JP2008087199A - Data generating method, control unit, and light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data generating method which can reduce the amount of data for being transferred to an optical head, a control unit, and a light-emitting device. <P>SOLUTION: When image data Di are supplied, a correction operation portion 12 of a host controller 10 generates light emission amount data Do1 in accordance with correction data Dh which are read out from a correction value memory 11. A compressive encoding portion 14 logarithmizes the light emission amount data, quantizes them through a prescribed quantization step S, and generates compressed light emission amount data Db by encoding a value after quantization, so as to supply them to a decoding decompression processing portion 21. The processing portion 21 acquires light emission amount data Do2, corresponding to a supplied code, from an LUT 22, and supplies them a constant current driver 23. The constant current driver 23 drives a light-emitting element 24 in accordance with the supplied light emission amount data Do2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for compressing data to be transmitted to an optical head configured by arranging a plurality of light emitting elements.

  A printer as an image forming apparatus uses a light emitting device in which a large number of light emitting elements are arranged in an array as a head unit for forming an electrostatic latent image on an image carrier such as a photosensitive drum. The head portion is often composed of a single line in which a plurality of light emitting elements are arranged along the main scanning direction.

In addition, a method for realizing high-speed printout by transmitting compressed print image data from an information processing apparatus to a printer is known (see, for example, Patent Document 1). Also, an encoding method is known that reduces quantization error in small value data by logarithmically transforming data such as speech and the like.
Japanese Patent Laid-Open No. 9-244832 (FIGS. 1 and 6)

  As the above light emitting element, an organic light emitting diode (hereinafter simply referred to as “OLED”) element is known. A light emitting element such as an OLED element has a light emission amount, specifically a luminous intensity, which varies depending on the magnitude of the drive current. However, in a head portion in which a plurality of light emitting elements as described above are arranged in a line, variations in manufacturing are possible. As a result, there is a problem in that the luminous intensity varies depending on the individual light emitting elements even when the magnitude of the drive current is the same. For this reason, data for correcting the driving current is stored for each light emitting element, and the driving current of the light emitting element is finely adjusted to compensate for variations in luminous intensity.

  However, in order to perform such compensation, it is necessary to supply correction data to the head unit, which increases the amount of data to be transferred. In the method disclosed in Patent Document 1 described above, variations in luminous intensity of individual light emitting elements are not taken into consideration, and therefore no measures are taken. The present invention has been made in view of such circumstances, and an object of the present invention is to reduce the amount of data transferred to the head unit. Further, if the logarithmized data is simply quantized, an approximation error occurs, and there is room for improvement in terms of print quality.

  In order to solve this problem, a data generation method according to the present invention generates data to be transmitted between a control device and an optical head including a plurality of light emitting elements, and includes a light amount of the plurality of light emitting elements. Based on correction data (for example, Dh in FIG. 1) and image data (for example, Di in FIG. 1), a predetermined calculation is performed to obtain M (M is a natural number) values. The light emission amount data that can be taken (for example, Do1 in FIG. 1) is generated, the light emission amount data is logarithmically converted to generate logarithmic conversion data (for example, Dlog in FIG. 4), and the logarithmic conversion data is quantized. The quantization step is determined so that the number of data that can be taken is N (N is a natural number, N <M), and the logarithmic transformation data is quantized to generate quantized data (for example, Da in FIG. 4). N of the quantized data Compressed data (e.g., Db in FIG. 4) by assigning a sign value and generates a.

  According to the present invention, since the compressed data to be transmitted to the optical head is generated based on the corrected light emission amount data, it is not necessary to correct the image data based on the correction data in the optical head. Further, since the corrected light emission amount data is logarithmically converted, a quantization error can be reduced in a region with a small gradation. Furthermore, since the quantization step is determined so that the value that can be obtained by quantization is reduced, the amount of compressed data can be reduced. In addition, when the amount of compressed data transmitted to the optical head is limited by the transfer speed, compressed data that is compressed within the allowable transfer speed can be generated by adjusting the quantization step. .

In the above-described data generation method, the image data is i (i is a natural number) bit data, the correction data is j (j is a natural number) bit data, and the predetermined calculation is performed when M is M <M < 2 ^{(i + j)} is preferable. In this case, the data can be compressed even in the process of generating the light emission amount data.

In the data generation method described above, when the number of bits of the compressed data is K (K is a natural number), 2 ^K > N, and the quantized data is assigned to N of the 2 ^K compressed data. assignment, wherein the assignment of 2 ^K -M pieces without the quantized data to the compressed data preferably including those frequency components higher than the bit pattern with the bit pattern of the compressed data with a assigned. When the inversion period of the bit pattern is short, a high frequency component is included. When such compressed data is transmitted, unnecessary radiation may occur. Furthermore, power consumption increases. According to the present invention, since the bit pattern without the allocation of the quantized data includes the one having a higher frequency component than all the bit patterns with the allocation, the unnecessary radiation is suppressed and the power consumption is reduced. Can do.

