JPH0660188A - Picture drawing device - Google Patents

Abstract

PURPOSE:To relieve the load of a CPU required when a picture memory is cleared or a same color is filled in a wide range of the picture memory including drawing of a background portion. CONSTITUTION:When a drawing start recognition section 3c of a CPU 3 recognizes the start of drawing to a picture memory 2 and a vector expansion section 3b generates data representing a clear area and data of a relevant density to clear the picture memory 2, a picture drawing controller 34 draws white dots to a clear area of the picture memory 2. Moreover, a background detection section 3d detects a background portion drawing instruction and the vector expansion section 3b generates data of the relevant density and data representing the drawing area to draw the background portion, the picture drawing controller 34 draws data corresponding to the density to the drawing area of the picture memory 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image drawing apparatus capable of drawing straight-line vector data, and more particularly to an image drawing apparatus for executing a work of clearing an image memory or filling the same color.

[0002]

2. Description of the Related Art As an image drawing device using a straight line vector, for example, there is one shown in Japanese Patent Laid-Open No. 2-181886, and the operation of an information system having such an image drawing device will be described with reference to FIG. To do. This information processing system draws in the image memory 2 image data created in a page description language represented by Postscript in the host computer 1.

All of the vector data are represented by vectors. The CPU 3 redistributes all the described vectors into straight line vectors in the main scanning direction, and the coordinates of the start and end points of the straight line vectors and the density values are first-in first-out memory. (Hereinafter referred to as "FIFO") 4 is temporarily stored. FIF
Each data stored in O4 is a main scanning direction start address register (hereinafter referred to as “XS register”) 5, a main scanning direction end address register (hereinafter referred to as “XE register”)
6, the sub-scanning direction start address register (hereinafter referred to as "YS register") 7, and the density register (hereinafter referred to as "RGB register") 8 are respectively latched.

When a drawing command is issued from the CPU 3, the memory controller 9 generates a write signal, and the density specified by the RGB register 8 at the address specified by the XS register 5 and the YS register 7 on the image memory 2. Write with. When the write operation is started, the main scanning direction address counter (hereinafter referred to as “X address counter”) 10 starts counting operation, and the address (load value from the XS register 5) is incremented (+1).

After that, when the address becomes the same as the value of the XE register 6, the X-comparator 11 which is the main scanning direction comparator notifies the memory controller 9 that the drawing end dot has been reached. As a result, a straight line vector can be drawn. Then, by repeating the above operation, one page of image data created by the host computer 1 can be drawn in the image memory 2.

The operation of the information processing system having the image drawing device for drawing the image data of the two-dimensional rectangular area in the image memory will be described with reference to FIG. This information processing system stores text data and the like once drawn in the image memory in the cache memory as image data, and draws the same text data as the data read from the cache memory after the second time.

The image drawing apparatus is similar to that shown in FIG.
FIFO 4 for temporarily storing each data from the table and XS register 5 for storing a drawing start address in the main scanning direction
And XE for storing the drawing end address in the main scanning direction
Register 6 and Y indicating the drawing start address in the sub-scanning direction
S register 7, an RGB register 8 for storing RGB data indicating a density value, an X address counter 10 for designating a drawing address of the image memory 2 in the main scanning direction, and an end of drawing of the image memory 2 in the main scanning direction. And an X-comparator 11 for informing.

Further, a cache memory 12 for registering image data from the CPU 3 for each predetermined rectangular area, and F
An import control device (hereinafter referred to as "operation controller") that receives data from the IFO 4 and determines the type of the data.
13) and a parallel / serial converter 14 for converting parallel data fetched from the FIFO 4 into serial data.
, A sub-scanning direction end address register (hereinafter referred to as “YE register”) 15 for storing a drawing end address in the sub-scanning direction, and a sub-scanning direction address counter (hereinafter, “YE register”) for counting the number of lines drawn in the sub-scanning direction. 16), a sub-scanning direction comparator (hereinafter referred to as "Y comparator") 17 for notifying the end of the line to be drawn, an OR gate 18 for controlling the read-modify-write function of the image memory 2, and a latch circuit 19 , 2
0, a memory data control device including an inverter 21.

