part data of the read data are stored in the original expansion buffer according to the write pointer and the other part data are assigned to new errors R0, R1 (S6060), each pointer is updated, and the processing above is repeated until the entire interleaving (compression) of the expansion buffer is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser printer, when a memory required for the processing for forming an output image is insufficient when the processing for forming the output image is insufficient, the resolution of image data on the memory representing the output image may be reduced. By compressing the image data, a memory area for storing the image data is reduced, and a process of allocating the memory to an available memory for continuing the process is performed.

[0003]

As a method of reducing the resolution of the image data, a method of simply thinning out either the odd position or the even position of the image data or a method of thinning using a matrix mask is generally used. It is a target.
These methods have the advantage that the processing can be completed in a short time because the processing is simple, but on the other hand, if the original image data has a regularity, the density state of the thinned-out output image is the original image. It has been pointed out that, despite the fact that they are the same, they vary depending on the output position, such as whether printing is performed from an odd position or from an even position.

[0004] Further, for example, a thinning method based on an average density of a predetermined area of an original image and an evaluation of an arrangement state of pixels in the area as disclosed in Japanese Patent Application Laid-Open No. 1-122267 are disclosed. Or a method of changing the compression method). While these methods improve the quality of the image after compression or thinning, the processing speed is slow for software processing, or it is complicated to configure with hardware, There are problems such as an increase in cost.

The present invention has been made in order to solve such problems in the prior art, and provides an image forming apparatus which is simple and capable of creating a high-quality compressed image at high speed. The purpose is to do.

[0006]

SUMMARY OF THE INVENTION One or more inventions are described herein, each having the construction and advantages described below.

[0007] The image forming apparatus according to the first aspect of the present invention uses an application software operating on a personal computer or the like, image data received from various image input sources such as an image scanner or a digital camera, or an image. For example, original image data representing the density of an image composed of a plurality of pixels, such as image data obtained by converting language expression data described in the PCL language according to the embodiment into pixels by a known method, is stored in an image storage unit. Means, sets a compressed area composed of a plurality of pixels, and sequentially moves the compressed area, creates compressed image data representing the density of pixels smaller than the number of pixels in the compressed area, and generates the compressed image. An image forming apparatus that forms an image based on data, wherein an image corresponding to each pixel of a compressed area (for example, a pixel group in the embodiment) Area density calculating means for reading the density of the data from the image storage means and adding those densities; a density output as compressed image data for the compressed area; and a density calculated by the area density calculating means. Error calculating means for calculating an error based on the difference, error storing means for storing the error calculated by the error calculating means in association with the compression area, and compression adjacent to the compression area of interest stored in the error storing means. Evaluation density calculation means for calculating an evaluation density of the noted compressed area based on an error for the area and the density calculated by the area density calculation means; and an evaluation density calculated by the evaluation density calculation means and a predetermined value. Generating means for generating compressed image data by assigning a predetermined density based on the threshold value and the comparison.

[0008] Then, a compression area consisting of a plurality of pixels is set for the image data stored in the image storage means, and while the compression area is sequentially moved, the evaluation density calculation means sets the compression area adjacent to the compression area of interest. The error for the compressed region that has already been processed is read from the error storage unit, a predetermined weight is applied to each error, and a value obtained by performing a predetermined weight on the density calculated by the region density calculation unit is added. Calculating the evaluation density of the compressed area,
The generating means compares the evaluation density with a predetermined threshold value, and assigns a predetermined density to the compression area according to the magnitude of the evaluation density to generate compressed image data, and generates the compressed image data and the original of the compression area. An error, which is a difference from the density, is calculated by the error calculating means, and this error is stored in the error storage means in association with the compression area, so that the error can be used for the processing of the next compression area.

Thus, the compressed image data is created from the original image data and the number of pixels is reduced by simply performing a simple calculation and storage process for each compressed area, so that the capacity of the image storage means used is reduced. it can.

Further, when assigning a new density based on comparison with a predetermined threshold value, by making the assigned density smaller than the density range of the original image data, the quality of the image is slightly reduced. It is possible to reduce the capacity of the image storage means to be used, and it is possible to further reduce the memory used.

Further, the image forming apparatus according to claim 2 is
In addition to the above configuration, the image processing apparatus further includes a compressed image registration unit that sequentially stores the compressed image data obtained by the generation unit in the image storage unit. In this method, the compressed image data calculated by the generating means is sequentially stored by the compressed image registration means in an area where the above-described compression processing has been performed on the original image data in the image storage means.

As a result, the compressed image data is sequentially stored in the area of the image storage means in which the processed original image data is stored. Therefore, an area different from the storage area of the original image data is stored as the compressed image data. There is an effect that there is no need to allocate, and when the compression processing is completed, areas that are no longer needed (and thus may be released so that they can be used for other purposes) can be collectively obtained.

Further, in the image forming apparatus according to the third aspect, the density of the image does not have a plurality of density levels, but has only two values, for example, 0 and 1. In this case, since the density is represented by one bit, the number of pixels can be reduced by a simpler operation, which is suitable for high-speed processing.

In the image forming apparatus according to a fourth aspect of the present invention, the image storage means for storing the original image data representing the density of the image composed of a plurality of pixels is stored in the image storage means. An evaluation area (for example, a block in the embodiment) including at least one area and its compression area is set, and the density of pixels smaller than the number of pixels in the compression area is represented while sequentially moving the evaluation area. An image forming apparatus that creates compressed image data and forms an image based on the compressed image data, wherein an evaluation bit string creating unit creates an evaluation bit string based on the density of image data corresponding to each pixel in an evaluation area And the difference between the density of the compressed image data output to the compressed area adjacent to the evaluation area of interest in the moving direction of the evaluation area and the original image data of the compressed area An error bit string creating means for creating respective errors based on the error bit string, an evaluation bit string created by the evaluation bit creating means, and an error bit string created by the error bit string creating means, and an address bit string representing an address. , And conversion means for outputting a compressed bit string indicating the compressed image data based on the address bit string created by the address bit string creating means.

Thus, an evaluation area including at least one compression area including a plurality of pixels is set, and an evaluation bit string indicating the density of the pixels in the evaluation area and a processing performed before the evaluation area are performed. An error bit string indicating the error is generated, and these bit strings are configured to be provided as an input bit string to the conversion means, and the resulting address bit string is input (accessed) to the conversion means.
Thus, a compressed bit string indicating the compressed image data is obtained from the conversion means.

Therefore, since the compression processing for the compression area can be performed from only the data of the address bit string input to the conversion means, the compression processing can be easily separated from a series of processing, and the apparatus configuration can be simplified.

Further, the image forming apparatus according to claim 5 is
The image forming apparatus according to claim 4, further comprising a compressed image data output unit that sequentially stores a compressed bit string indicating the compressed image data obtained by the conversion unit in the image storage unit.

In this method, the compressed image data output by the conversion means is sequentially stored by the compressed image data output means in an area in the image storage means where the above-described compression processing has been performed on the original image data. It is.

Thus, the compressed image data is sequentially stored in the area of the image storage means in which the processed original image data is stored. Therefore, an area different from the storage area of the original image data is stored as the compressed image data. There is an effect that there is no need to allocate, and when the compression processing is completed, areas that are no longer needed (and thus may be released so that they can be used for other purposes) can be collectively obtained.

