JP2002354216A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the use efficiency of a page memory by not allowing image formation data transfer to occupy all page memories during image formation and reserving part of the page memories for input of a read picture. SOLUTION: Read pictures of different colors inputted from a scanner 300 are temporarily stored in page memories 700 and are sent to a printer control part 400 from them for forming an image. Memories required for continuous transfer of page pictures to a printer are defined as memories only for image formation and are set as page memories for holding the pertinent pictures, and other page memories are used for input of scanner read pictures. Read pictures completely inputted in the unit of documents are transferred from page memories to an HDD 500 and stored therein, and a space is reserved to prepare for the next input. Pictures which do not exist in the page memories at the time of forming an image are read from the HDD and are used. This method is effective in the case of image formation for double pages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a copying machine, a printer, a facsimile, and the like. More specifically, a plurality of originals are continuously read, and input color image data is formed into an image. The present invention relates to a color image forming apparatus including a control unit for efficiently using a page memory used for data transfer operation such as transfer to a copy unit.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic color image forming apparatus (copier, printer, facsimile, etc.) for forming a color image by synthesizing images of a plurality of constituent colors, an intermediate transfer member is formed in an image forming section. 2. Description of the Related Art There is known an apparatus that outputs a color image on paper by combining images of a plurality of constituent colors with an intermediate transfer body and transferring the synthesized image to transfer paper. Also, in a color image forming apparatus employing this method, based on image data of a plurality of standard-size originals read continuously, images of two surfaces are arranged side by side and formed on an intermediate transfer member, and one sheet is formed. There is also known a full-color image forming apparatus for creating a color image of two originals on a transfer paper. When an image is formed on an intermediate transfer member, an apparatus using this method reads an original or the like and holds one page of image data of a standard-size original in order to send input color image data to an image forming unit. The page memory of the capacity that can be used is the number of colors constituting the color image (usually, for full color, Y: yellow, M: computer,
(C: cyan, K: black). That is, in order to form a full-color image on two surfaces side by side on an intermediate transfer member, a page memory for eight pages is prepared and used.

[0003]

However, when the number of memories that can be used as page memories is small due to system limitations, for example, when only 10 pages of page memory are given in the above-described two-chamfering example, the operation is difficult. If the page memory for eight pages is used (locked) at the time of image formation, even if an attempt is made to read the third consecutive document in parallel, the page memory required for reading is insufficient for two pages. The original reading operation cannot be performed. In this example, the next reading operation becomes possible after the image forming of two chamfers is performed, that is, after the image forming operation of serially writing 8 pages one by one on the intermediate transfer body is performed. ,
In the meantime, the page memory for two pages remains unused, and the reading operation cannot be performed, and each page memory for eight pages continues to hold data until the image formation for all colors is completed. The use efficiency of the page memory is extremely reduced. According to the present invention, the number of usable memories is small in a page memory used for a data transfer operation such as continuously reading a plurality of originals and transferring input color image data to an image forming unit. It is made in view of the problem that occurs in the conventional color image forming apparatus that the memory use efficiency decreases in the case described above,
The purpose is to increase the utilization efficiency of the page memory by making a part of the page memory available for reading and inputting the image without occupying the entire page memory for image data transfer during image formation. An object of the present invention is to provide a color image forming apparatus which improves throughput.

[0004]

According to a first aspect of the present invention, there is provided a reading unit capable of continuously reading a plurality of originals and outputting a color image, and a page memory for temporarily storing an input read image in page units. Image storage means capable of storing images and reading stored images through the page memory; means for forming a color image based on the image transferred from the page memory; and Means for controlling the transfer of the read image of the color image forming apparatus, wherein the transfer control means includes a dedicated memory of the page memory for enabling the transfer of the image in page units continuously to the image forming means. A color image forming apparatus characterized in that a part of the color image forming apparatus is set and transferred to the image forming means using only the set dedicated memory.

According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, the transfer control means allocates a page memory set as the dedicated memory according to an image forming state and a use state of the page memory. It is characterized in that it is changed.