In the image drawing apparatus configured as described above, the data obtained from the host computer 1 is converted into a straight line vector by the CPU 3 in the same manner as in FIG. 8 when the first drawing before registration in the cache memory 12 is performed. To be done. The data converted into the straight line vector is stored in the FIFO 4, and at the same time, an image is developed for each predetermined rectangular area and registered in the cache memory 12.

Then, it is checked whether or not the image data to be drawn is registered in the cache memory 12, and if it is registered, the drawing start coordinates (XS, YS) of the rectangular area for drawing the image data, The drawing end coordinates (XE, YE), the drawing command for the rectangular area, and the image data to be drawn in the cache memory 12 are sequentially written in the FIFO 4.

When the necessary data is prepared in the FIFO 4, the operation controller 13 takes out the data and performs an operation according to each data. That is, the first data is the drawing start coordinates (XS, YS) and the drawing end coordinates (XE, YE) of the rectangular area for drawing the image data.
Therefore, set them as XS register 5, YS register 7, X
The E register 6 and the YE register 15 are made to latch respectively. Since the next data is the drawing command for the rectangular area, the drawing operation for the rectangular area is started, and since the data following the drawing command is image data, the image data is loaded into the parallel / serial converter 14.

At this time, the parallel / serial converter 14
The first data input to is the drawing start coordinate (XS, Y
Since the data is to be drawn in S), the parallel / serial converter 14 converts the data into serial data and outputs it dot by dot. When the output of the parallel / serial converter 14 is the drawing dot “1”, the OR gate 18 inverts “1” by the inverter 21 to “0”.
Is inputted, the OR gate 18 makes the RGB register 8
Output data and the data previously written in the address to be written in the image memory 2 are logically ORed, and the data obtained thereby is rewritten to the same address in the image memory 2 via the latch circuit 19.

Further, when the output of the parallel / serial converter 14 is the drawing dot "0", "1" which is obtained by inverting "0" by the inverter 21 is input to the OR gate 18, so that the OR gate 18 is supplied. Does not operate, and the data previously written to the address to be written on the image memory 2 is written to the same address on the image memory 2 as it is via the latch circuit 19.

Further, at the same time when the image data is output from the parallel / serial converter 14, the operation controller 13 causes the X address counter 10 and the XS counter 5 to operate.
Value is loaded and the address increment (+1) is started. At this time, the X comparator 11 compares the value of the X address counter 10 with the value of the XE register 6,
When the respective values match, a signal notifying the end of drawing one line of the image memory 2 is output to the Y address counter 16. The Y address counter 16 increments (+1) to update to the next line when receiving a signal indicating the end of drawing of one line from the X comparator 11, and reloads the value of the XS counter 5 into the X address counter 10. Then, the address increment (+1) is started, and thereafter the same operation as described above is repeated for each of the second and subsequent lines of the designated rectangular area of the image memory 2.

When the drawing of the final line of the rectangular area is completed and the signal for notifying the completion of the drawing of one line is output from the X comparator 11, the value of the Y address counter 16 and the value of the YE register 15 are changed. Y because it matches
The comparator 11 outputs a signal notifying that the drawing on the last line is completed to the operation controller 13 to complete the drawing of the image data in the specified rectangular area of the image memory 2.

[0016]

However, in the conventional image drawing apparatus as described above, when clearing the image memory when drawing new image data, one line as shown in FIG. 10 is used. It is necessary to register the white data into the FIFO 4 one by one, and when the image data to be drawn is the background portion, the drawing is performed as shown in FIG. 11, and therefore the same processing as when clearing the image memory is performed. I will do it.

Further, when the drawing function of the two-dimensional rectangular area is used, as shown in FIG. 12, the image memory must be cleared and the background part must be drawn, whichever method is used. Not only is the load on the CPU 3 increased due to the data calculation at the time of registration in the FIFO 4,
There is a problem that the waiting time for drawing due to the wait when O4 is in a full state becomes long.

The present invention has been made in view of the above points, and reduces the load on the CPU when clearing the image memory or drawing the same color in a wide range of the image memory including the drawing of the background portion. The purpose is to

[0019]

In order to achieve the above-mentioned object, the present invention develops image data input from the outside into a straight line vector to generate address and density value data of the start and end points of the straight line. In an image drawing device provided with a microcomputer and an image drawing control device for writing vector drawing data in an image memory based on each data generated thereby, the microcomputer (CPU) transfers the image drawing control device to the image memory. It is provided with a means for drawing a white dot in the image memory when the data of the density value corresponding to clearing the image memory is generated by recognizing the drawing start.

