JP3635808B2 - Image processing apparatus and image processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus that reduces the capacity of a buffer memory that temporarily stores image data and does not deteriorate image quality when supplying the image data in synchronization with a drawing operation of a printing unit or the like. .
[0002]
[Prior art]
When image data from the host computer is output to a printing device such as a printer, the image data is supplied to the printing device via a network such as Ethernet, SCSI bus, Centronics, RS-232C serial communication, or the like. . Here, the image data output from the host computer is mainly a raster in which code data described in a page description language (PDL) and data indicating each pixel of the image are arranged in order of the main and sub scanning directions. Broadly divided into image data.
[0003]
Next, as shown in FIG. 13A, when the image data by the host computer 101 is code data, the image forming unit 102 installed in the printing apparatus interprets the description content of the code data and performs rasterization. Image data is generated (rendering process). Since the raster image data needs to be supplied in synchronization with the drawing operation in the main scanning direction and the sub-scanning direction in the printing unit 105, the raster image data is temporarily stored in the buffer memory 103. After the storage, raster image data is read from the buffer memory 103 in synchronization with the drawing operation of the printing unit 105 by the printing unit control mechanism unit 104 and supplied to the printing unit 105.
Further, as shown in FIG. 13B, when the image data by the host computer 101 is raster image data, the content interpretation by the image forming unit 102 in FIG. The raster image data is directly stored in the buffer memory 103, and thereafter, the raster image data is read from the buffer memory 103 in synchronization with the drawing operation of the printing unit 105 by the printing unit control mechanism unit 104 and supplied to the printing unit 105.
[0004]
On the printing side, there is a method of applying a screen to input raster image data in order to improve the expression of gradation. As an example, a full color printer using a laser beam and having a resolution of 400 dpi will be described. An example of this screen is shown in FIG. FIG. 14A shows a 400-line screen, and the 400 dpi resolution matches the 400-line screen. FIGS. 2B and 2C show 200-line screens. In this case, two dots are used as one screen unit in the sub-scanning direction of the laser beam. As a method of switching between these two types of screens, there is a method of changing the laser beam irradiation time by modulating the pulse width of the laser beam ("On-demand printing market and technical issues": published by Japan Printing Technology Association) ). This method is shown in FIGS. 11 (a) and 11 (b). FIG. 4A shows the relationship between the image density level and the laser output waveform when a 400-line screen is used. As shown in the figure, the laser beam is turned on when the level of a triangular wave having a period of 400 lines exceeds the image density level. As a result, the line width changes according to the irradiation time of the laser beam, and gradation expression can be performed. In the case of a 200-line screen, as shown in FIG. 11B, a triangular wave having a period of 200 lines is generated, and the laser beam is turned on when the level of this triangular wave similarly exceeds the image density level. In both the 400-line screen and the 200-line screen, gradation can be expressed by changing the line width according to the laser beam irradiation time. However, when powder toner is used as the color material, the granularity of the powder toner Due to the limitation of the nature, if a 400-line screen is used, sufficient gradation expression may not be achieved. Such a phenomenon can be said to be the same not only for powder toner but also for liquid toner and liquid ink.
[0005]
Therefore, when printing an image such as a photograph with a large color change, a 200-line screen is used to ensure sufficient gradation.
Furthermore, screens such as those shown in FIGS. 14D to 14F have been devised in order to improve tone reproduction stability and toner granularity reproduction. Such a screen becomes a complicated control circuit if only the pulse width modulation method of the laser beam using the triangular wave as described above is used. Therefore, after the input image data is converted in accordance with the screen, 200 This is realized by applying a pulse width modulation method at the time of line screen.
As described above, the host computer that generates the image data sends image data that matches the resolution of the printing apparatus to the printing apparatus, and a screen that matches the gradation expression of the printing apparatus is applied within the printing apparatus. Printing is realized.
[0006]
Incidentally, even if the image data from the host computer 101 is code data or raster image data, the raster image data needs to be temporarily stored in the buffer memory 103 for the following reason.