In the data generation method described above, when the number of bits of the compressed data is K (K is a natural number), 2 ^K > N, and the quantized data is assigned to N of the 2 ^K compressed data. assignment, wherein the 2 ^K -M number assignment is not the quantized data to the compressed data preferably including those frequency components lower than the bit pattern with the bit pattern of the compressed data with a assigned. When the bit pattern inversion period is long, low frequency components are included. Such a bit pattern is not easy to transmit the waveform accurately because the DC balance is broken. According to the present invention, the bit pattern without the allocation of the quantized data includes the bit pattern having a lower frequency component as compared with all the allocated bit patterns, so that the DC balance can be improved.

  In the data generation method described above, when N values that can be taken by the quantized data are arranged in the order of occurrence frequency, the compressed data is assigned to the compressed data corresponding to the quantized data having a lower occurrence frequency. It is preferable to set so that the frequency component of the bit pattern is away from the center of the frequency distribution. In this case, since the quantized data having a low occurrence frequency is allocated so as to be away from the center of the frequency distribution of the bit pattern, the bit pattern of the compressed data includes a bit pattern having a low frequency component and a bit pattern having a high frequency component. Can be reduced in frequency. As a result, the DC balance can be improved.

  Next, a control device according to the present invention controls an optical head including a plurality of light emitting elements, and is based on correction data and image data for correcting variations in light amounts of the plurality of light emitting elements. A correction calculation unit that performs predetermined calculation to generate light emission amount data that can take M (M is a natural number) values, and a logarithmic conversion unit that generates logarithmic conversion data by logarithmically converting the light emission amount data. The quantization step is determined so that the number of data obtained by quantizing the logarithmically transformed data can be N (N is a natural number, N <M), and the logarithmically transformed data is quantized to obtain quantized data. And a coding unit that assigns a code to each of the N values of the quantized data, generates compressed data, and outputs the compressed data to the optical head.

  According to the present invention, since the compressed data to be transmitted to the optical head is generated based on the corrected light emission amount data, it is not necessary to correct the image data based on the correction data in the optical head. Further, since the corrected light emission amount data is logarithmically converted, a quantization error can be reduced in a region with a small gradation. Furthermore, since the quantization step is determined so that the value that can be obtained by quantization is reduced, the amount of compressed data can be reduced. In addition, when the amount of compressed data transmitted to the optical head is limited by the transfer speed, compressed data that is compressed within the allowable transfer speed can be generated by adjusting the quantization step. .

Further, in the above-described control device, when the number of bits of the compressed data is K (K is a natural number), 2 ^K > N, and the encoding unit sets N of 2 ^K compressed data. allocating the quantized data, the assignment of 2 ^K -M pieces without the quantized data to the compressed data, those frequency components higher than the bit pattern with the bit pattern of the compressed data with a assigned It is preferable to include. According to the present invention, since the bit pattern without the allocation of the quantized data includes the one having a higher frequency component than all the bit patterns with the allocation, the unnecessary radiation is suppressed and the power consumption is reduced. Can do.

Further, in the above-described control device, when the number of bits of the compressed data is K (K is a natural number), 2 ^K > N, and the encoding unit sets N of 2 ^K compressed data. allocating the quantized data, wherein the 2 ^K -M number assignment is not the quantized data to the compressed data, those frequency components lower than the bit pattern with the bit pattern of the compressed data with a assigned It is preferable to include. According to the present invention, the bit pattern without the allocation of the quantized data includes the bit pattern having a lower frequency component as compared with all the allocated bit patterns, so that the DC balance can be improved.

  Further, in the control device described above, when the pre-encoding unit arranges the N values that can be taken by the quantized data in order of occurrence frequency, the code assignment of the compressed data is performed for quantized data having a lower occurrence frequency. It is preferable that the frequency component of the bit pattern of the corresponding compressed data is set so as to be away from the center of the frequency distribution. In this case, since the quantized data having a low occurrence frequency is allocated so as to be away from the center of the frequency distribution of the bit pattern, the bit pattern of the compressed data includes a bit pattern having a low frequency component and a bit pattern having a high frequency component. Can be reduced in frequency. As a result, the DC balance can be improved.