According to a third aspect of the present invention, in the color image forming apparatus according to the first or second aspect, the image forming means is means capable of forming images of a plurality of documents together. Things.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the third aspect, when the size of the image forming area or the size of the original reading exceeds a predetermined condition, the transfer control means sets the dedicated memory. Is increased or decreased according to the image forming state.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A color image forming apparatus according to the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a digital color copying apparatus according to an embodiment of the color image forming apparatus of the present invention. The operation unit 100 includes a print start key, a numeric keypad for determining the number of copies, an apparatus function setting key for setting functions provided in the digital color copying apparatus, a system function setting key for setting functions relating to the image forming system, and set functions. A liquid crystal touch panel for displaying data and the like is provided. The ADF unit 200 feeds originals one by one from a bundle of originals set on an original tray onto a contact glass (original platen) at a predetermined timing, enables continuous reading of a plurality of originals, and reads originals. Thereafter, the document is discharged at a predetermined timing. Scanner / IPU section 300
Irradiates a document set on a contact glass with a lamp, forms an image of the reflected light on a CCD which is a color image sensor via a mirror group, a filter, and a lens, amplifies the photoelectrically converted signal, and performs A / D conversion. Then, digital color image (R: let, G: clean, B: true) data is obtained. This reading operation is performed in response to a document that is continuously fed in conjunction with the operation of the ADF unit 200. Further, the scanner / IPU unit has image data patterned therein, and can output the internal pattern according to an instruction from the main control unit. The digital image data is subjected to predetermined processing such as shading correction and gamma correction. Also, if there are scaling processing, processing, etc. specified by the operation unit 100 or the main controller 600, these processings are also performed, and the digital image data of the effective image area is transmitted to the main controller 600 at a predetermined timing. . In this example, the scanner / IPU unit 300 performs a color conversion process from (R, G, B) of color image data to (Y, M, C, K).

The main controller 600 has a scanner I
The image data sent from the PU unit 300 is stored in a page memory (a memory which is prepared for each of the constituent colors of a color image and has a capacity capable of holding image data of one page) 700
To hold. Further, the image data temporarily stored in the page memory 700 is stored in the HDD 500, and necessary data in the stored image data is read and transferred to the page memory 700. Further, when there is a request for image formation from the printer control unit 400, the main controller 600 reads the image from the page memory 700, that is, if it exists in the page memory 700, or from the HDD 500 to the page memory 7
00, or sends the requested image data to the printer control unit 400. Printer control unit 4
00 has a bank 900 and the main controller 60
The digital image data sent from 0 is subjected to gamma conversion or the like to match the characteristics unique to the printer, thereby creating data for image formation. An LD (laser diode) is driven based on the image forming data, an electrostatic latent image is formed on the charged photoconductor, and toner is applied to the electrostatic latent image to visualize the image. In this example, writing on the photoreceptor can be performed with two chamfers (described in detail below).
A method of synthesizing each color image on the intermediate transfer member is adopted. The color-combined toner image on the intermediate transfer body is transferred to a transfer material such as paper, the transferred image is fused and fixed by a fixing device, and the transfer material is discharged out of the digital color image forming apparatus. The sorter unit 800 sorts and discharges the discharged transfer material according to the mode set by the operation unit.

Next, an embodiment of the present invention relating to memory control for improving the use efficiency of the page memory 700 will be described. The page memory 700 holds the input color image data of the read document, and transfers the image data held in the page memory 700 to the printer control unit 400 as image forming data during image formation. Conventionally, when reading a plurality of originals and manipulating the color image data of the input original to be read, in the related art, all the page memories are occupied for transferring the image forming data during image forming. In the present embodiment, a part of the page memory can be used for reading the next read image without occupying the entire page memory for transferring the image forming data unlike the related art. The purpose is to improve the use efficiency of the page memory. For this reason, in the present embodiment, the number of page memories (here, the minimum required number of memories) necessary for continuously performing data transfer for image formation in page units is set as a page memory dedicated to image formation. The page memory other than the page memory dedicated to image formation is used to receive and hold the input document reading data. At this time, in order to provide as much page memory as possible other than the page memory dedicated to image formation for receiving the original read data, the completed original read data is transferred from the page memory to the HDD 500 in units of originals. The page memory is emptied and used for use.