As shown in FIG. 13A or 13B, a medium for connecting the host computer 101 and the printing apparatus is a network such as Ethernet, a SCSI bus, Centronics, RS-232C serial communication, or the like. The upper limit of the transfer speed of these media is determined by the standard, but the buffer memory 103 is essentially unnecessary if it is sufficiently higher than the drawing speed of the printing unit 105.
However, in recent years, high speed and high quality have been demanded of printing apparatuses, and the drawing speed of the printing unit 105 has become extremely high. As a result, the transfer speed of the communication medium is higher than the drawing speed of the printing unit 105. It became low.
Further, when the printing unit 105 draws an image with a laser beam, once an activation command is given to the printing unit 105, even if the raster image data is not in time for drawing, the printing unit With the mechanism 105, the drawing operation cannot be stopped during the output of one page. If it is stopped, the paper may be discolored due to heat from the fixing unit, or image misalignment may occur between the stop time and the restart time due to the limit of drawing position alignment accuracy.
For these reasons, the buffer memory 103 is essential.
[0007]
As described above, whether the image data from the host computer 101 is code data or raster image data needs to be temporarily stored in the buffer memory 103. However, this capacity is printed with high speed and high quality. As many as required by the unit 105 are required. For example, when the printing unit 105 performs A4 size 400 dpi and full color (8 bits / color) printing of YMCK4 colors, the capacity of the buffer memory 103 is as follows.
3312 (dot) x 4677 (line) x 4 (color) ≒ 60 (Mbytes)
It becomes. For this reason, the cost for the memory becomes extremely high.
[0008]
Therefore, conventionally, compression processing has been used in order to keep the capacity of the buffer memory small.
Such compression processing is broadly classified into reversible compression such as run length compression and Lempel-Zip compression, and lossy compression such as JPEG. In the lossless compression, a technique for guaranteeing a certain compression rate has not been established so far, and rather, it may even exceed the original image data capacity. For this reason, a technique is employed in which the lossless compression is used to compensate for the worst compression rate and reduce the capacity of the buffer memory.
[0009]
[Problems to be solved by the invention]
However, in lossy compression, the image quality of image data and the compression rate are in a mutually contradictory relationship. That is, if the image quality is improved, the compression rate is deteriorated, while the image quality is deteriorated when the compression rate is increased. When JPEG compression is taken as an example, block distortion, mosquito noise, and the like appear in the decompressed image, and there is a problem that the image quality is worse than the original image.
Therefore, in the current printing apparatus, either the capacity of the buffer memory is reduced at the expense of the image quality, or the capacity of the buffer memory is increased by giving priority to the image quality.
The present invention has been made in view of the above-described background, and an object of the present invention is to provide an image processing apparatus capable of reducing the capacity of a buffer memory without degrading image quality. .
[0010]
[Means for Solving the Problems]
In order to solve the above-described problem, in the present invention, representative value calculation means for calculating a representative value according to a screen to be applied from image data, By the representative value calculation means First storage means for buffering the computed representative value; In the first storage means From the buffered representative value to the screen to be applied Multi-value raster image data Drawing image data generating means for generating A drawing means for drawing an image by performing pulse width modulation of a laser beam on the basis of the image density level of the multi-value raster image data generated by the drawing image data generating means; It is characterized by comprising.
[0011]
(Operation) According to the present invention, the representative value is calculated from the image data in accordance with the number of screen lines to be applied, and the representative value is buffered. Multi-value raster image data Are generated from the buffered representative values in accordance with the number of screen lines to be applied. Therefore, what is buffered is not the image data itself but a representative value according to the number of screen lines applied to the image data. For this reason, it is possible to suppress the necessary capacity in the first storage unit to be smaller than that of buffering image data as it is. further, Multi-value raster image data Since the screen is applied to enrich the color gradation expression, it is possible to suppress deterioration in image quality.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
<First Embodiment>
First, a first embodiment according to the present invention will be described. FIG. 1A is a block diagram illustrating a configuration of an image processing apparatus according to the present embodiment. In this figure, the host computer 101 outputs raster image data or code data via a medium such as Ethernet or SCSI. When the data output from the host computer 101 is code data described in PDL, the image forming unit 102 interprets the content and develops it into YMCK frame sequential type raster image data. Therefore, in this embodiment, raster image data for one dot is represented by 8 bits. The screen application representative value calculation unit 111 applies a screen suitable for the gradation expression capability of the printing unit 105, and calculates a representative value of raster image data according to the screen.