Further, when the CPU recognizes the start of drawing in the image memory and generates the data indicating the clear area and the data of the corresponding density value to clear the image memory in the image drawing control device, There is also provided an image drawing device having means for drawing a white dot in the clear area.
Further, when the CPU generates data indicating the drawing area and data of the corresponding density value in the image drawing control device so as to draw the same color in a wide range of the image memory including the drawing of the background portion, There is also provided an image drawing apparatus having means for drawing data according to the density value in the drawing area.

[0021]

According to the image drawing apparatus of the present invention, when the CPU recognizes the start of drawing in the image memory and generates the data of the corresponding density value for clearing the image memory, the image drawing control apparatus makes the image Since white dots are drawn in the memory, the load on the CPU when clearing the image memory is reduced.

According to the image drawing apparatus of the second aspect, the CPU
When the device recognizes the start of drawing in the image memory and generates the data indicating the clear area and the data of the corresponding density value to clear the image memory, the image drawing control device creates a white dot in the clear area of the image memory. Since the drawing is performed, the same effect as described above can be obtained. According to the image drawing apparatus of claim 3, when the CPU generates the data showing the drawing area and the data of the corresponding density value so as to draw the same color in a wide range of the image memory including the drawing of the background portion, Since the image drawing control device draws data according to the density value in the drawing area of the image memory, the load on the CPU when drawing the same color in a wide range of the image memory is reduced.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. 2 is a block configuration diagram showing an information processing system embodying the present invention, and FIG. 3 is a block configuration diagram showing an example of the configuration of the printer controller (image drawing device) thereof. Is attached.

This information processing system includes a host computer 1 and a printer controller 3 which is an image drawing device.
0 and a printer device including a printer engine 31. The printer controller 30 is
It includes a microcomputer including a CPU 3, a ROM 32, and a RAM 33, an image memory (frame memory) 2, an image drawing control device 34, a receiving device 35, and a transmitting device 36.

The CPU 3 is a central processing unit that controls the printer controller 30 as a whole according to a program in the ROM 32 and a command from the host computer 1. The ROM 32 is a read-only memory that stores control programs for the CPU 3 to operate and fixed data such as fonts. The RAM 33 is a work memory for the CPU 3, an input buffer for storing input data, a page buffer for storing page data, a random access memory used for a font file for storing downloaded fonts, and an image memory 2. Is image data (bitmap data)
Is a random access memory for writing.

The image drawing control device 34 controls drawing in the image memory 2, and will be described in detail later.
The receiving device 35 is responsible for receiving data transmitted from the host computer 1, and the transmitting device 36 is responsible for transmitting image image data to the printer engine 31 that actually prints.

FIG. 4 is a block diagram showing the details of the image drawing controller 34 of FIG. 3, and as shown in FIG.
A FIFO 4 for temporarily storing each data from the PU 3, an XS register 5 for storing a drawing start address in the main scanning direction, an XS register 6 for storing a drawing end address in the main scanning direction, and a sub scanning direction A YS register 7 indicating a drawing start address, an RGB register 8 for storing RGB data indicating a color density value, an X address counter 10 for specifying a drawing address of the image memory 2 in the main scanning direction, and an image memory 2 And an X-comparator 11 that notifies the end of drawing in the main scanning direction.

Further, a fetch control device (hereinafter referred to as "operation controller") 13 for fetching data from the FIFO 4 and discriminating its type, and a sub-scanning direction end address register (hereinafter, referred to as a sub-scanning direction end address register for storing a drawing end address in the sub-scanning direction) 15 and a sub-scanning direction address counter (hereinafter referred to as "Y address counter") that counts the number of lines drawn in the sub-scanning direction.
16, a sub-scanning direction comparator (hereinafter referred to as “Y comparator”) 17 for notifying the end of a line to be drawn, a memory controller 37, and a rectangular area filling controller 38.