Further, the image forming apparatus according to claim 6 is
6. The image forming apparatus according to claim 4, wherein the evaluation area includes a plurality of continuous compression areas, and the conversion unit includes an error represented by an error bit string in the address bit string. A first bit density calculating means for calculating a first density sum, a second bit density calculating means for calculating a second density sum from bits associated with one compression area of the evaluation bit string in the address bit string, A threshold means for calculating an evaluation density based on the first density sum and the second density sum, comparing the evaluation density with a predetermined threshold, and creating compressed image data based on the comparison result; For a region, a new first density sum is obtained using a difference between the compressed image data obtained by the threshold means and the second density sum as a new error, and a next compressed region adjacent to the compressed region is obtained. Against calculated by said second density sum second bit density calculation means, these first density sum and the second
Control means for repeating input of the sum of densities to the threshold means.

The conversion means cyclically repeats the compression processing while taking out information corresponding to the density of the original image data from only the input address bit string according to a specific bit position constituting the address bit string. ,
The compressed image data as the compression result and the error at that time are output.

Thus, compression processing (conversion processing by the conversion means) for a plurality of compression areas can be performed from data of only the address bit string input to the conversion means. Therefore, it is not necessary to divide and access the image storage means many times, and the speed is increased.

Further, the image forming apparatus according to claim 7 is
7. The image forming apparatus according to claim 6, wherein the conversion unit converts the compressed image data sequentially output by the threshold unit into a bit string, and the error has the same format as a bit string created by the error bit string creation unit. It is characterized in that it is output as a bit string.

Thus, the compressed image data is output for each evaluation area unit, so that the writing processing to the image storage means can be executed intensively at one time, and the processing efficiency is improved. In particular, when the image data is binary, the process of storing the compressed image data in the image storage unit can be simplified. Further, by making the bit string representing the error at the time of output the same as that at the time of input, input to the processing of the subsequent evaluation area becomes easy, and the speed can be increased including the subsequent processing.

Further, the image forming apparatus according to claim 8 is
8. The image forming apparatus according to claim 4, wherein the conversion unit includes a conversion value storage unit that stores the address bit sequence, the compression bit sequence, and the error bit sequence in association with a combined bit sequence. It is characterized.

Based on all combinations of image data that can be taken in the evaluation area and all combinations of errors that can be input to the evaluation area, conversion values are stored in association with address bit strings representing those combinations. Therefore, the conversion process is extremely simple. At this time, instead of storing all the combinations, it is also possible to preferentially store those having a high frequency of occurrence of the combinations.

The functions of the image forming apparatus described above are provided as a program that is activated by a computer system provided therein. In the case of such a program, for example, a floppy disk, a magneto-optical disk,
It can be used by storing it in a storage medium such as a D-ROM, loading it into a memory in a computer system as needed, and starting up. In addition, ROM and nonvolatile R
A program may be stored using an AM or the like as a storage medium, and the ROM or the nonvolatile RAM may be incorporated in a computer system and used.

[0028]

FIG. 1 shows a laser printer 2 as an embodiment and a personal computer 4 as a host computer to which some of the above-mentioned inventions are applied. The laser printer 2 and the personal computer 4 are connected to each other. It shows the state where it was turned on. FIG. 2 shows a schematic block diagram thereof.

The laser printer 2 and the personal computer 4 employ parallel interfaces 6 and 8 conforming to a predetermined standard, here, the IEEE 1284 standard, and are connected by an IEEE 1284 cable 10 for connecting the interface. .

The laser printer 2 includes, in addition to the parallel interface 6, a CPU 12 for executing various controls in accordance with programs, a ROM 14 in which various control programs are stored, a work area for calculation by the CPU 12, a calculation result, and various setting states. RAM 1 for storing and forming a memory area such as a packet structure and a development buffer described later
6, paper feed sensor, paper discharge sensor and toner remaining amount sensor,
Other sensors 18 such as a main motor for driving mechanical parts of the laser printer 2 and other engines 2
0, and an operation unit 22 for giving simple instructions to the laser printer 2 with a push button switch 22a, and for displaying an instruction operation or state for displaying a predetermined state with an LED lamp 22b. A power switch 3 is provided on a side surface of the main body 2a of the laser printer 2.

Further, in the ROM 14, adjacent two
A conversion table for compressing a line into one line is stored.

In this compression, each pixel of each of two adjacent lines is taken as one set, and the set is compressed to a new pixel.
This takes into account errors that occur not only in one pixel but also in an adjacent pixel group that has already been compressed. The error referred to here is a difference between the total density of the pixel set and the density of the compressed and output pixels. In the laser printer 2 of the present embodiment, the past two sets are used as errors.

FIG. 11 is an explanatory diagram showing the relationship between pixel data to be compressed (original image data) and compressed pixel data (compressed image data). In the figure, A [i] and B
[I] represents pixel information (density) at the pixel position i in the x direction of two adjacent lines, and R [i−1] and R [i−
2] indicate errors at pixel positions i-1 and i-2, respectively. The pixel output F [i] after compression at the pixel position i is the corrected input Im at the pixel position i corrected as shown in Expression 1.
It is obtained by comparing [i] with a threshold value d.

[0034]

(Equation 1)

Here, it is preferable that each coefficient becomes larger as it is closer to the pixel position i. That is, a ≦ b ≦
It is good to be c.

The pixel output at the current target position i is F
When [i] is reached, the error R [i] at that pixel position is obtained as in Equation 2.

[0037]

(Equation 2)

In the laser printer 2 according to the present embodiment, this conversion table outputs compressed image data corresponding to four pixel positions by accessing the table once, and is an explanatory diagram relating to input information and output information. Figure 12
Shown in In the figure, eight pixels surrounded by a black frame, that is, A
[0] to A [3] and B [0] to B [3] are blocks serving as processing units.

One of the input information, R0 and R1, respectively represents an error at a pixel position one before and two before the first pixel position of the next block. These values are also output values from the conversion table in the immediately preceding block. A [0] to A [3] are four pieces of continuous pixel information on even-numbered lines (the leading line of the sheet is 0) in the block at the current target position i, and B [0] to B [3].
Is pixel information at positions corresponding to A [0] to A [3] on odd lines adjacent thereto. F [0]-F
[3] is compressed pixel information corresponding to each pixel position output from the conversion table. The pixel information may be a multi-level density value or a binary density value (in the laser printer 2 according to the present embodiment, it is dot ON / OFF information). In the case of a multi-valued density value, a plurality of bits are allocated to one pixel in the bit allocation described below.

This conversion table has input values R0, R1, A [0] to A [3] based on the following equations (3) and (4).
And B [0] to B [3] and output values R0, R1 and F [0] to F [3] calculated in advance based on the input values are stored in association with each other.

[0041]

(Equation 3)

[0042]

(Equation 4)

Further, by assigning bits as shown in FIG. 13, the above-described input value is configured to give an address to the conversion table, and the output value similarly assigned bits can be read. . That is, as the input, two bits are assigned to each of the above-described R0 and R1, and one bit is assigned to the pixel information, that is, a total of eight bits are assigned. Can be accessed. As the output, the new R0 and R1 are converted into 2 bits each and the converted pixel output is 4 bits of 1 bit each for 4 pixels, that is, 8 bits (1 byte) in total. Is 4 kilobytes.