  Further, a control device according to the present invention controls an optical head including a plurality of light emitting elements, and based on correction data and image data for correcting variations in the amount of light of the plurality of light emitting elements, A correction calculation unit that generates a light emission amount data that can take M (M is a natural number) values by executing a predetermined calculation, and N (N is a natural number, N <M) values of the light emission amount data. A compression unit for converting into compressed data to be obtained, and the compression unit includes a storage unit that stores each value of the light emission amount data and each value of the compressed data in association with each other, and is generated by the correction calculation unit. The compressed data is generated by referring to the storage unit based on the light emission amount data, and the compressed data stored in the storage unit logarithmically converts the light emission amount data to generate logarithmic conversion data, Quantize the logarithmic transformation data The quantization step is determined so that the number of data that can be obtained is N, the logarithmically transformed data is quantized to generate quantized data, and a code is assigned to each of the N values of the quantized data. It is generated. According to the present invention, since the storage unit is provided, it is not necessary to execute processes such as logarithmic transformation, quantization, and encoding. As a result, high-speed processing is possible with a simple configuration.

  The control device according to the present invention controls an optical head including a plurality of light emitting elements, and the plurality of light emitting elements are used for image data designating a gradation to be displayed by each of the plurality of light emitting elements. A correction compression unit (for example, 16 in FIG. 15) that performs processing for correcting variation in the light amount of the element and generates compressed data subjected to processing for compressing the data amount, and variation in light amount of the plurality of light emitting elements A correction data storage unit (for example, 11 in FIG. 15) that stores correction data for correcting the image data, and the correction compression unit includes each value of the image data, each value of the correction data, and each of the compressed data. A compressed data storage unit that stores each value in association with each other, and refers to the compressed data storage unit based on the image data and the correction data read from the correction data storage unit; Generating compressed data, the compressed data generating a light emission amount data that can take M (M is a natural number) values by executing a predetermined calculation based on the correction data and the image data; Logarithmically transform the light emission amount data to generate logarithmically transformed data, determine a quantization step so that the number of data obtained by quantizing the logarithmically transformed data is N, and quantize the logarithmically transformed data. Quantized data is generated, and a code is assigned to each of the N values of the quantized data. According to the present invention, since the compressed data storage unit is provided, it is not necessary to execute processing such as correction calculation, logarithmic transformation, quantization, and encoding. As a result, high-speed processing is possible with a simple configuration.

  Next, a light-emitting device according to the present invention includes a control device and an optical head including a plurality of light-emitting elements, and the control device corrects variations in light amounts of the plurality of light-emitting elements. Based on the correction data and the image data, a predetermined calculation is performed to generate light emission amount data that can take M (M is a natural number) values, and the light emission amount data is logarithmically converted. A logarithmic conversion unit that generates logarithmically transformed data, and a quantization step so that the number of data obtained by quantizing the logarithmically transformed data can be N (N is a natural number, N <M), A quantization unit that quantizes logarithmically transformed data to generate quantized data; and an encoding unit that assigns a code to each of the N values of the quantized data to generate compressed data and outputs the compressed data to the optical head. And the optical head receives A decoding / decompression unit (for example, 21 in FIG. 1) that decompresses the compressed data and decodes the light emission amount data, and a drive unit (for example, a drive unit that drives the plurality of light emitting elements based on the decoded light amount data) And 23) of FIG.

  According to the present invention, since the compressed data to be transmitted to the optical head is generated based on the corrected light emission amount data, it is not necessary to correct the image data based on the correction data in the optical head, and the compressed data is expanded. The light emission amount data can be decoded by Further, since the corrected light emission amount data is logarithmically converted, a quantization error can be reduced in a region with a small gradation. Furthermore, since the quantization step is determined so that the value that can be obtained by quantization is reduced, the amount of compressed data can be reduced. In addition, when the amount of compressed data transmitted to the optical head is limited by the transfer speed, compressed data that is compressed within the allowable transfer speed can be generated by adjusting the quantization step. .

A preferred embodiment of the present invention will be described with reference to the drawings.
<A. Configuration of Embodiment>
FIG. 1 is a block diagram showing a configuration of a main part of a light emitting device according to an embodiment of the present invention. The light emitting device 100 is used for forming an electrostatic latent image in a printing apparatus such as a printer. As shown in this figure, the light emitting device 100 includes a host controller 10 to which image data Di (tone data for each print dot) of a print image is supplied, and light emission amount data from the host controller 10. And an optical head 20 to be driven.

  The host controller 10 includes a correction value memory 11 in which correction data Dh is stored, a correction calculation unit 12 that corrects the image data Di according to the correction data Dh to generate the light emission amount data Do1, and compresses the light emission amount data Do1. And a compression encoding unit 14 that encodes and outputs compressed light emission amount data Db. The compressed light emission amount data Db is transmitted to the optical head 20 in a parallel format.

  The optical head 20 also includes a decoding / decompression processing unit 21 that decodes and expands the compressed light emission amount data Db received from the host controller 10, and a constant current driver that generates a drive current according to the expanded light emission amount data Do. 23 and a light emitting element 24 composed of, for example, an organic light emitting diode (hereinafter simply referred to as “OLED”) element. Note that the decryption / decompression processing unit 21 includes an LUT 22 that stores the compressed light emission amount data Db and the light emission amount data Do2 in association with each other.