FIG. 1 is a block diagram functionally showing this embodiment. The user uses the host computer 1 to create one page of image data (straight line vector, curve vector, etc.) to be printed in a page description language represented by Postscript. The created image data is sent to the CPU 3, converted again into a linear vector in the main scanning direction by the page description language decoding unit 3a, sorted, and sent to the vector expansion unit 3b.

At this time, the drawing start recognition section 3c judges that the user has issued a drawing command for a new page,
A clear instruction for clearing the image memory 2 is issued to the vector expansion unit 3b. Further, the background portion detection unit 3d sends a background drawing instruction to the vector expansion unit 3b when the user issues a rectangular area fill command such as a fill command for a rectangular area in Postscript, for example.

The vector expansion unit 3b reconverts the straight line vector in the main scanning direction into data suitable for the image drawing control device 34 such as the start coordinates, the end coordinates, and the density value of the straight line in the same manner as in the conventional configuration, and the inside thereof. Send to FIFO4. When a clear command is issued, the image drawing control device 34 is designated from 0 to the maximum value in each of the main scanning direction and the sub scanning direction. If 256 gradations are given, all RGB data are set to 0xFF ( (Maximum value) and send a two-dimensional rectangular area filling operation.

Further, when the background drawing command is issued, the drawing start coordinates, the end coordinates and the density value of the background part are specified to the image drawing control device 34, and a two-dimensional rectangular area filling operation is sent. The image drawing control device 34
Each operation sent from the CPU 3 is decoded, an address line, a data line and a control signal of the image memory 2 are generated and drawn in the image memory 2.

All the data converted into straight line vectors by the vector expansion unit 3b of the CPU 3 are stored in the FIFO 4.
Is temporarily stored in. Some bits of the data stored in the FIFO 4 are attached with TAG bits as shown in FIG. When this TAG bit is sent to the operation controller 13, the operation controller 13 decodes the TAG bit, and the data bit added together with the TAG bit is the data of the drawing start coordinate (XS) in the main scanning direction or the main scanning. Direction drawing end coordinate (X
E) data, drawing start coordinate (YS) data in the sub-scanning direction, drawing end coordinate (YE) data in the sub-scanning direction, or density value (RGB) data,
It outputs the latch signal of each register of XS, XE, YS, YE, and RGB.

In each register to which the latch signal is input, the XS register 5 has a drawing start coordinate (X
S), the XE register 6 is the drawing end coordinate (XE) in the main scanning direction, the YS register 7 is the drawing start coordinate (YS) in the sub scanning direction, and the YE register 15 is the drawing end coordinate (YZ) in the sub scanning direction. RGB register 8 displays the density value (RG
The data of B) are stored respectively.

However, although the RGB data is stored in the density (RGB) register 8 in this example, when the output printing device is a monochrome printer, the density register 8 stores the data for a single color. Alternatively, CMYK data may be stored when the configuration of the image memory 2 is not RGB.

Next, the operation of drawing a straight line vector in this embodiment will be described. When the vector decompression unit 3b of the CPU 3 stores the necessary vector drawing data in the FIFO 4, the operation controller 13 sequentially takes out each of the data and outputs them as described above.
S register 5, XE register 6, YS register 7, RG
After sequentially storing in each register of the B register 8 and confirming that the linear drawing operation (OP) flag of the TAG bit is set, the value of the XS register 5 is stored in the X address counter 10 and the value of the YS register 7 is stored in the Y address counter 16. The respective values are loaded and the count-up of the X address counter 10 is started.

At the same time, a chip select signal C which is a control signal for the image memory 2 is sent to the memory controller 37.
S, write enable signal WE, output enable signal O
X is generated, and the X address counter 10 of the image memory 2 is generated.
Is written in the address designated by the value of the Y address counter 16 and the density value designated by the RGB register 8.

At this time, the X comparator 11 compares the value of the X address counter 10 with the value of the XE register 6,
When the respective values match, a signal XEND which notifies the end of drawing one line of the image memory 2 is sent to the memory controller 3
7 and the operation controller 13. Signal XE
The operation controller 13 receiving the ND,
The next vector drawing data is received from the FIFO4. The above operation is repeated to expand all the vector drawing data stored in the FIFO 4 into the image memory 2 to create an image for one page.