The conversion table for compression configured as described above is stored in a predetermined address area of the ROM 14, and is used as needed when a memory shortage occurs as described later.

On the other hand, in addition to the parallel interface 8, the personal computer 4 has a CPU 24 for executing various controls in accordance with programs, a ROM 26 in which various control programs are stored, and an auxiliary storage medium in an auxiliary storage device 30. An OS, application software or a device driver such as a device driver, data or an operation result by the CPU 24 or an R for storing various setting states.
AM28, a floppy disk, a magneto-optical disk, a CD-ROM or the like as an auxiliary storage medium, an auxiliary storage device 30 for taking in programs and data from the outside, an OS
Graphic accelerator 3 for converting image data stored in a specific format into bitmap data
1, a display 32 for displaying calculation results, menus, status of the laser printer 2 at the time of printing, and the like;
It comprises a keyboard 34 for receiving an input from a user, and a mouse input device 38 for moving a mouse cursor displayed on the display 32 via a mouse interface 36 and for inputting an instruction.

The laser printer 2 is provided with a paper feed unit 2b above the rear part of the main body 2a. At the time of printing, the storage paper inside the paper feed unit 2b is sent one by one to a print unit inside the laser printer 2, and a laser beam is sent. After the toner image is formed on the recording paper from the transfer roller on which the toner image is formed on the electrostatic latent image formed by
The paper is discharged onto the paper discharge tray 2c.

The personal computer 4 is connected to the laser printer 2 by the printer driver read from the auxiliary storage device 30 and activated as a program.
The personal computer 4 exchanges handshake signals such as a strobe signal and an acknowledgment signal for a shake hand process through a control line of the cable for the IEEE1284, and a page description language from the personal computer 4 via a data line for the IEEE1284. The language expression data, the image data, and the command are transmitted. According to the result, the laser printer 2 performs printer processing to be described later, or transmits status data to the personal computer 4 when the laser printer 2 can perform bidirectional communication. I do.
When the status of the laser printer 2 at the time of printing is obtained, the personal computer 4 displays the status on the status display section 32a of the display 32.

FIG. 3 shows a flowchart of the printer driver started by the personal computer 4. This process is started when a print request is issued on the same personal computer 4.

First, the print data transmission / reception is prepared by the initial setting (S90), and then the print data transmitted from the application is acquired (S10).
0). Next, it is determined whether or not the print data is font data representing the type and shape of the character (S110).
If it is font data ("YE" in S110)
S "), and is temporarily stored in a predetermined memory area on the RAM 28 (S120).

If the print data is data other than font data ("NO" in S110), for example, if it is vector data, other graphic data, or image data such as an image, the host-based format is used. The data is converted into bitmap data and held (S130). This conversion is performed at high speed by the graphic accelerator 31 provided in the personal computer 4.

Step S120 or step S130
Is completed, it is determined whether or not the print data from the application has been completed (S14).
0). If the processing has not been completed ("NO" in S140), the processing in steps S100 to S130 described above is repeated until the processing is completed, the font data is stored in the font data memory area, and the bitmap data in the host-based format is stored in the bitmap. It is stored in the data memory area.

When the processing of all the print data is completed ("YES" in S140), it is next determined whether or not bitmap data is stored (S150). If the bitmap memory is stored in a predetermined memory area in the RAM 28 ("YES" in S150), the stored bitmap data is compressed and output to the laser printer 2 (S160). That is, since the bitmap data here represents the contents of the background in the print data, the bitmap data is output before the font data in order for the laser printer 2 to form a base bitmap in the RAM 16. You.

Note that this compression is performed in the same compression format as that conventionally performed when transmitting data to a host-based type printer. In order to inform the laser printer 2 of this compression mode, an escape sequence “<Esc> HBP” indicating a host-based type compression is added to the head of the compressed bitmap data.

Next, in step S120, the temporarily stored font data is converted into the PCL format, which is one of the page description languages, and output to the laser printer 2 (S170). The PCL format includes, for example, codes indicating coordinates and font shapes.

When all bitmap data and font data for one page are output to the laser printer 2 in this way, "<FF>" is finally output as a print command (S180), and the process ends. . If the print data of the next page is sent from the application,
The above process is repeated again.

As a result, for example, print data having a configuration as shown in FIG.

Next, the processing on the side of the laser printer 2 will be described with reference to the flowcharts shown in FIG.

First, initialization is performed (S200), and the buffer of the parallel interface (I / F) 6
One byte of data received from the personal computer 4 is acquired (S210).

Next, this one byte is an escape (<Esc>: 16) which is the start code of the escape sequence.
It is determined whether it is a 1B) code in hexadecimal code notation (S220). Here, if it is an escape code (S
“YES” at 220), an escape sequence process is performed (S1000).

FIG. 5 shows the escape sequence processing.
First, all data up to the end of the command by the escape sequence is obtained (S1010). Next, the process proceeds to a process corresponding to the command (S1020).

Assuming that the print data shown in FIG. 10 is transmitted from the personal computer 4 to the laser printer 2, first, the graphic compression mode setting command D1 is obtained, and the graphic compression mode is set (S1).
030). In the example of FIG. 10, the graphic mode = “H
In step S1030, the graphic compression mode is "HBP" (indicating the same compression format as the image data to be transmitted to the conventional host-based printer) because the command "BP (host-based printer)" is transmitted.
Is set as Then, the process returns to step S210.

Next, the graphic data D2 is transmitted. Since the graphic data D2 has a graphic data reception command set as an escape sequence at the head of each raster ("YES" in S220), In S1020, it is determined that the received command is a graphic data reception command, and it is determined whether the graphic compression mode is set to “HBP” (S1040). In this example, since the graphic compression mode is set to “HBP” (“YES” in S1040), host-based data reception processing is performed (S2000).

FIG. 6 shows a flowchart of the host-based data reception processing. First, it is determined whether the received host-based type print data corresponds to the first raster of the band (S2010). Here, the band means a predetermined number of rasters of one page to be printed (for example, 128 rasters).
This means each area divided for each raster. In the printer processing, print data is managed for each band.

If the print data is the first raster of the band ("YES" in S2010), a maximum memory area necessary for storing one band is secured in the RAM 16, and this memory area is managed. To set a BG (background) handle of the camera (S202)
0). Next, in step S2020, it is determined whether or not the memory allocation has succeeded (S2030). If the memory allocation has succeeded ("YES" in S2030), then one raster of the data received from the personal computer 4 is received. Is acquired and stored in the memory area indicated by the BG handle (S2040).

Next, it is determined whether the print data acquired in step S2040 is the raster at the end of the band (S2050). If not, the process returns to step S210.

As long as the graphic data D2 continues, print data for one raster is sequentially processed in step S2000. If the print data is not the head of the band (“NO” in S2010), since the memory has already been secured in step S2020,
In step S2040, the data is stored in the memory area indicated by the BG handle.

If the print data is the data at the end of the band ("YES" in S2050), the graphic data D2 corresponding to the band has been completed, so the maximum size of the memory area secured in step S2020 is determined. A memory resizing process is performed to release unused areas in the memory so that the areas can be used for other purposes (S2060). Then, the resized memory area is set in the RAM 16 and registered in the background (BG) area of the band. For example, the head address of the memory area and the number of bytes are registered. Thereafter, the processing is repeated as described above from the beginning of the next band.