Here, in order to improve the use efficiency of the page memory 700 used for transferring the read image, the page memory 700 and the HD
An example relating to the control of D500 will be described. In this embodiment, a plurality of originals are read continuously, and the read original images are prepared as full-color image data for four colors (Y, M, C, K) from the scanner / IPU 300 in a page memory for ten pages. Is sent to the page memory 700. The page memory 700 stores the input color image data in the respective memories, and uses the stored color image data as image forming data in the printer control unit 400.
To the intermediate transfer unit, and as stored data H
The data is transferred to the DD 500, and image data for four colors is written in the order of the original. In order to continuously send image data for a plurality of documents to the intermediate transfer unit as image forming data, a predetermined number of page memories dedicated to image forming are provided. In the setting of the page memory dedicated to image formation, a page memory holding image data to be sent is assigned as a page memory dedicated to image formation so that the page memory cannot be used for data input from the reading unit. In addition, as image forming data in an image forming dedicated page memory in which data input from the reading unit is disabled, the HDD is used.
It is possible to read the stored image data from the storage device 500.
Here, it is assumed that the image transfer speed from the page memory 700 to the HDD 500 and the image transfer speed from the HDD 500 to the page memory 700 are faster than the linear speed of reading the original, and the image transfer from the page memory 700 to the HDD 500 is performed by reading the corresponding original. The operation has been completed.

FIG. 2 is a view showing an example of an intermediate transfer unit according to the present embodiment.
FIG. 6 is a diagram showing a document reading state, a page memory state, an image writing (accumulation) / reading state to an HDD, and an image forming state in the case where image formation is performed together with time, with time. Here, the page memory 700 has 10 pages,
These are designated by P1 to P10, and the image-dedicated page memories are set at two locations, and they are designated as dedicated memories 1 and 2, respectively. Also, the full-color image data is associated with the original and given a common numeral (for example, original 1: Y1, M1, C1, K1). Referring to FIG. 2, a description will be given of the operation of the page memory in the case where a plurality of originals are continuously read and a two-chamfered image is formed based on an input image. In an initial state, P9 and P10 are dedicated to image formation. Allocated as page memory. It is impossible to input read data to the page memory allocated to the page memory dedicated for image formation. When reading of the document 1 is started by optical scanning of the scanner in the scanner / IPU 300, input of a document read image (Y1, M1, C1, K1) to each of the page memories P1 to P4 is started. After the input of the read image of the original 1 into the page memory is started, an image forming sequence (hereinafter, referred to as “two-sided printing”) for arranging and transferring images for two surfaces to the intermediate transfer unit of the printer control unit 400 is started. Is done.

Since the image Y1 as the first image exists on the page memory P1, the main controller 600 starts outputting the image Y1 from the page memory P1. In this case, since the image is formed from the page memory P1, the page memory P1
Is changed to the dedicated image page memory (dedicated memory 1: P9 → P1). When reading of the original 1 is completed, H
The image transfer to the DD 700 is executed. Images are transferred in units of originals, that is, in units of images (Y1, M1, C1, K1), and the images in the page memory are guaranteed until image transfer to the HDD is completed. After the ADF 200 completes the operation of replacing the original 2, the scanner / IPU unit 300 starts the operation of reading the original 2. As in the case of the image Y1, the image Y2 which is the second surface of the two chamfers exists on the page memory P5.
Y2 is output from page memory P5. Since the output is performed from P5, the page memory dedicated for image formation is changed to the page memory P5 (dedicated memory 2: P10 → P5). During the formation of the Y2 image, the states of the page memories P1 to P10 are as follows. P1: Transfer of Y1 image to HDD is completed, and read data can be input. P2: To perform image formation of M1 next to Y2, it is assigned using image formation of Y2 as a trigger, and becomes a dedicated page memory for image formation. Yes P3: Transfer of C1 image to HDD, input of read data is possible P4: Transfer of K1 image to HDD, input of read data is accepted P5: Y2 image is being output (dedicated memory 2 allocation), Y2
Start transfer of image to HDD P6: Wait for start of transfer of M2 image to HDD P7: Wait for start of transfer of C2 image to HDD P8: Wait for start of transfer of K2 image to HDD P9: Empty (reading data can be input) P10: Free (read data can be input)