  In the optical head 20, a plurality of (for example, n) light emitting elements 24 are arranged in a line. Even when the same driving current is supplied, the luminous intensity of each light emitting element 24 is different due to variations in manufacturing. For this reason, in the light emitting device 100, the correction data Dh of each light emitting element 24 is stored in the correction value memory 11, and the correction calculation unit 12 generates the light emission amount data Do1 based on the image data Di and the correction data Dh. The light intensity of each light emitting element 24 is corrected by generating and driving the light emitting element 24 according to this. In other words, the correction data Dh is determined so that the variation in luminous intensity for each light emitting element 24 can be corrected.

  FIG. 2 illustrates the correction data Dh stored in the correction value memory 11. The correction data Dh is set in accordance with the light emission characteristics of the light emitting element 24 measured in advance after the manufacture of the optical head 20 or the like. In this example, the image data Di has 16 gradations (4 bits) and is corrected by 6 bits (64 values) in a range of about −20% to + 5% with respect to the reference light amount for each of the n light emitting elements 24. The case where data Dh can be set is shown.

When the image data Di is supplied from the outside, the correction calculation unit 12 acquires the correction data Dh corresponding to the light emitting element 24 at the printing position of the image data Di from the correction value memory 11, and for example, the following equation (1) ), The light emission amount data Do1 corresponding to the image data Di is obtained and supplied to the compression encoding unit 14.
Do1 = (0.25 × Dh + 52.25) × Di (1)

FIG. 2 shows the value of the light emission amount data Do1 that can be generated from the combination of the 4-bit image data Di and the 6-bit correction data Dh. The light emission amount data Do1 is 10-bit data. FIG. 3 is a graph showing the light emission amount data Do corresponding to the image data Di. As shown in these figures, the value of the light emission amount data Do1 includes unused values such as 1 to 52 and 69 to 104, for example. This is because “52.25” is given as an offset by the above-described equation (1). In addition, there is a portion where the same light emission amount data Do1 is overlapped. In this example, there are only 674 values of the light emission amount data Do1, and encoding with 10 bits that can represent 1024 is wasteful. That is, when the light emission amount data Do1 has M values, the image data Di is i (i is a natural number) bits, and the correction data Dh is j (j is a natural number) bits, the calculation of Expression (1) is executed. Then, M <2 ^{(i + j)} .

  For this reason, in the light emitting device 100, the host controller 10 side compresses and encodes the light emission amount data Do1 in 256 ways, and transfers it to the optical head 20 as 8-bit compressed light emission amount data Db. Do1 is restored. Specifically, the compression encoding unit 14 executes this process. The compression encoding unit 14 includes an LUT 15. The LUT 15 stores each value of the light emission amount data Do1 and each value of the compressed data Db in association with each other. The compression encoding unit 14 refers to the LUT 15 based on the light emission amount data Do1, and generates compressed data Db.

Note that the compression encoding unit 14 may generate the compressed data Db by arithmetic processing without using the LUT 15. In this case, the compression encoding unit 14 is configured as shown in FIG. The compression encoding unit 14 performs compression encoding in three steps: 1) logarithmic conversion, 2) quantization, and 3) encoding. The logarithmic conversion unit 141 performs logarithmic conversion on the light emission amount data Do1 (10 bits) supplied from the correction calculation unit 12 to generate logarithmic conversion data Dlog. This is done to reduce the relative quantization error at small values. Next, the quantization unit 142 quantizes the logarithmically transformed data Dlog in a quantization step S set in advance as will be described later, and generates quantized data Da. The quantized data Da is 10-bit data, but the quantization step S is set so that the total number of possible values is 256. Next, the encoding unit 143 converts the quantized data Da into 8-bit compressed light emission amount data Db. That is, although the quantized data Da is expressed by 10 bits, it has a jump value, which is converted into compressed light emission amount data Db from “0” to “255” and output. For example, the encoding unit 143 may be configured by a lookup table stored in association with 10-bit quantized data Da and 8-bit compressed light emission amount data Db.
FIG. 5 shows a relationship between the light emission amount data Do1 and the compressed light emission amount data Db, which are inputs to the compression encoding unit 14. As shown in this figure, 674 kinds of light emission amount data Do1 are compression-encoded into 256 kinds of compressed light emission amount data Db. In the LUT 15 described above, for example, as shown in FIG. 5, light emission amount data Do1 and compressed light emission amount data Db are stored in association with each other.

  Next, in the optical head 20, the LUT 22 stores 8-bit compressed light emission amount data Db and 10-bit light emission amount data Do2 in association with each other. FIG. 6 shows the stored contents of the LUT 22. When the compressed light emission amount data Db is supplied from the compression encoding unit 14, the decoding / decompression processing unit 21 refers to the LUT 22 to obtain the light emission amount data Do2 corresponding to the value of the compressed light emission amount data Db. This is supplied to the current driver 23. The constant current driver 23 drives the light emitting element 24 according to the supplied light emission amount data Do2. Thereby, the light emitting element 24 is driven in accordance with the light emission amount data Do1 corrected for each light emitting element 24 in the correction calculation unit 12, and the variation in luminous intensity for each light emitting element 24 is corrected.