The processing for registering the received graphic data D2 in the packet structure while securing an appropriate memory area for each band is performed.

If this process is repeated and the available memory is insufficient and the memory allocation fails (S20)
90 is "NO", an error occurs, and error processing is performed (S210).
0) is executed. If the memory allocation succeeds again (S
"YES" in step 2090), the above-described step S2040
Start processing from.

FIG. 7 shows a flowchart of the used memory reduction process in step S3000.

First, the number of the head band (for example, “0”) is set in a variable i indicating the order from the head of the band (S3010). Next, B corresponding to the i-th band
It is determined whether the G handle is “<NULL>” (indicating that the BG handle is not set) (S30).
20). If the graphic data D2 is acquired and stored in the memory area in which the BG handle is set (“NO” in S3020), first, the graphic data of the i-th band is stored in the expansion buffer set in the RAM 16. It is expanded and expanded (S3030). If the BG handle is “<NULL>” (S3020
Then, it is determined whether registration data exists (S3110). That is, it is determined whether or not linguistic expression data described in PCL is registered at a predetermined position of the packet structure corresponding to the i-th band. If it is registered ("YE" in S3110
S "), first, the development buffer is cleared (S311
5) Create a white background.

Step S3030 or step S31
After step 15, it is determined whether registration data exists (S3040). That is, it is determined whether or not linguistic expression data described in PCL is registered at a predetermined position of the packet structure corresponding to the i-th band.

If the linguistic expression data is registered (S3
040, “YES”), and the data is taken out (S3).
050), the image is formed into bitmap data and written into the expansion buffer (S3060). That is,
The data is synthesized by being written from above the background data existing in the expansion buffer.

Thereafter, as long as the registered data exists, the data is written into the expansion buffer, and if there is no more registered data (S304).
If “0” is “NO”, the thinning process is performed to reduce the data amount by reducing the resolution by thinning out the bitmap data written in the expansion buffer (S3070).

FIG. 14 shows a flowchart of the thinning-out processing (compression processing) of the expansion buffer in step S3070.
At this time, the arrangement state of the bit map of the expansion buffer (before thinning and after thinning) is as shown in the explanatory diagram of FIG.

First, a pointer Elin representing an even-numbered line
The top address of the expansion buffer to be thinned is set in eTop, and the pointer OlineTop of the next odd line, which is the next adjacent line, is added with the width of one line on the expansion buffer to the start address of the expansion buffer. The object is set (S6000). Next, a variable Ly indicating the position of the processing line is set to 0, and a pointer FoutPtr for storing the compressed image data after thinning is set.
Is set to the start address of the development buffer (S601).
0). Next, a variable R0 representing an error at two pixels to the left of the target pixel position (the processing direction is now set from left to right, which corresponds to a pixel position already processed) and an error at one pixel left are The variable R1 is cleared to 0 (S602).
0). A variable Lx indicating the pixel position of interest in the line direction is set to 0
(S6030).

Subsequently, a reference address for referencing the conversion table for thinning stored in the ROM 14 is created (S6040). Here, the reference address is obtained as follows. First, of the bitmap data in the expansion buffer of the RAM 16, ELineTop and OlineTo
The bitmap data (4 bits in this embodiment), which is a unit for converting from a position where p and p are respectively offset by a variable Lx, is read. These eight pixels are a block serving as a processing unit. The bit map data of this block and the two bits R0 and R1 stored in the RAM 16 as variables are subjected to well-known bit shift processing, AND processing, OR processing, and the like to form a 12-bit data as shown in FIG. (Which is an offset from the top of the conversion table) is created. Then, the start address value of the address of the conversion table in the ROM 14 is added to the reference address.

Next, based on the reference address, the ROM 1
The conversion table No. 4 is accessed, and 8-bit data is read (S6050). Of the read 8-bit data, 4 bits from bit 0 to bit 3 are written as compressed image data in the expansion buffer area indicated by the pointer FoutPtr, the pointer FoutPtr is advanced by 4 bits, and the bits 4 and 5 are set to the variable R0. Are stored in the variable R1 (S6060). Next, the conversion unit 4 is added to the variable Lx indicating the target pixel position (S607).
0), it is determined whether or not the variable Lx has exceeded the width representing the line width (S6080). In the present embodiment, the width is configured to be a multiple of 4, so that the odd portion less than 4 bits does not need to be separately processed.

If the variable Lx is smaller than the Width ("NO" in S6080), the processing for one line has not been completed yet, so the flow returns to step S6040 to repeat the processing from step S6040 to step S6070. If the variable Lx is equal to or greater than the width (S60
("YES" at 80) Since the compression for one line has been completed, the pointer Eline is used to process the next line.
By adding twice the value of Width to Top and LineTop, respectively, the start address of the next processing line is given (S6090), and 2 as the processing unit is added to the variable Ly representing the processing line in the expansion buffer (S610).
0).

Then, in order to determine whether or not compression of one band (all bitmap data in the current expansion buffer) has been completed, the variable Ly is compared with the total number of lines High in the expansion buffer (S6110). ), Variable Ly
Is smaller than Height (“N” in S6110).
O ") Since the processing for one band has not been completed, step S6
Returning to step 020, the processing of the next line is continued. If the variable Ly is equal to or higher than Height (“YE
S "), the compression of the expansion buffer is terminated. At this point, half of the compressed image data before the capacity is compressed is stored in the expansion buffer in order from the start address. Here, the thinning process is temporarily ended, and the process returns to the original process.

Although the data unit for writing and reading data to and from the development buffer in the RAM 16 has been described as 4 bits, 8 bits (1 byte) are actually more suitable for the current system configuration of various CPUs. In this embodiment, the RAM 16 is accessed in units of 4 bits in order to reduce the capacity of the conversion table. However, in practice, buffering is performed on a general-purpose register of the CPU so that the RAM 16 is accessed in units of 8 bits. , Higher-speed processing can be performed. In that case, that is, reading and writing are performed on the RAM 14 in units of 8 bits, and processing is performed on the general-purpose register of the CPU for each of the lower 4 bits and the upper 4 bits. Updating of each pointer is performed collectively at the time when processing for 8 bits is completed.

The processing after the thinning processing of the expansion buffer is performed will be described again with reference to the flowchart shown in FIG.

The data amount is reduced in this way, a part of the memory is released, and the contents of the decompression buffer, which is reduced, are set in the handle and registered in the BG area of the packet structure (S3080). It is determined whether the processing for one page is completed (S3090).

If the BG handle = <NULL> (“YES” in S3020) and there is no registered data (“NO” in S3110), the data is not directly written to the development buffer, and the process proceeds directly to step S3090. Move to

If the processing for all the bands for one page has not been completed ("NO" in S3090), i is incremented (S3100), the next band is designated, and the above-described processing is repeated. .

When the processing for one page is completed ("YES" in S3090), the processing is performed along with the graphic cache secured with the graphic data written in the expansion buffer and the font data described in the PCL. ,
A font cache that stores font data,
The memory is released as a reusable memory (S3120).

As described above, since the contents of the expansion buffer are thinned out (S3070) and the font cache and the graphic cache are released (S3120), a part of the used memory is released and the usable memory is released. Can be increased. As a result, if the available memory is sufficiently increased, the memory can be secured again.