Therefore, in the above state, the page memory P1,
Since the reading operation of the original 3 can be performed using P3, P4, and P9 (however, when the original has been replaced by the ADF), the image to the HDD in units of images (Y1, M1, C1, K1) The reading operation of the document 3 is started from the time when the transfer is completed. Next, imaging of M1 is performed. In this case, M1
At the image forming timing, the M1 image is already stored in the HDD. However, the main controller 600 uses the image formation of Y2 as a trigger and changes the allocation of the image-dedicated page memory allocated to P1 to the page memory of P2 holding the M1 image in the next image formation order. Because the M1 image exists on the page memory of P2,
There is no need to read from D. Similarly, at the time of image formation of M2, by changing the assignment of the image formation dedicated page memory from P5 to P6, the read image M2 stored in P6 is used instead of using the image of the HDD. I have to. After the image of M2 is formed, the image of C1 is formed. In this case, the image of C1 is already stored in the HDD and does not exist in the page memory.
From C, the C1 image is read out to the dedicated page memory for image formation. The page memory dedicated to image formation in this case is P2. That is, H
The page memory for reading the image from the DD is the one allocated to the image-dedicated page memory first of the two image-dedicated page memories (the P2 page memory that has already held the image M1 for which image formation has been completed). To do.

At the time of image formation of M2 (also when reading out the C1 image from the HDD to the page memory dedicated for image formation), the next original 4
Is performed, and an input is made to the page memory. At this time, the operation is started by the status of the page memory (image transfer status to the HDD) other than the page memory dedicated for image formation and the replacement of the original by the ADF. In FIG. 2, P
5, P7, P8, P10 free page memory (image input available)
Therefore, the read image data of the document 4 is input here. In the next C2 image formation, similarly to C1, the C2 image does not exist in the page memory, so the image of C2 is read from the HDD to the image formation dedicated page memory. Here, the image is read from the HDD to the assigned page memory of P6. As described above, the setting of the two image forming dedicated page memories is controlled on a page basis, image forming data transfer is performed with the minimum necessary number of page memories, and read data other than the image forming dedicated page memory can be input. In the page memory, the read-completed data is transferred and accumulated from the page memory to the HDD in document units so that the page memory is opened so that the page memory to which read data can be input is increased as much as possible. At times, an image that does not exist in the page memory is read from the HDD to the image-dedicated page memory, so that the image data can be transferred continuously even in the case of two-sided printing. It is possible to prevent a decrease, and in turn, a decrease in productivity.

FIG. 3 shows an example of a flow chart of the allocation control operation of the page memory dedicated to image formation in the above-mentioned page memory when a plurality of originals are continuously read and two-chamfered image formation is performed based on an input image. Show. In the flow of this embodiment, when a preparation operation for the next image is performed with the start of image formation of an image to be currently executed as a trigger, an image formation dedicated page memory is stored in a page memory having an image used for the next image formation. It is executed when assigning. FIG.
It is necessary to hold the next image requested for image formation in the set image-dedicated page memory. Therefore, which one of the image-dedicated page memories is used first should be used for the current assignment. Search for dedicated page memory 1, 2
Is determined (S31). Next, it is checked whether or not the next image requested to be formed exists in the page memory (S32).
The dedicated page memory determined in 1 is allocated to the page memory where the image exists (S33). At this time, the assigned page specifies any one of P1 to P10. FIG. 2 shows an example of this flow, at the start of image formation of the image M1, M2 is requested as the next image formation image. At this time, since the image M2 exists in the page memory P6, the dedicated page memory 2 for which image formation has already been completed is allocated to the page memory P6 in which M2 exists. That is, the page memory to which the dedicated page memory 2 is assigned is changed from P5 to P6. On the other hand, if the result of the check in step S32 indicates that the next image does not exist in the page memory, the dedicated page memory determined in step S31 is left unchanged and remains unchanged (S34). An example of this flow is shown in FIG.
At the start of M2 image formation, C1 is requested as the next image formation image. At this time, the image C1 does not exist anywhere in the page memory.
Is assigned to the page memory P2 as it is. However, it is necessary to read C1 from the HDD and input it to the page memory P2.