<B. Quantization step decision processing>
FIG. 7 is a flowchart showing a process for determining the quantization step S described above. This processing is executed in advance by an external information processing apparatus or the like according to a calculation formula for obtaining the number of bits of the image data Di, the number of bits of the correction data Dh, and the light emission amount data Do1, and the obtained quantization step S is hosted. The data is stored in a nonvolatile memory or the like in the controller 10.

  In this process, first, all possible values of the image data Di and the correction data Dh are put in the calculation formula of the given light emission amount data Do1, and all of the light emission amount data Do1 that can be obtained (the above-described figure). (Correction calculation table corresponding to 2) is obtained (S1). Next, the light emission amount data Do1 in the obtained correction calculation table is logarithmically converted (S2). Thereafter, an optimum quantization step Δ is obtained by, for example, a binary search method (S3 to S8). Specifically, first, an initial value of a temporary quantization step Δ is set (S3). The optimum quantization step Δ for quantizing the logarithmized correction calculation table into 256 patterns (8 bits) is considered to be between log (1023) / 255 to log (1023) / 1023. Log (1023) / 639, where 639 is an intermediate value between 1023 and 255, is the initial value of the temporary quantization step Δ. Next, the contents of the logarithmically converted correction calculation table are quantized by a temporary quantization step Δ (S4), and the number of unique values in the result of the correction calculation table resulting from the quantization is counted (S5).

  If the number of unique values is 254 or less, the quantization step Δ is set small (S6), and the process returns to S4. For example, if the initial value is log (1023) / 639, the optimal quantization step Δ is considered to be between log (1023) / 1023 to log (1023) / 639, so the denominator is 1023 And log (1023) / 831, which is 831 which is an intermediate value between 639 and 639, is set as the next temporary quantization step Δ. If the number of unique values is 256 or more, the quantization step Δ is set large (S7), and the process returns to S4. For example, if the initial value is log (1023) / 639, the optimal quantization step Δ is considered to be between log (1023) / 255 and log (1023) / 639, so the denominator is 255. Log (1023) / 447, which is 447 which is an intermediate value between 1 and 639, is set as the next temporary quantization step Δ. If the number of unique values is 256, the content of the correction calculation table is converted to linear (light emission amount data Do1) and the process ends (S8).

  By the above processing, for example, as shown in FIG. 8, a correction calculation table having 256 unique values and a quantization step Δ at this time (corresponding to the quantization step S in FIG. 1) are obtained. If a unique 8-bit code is assigned to the 256 unique values (compressed emission amount data Db) obtained, the 10-bit emission amount data Do1 is finally compressed to 8 bits. FIG. 5 shows the relationship between the light emission amount data Do1 and the 8-bit compressed light emission amount data Db. Further, the reverse of this relationship corresponds to the LUT 22 shown in FIG. These quantization steps S and LUT 22 are stored in advance in the host controller 10 and the optical head 20, but can be rewritten from an external device. For example, when new correspondence table data is supplied to the host controller 10, the host controller 10 stores the supplied data in the LUT 15 and the LUT 22. As a result, it is possible to easily cope with a change in the LUT corresponding to the rewriting of the value in the correction value memory 11.

  FIG. 9 shows a case where the 10-bit light emission amount data Do1 is simply compressed to 8 bits by deleting the lower 2 bits (linear compression), and the light emission amount data Do1 is converted to logarithm and simply compressed to 8 bits. FIG. 8 is a diagram showing the light emission amount corresponding to the light emission amount data compressed to 8 bits in the case of the present embodiment. The slope of the graph indicates the increment of the light emission amount, and the steeper the slope becomes, the steeper the slope. That is, the relative quantization step is large. From FIG. 9, it can be seen that in the linear compression, the step with a small value is extremely rough, and in the logarithmic compression, the step is slightly rough for all values compared to the present embodiment.

  FIG. 10 shows light emission amount data compressed to 8 bits in the case of linear compression, logarithmic compression, and the case of this embodiment, except for values other than 0 to 51, which are not used as light emission amount data values. It is the figure which showed the light-emission quantity corresponding to these. Similar to FIG. 9, the slope of the graph indicates the increment of the light emission amount, and the steeper the slope, the coarser the increment, that is, the greater the relative quantization step. From FIG. 10, it can be seen that in the linear compression, the step with a small value is very rough, and in the logarithmic compression, the step is slightly rough for all values compared to the present embodiment.