Next, the operation for clearing the image memory 2 will be described. When a clear command for clearing the image memory 3 is issued from the drawing start recognition unit 3c of the CPU 3 or when a clear command for one page is issued by the user, the vector expansion unit 3b uses, for example, a printer for printing. Resolution is 400 DPI (dots / inch),
If the area to be printed (cleared) is A3 size paper, the values of XS and YS are "0" and the value of XE is "467".
7 "and YE are set to" 6614 "(however, those values differ depending on the resolution and the paper size of the printer), and the data showing the respective values, the data showing the density value, and the two-dimensional rectangular area filling operation are shown in FIG. As shown in F
Write to IFO4.

When the respective data are stored in the FIFO 4, the operation controller 13 takes out the respective data and puts "0" in the XS register 5 and the YS register 7.
, "4677" in the XE register 6, and the YE register 1
5, "6614" is stored in the RGB register 8, and all bits "1" are stored in the RGB register 8 ("255" if the bit width of the RGB register 8 is 8 bits). However, if this printer device is a monochrome printer or CMY
When K data is used, “0” is input to the RGB register 8.

When it is confirmed that the TAG bit rectangular area operation flag is set in the state set as described above, the value of the XS register 5 is set in the X address counter 10 and the value of the Y address counter 16 is set in the Y address counter 16 as in the case of the straight line drawing. YS
The value of the register 7 is loaded, and the count-up of the X address counter 10 is started.

At the same time, the rectangular area filling controller 38 is caused to generate the chip select signal CS, the write enable signal WE, and the output enable signal OE which are the control signals of the image memory 2, and the value of the X address counter 10 of the image memory 2 and Y. Writing is performed with the density value designated by the RGB register 8 at the address designated by the value of the address counter 16. That is, a white dot is written.

At this time, the X comparator 11 compares the value of the X address counter 10 with the value of the XE register 6,
When the respective values match, the clearing of one line in the main scanning direction of the image memory is completed, and at that time, the signal XEND
Is output to the Y address counter 16. When the Y address counter 16 receives the signal XEND from the X comparator 11, the Y address counter 16 counts up (+1) to update to the next line, and the X address counter 10 is reloaded with the value of the XS register 5 to update the address. The counting up is started, and thereafter, the same operation as described above is repeated for each of the second and subsequent lines of the image memory 2.

When the drawing on the last line of one page is completed and the signal XEND is output from the X comparator 11, the value of the Y address counter 16 and the YE register 1 are output.
Since the value of 5 coincides with the value of 5, the Y comparator 17 issues a signal YEND indicating that the drawing (clearing) of the last line is completed to the rectangular area filling controller 38, and the clearing of one page specified in the memory 2 is completed. Tell what you did.

As described above, the operation controller 1 which can clear the image memory 2 and receives the signal YEND
3 enters the next step, and if vector drawing data and the like are stored in the FIFO 4, drawing is performed. If you want to clear only an arbitrary area of the image memory 2,
Data indicating the area to be cleared may be stored in the S, XE, YS, and YE registers.

Next, the operation of drawing the background portion on the image memory 2 will be described. When the background drawing command is issued from the background detection unit 3d of the CPU 3, the vector expansion unit 3b causes the drawing start coordinates (XS, YS) and the drawing end coordinates (XE, YE) of the rectangular area of the background as shown in FIG. ), The data indicating the background color, and the two-dimensional rectangular area filling operation are sequentially written in the FIFO 4.

When the respective data are stored in the FIFO 4, the operation controller 13 takes out the respective data and sequentially stores them in the XS register 5, XE register 6, YS register, YE register 15, and RGB register 8, and thereafter the image By performing the same operation as when clearing the memory 2, the background portion can be drawn in an arbitrary rectangular area of the image memory 2.

Thus, according to this embodiment, the CPU
3 recognizes the start of drawing on the image memory 2 and generates data indicating the clear area (two points of the rectangular area to be cleared in this embodiment) and corresponding density value data in order to clear the image memory. At this time, the image drawing control device 34 draws a white dot in the clear area of the image memory 2, so that the load on the CPU required for clearing the image memory is reduced, and the FIFO 4 has only 10 stages.
The full state of is gone. For example, A3 size 400d
When clearing the pi area, the time required for the CPU 3 to access the image memory 2 is about 1 / 31,000,000, which is a significant speedup.