When the graphic data is completed in this manner, and the language expression data D3 by PCL, here, font data, is read in step S210,
First, since an escape sequence for specifying a font is obtained (S210), an escape sequence process (S210) is performed.
In (1000), a font is specified (S1).
050). The font data obtained thereafter is treated as the same font until a new font is specified.

Next, if the acquired data is font data (here, character data), it is not <Esc> (“NO” in S220), and then it is determined whether it is <LF> (line feed). Is performed (S230). If <LF>, a cursor position moving process for line feeding the print position in the laser printer 2 is performed (S240).

Here, since it is font data and not <LF> (“NO” in S230), the print command <
It is determined whether or not FF> (S250). Again <F
F> (“NO” in S250), the value is <
It is determined whether or not <NULL> (S260), and <NULL>
>> (“NO” in S260), the character indicated in the font data is registered as registration data in the above-described packet structure (S270).

Next, it is determined whether or not the registration in step S270 is successful (S280). If the registration is successful ("YES" in S280), the process starts again from step S210.

If the available memory is insufficient,
If registration failed ("NO" in S280),
The process of reducing the used memory is executed (S290). In this used memory reduction processing, the same processing as the processing shown in FIG. 7 described above is performed, and the available memory is increased.

Next, a process of re-registering the character in the packet structure is performed (S300), and it is determined whether or not the registration is successful (S310).
"YES"), the process returns to step S210, and the above-described process is repeated. If unsuccessful ("NO" in S310),
Error processing is performed (S320).

When the processing of the language expression data D3 is completed in this way and a print command <FF> indicating the end of one page is obtained in step S210 ("YE" in S250).
S "), and then the unregistered data processing shown in the flowchart of FIG. 8 is executed.

This is because if the host-based data does not exist up to the end of the band, step S2 shown in FIG.
060 and S2070 are not performed and are not registered in the packet structure. Therefore, before printing is performed, this unregistered data is registered in the packet structure to enable printing.

First, it is determined whether or not unregistered data exists (S4120). If there is no unregistered data ("NO" in S4120), the process ends, and the process proceeds to the next process (S330).

If unregistered data exists (S412)
If “0” is “YES”, white is set to the remaining raster of the corresponding band (S4130). That is, plain white is set for a nonexistent raster. Next, the memory is resized (S4140). This resizing process is performed in step S206.
This is the same process as 0. Next, it is registered in the packet structure (S4150). This registration processing is the same processing as step S2070.

Next, the data of the packet is expanded into three expansion buffers for three bands, and the first raster is written to the laser output FIFO. Thereafter, the interruption execution of the print processing for starting the engine 20 is permitted (S33).
0). FIG. 9 shows a flowchart of the printing process. In this printing process, every time a print output of one raster data (for example, output of a laser beam for one raster by a laser diode) is completed by a DMAC (direct memory access controller) and the FIFO for laser output becomes empty, This is a process executed by interruption. This FIFO data is a line synchronization signal B output from the engine 20.
It is output by the D signal.

In step S330, execution of an interrupt is permitted, and when a BD signal is input from the engine 20, data for one raster in the FIFO is output. As soon as the FIFO becomes empty, an interrupt occurs, and it is first determined whether printing of one page has been completed (S5010). Since printing is at the beginning and printing for one page has not been completed (S501).
Then, the raster data existing in the expansion buffer of the first band is set as a DMA processing target (S5020). As a result, the next raster data is printed out the next time an interrupt occurs due to the BD signal. Next, it is determined whether or not there is an empty expansion buffer (S5030). If there is no empty development buffer ("NO" in S5030), the process is temporarily terminated as it is. Then, when the print output for one raster is completed and an interrupt is applied again, the next raster data is set as a DMA processing target (S5020) and printed.

Therefore, until all the expansion buffers of one band are printed out, the determination in step S5030 is "NO", and only the process of sequentially printing out raster data (S5020) is performed.

Thus, when all the raster data in the expansion buffer of the first band is printed out, or
If an empty expansion buffer exists from the beginning, an empty expansion buffer is generated ("YES" in S5030), and it is next determined whether or not multiple interrupts have been issued (S50).
40). If two or more main printing processes have been interrupted ("YES" in S5040), the process proceeds to step S50.
Since the processing of 50 or less has been performed, the interrupt processing is temporarily ended without performing the processing of step S5050 and subsequent steps.

If multiple interrupts have been issued (S504)
If “0” is “NO”, the registration data of the band not yet developed in the development buffer is extracted (S505).
0). Since the number of expansion buffers (three in this example) is smaller than the number of bands, not all bands are expanded in the expansion buffer. Therefore, step S50
In the processing of 60 or less, the undeveloped band is developed in the development buffer that has become empty after the printout is completed. Note that, also during this expansion processing, for an expansion buffer that has already been expanded and printout has not been completed, step S5020 is executed by the multiple interrupt processing, and the printout processing is continued.

First, it is determined whether or not the BG handle of the extracted band is "<NULL>" (S506).
0). If it is not “<NULL>” (S5060
Then, the contents of the memory area pointed to by the BG handle are developed in an empty development buffer (S5070), and background bitmap data is formed.

If the BG handle is "<NULL>"("YES" in S5060), the empty development buffer is cleared (S5080) to form a white background.

Next, the registration data of the extracted band,
That is, it is determined whether or not the language expression data exists (S5090). If it does not exist ("NO" in S5090), the development in the development buffer has been completed, and the process is once terminated as it is.

If registered data exists (S5090)
"YES"), and the data is taken out (S510).
0), the language expression data is converted into an image into bitmap data and written into the development buffer (S511).
0). This process is executed for all the registered data, and if there is no unexecuted registered data ("NO" in S5090), the process is once ended.

In this way, the registration data of the packet structure is sequentially developed, and the raster data is sequentially printed out from the development buffer. When the print output for one page is completed ("YES" in S5010), the interrupt processing of the print processing is prohibited (S5120), and the print processing ends.

Thereafter, each time the print command “<FF>” is acquired, each page is printed by the above-described processing.

In FIG. 5, if the graphic print mode is not "HBP"("N" in S1040)
O "), and received as graphic data transmitted as part of the PCL language (S1045). This is to enable the reception of graphic data in the traditional language expression.

If it is determined in step S1020 that the command is a cursor movement command, cursor movement processing for moving the print position is performed (S1025).

In this embodiment, the personal computer 4 performs printer driver processing,
The data is transmitted to the laser printer 2 as language expression data described in the L language, and other than font data is transmitted to the laser printer 2 as conventional host-based format image data.

Therefore, on the laser printer 2 side, P
Data having a high addition to create bitmap data, such as data described as a vector in the CL language, can be received as host-based image data. As a result, in the case of non-compression, the data may be simply expanded and used as bitmap data in the case of compression, and there is no need to convert the language expression data into bitmap data. In addition, no time is required for processing. Accordingly, printing delay can be prevented, and processing on the personal computer 4 side is not delayed.

The laser printer 2 performs not only the printer driver processing shown in FIG. 3 but also all print data transmitted from the personal computer 4 as language expression data, or all of the print data transmitted from the host-based type. Even if image data is transmitted from the personal computer 4, all of the data can be developed in the development buffer as a print data composition area and combined into one, so that print data transmitted by the conventional data transmission system can be printed. In this case, the compression method of the bitmap data from the personal computer 4 and the compression method of the image data that can be decompressed by the laser printer 2 are the compression methods used in the conventional host-based printer.