[0014]
Here, assuming that the resolution of the printing unit 105 is 400 dpi and the screen for maximum gradation reproduction is 200 lines, the screen application representative value calculation unit 111 calculates a representative value for 400 dpi raster image data. . Various types of calculation of the representative value can be considered. Here, as an example, the calculation of the average value of raster image data for two dots is used as the representative value. A configuration example of the screen applied representative value calculation unit 111 in this case is shown in FIG.
In FIG. 2, a latch circuit 1111 latches 8-bit raster image data with a clock obtained by dividing the system clock by two. Thereby, the raster image data latched by the latch circuit 1111 becomes every other dot. The adder 1112 adds the raster image data latched every other dot by the latch circuit 1111 and the unlatched raster image data. This addition result is 9 bits, but the lower 1 bit is discarded and only the upper 8 bits are used as the representative value. That is, an average value obtained by dividing the addition result by 2 is used as the representative value.
In addition to the above, the calculation of the representative value by the screen application representative value calculation unit 111 may be various, such as a calculation based on a primary calculation or a conversion using a lookup table.
[0015]
Now, referring back to FIG. 1, the band buffer 103 stores the representative value calculated by the screen application representative value calculation unit 111. The screen applied drawing image data generation unit 112 converts the representative value read from the buffer memory 103 into raster image data that matches the resolution of the printing unit 105. Here, the configuration of the screen application drawing image data generation unit 112 corresponds to the screen application representative value calculation unit 111, and FIG. 3 shows a configuration corresponding to the example of FIG.
In this figure, a latch circuit 1121 latches a representative value with a clock obtained by dividing a video clock synchronized with the drawing operation of the printing unit 105 by two. As a result, the representative value on the 200-line screen is converted into 400 dpi raster image data, which is the resolution of the printing unit 105.
[0016]
In this configuration, the representative value is calculated by the screen application representative value calculation unit 111 from the input or developed raster image data according to the 200-line screen suitable for the gradation expression capability of the printing unit 105. When one page of the representative value is stored in the buffer memory 103, the printing unit control mechanism unit 113 activates the printing unit 105, and the representative value is read from the buffer memory 103. The read representative value is converted into raster image data having the resolution of the printing unit 105 by the screen application drawing image data generation unit 112 and supplied to the printing unit 105, and the printing unit 105 determines the raster image data based on the raster image data. One page of image output is performed.
[0017]
Here, the necessary capacity in the buffer memory 103 is half that of the capacity for storing 400 dpi raster image data as it is because the stored representative value corresponds to the 200-line screen. For example, as described above, when full-color printing with A4 size of 400 dpi and YMCK four colors is performed, the capacity of the buffer memory 103 can be reduced to about 30 (M bytes), which is half.
[0018]
Even when the printing unit 105 uses the raster data converted from the representative value in this way and performs gradation expression by pulse width modulation of the laser beam as described in the prior art, image quality deterioration does not occur. That is, conventionally, as shown in FIG. 11B, when raster image data having a resolution of 400 dpi is input and the level of the triangular wave that is the reference wave exceeds the density level indicated by the raster image data, the laser beam However, in this embodiment, since the representative value is determined, the output of the laser beam is as shown in FIG. Here, when both are compared, it can be seen that the irradiation time of the laser beam is not changed, but only the irradiation position is different. In the first embodiment, the average value of two dots is used in determining the representative value, but even in this case, the irradiation time of the laser beam is unchanged as compared with the prior art.
Further, regarding the maximum difference in beam position, when the resolution of the raster data image data is 400 dpi, 1/800 (as shown in FIG. 12B, compared with the example of the related art shown in FIG. Inch), that is, 0.03 (mm) at most. This amount of deviation cannot be discriminated with the naked eye, so it can be said that substantial image degradation does not occur.