  FIG. 11 is a diagram showing a relative quantization step for each light emission amount data compressed more specifically to 8 bits in these cases. From FIG. 11, it can be seen that the compression method of this embodiment has a smaller relative quantization step, that is, a smaller quantization error, in the entire region of the light emission amount data.

  As described above, in the light emitting device 100, since the compression encoding unit 14 compresses the light emission amount data Do1, the amount of data transferred between the host controller 10 and the optical head 20 can be reduced. it can. As a result, it is possible to contribute to speeding up the operation. Further, in the light emitting device 100, as described above, by setting the quantization step S corresponding to the range of the light emission amount data Do1, errors can be reduced, and deterioration in print quality can be suppressed. .

  In order to reduce the amount of data transferred between the host controller 10 and the optical head 20, the correction value memory 11 itself is provided on the optical head 20 side, and only the image data Di is transferred to the optical head 20. In this case, the circuit scale on the optical head 20 side increases, and rewriting of the contents of the correction value memory 11 becomes difficult unless a connector or the like is separately provided on the optical head 20 side. On the other hand, by providing the correction value memory 11 on the host controller 10 side as in this embodiment, the circuit scale on the optical head 20 side can be suppressed, and the correction value memory 11 can be easily rewritten. There are advantages that can be made.

<C. Modification>
(1) FIG. 12 is a block diagram illustrating a configuration of a main part of a light emitting device according to a modification. In the embodiment described above, the compression encoding unit 14 and the decoding / decompression processing unit 21 are connected in parallel, but the connection between them is a serial connection. Therefore, the host controller 10 includes a parallel / serial (P / S) conversion unit 15 that converts the compressed light emission amount data from the compression encoding unit 14 into a serial signal. The serial / parallel (S / P) conversion unit 25 converts the serial signal into a parallel signal. Other configurations and operations are the same as those of the light emitting device shown in FIG. By using serial connection in this way, the number of wires between the compression encoding unit 14 and the decoding / decompression processing unit 21 can be reduced. Moreover, it is preferable that the parallel / serial conversion unit 15 transmits the compressed light emission amount data in a differential format, and the serial / parallel conversion unit 25 receives the compressed light emission amount data in a differential format. In this case, noise resistance can be improved by transmitting the compressed light emission amount data through the twisted pair wiring.

  (2) In the above-described embodiment, when the light emission amount data is compressed to 8 bits, there are 256 quantization results. However, as shown in FIG. 0 “00000000” [Fig. (A)], 1 “11111111” [Fig. (B)], a code pattern with a biased DC balance, 170 “10101010” [Fig. (C)], There is a pattern of increasing power consumption and radiation noise, such as 85 “01010101” [(D) in FIG. For this reason, these may not be used. In this case, in the flow shown in FIG. 7 described above, the quantization step is determined so that there are 252 quantization results excluding these, and 252 codes other than the above four codes are assigned. Good. This is effective in improving DC balance, power consumption, and radiation noise.

More generally, when the number of bits of the compressed light emitting amount data Db was the K, it assigns a quantized data Da to ^N (2 ^K> N) pieces of 2 ^K pieces of compressed emitting amount data Db, the quantized data set as the 2 ^K -M pieces of compressed emitting amount data Db allocation is not of Da, including those frequency components higher than the bit pattern with all bits pattern of the compressed light emitting amount data Db with assignment do it. For example, “10101010” and “01010101” correspond to 2 ^K− M compressed light emission amount data Db to which no quantization data Da is assigned.
Further, when the number of bits of the compressed light emission amount data Db is ^{K, the} 2K-M compressed light emission amount data Db to which the quantized data Da is not assigned includes the compressed light emission amount data Db to which the bit pattern is assigned. What is necessary is just to set so that a thing with a low frequency component may be included compared with all the bit patterns. For example, “00000000” and 11111111 correspond to 2 ^K− M compressed light emission amount data Db to which no quantization data Da is assigned.

(3) Since the actual correction data Dh has a distribution of occurrence frequencies, the emission frequency data Do1 also has a distribution of occurrence frequencies as shown in FIG. In accordance with this distribution, a code corresponding to the value of the light emission amount data Do1 having a low occurrence frequency is assigned a code having a pattern in which the DC balance is poor or power consumption and radiation noise increase as described above, and the light emission amount data having a high occurrence frequency is assigned. You may make it allocate the code | symbol of the pattern with which direct current | flow balance is good or power consumption and radiation noise reduce to the value of Do. This is effective in improving the DC balance, power consumption, and radiation noise as a whole.
More generally, when N possible values of the quantized data Da are arranged in the order of occurrence frequency, the code of the compressed light emission amount data Db is assigned to the corresponding compressed light emission as the quantized data Da has a lower occurrence frequency. What is necessary is just to set so that the frequency component of the bit pattern of quantity data Db may leave | separate from the center of frequency distribution. As a result, the frequency of occurrence of “00000000” and “11111111”, which are low frequency bit patterns, or “10101010” and “01010101”, which are high frequency bit patterns, can be reduced.