As described above, even when the host-based type image data is transmitted in the conventional transmission system, it is different from the case where the conventional host-based type printer receives and prints out by hardware. The laser printer 2 temporarily stores the image data in the memory, and when the available memory becomes smaller, the laser printer 2 develops the image data as bitmap data in a development buffer and thins out the contents of the development buffer in software. To lower the resolution. For this reason, the problem that image formation cannot be performed due to lack of memory is reduced.

In the laser printer 2 of this embodiment, two lines are compressed into one line (resolution is reduced) by thinning out pixels adjacent in the vertical direction as described above. It is also possible.

In this case, 8 bits in the horizontal direction are A [0],
Assuming that B [0], A [1], B [1]... A [3], B [3] are arranged, a conversion table can be created in the same manner as described above. The configuration of the bit string for giving the address to the conversion table does not need to be the same bit arrangement as that described above, and may be configured so as to be compatible.

Furthermore, it is also possible to compress both vertically and horizontally. For example, when compressing a 3 × 3 pixel set (9 pixels in total) into one pixel, the first line is represented by A [0,0], A [0,0]
[0,1], A [0,2], A [1,0], A [1,
1], A [1, 2]..., The next line is B [0, 0],
B [0,1], B [0,2], B [1,0], B [1,
1], B [1, 2]..., The third line is C [0,
0], C [0,1], C [0,2], C [1,0], C
Assuming that they are arranged as [1, 1], C [1, 2], the density calculation is performed as in Expression 5, and A [i] + B [i] in Expressions 1 to 4 described above. The conversion table can be created as described above by replacing the portions described as (i is a variable) with A [i] + B [i] + C [i] (i is a variable).

[0118]

(Equation 5)

In this case, the coefficients (a, b, c, d) represented by the equations (1) and (3) are appropriately changed. Also, a bit string indicating an address may be appropriately configured so as to be able to be associated with an output value.

Further, in the laser printer 2 of the present embodiment, the error of the processed pixel set to be referred to is two.
It is not limited to that. What is necessary is just to set according to the capacity of the storage means which can be used for a conversion table, and the required image quality.

Furthermore, since different offsets can be provided when constructing a bit string indicating an address, a plurality of conversion tables having different compression methods (for example, when compressing horizontally and vertically) are used. It is possible to access by switching as needed.

When the image information has a multi-value density, a plurality of bits are assigned to one pixel to form a bit string representing an address, and the bit string is input to a conversion table (that is, the conversion table is accessed by the address). Then, the output may be performed at a level lower than the input multi-value level. For example, when the density of the pixel information of the original pixel data is four levels, two bits are assigned to one bit in the bit string input to the conversion table. On the other hand, the output is the correction input Im at the pixel position i.
According to the result of comparing [i] with the threshold value d, the conversion table can be implemented by creating a conversion table so as to associate the output allocated to one bit as two levels. That is, it is possible not only to compress (thin out) the number of pixels but also to reduce the amount of pixel data after conversion by reducing the level of pixel information.

At this time, it is assumed that the size (capacity) of the conversion table becomes too large if a conversion table in which the input and the output are associated with each other is prepared. In that case, depending on the characteristics of the image data to be processed, the range with a high frequency of occurrence is compressed by a conversion table (for example, when the pixel set to be compressed has a pattern of a specific density), and otherwise, FIG. 15 or FIG.
CPU 12 as described based on the flowchart of FIG.
May be performed. These processes will be described sequentially.

First, based on the flowchart shown in FIG. 15, the compression processing which has been performed by holding the conversion table as described above is converted into a series of processing by the CPU 1.
2 will be described. This is shown in FIG.
Before the process proceeds to step S6000 of the flowchart of FIG. 7, it is determined whether or not the conversion table can be used for the image set to be processed, and the process is performed when it is determined that the conversion table cannot be used as a result of the determination. is there.

First, the read pointers ELineTop and O indicating the memory location where the original image data is stored are stored.
lineTop is set to indicate the start address of the expansion buffer and the address of a memory position separated by the print width from the start of the expansion buffer (S7000). Where E
LineTop is a pointer that gives A [i] at the pixel position i in the horizontal direction shown in FIG.
Is also a pointer giving B [i].

Next, a write pointer FoutPtr for storing the compressed result is set at the head of the expansion buffer, and R0 and R1 set as temporary work areas in the RAM 16 are cleared to 0 (S7010). Then, pixel data A [i] and B [i] constituting a pixel set to be compressed are read from the position indicated by each read pointer, respectively (S7020). Also, the errors R0 and R
1 is read out (S7030), and the correction input Im [i] at the pixel position i is calculated (S7040). This correction input I
m [i] is obtained according to the above-described equation (1). Calculated Im
[I] is compared with the threshold value d (S7050). If the value is equal to or smaller than the threshold value d (“YES” in S7050), the output value F [i] is set to a predetermined value f0, and if the output value exceeds the threshold value d (“NO” in S7050). ) Sets the output value F [i] to a predetermined value f1. Here, if the original pixel data is a bitmap (binary), f0 and f1 are f0 = 0 (white) and f1 = 1 (black).
What is necessary is just to correspond as follows.

Next, the output value F [i] is stored in the expansion buffer indicated by the write pointer FoutPtr (S
7080). Since the original pixel data size (the number of bits of pixel information assigned according to the density level of one pixel) and the output compressed pixel data size are the same,
At this point, the original pixel data stored at the address of the expansion buffer pointed to by FoutPtr has already been read and compressed, and the output value F [i] may be written. Continue to FoutPt
The pixel data size is added to r, and the write pointer is updated to indicate the next write position (S7090).
An error R [i] at this pixel position is determined (S7100),
The current R1 is copied to R0, and this R [i] is stored in R1 to prepare for the processing of the next pixel position i + 1 (S711).
0).

Then, each reading pointer is advanced by the pixel data size to indicate the next pixel data to be compressed. At this time, it is also determined whether or not the processing corresponding to the print width (Width) (one line) has been completed.
If one line is completed, each pointer is skipped by one line so as to indicate the next even-numbered line or odd-numbered line so as to perform the processing of the next line (S7120). Then, it is determined whether the number of lines to be compressed has been exceeded (S7130). If there is still pixel data to be compressed ("NO" in S7130), the process returns to step S7020 to return to step S7020. Compression. If there is no more pixel data to be compressed (S
If “YES” in step 7130), the compression processing of the expansion buffer is ended.

At this point, since the compressed data is stored in order from the top of the decompression buffer, FoutPt
The subsequent expansion buffer indicated by r will be released.

In the case of compressing pixel data of a plurality of expansion buffers, the write pointer Fou in step S7010 is used when compressing the second and subsequent expansion buffers.
The initialization of tPtr is omitted, and step S7090
At the time of updating the write pointer in, it is determined whether or not the decompression buffer currently being written is full of compressed image data, and if it is, reading of pixel data for the next compression process ends. A write pointer may be set at the head of the expanded buffer.
In this case, if a plurality of expansion buffers are set in the continuous area of the RAM 16, the continuous area can be released when the compression of all the expansion buffers is finally completed.