Next, another embodiment of a memory control operation performed by setting a dedicated page memory in a page memory of the same size as above will be described. In the present embodiment, an operation suitable for a case where the document size exceeds the page memory size and only one image can be formed on the intermediate transfer unit (hereinafter, referred to as “single-panning”) is performed. FIG. 4 shows a document reading state, a page memory state, an image writing (accumulation) / reading state to the HDD, and an image reading / writing state when an image is formed by single chamfering in the present embodiment.
FIG. 4 is a diagram illustrating an image forming state according to a change in time. Again, we have 10 pages of page memory 700,
P1 to P10, two dedicated page memories for image formation are set, and each is dedicated memory 1 and 2. Also, the full-color image data is associated with the original and given a common numeral (for example, original 1: Y1, M1, C1, K1). In this example, it is impossible to input a document read image in one page memory, so that two continuous page memories are set as one unit (one frame) and four frames (page memory for eight pages) are secured. An image is input to the page memory.

Referring to FIG. 4, the operation of the page memory in the case where a plurality of originals are continuously read and one-chamfered image is formed based on an input image will be described. Allocated as page memory dedicated to image formation. It is impossible to input read data to the page memory allocated to the page memory dedicated for image formation. The preparation of the next image to be stored in the page memory (assignment of the page memory dedicated to image formation) is performed with the start of the previous image formation as a trigger. When the image reading of the original 1 is started, the image formation of Y1 is started. As described above, the page memory 1 dedicated to image formation is allocated to the page memories P1 and P2. At this time, Y1
With the start of image formation as a trigger, the next image to be formed is prepared. The next image is M1, so the M1 image is stored
Allocate image-dedicated page memory 2 to P3 and P4. Furthermore, at the start of M1 image formation, the next page C1
Assign. Also used for the next image formation at the start of C1 image formation
Prepare the image of K1, but since K1 is the last image, C1
At the end of the image formation, one of the two image formation-specific page memories, that is, P5 and P6 is deleted, and the image formation-only page memory is changed to P7.
・ Make it one of P8. In other words, when the image formation immediately before the last color is completed (image formation of C1 is completed), the two image-dedicated page memories are reduced to one, and at this point, four frames (page memory for eight pages) are obtained. , And the reading operation of the document 2 can be performed, and the read image is input in another page memory except P7 and P8. Further, when the image formation of K1 is started, the preparation of the image of Y2 which is the next image formation color is started, so that the image formation dedicated page memory is reduced to one and increased to two. By repeating these operations, 1
Performs chamfer imaging efficiently.

FIGS. 5 and 6 show an example of a flowchart of the control operation in the page memory when a plurality of originals are continuously read and one-chamfered image is formed based on an input image. Deletion of page memory dedicated to images,
FIG. 6 relates to the allocation of the page memory dedicated to image formation. In the state diagram shown in FIG. 4, for example, in order to enable reading of the original 2, four blocks of the page memory in which P5 and P6 are deleted and connected are shown in the state diagram shown in FIG. This is a process of making input possible, and is performed at the stage when the image formation of the C1 image immediately before the final color is completed. FIG.
Referring to FIG. 4, the color immediately before the final color (in the example of FIG. 4, C
It is checked whether the image formation of 1) is completed (S51),
After confirming the completion, the page memory dedicated for image formation set to image this color (in the example of FIG. 4, P5 and P6 holding C1)
A process for deleting the image-dedicated page memory 1) allocated to the memory is performed. As a flow, as an image forming dedicated page memory to be deleted, an image forming dedicated page memory (image forming dedicated page memory 1 in the example of FIG. 4) set for forming an image of a completed color is set ( (S52), the deletion is executed (S53), and the flow ends.