When the CPU 3 generates the data indicating the drawing area and the data of the corresponding density value for drawing the background portion, the image drawing control device 34 responds to the density value in the drawing area of the image memory 2. Since the data is drawn, the load on the CPU when drawing the background portion in the image memory 2 is reduced, and the FIFO 4 is not in the full state as described above, so that the speed can be significantly increased.

When the CPU 3 recognizes the start of drawing on the image memory 2 and clears the entire image memory 2 for one page, if there is data indicating the density value, a white dot is drawn on the entire image memory 2. Image memory 2
Since it can be cleared, it is not necessary to generate data indicating the area to be cleared.

[0051]

As described above, according to the present invention, the CP required when clearing the image memory or when drawing the same color in a wide range of the image memory including the drawing of the background portion.
U's burden is reduced.

[Brief description of drawings]

FIG. 1 is a block configuration diagram functionally showing the embodiment of FIG.

FIG. 2 is a block diagram showing an information processing system embodying the present invention.

3 is an image drawing apparatus (printer controller) of FIG.
It is a block diagram which shows an example of 30.

FIG. 4 is a block configuration diagram showing details of the image drawing control device 34 in FIG.

5 is an explanatory diagram showing a configuration example of each data taken in by the operation controller 13 from the FIFO 4 of FIG.

FIG. 6 is a flowchart showing the flow of processing when the CPU 3 of FIG. 1 clears the image memory 2.

FIG. 7 is a flowchart showing a flow of processing when a background portion is drawn on the image memory 2 by the CPU 3 of FIG.

FIG. 8 is a block diagram showing an information processing system having a conventional image drawing device.

FIG. 9 is a block diagram showing another information processing system.

FIG. 10 is an image memory 2 by the CPU 3 shown in FIGS. 8 and 9;
It is a flowchart showing a flow of processing when clearing.

FIG. 11 is a flowchart showing the flow of processing when drawing a background portion in the image memory 2 in the same manner.

12 is a flowchart showing another processing flow when clearing the image memory 2 by the CPU 3 of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Host computer 2 Image memory 3 CPU 3a Page description language decoding unit 3b Vector expansion unit 3c Drawing start recognition unit 3d Underground portion detection unit 4 First-in first-out memory (FIFO) 5 Main scanning direction start address register (XS register) 6 Main scanning direction end Address register (XE register) 7 Sub-scanning direction start address register (YS register) 8 Density register (RGB register) 10 Main scanning direction address counter (X address counter) 11 Main scanning direction comparator (X comparator) 13 Acquisition control device (Operation controller) 15 Sub-scanning direction end address register (YE register) 16 Sub-scanning direction address counter (Y address counter) 17 Sub-scanning direction comparator (Y comparator) 30 Image drawing device 31 Printer engine 32 ROM 33 RAM 34 Image drawing control device 37 Memory controller 38 Rectangular area filling controller

Claims (3)

[Claims] 1. A microcomputer which develops image data input from the outside into a straight line vector to generate address and density value data of a start point and an end point of a straight line, and a microcomputer based on each data generated by the microcomputer. In an image drawing device provided with an image drawing control device for writing vector drawing data in an image memory, the image drawing control device is adapted to recognize that the microcomputer has started drawing in the image memory and clear the image memory. An image drawing apparatus comprising means for drawing a white dot in the image memory when data of a density value to be generated is generated. 2. A microcomputer which develops image data input from the outside into a straight line vector to generate address and density value data of a start point and an end point of a straight line, and based on the respective data generated by the microcomputer. In an image drawing device provided with an image drawing control device for writing vector drawing data in the image memory, the image drawing control device recognizes the start of drawing in the image memory and clears the image memory to clear the image memory. An image drawing apparatus comprising means for drawing a white dot in a clear area of the image memory when data indicating an area and data of a corresponding density value are generated. 3. A microcomputer which develops image data input from the outside into a straight line vector to generate address and density value data of the start and end points of the straight line, and a microcomputer based on the respective data generated thereby. In an image drawing device provided with an image drawing control device for writing vector drawing data in an image memory, in the image drawing control device, the microcomputer draws the same color in a wide range of the image memory including drawing of a background portion. An image drawing apparatus comprising means for drawing data corresponding to a density value in the drawing area of the image memory when data indicating the drawing area and data of a corresponding density value are generated.