In the above flowchart,
In the above description, the expansion buffer is accessed for each pixel data size. However, if the pixel data size is different from a general CPU processing unit such as 1 bit or 2 bits (for example, 1 byte), once the CPU 12 Is read or written in the general-purpose register by an amount corresponding to the processing unit, and the bit processing is easily performed.

Next, based on the flowchart shown in FIG. 16, the compression processing which has been performed by holding the conversion table as described above is converted into a series of processing by the CPU 1.
2 will be described. This is shown in FIG.
After creating an address bit string indicating a reference address in step S6040 of the flowchart of FIG. 7, it is determined whether or not the conversion table can be used for the image set to be processed, and as a result of the determination, it is determined that the conversion table cannot be used. This processing is performed in place of the processing by the conversion table in S6050, and an address bit string indicating a reference address is input data to this processing (compression processing 2). Also. In this processing, as shown in FIG. 12, a block composed of four pixels on adjacent lines is processed at a time, and the block includes four pixel sets to be compressed.

Therefore, first, a counter n indicating which pixel set in the block is to be processed is cleared to 0 (S8000). Then, the above-described step S604 in the address bit string indicating the input reference address is performed.
A part corresponding to a bit string indicating an error synthesized by using 0 is extracted, and R0 assigned to a general-purpose register in the CPU 12 is extracted.
And R1 (S8010), add a predetermined weight to those errors, and obtain a corrected density relating to erroneous calculation (S8020).

Next, A [n] and B in the address bit string
[N] (initially n = 0) is extracted (S803)
0), a predetermined weight is added to the sum of them, and a corrected density of the pixel set to be compressed is obtained (S8040), and the corrected density and the corrected density related to the error calculated in step S8020 are added to obtain a corrected input Im [n ] (Initially n = 0
Is calculated (S8050). Then, the correction input Im [n] is compared with the threshold value d (S8060). If the correction input Im [n] is smaller than the threshold value d ("YES" in S8060), the output value f0 is assigned as the compressed image data F [n] (S80).
70), if it is equal to or larger than the threshold value d (“N” in S8060)
O "), and assigns the output value f1 as the compressed image data F [n] (S8080).

Thereafter, the value of the compressed image data F [n] is stored in the bit position corresponding to the n-th pixel set of the general-purpose register in the CPU 12 allocated to hold the sequentially calculated compressed image data. Set (S809)
0). Then, the difference between F [n] and A [n] + B [n] is calculated to calculate the error, the current R1 is copied to R0, and the newly obtained error is set to R1 (S810).
0). Then, in order to perform the processing of the next pixel set in the block, 1 is added to n (S8110), and it is determined whether or not n exceeds 3 (ie, has become 4) (S812).
0). If not exceeded ("NO" in S8120), the process returns to step S8020 to perform processing of the next pixel set, and if exceeded ("YES" in S8120), current R0 and R1 are output for output. An error bit string is set at a predetermined position in a general-purpose register of the CPU 12 that holds the compressed image data, an output bit string is generated as an output from this compression processing (S8130), and this compression processing 2 ends. With this output bit string, the process returns to step S6060, which is the original processing. In this way,
The thinning (compression) processing of the expansion buffer is continued.

The functions of the laser printer 2 or the print data transmitting apparatus and the personal computer 4 shown in the flowcharts of FIG. 3 and subsequent figures are provided in each apparatus as, for example, a program to be activated as a computer system. In the personal computer 4, for example, it is stored in a storage medium such as a floppy disk, a magneto-optical disk, a CD-ROM or the like, and is used by being loaded into a computer system and activated as needed. In the laser printer 2, the program is stored using a ROM or the like as a storage medium, and the ROM is incorporated in the laser printer 2 as a computer system.

In this embodiment, a laser printer is used as the printing apparatus. However, the present invention is not limited to a laser printer, and can be suitably used for a printing apparatus such as an ink jet printer or a thermal head printer.

In this embodiment, step S704
The processing procedure of calculating A [i] + B [i] of Equation 1 at 0 corresponds to the processing as the area density calculating means, step S7100 corresponds to the processing as the error calculating means, and R
R0 or R1 in the work memory of the AM 16 corresponds to the error storage means, step S7040 corresponds to processing as evaluation density calculation means, step S7050 corresponds to processing as generation means, and step S7080 corresponds to compressed image registration means. It corresponds to the processing as.

Also, the portion of the image data for four pixels read from each of the even-numbered line and the odd-numbered line in step S6040 is subjected to bit processing, which corresponds to the processing of the evaluation bit string creating means.
And the bit processing part of R1 correspond to the processing as the error bit string generating means, and the processing of generating a 12-bit address by the error bit string and the bit string of the image data in step S6040 corresponds to the processing as the address bit string generating means. Step S6050 corresponds to processing as a conversion unit, and step S6060 corresponds to processing as a compressed image data output unit.

Step S8020 corresponds to the processing as the first bit density calculating means, and step S8040
Corresponds to the processing as the second bit density calculating means, step S8060 corresponds to the processing as the threshold means, and steps S8000, S8110, and S8
120 corresponds to the processing as the control means.

Further, the conversion table stored in the ROM 14 corresponds to the conversion value storage means.

[0142]

As is apparent from the above description,
According to the image forming apparatus of the present invention, image data or images received from various image input sources such as application software operating on a personal computer or the like, an image scanner, a digital camera, or the like can be written in a language (for example, in the embodiment). Original image data representing the density of an image composed of a plurality of pixels, such as image data obtained by converting language expression data described in (PCL language) into pixels by a well-known method, and storing the original image data in the image storage means. A compression area composed of a plurality of pixels is set for the image data stored in the image storage means, and while the compression area is sequentially moved, the compression area of interest stored in the error storage means is evaluated by the evaluation density calculation means. Based on the error with respect to the compressed area already processed and the density calculated by the area density calculating means,
Calculating the evaluation density of the compression area of interest, and generating compressed image data by assigning a predetermined density to the compression area of interest based on a comparison between the evaluation density and a predetermined threshold value by the generation unit, An error, which is a difference between the compressed image data and the original density of the compressed area, is calculated by the error calculating means, and the error is stored in the error storage means in association with the compressed area, and used for processing of the next compressed area. It can be so.

Thus, the compressed image data is created from the original image data and the number of pixels is reduced by simply performing a simple operation and storage process sequentially for each compression area, so that the capacity of the image storage means used is reduced. it can.

When assigning a new density based on a comparison with a predetermined threshold value, by making the assigned density smaller than the density range of the original image data, the quality of the image is slightly reduced. It is possible to reduce the capacity of the image storage means to be used, and it is possible to further reduce the memory used.

The image forming apparatus according to claim 2 is
Since the compressed image data is sequentially stored in the area of the image storage means in which the processed original image data is stored, it is not necessary to allocate an area different from the storage area of the original image data to the compressed image data, and At the time when the compression process is completed, there is an effect that areas which are no longer needed (and thus may be released so that they can be used for other purposes) can be collectively obtained.

Further, according to the image forming apparatus of the present invention,
The density, which is pixel information, does not have a plurality of density levels, but has only two values, for example, 0 and 1. In this case, the density is represented by one bit. The number can be reduced, which is suitable for high-speed processing.