[0019]
In the first embodiment, as shown in FIG. 1B, the representative value calculated by the screen application representative value calculation unit 111 is compressed by the compression unit 121 and stored in the buffer memory 103, and thereafter The compressed representative value may be expanded by the expansion unit 122. In this case, any compression method may be used regardless of reversible or irreversible.
[0020]
Second Embodiment
Next, a second embodiment according to the present invention will be described. FIG. 4 is a block diagram illustrating a configuration of an image processing apparatus according to the second embodiment. The image processing apparatus shown in this figure is basically the same as that of the first embodiment in FIG. 1 except that the screen application representative value calculation unit 211 and the screen application drawing image data generation unit 212 are respectively stored in the screen storage unit 213. It differs from the first embodiment in that representative value calculation and raster image data conversion are performed using the stored screen information.
Therefore, this difference will be mainly described below.
[0021]
As shown in FIG. 5B, when the screen storage unit 213 applies, for example, a screen having a pattern of 3 dots × 3 dots as shown in FIG. 5A as the screen in the present embodiment. Information of “0” and “1” is stored. In this case, the configurations of the screen application representative value calculation unit 211 and the screen application drawing image data generation unit 212 are as shown in FIGS. 6 and 7, respectively.
First, in FIG. 6, the screen application representative value calculation unit 211 has a screen unit of 3 dots × 3 dots, so two sets of line buffers 1001 to 1003 and 1004 to 1006 each having a capacity of 3 lines in total. Is prepared. That is, raster image data for three lines is stored by the line buffers 1001 to 1003 (1004 to 1006). Here, two sets of line buffers are prepared in order to prevent the processing speed from being lowered by alternately switching the set of line buffers for storing raster image data by the selectors 1011 to 1013. Each of the latch circuits 1021 to 1029 latches the raster image data via the selector with the system clock. In other words, if one line is viewed, raster image data for three dots can be obtained.
The adder circuit 1030 adds raster image data, that is, raster image data for a total of 9 dots of 3 dots × 3 dots, to each of 3 dots for 3 lines latched by the latch circuits 1021 to 1029.
[0022]
On the other hand, the adding circuit 1041 adds screen information composed of 3 dots × 3 dots stored in the screen storage unit 213. In the example shown in FIG. 5B, the addition result is “5 (decimal notation)”. The division circuit 1042 divides the addition result by the addition circuit 1030 by the addition result by the addition circuit 1041. This division result is stored in the buffer memory 103 as a representative value in the screen application representative value calculation unit 211.
[0023]
Next, in FIG. 7, the screen application drawing image data generation unit 212 converts the representative value calculated by the screen application representative value calculation unit 211 having the configuration of FIG. 6 into raster image data that matches the resolution of the printing unit 105. To do.
In FIG. 7, the representative value is supplied as a clock obtained by dividing the video clock synchronized with the drawing operation of the printing unit 105 by 3 and is input to the selectors 1101 to 1103, respectively. The selectors 1101 to 1103 select one line of the first to third lines of the screen information stored in the screen storage unit 213 as selection information. When the screen information is “1”, the selectors 1101 to 1103 are representative. While the value is selected, zero data is selected when the screen information is “0”. The selector 1104 selects the three selection results of the selectors 1101 to 1103 in order at the cycle of the video clock. As a result, the representative value corresponding to the screen pattern is converted into 400 dpi raster image data, which is the resolution of the printing unit 105.
[0024]
In this configuration, the representative value is calculated from the raster image data input or developed by the screen application representative value calculation unit 211 according to the screen pattern stored in the screen storage unit 213. When one page of the representative value is stored in the buffer memory 103, the printing unit control mechanism unit 113 activates the printing unit 105, and the representative value is read from the buffer memory 103. The read representative value is converted into raster image data having the resolution of the printing unit 105 by the screen application drawing image data generation unit 212 and supplied to the printing unit 105, and the printing unit 105 determines the raster image data based on the raster image data. One page of image output is performed.