Next, with reference to the flowchart of FIG. 6, the operation of controlling the allocation of the image-dedicated page memory when the image-dedicated page memory is deleted will be described. In the flow of this embodiment, when a preparation operation for the next image is performed with the start of image formation of an image to be currently executed as a trigger, an image formation dedicated page memory is stored in a page memory having an image used for the next image formation. It is executed when assigning. Referring to FIG. 6, since it is necessary to hold the next image requested for image formation in the set image formation dedicated page memory, which of the two image formation dedicated page memories is first provided for the current assignment. A search is made to determine whether to use the dedicated page memory 1 or 2 (S61). Next, it is checked whether or not the next image requested to be imaged exists in the page memory (S62). If there is, the image-specific page memory determined in step S61 is stored in the page where the image exists. Assigned to memory (S63). On the other hand, if the result of the check in step S62 shows that the next image does not exist in the page memory, it is checked whether or not the image-dedicated page memory determined in step S61 is the deleted image-dedicated page memory. (S64). If not deleted (S64-NO), the dedicated page memory determined in step S61 is left as the page memory allocated so far,
No change is made (S66). If it has been deleted (S64-
YES), restore the deleted image-dedicated page memory,
The restored page memory dedicated to image formation is allocated to the page memory holding the next image requested for image formation (S65).
As described above, although the original image reading and image forming operations have been described in this example, even when the image is read from the HDD to the page memory as in the case of the electronic sort, the image formation of the color immediately before the final color is completed. Since the page memory for eight pages can be secured, the original reading operation can be performed without waiting for the end of the image formation of the final color, and a decrease in productivity can be prevented.

[0021]

(1) Effects corresponding to the first and second aspects of the present invention A memory dedicated to image formation is set in a part of the page memory, and pages are continuously provided to the image forming means using only the set dedicated memory. Images can be transferred in units, and a page memory other than the dedicated memory is used for image input from the reading unit, so that the page memory lock state due to the original reading operation and the page memory lock state due to the printing operation do not occur, The use efficiency of the page memory can be improved. In addition, since the page memory set as the dedicated memory is dynamically assigned, it is possible to use the page memory more efficiently. (2) Effects corresponding to the invention of claim 3 In addition to the effect of (1), an image forming apparatus having a function of forming images of a plurality of documents together, such as double-sided printing, is provided. By applying the inventions of the first and second aspects, in this type of image forming apparatus, it is possible to remarkably improve the productivity reduction caused by the deterioration of the use efficiency of the page memory, which has conventionally occurred. (3) Effects corresponding to the fourth aspect of the invention In addition to the effects of the above (2), by changing the set number of dedicated memories for image formation in accordance with the image formation state, a size capable of performing only one-plane image formation is provided. In this case, the reading operation and the printing operation can be performed in parallel with each other, and a decrease in productivity can be prevented.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration of a digital color copying apparatus according to an embodiment of a color image forming apparatus of the present invention.

FIG. 2 shows a document reading state, a page memory state, an image writing / reading state to / from an HDD, and a state of image reading / reading at the time of two-sided image formation.
The image forming state is shown according to the change of time.

3 shows an example of a flowchart of an operation of controlling the allocation of an image-dedicated page memory in the operation of FIG. 2;

FIG. 4 illustrates a document reading state, a page memory state, an image writing / reading state to / from an HDD, and an image reading / reading state at the time of single-pane image formation.
The image forming state is shown according to the change of time.

5 shows an example of a flowchart of an operation of deleting an image-dedicated page memory in the operation of FIG. 3;

6 shows an example of a flowchart of an operation of allocating a page memory dedicated to image formation in the operation of FIG.

[Explanation of symbols]

300: scanner / IPU, 400: printer control unit, 500: HDD, 600:
Main controller, 700: page memory.

Claims (4)

[Claims] 1. A reading means capable of continuously reading a plurality of originals and outputting a color image, a page memory for temporarily storing an input read image in page units, and storing images via the page memory Image storing means capable of reading stored images, means for forming a color image based on an image transferred from the page memory, and means for controlling transfer of a read image to the image forming means. A color image forming apparatus, wherein the transfer control unit sets a dedicated memory for enabling image transfer in a page unit continuously to the image forming unit to a part of the page memory;
A color image forming apparatus wherein transfer to an image forming means is performed using only a set dedicated memory. 2. The color image forming apparatus according to claim 1, wherein the transfer control unit changes the allocation of a page memory set as the dedicated memory according to an image forming state and a use state of the page memory. A color image forming apparatus, comprising: 3. A color image forming apparatus according to claim 1, wherein said image forming means is means capable of forming images of a plurality of documents together. 4. The color image forming apparatus according to claim 3, wherein the transfer control unit generates the set number of the dedicated memory when a size of an image forming area or a document reading size exceeds a predetermined condition. A color image forming apparatus characterized by increasing or decreasing according to an image state.