(4) In the above-described embodiment, the correction calculation unit 12 and the compression encoding unit 14 are provided separately. However, as shown in FIG. 15, the correction compression encoding unit 16 may be provided as a unit. .
In this case, the correction compression encoding unit 16 includes an LUT 17. The LUT 16 stores 4-bit image data Di, 6-bit correction data Dh, and 8-bit compressed light emission amount data Db in association with each other. The correction compression encoding unit 16 reads the compressed light emission amount data Db corresponding to the image data Di and the correction data Dh with reference to the LUT 17. Thereby, it is possible to generate the compressed light emission amount data Db by simply referring to the LUT 17 while omitting the correction calculation process, the logarithmic conversion process, the quantization process, and the encoding process shown in Expression (1).
Also, when the correction compression encoding unit 16 is employed, the compressed light emission amount via the parallel / serial (P / S) conversion unit 15 and the serial / parallel (S / P) conversion unit 25 as shown in FIG. Data Db may be transmitted.

<D. Application example>
FIG. 17 is a longitudinal sectional view of an image forming apparatus using the light emitting device as described above. This image forming apparatus is a tandem type full color image forming apparatus using a belt intermediate transfer body system.

  In this image forming apparatus, four optical heads 20K, 20C, 20M, and 20Y having the same configuration as the optical head 20 described above are exposed to four photosensitive drums (image bearing members) 110K, 110C, 110M, and 110Y. It is arranged at each position.

  As shown in FIG. 17, this image forming apparatus is provided with a driving roller 121 and a driven roller 122, and an endless intermediate transfer belt 120 is wound around these rollers 121 and 122, as indicated by arrows. Thus, the periphery of the rollers 121 and 122 is rotated. Although not shown, tension applying means such as a tension roller that applies tension to the intermediate transfer belt 120 may be provided.

  Around the intermediate transfer belt 120, photosensitive drums 110K, 110C, 110M, and 110Y having photosensitive layers on four outer peripheral surfaces are arranged at predetermined intervals. The subscripts K, C, M, and Y mean that they are used to form black, cyan, magenta, and yellow visible images, respectively. The same applies to other members. The photosensitive drums 110K, 110C, 110M, and 110Y are rotationally driven in synchronization with the driving of the intermediate transfer belt 120.

  Around each photosensitive drum 110 (K, C, M, Y), there is a corona charger 111 (K, C, M, Y), an optical head 20 (K, C, M, Y), and a developing unit. 114 (K, C, M, Y) are arranged. The corona charger 111 (K, C, M, Y) uniformly charges the outer peripheral surface of the corresponding photosensitive drum 110 (K, C, M, Y). The optical head 20 (K, C, M, Y) writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum. Each optical head 20 (K, C, M, Y) is installed such that the arrangement direction of the plurality of light emitting elements 21 is along the bus (main scanning direction) of the photosensitive drum 110 (K, C, M, Y). The The electrostatic latent image is written by irradiating the photosensitive drum with light by the plurality of light emitting elements 21 described above. The developing device 114 (K, C, M, Y) forms a visible image, that is, a visible image on the photosensitive drum by attaching toner as a developer to the electrostatic latent image.

  The black, cyan, magenta, and yellow developed images formed by the four-color single-color image forming station are sequentially transferred onto the intermediate transfer belt 120 to be superimposed on the intermediate transfer belt 120. As a result, a full-color visible image is obtained. Four primary transfer corotrons (transfer devices) 112 (K, C, M, Y) are arranged inside the intermediate transfer belt 120. The primary transfer corotron 112 (K, C, M, Y) is disposed in the vicinity of the photosensitive drum 110 (K, C, M, Y), and the photosensitive drum 110 (K, C, M, Y). The electrostatic image is electrostatically attracted from the toner image to transfer the visible image to the intermediate transfer belt 120 passing between the photosensitive drum and the primary transfer corotron.

  A sheet 102 as an object on which an image is to be finally formed is fed one by one from the sheet feeding cassette 101 by the pickup roller 103, and between the intermediate transfer belt 120 and the secondary transfer roller 126 in contact with the driving roller 121. Sent to the nip. The full-color visible image on the intermediate transfer belt 120 is secondarily transferred to one side of the sheet 102 by the secondary transfer roller 126 and fixed on the sheet 102 through the fixing roller pair 127 as a fixing unit. . Thereafter, the sheet 102 is discharged onto a paper discharge cassette formed in the upper part of the apparatus by a paper discharge roller pair 128.