[0025]
As a result, the necessary capacity in the buffer memory 103 corresponds to the screen pattern whose representative value stored in the screen storage unit 213 is stored, so that the capacity required for storing 400 dpi raster image data as it is is compared. Thus, the reciprocal of the number of dots constituting the screen pattern can be reduced. For example, assuming that A4 size is 400 dpi and full color printing of 4 colors of YMCK, assuming that the number of dots constituting the screen pattern is 9 as in this embodiment, the capacity of the buffer memory 103 is reduced to 1/9. 6.7 (M bytes).
[0026]
In the second embodiment, as in the example shown in FIG. 1B, the representative value calculated by the screen application representative value calculation unit 211 is compressed by the compression unit and stored in the buffer memory 103. Thereafter, the compressed representative value may be expanded by the expansion unit. The same applies to the compression method regardless of whether it is reversible or irreversible.
[0027]
<Third Embodiment>
Next, a third embodiment according to the present invention will be described. FIG. 8 is a block diagram illustrating a configuration of an image processing apparatus according to the third embodiment. The image processing apparatus shown in this figure is basically the same as that of the first embodiment shown in FIG. 1, except that tag bits for selecting a screen to be applied are added to the input or expanded raster image data, and the screen The application representative value calculation unit 311 and the screen applied drawing image data generation unit 312 are different from the first embodiment in that the calculation of the representative value and the conversion of the raster image data are performed using the screens that the tag bits mean. .
Therefore, this difference will be mainly described below.
[0028]
Since the host computer 101 or the image forming unit 102 selects a 400-line screen for raster image data such as a font (character) part or a graphic (line drawing) part with little change in color gradation, the value is “0”. On the other hand, a tag bit with a value of “1” is added to select a 200-line screen for an image portion such as a photograph where the color change is significant. The determination of the font part, the graphic part, or the image part may be performed manually by the user himself or may be automatically designated by raster analysis of the raster image data.
[0029]
The screen application representative value calculation unit 311 calculates a representative value in accordance with the screen indicated by the tag bits. For example, when the resolution of the printing unit 105 is 400 dpi, the screen application representative value calculation unit 311 matches the resolution and the screen line number if the tag bit value is “0”, which means application of a 400-line screen. Therefore, while the supplied raster image data is used as a representative value as it is, if the value of the tag bit is “1” which means application of a 200-line screen, the number of screen lines is ½ with respect to the resolution. The representative value is obtained by the configuration of FIG. 2 in one embodiment.
In addition, since it is necessary to discriminate | determine in the next screen application drawing image data generation part 312 about the screen applied, the screen application representative value calculating part 311 attaches the said tag bit to the calculated representative value.
[0030]
The screen application drawing image data generation unit 312 converts the representative value into raster image data in accordance with the screen indicated by the tag bit. For example, if the tag bit value is “0”, the screen application drawing image data generation unit 312 uses the supplied representative value as the raster image data as it is, while if the tag bit value is “1”, According to the configuration of FIG. 3 in the first embodiment, the supplied representative value is converted into 400 dpi raster image data.
[0031]
In this configuration, the screen applied representative value calculation unit 311 calculates the representative value in accordance with the screen indicated by the tag bits. When the representative value is stored for one page in the buffer memory 103 together with the tag bit, the printing unit control mechanism unit 113 starts the printing unit 105 and reads the representative value from the buffer memory 103. The read representative value is converted into raster image data in accordance with the tag bit by the screen application drawing image data generation unit 312 and supplied to the printing unit 105, and the printing unit 105 uses the raster image data based on the raster image data. The image output for the page is performed.
[0032]
Here, the necessary capacity in the buffer memory 103 differs depending on the ratio of the image portion to the raster image data, and cannot be said to be reduced to a certain extent. However, when the ratio of the image portion is, for example, half, the image portion can be halved. Therefore, when viewed as a whole, the capacity is 3/4 compared to the capacity for storing raster image data as it is. Can be reduced. For example, if full-color printing of A4 size at 400 dpi and YMCK 4 colors is performed, if the ratio of the image portion is half, the capacity of the buffer memory 103 can be reduced to about 45 (Mbytes) of 3/4. it can.