The image forming apparatus according to claim 4 is
At least one compressed area (pixel group) consisting of a plurality of pixels
An evaluation area (block) including the evaluation area is set, and an evaluation bit string indicating the density of the pixel in this evaluation area and an error bit string indicating an error generated when processing is performed before this evaluation area are created. The bit stream is provided as an input bit stream to the conversion means, and the resulting address bit string is input (accessed) to the conversion means to obtain compressed image data from the conversion means. Conversion means) can be carried out from only the data of the address bit string input to the conversion means, and there is no need to access the image storage means during the conversion (compression) processing. Can be easily programmed, and can be programmed so that the well-known cache function works efficiently in the CPU processing. Will be easy, it can be performed faster.

Further, according to the image forming apparatus of the present invention,
Since the compressed image data output by the conversion means is sequentially stored by the compressed image data output means in the area where the original image data has been compressed in the image storage means,
There is no need to allocate an area other than the storage area of the original image data to the compressed image data, and it becomes unnecessary at the time of completion of the compression processing (thus, even if it is released so that it can be used for another purpose). There is an effect that the (good) region can be obtained as a unit.

The image forming apparatus according to claim 6 is
Compression processing (conversion processing by the conversion means) for a plurality of compression areas can use the data of only the address bit string input to the conversion means cyclically, and there is no need to access the image storage means over and over again. Speed up.

Further, according to the image forming apparatus of the present invention,
Since the compressed image data is output in the form of a bit string for each evaluation area unit, the processing of storing the compressed image data in the image storage means can be performed intensively at one time, and the processing efficiency is increased. In particular, when the image data is binary, the process of storing the compressed image data sequence in the image storage unit can be simplified. Further, by making the bit string representing the error at the time of output the same as that at the time of input, the input to the compression processing of the subsequent evaluation area becomes easy, and the speed can be increased including the subsequent compression processing.

The image forming apparatus according to claim 8 is
Based on all combinations of image data that can be taken in the evaluation area (block) and all combinations of errors that can be input to the evaluation area, the conversion value is stored in association with the address bit string representing the combination. The conversion process is extremely simple. At this time, instead of storing all the combinations, it is also possible to preferentially store those having a high frequency of occurrence of the combinations.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a state in which a personal computer and a laser printer according to an embodiment of the present invention are connected.

FIG. 2 is a schematic block diagram in the embodiment.

FIG. 3 is a flowchart of a printer driver process in a personal computer.

FIG. 4 is a flowchart of a printer process in the laser printer.

FIG. 5 is a flowchart of an escape sequence process in the laser printer.

FIG. 6 is a flowchart of a host-based data receiving process in the laser printer.

FIG. 7 is a flowchart of a memory usage reduction process in the laser printer.

FIG. 8 is a flowchart of unregistered data processing in the laser printer.

FIG. 9 is a flowchart of a printing process in the laser printer.

FIG. 10 is a diagram illustrating the configuration of print data output by a printer driver.

FIG. 11 is an explanatory diagram showing a relationship between original image data and compressed image data.

FIG. 12 is an explanatory diagram regarding input information and output information to a conversion table.

FIG. 13 is an explanatory diagram regarding an address bit string input to a conversion table and a bit string output.

FIG. 14 is a flowchart of a thinning process using a conversion table in a laser printer.

FIG. 15 is a flowchart of a compression process in the laser printer.

FIG. 16 is a flowchart of a compression process in the laser printer.

[Explanation of symbols]

 2 laser printer 4 personal computer 6, 8 parallel interface 10 cable for IEEE 1284 12 CPU 14 ROM 16 RAM 18 sensors 20・ Engine 22 ・ ・ ・ Operation unit 24 ・ ・ ・ CPU 26 ・ ・ ・ ROM 28 ・ ・ ・ RAM 30 ・ ・ ・ Auxiliary storage device

Claims (9)

[Claims] 1. A compression area comprising a plurality of pixels is set in an image storage means for storing original image data representing the density of an image comprising a plurality of pixels. An image forming apparatus that creates compressed image data representing the density of pixels smaller than the number of pixels and forms an image based on the compressed image data, wherein the density of the image data corresponding to each pixel in a compressed area is An area density calculating means for reading out from the image storing means and adding the densities; calculating an error based on a difference between the density output as compressed image data for the compressed area and the density calculated by the area density calculating means; Error calculating means, an error storing means for storing the error calculated by the error calculating means in association with the compression area, and a note stored in the error storing means. Evaluation density calculation means for calculating an evaluation density of the compressed area of interest based on an error with respect to a compression area adjacent to the compression area to be observed and the density calculated by the area density calculation means; And a generation unit that generates compressed image data by assigning a predetermined density based on a comparison between the evaluation density calculated by the above and a predetermined threshold. 2. The image forming apparatus according to claim 1, further comprising a compressed image registration unit for sequentially storing the compressed image data obtained by said generation unit in said image storage unit. 3. The image forming apparatus according to claim 1, wherein the density of the image is binary. 4. A compressed area composed of a plurality of pixels and an evaluation area including at least one of the compressed areas are set in image storage means for storing original image data representing the density of an image composed of a plurality of pixels. While sequentially moving the evaluation area,
An image forming apparatus that creates compressed image data representing the density of pixels smaller than the number of pixels in the compressed area and forms an image based on the compressed image data, the image data corresponding to each pixel in an evaluation area Evaluation bit string creation means for creating an evaluation bit string based on the density of compressed image data output to a compressed area adjacent to the evaluation area of interest in the moving direction of the evaluation area; An error bit string creating means for creating each error based on the difference in density of image data as an error bit string; combining the evaluation bit string created by the evaluation bit creating means with the error bit string created by the error bit string creating means Address bit string creating means for creating an address bit string representing an address by means of Conversion means for outputting a compressed bit string indicating compressed image data based on the address bit string created as described above. 5. The image forming apparatus according to claim 4, further comprising a compressed image data output unit that stores the compressed bit string output by the conversion unit in the image storage unit. 6. A first bit density calculation for calculating a first density sum from an error represented by an error bit string in the address bit string, wherein the evaluation area includes a plurality of continuous compression areas. Means, a second bit density calculating means for calculating a second density sum from bits associated with one compression area of the evaluation bit string in the address bit string, and a first density sum and a second density sum. Threshold value means for calculating an evaluation density based on the threshold value, comparing the result with a predetermined threshold value, and generating compressed image data based on the comparison result; and for all compressed areas in the evaluation area, the compressed image data obtained by the threshold value means. A new first density sum is obtained by using the difference between the first density sum and the second density sum as a new error, and a second density sum for the next compression area adjacent to the compression area is calculated by the second bit density calculation means. 6. An image forming apparatus according to claim 4, further comprising: control means for repeating input of said first density sum and said second density sum to said threshold means. apparatus. 7. The conversion means converts the compressed image data sequentially output by the threshold means into a bit string, and converts the error into a bit string in the same format as the bit string created by the error bit string creation means and outputs the bit string. 7. The image forming apparatus according to claim 6, wherein the image forming apparatus is characterized in that: 8. The conversion means according to claim 4, wherein said conversion means includes conversion value storage means for storing an address bit string and a bit string obtained by combining a compressed bit string and an error bit string in association with each other. An image forming apparatus according to any one of the above. 9. A storage medium, wherein a program for realizing a function of the image forming apparatus according to claim 1 by a computer program is described.