Furthermore, in the third embodiment, unlike the first embodiment, the number of screen lines to be applied is selected according to the image portion. For example, 400 lines are used for a font portion and a graphic portion with little color gradation change. Since the screen and the 200-line screen are selected for the image portion where the color gradation changes drastically, it is possible to draw with clear and rich color gradation expression.
[0033]
<Fourth embodiment>
Next, a fourth embodiment according to the present invention will be described. FIG. 9 is a block diagram illustrating a configuration of an image processing apparatus according to the fourth embodiment. The image processing apparatus shown in this figure is basically the same as that of the first embodiment shown in FIG. 1, except that tag bits for selecting a screen to be applied are added to the input or expanded raster image data. The screen application representative value calculation unit 411 and the screen application drawing image data generation unit 412 respectively read the screen information indicated by the tag bits from the screen storage unit 413 and perform the calculation of the representative value and the conversion of the raster image data. This is different from the first embodiment.
Therefore, this difference will be mainly described below.
[0034]
The host computer 101 or the image forming unit 102 adds a tag bit (2 bits) for selecting a screen according to the type of image data. Here, the basic pattern of the screen includes, for example, 3 dots × 3 dots as shown in FIGS. 10A to 10C, and any one is selected according to the type of image. The determination of the image type may be performed manually by the user himself / herself, or may be automatically specified by raster image data or the like.
[0035]
As shown in FIGS. 10A to 10C, the screen storage unit 413 stores “0” and “1” information corresponding to the basic pattern for each pattern.
The screen applied representative value calculation unit 411 calculates a representative value from the raster image data with the configuration shown in FIG. The screen information used in this case is read from the screen storage unit 413 corresponding to the tag bit added to the raster data.
In the next screen application drawing image data generation unit 412, it is necessary to determine the screen to be applied, so the screen application representative value calculation unit 411 attaches the tag bit to the calculated representative value.
The screen applied drawing image data generation unit 412 converts the representative value into raster image data in accordance with the screen information indicated by the tag bits with the configuration shown in FIG. The screen information used in this case is read from the screen storage unit 413 corresponding to the tag bit added to the raster data, as with the screen application representative value calculation unit 411.
[0036]
In this configuration, the screen application representative value calculation unit 411 calculates a representative value according to the screen information indicated by the tag bits. When the representative value is stored for one page in the buffer memory 103 together with the tag bit, the printing unit control mechanism unit 113 starts the printing unit 105 and reads the representative value from the buffer memory 103. The read representative value is converted by the screen application drawing image data generation unit 412 into raster image data in accordance with the screen information indicated by the tag bit, and is supplied to the printing unit 105, and the printing unit 105 performs the raster image data. The image for one page is output based on the above.
[0037]
As a result, the necessary capacity in the buffer memory 103 corresponds to the screen pattern in which the stored representative value is stored in the screen storage unit 413, as in the second embodiment, so that 400 dpi raster image data can be stored. Compared with the capacity for storing the data as it is, it can be reduced to the reciprocal of the number of dots constituting the screen pattern. That is, when full-color printing of A4 size of 400 dpi and YMCK 4 colors is performed and the number of dots constituting the screen pattern is 9 dots as in this embodiment, the capacity of the buffer memory 103 is reduced to 1/9. 6.7 (M bytes).
Furthermore, according to the fourth embodiment, since an appropriate screen can be selected for various images, image quality deterioration such as so-called moire that is peculiar to images is prevented, and the maximum gradation is realized in the printing unit 105. can do.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the capacity of the buffer memory without degrading the image quality.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a screen applied representative value calculation unit in the present embodiment.
FIG. 3 is a block diagram illustrating a configuration of a screen application drawing image data generation unit according to the present embodiment.
FIG. 4 is a block diagram showing a configuration of an image processing apparatus according to a second embodiment of the present invention.
5A is a diagram illustrating a basic pattern of a screen applied to the present embodiment, and FIG. 5B is a diagram illustrating the content of the basic pattern stored in the screen storage unit in the present embodiment. is there.
FIG. 6 is a block diagram showing a configuration of a screen application representative value calculation unit in the present embodiment.
FIG. 7 is a block diagram illustrating a configuration of a screen application drawing image data generation unit according to the present embodiment.
FIG. 8 is a block diagram showing a configuration of an image processing apparatus according to a third embodiment of the present invention.
FIG. 9 is a block diagram showing a configuration of an image processing apparatus according to a fourth embodiment of the present invention.
FIGS. 10A to 10C are diagrams showing the relationship between the basic pattern of the screen applied to the present embodiment and the content of the basic pattern stored in the screen storage unit, respectively.
11A is a diagram showing a relationship among an image density level, a triangular wave (reference wave), and laser irradiation when a conventional 400-line screen is applied, and FIG. 11B is a conventional 200-line screen. Is a diagram showing a conventional relationship between an image density level, a triangular wave, and laser irradiation in the case of applying the image, and (c) of FIG. It is a figure which shows a relationship.
12A is a diagram showing a conventional relationship between an image density level, a triangular wave, and laser irradiation when a 200-line screen is applied in the past, and FIG. 12B is a diagram showing laser irradiation in the present invention. It is a figure which shows the largest difference amount with the past.
FIG. 13A is a block diagram showing a configuration of a conventional image processing apparatus when data from a host computer is described in PDL, and FIG. 13B is a block diagram showing data from the host computer. It is a block diagram which shows the structure of the conventional image processing apparatus in the case of raster image data.
FIGS. 14A to 14F are diagrams illustrating examples of screens. FIG.
[Explanation of symbols]
103... Buffer memory (first storage means), 111, 211, 311, 411... Screen applied representative value calculating means (representative value calculating means), 112, 212, 312, 412. Means (drawing image data generation means), 213, 413... Screen storage unit (second storage means)

Claims (6)

Representative value calculating means for calculating a representative value according to the screen to be applied from the image data;
First storage means for buffering the representative value calculated by the representative value calculating means ;
Drawing image data generation means for generating multi-value raster image data in accordance with the screen to be applied from the representative values buffered in the first storage means ;
Image processing comprising: a drawing means for drawing an image by performing pulse width modulation of a laser beam based on an image density level of multi-value raster image data generated by the drawing image data generating means apparatus. The representative value calculation means is configured to collect the image data in units of the number of pixels corresponding to the basic structure of the screen to be applied, and obtain a representative value thereof.
The image processing apparatus according to claim 1, wherein the drawing image data generation unit generates multi-value raster image data corresponding to a basic structure of a screen to be applied. The invention according to claim 1, further comprising second storage means for storing a basic pattern of a screen to be applied,
The representative value calculation means aggregates the image data in units of the number of pixels corresponding to the unit structure of the basic pattern, and obtains a representative value thereof.
The drawing image data generating means generates multi-value raster image data corresponding to the stored unit structure of the basic pattern. The invention according to claim 1, further comprising separation means for separating the image portion indicated by the image data for each content,
The representative value calculating means changes the number of pixels corresponding to the basic structure of the screen to be applied according to the content of the separated image portion, and aggregates the image data in units of the number of pixels. Find the representative value
The drawing image data generation means generates multi-value raster image data corresponding to the applied basic structure of the screen. In the invention of claim 1, further, a second storage means for storing a plurality of basic patterns of the screen to be applied;
Separating means for separating the image portion indicated by the image data for each content,
The representative value calculation means selects a screen to be applied according to the contents of the image portion, aggregates the image data in units of the number of pixels corresponding to the unit structure of the basic pattern of the selected screen, and represents the representative Find the value
The drawing image data generating means generates multi-value raster image data corresponding to the unit structure of the selected basic pattern. When the representative value calculating means calculates the representative value from the image data according to the screen to be applied, a representative value calculating step;
When the first storage means buffers the representative value calculated by the representative value calculation means, a first storage step;
A drawing image data generation unit for generating multi-value raster image data in accordance with a screen to be applied, from a representative value buffered in the first storage unit;
A drawing step in which the drawing means draws an image by performing pulse width modulation of the laser beam based on the image density level of the multi-value raster image data generated by the drawing image data generating means.
An image processing method comprising:

Images