  FIG. 18 is a longitudinal sectional view of another image forming apparatus according to the embodiment of the present invention. This image forming apparatus is a rotary developing type full-color image forming apparatus using a belt intermediate transfer body system. In the image forming apparatus shown in FIG. 18, a corona charger 168, a rotary developing unit 161, an optical head 20, an intermediate transfer, and the like are disposed around a photosensitive drum (image carrier) 165 corresponding to the photosensitive drum 110 described above. A belt 169 is provided.

  The corona charger 168 uniformly charges the outer peripheral surface of the photosensitive drum 165. The optical head 20 configured in the same manner as described above writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum 165. The plurality of light emitting elements 24 are arranged so that the arrangement direction thereof is along the bus line (main scanning direction) of the photosensitive drum 165. The electrostatic latent image is written by irradiating the photosensitive drum with light by the plurality of light emitting elements 24 described above.

  The developing unit 161 is a drum in which four developing units 163Y, 163C, 163M, and 163K are arranged at an angular interval of 90 °, and can rotate counterclockwise about the shaft 161a. The developing units 163Y, 163C, 163M, and 163K supply yellow, cyan, magenta, and black toners to the photosensitive drum 165, respectively, and attach the toner as a developer to the electrostatic latent image, thereby the photosensitive drum 165. A visible image, that is, a visible image is formed.

  The endless intermediate transfer belt 169 is wound around a driving roller 170a, a driven roller 170b, a primary transfer roller 166, and a tension roller, and is rotated around these rollers in a direction indicated by an arrow. The primary transfer roller 166 transfers the visible image to the intermediate transfer belt 169 that passes between the photosensitive drum and the primary transfer roller 166 by electrostatically attracting the visible image from the photosensitive drum 165.

  Specifically, in the first rotation of the photosensitive drum 165, an electrostatic latent image for a yellow (Y) image is written by the exposure head 20, and a developed image of the same color is formed by the developing unit 163Y. The image is transferred to the transfer belt 169. Further, in the next rotation, an electrostatic latent image for a cyan (C) image is written by the exposure head 20 and a developed image of the same color is formed by the developing unit 163C, and an intermediate transfer is performed so as to overlap the yellow developed image. Transferred to the belt 169. Then, during the four rotations of the photosensitive drum 165, yellow, cyan, magenta, and black visible images are sequentially superimposed on the intermediate transfer belt 169. As a result, a full-color visible image is formed on the transfer belt 169. It is formed. When images are finally formed on both sides of a sheet as an object on which an image is to be formed, the same color images of the front and back surfaces are transferred to the intermediate transfer belt 169, and then the front and back surfaces are transferred to the intermediate transfer belt 169. A full-color visible image is obtained on the intermediate transfer belt 169 by transferring the visible image of the next color.

  The image forming apparatus is provided with a sheet conveyance path 174 through which a sheet passes. The sheets are picked up one by one from the paper feed cassette 178 by the pick-up roller 179, advanced through the sheet transport path 174 by the transport roller, and between the intermediate transfer belt 169 and the secondary transfer roller 171 in contact with the drive roller 170a. Pass through the nip. The secondary transfer roller 171 transfers the developed image to one side of the sheet by electrostatically attracting a full-color developed image from the intermediate transfer belt 169 collectively. The secondary transfer roller 171 can be moved closer to and away from the intermediate transfer belt 169 by a clutch (not shown). The secondary transfer roller 171 is brought into contact with the intermediate transfer belt 169 when a full-color visible image is transferred onto the sheet, and is separated from the secondary transfer roller 171 while the visible image is superimposed on the intermediate transfer belt 169.

  The sheet on which the image has been transferred as described above is conveyed to the fixing device 172 and is passed between the heating roller 172a and the pressure roller 172b of the fixing device 172, whereby the visible image on the sheet is fixed. The sheet after the fixing process is drawn into the discharge roller pair 176 and proceeds in the direction of arrow F. In the case of double-sided printing, after most of the sheet passes through the paper discharge roller pair 176, the paper discharge roller pair 176 is rotated in the reverse direction and introduced into the double-sided printing conveyance path 175 as indicated by an arrow G. The Then, the visible image is transferred to the other surface of the sheet by the secondary transfer roller 171, the fixing process is performed again by the fixing device 172, and then the sheet is discharged by the discharge roller pair 176.

  Each of the image forming apparatuses described above uses the above-described light emitting device, and the amount of data transferred between the host controller 10 and the optical head 20 can be reduced while suppressing quantization error, thereby suppressing deterioration in print quality. However, it can contribute to speeding up of the operation. The light-emitting device described above can also be applied to other electrophotographic image forming apparatuses, and such image forming apparatuses are within the scope of the present invention. For example, the present invention can be applied to an image forming apparatus that transfers a visible image directly from a photosensitive drum to a sheet without using an intermediate transfer belt, and an image forming apparatus that forms a monochrome image.

It is a block diagram which shows the structure of the principal part of the light-emitting device which concerns on embodiment of this invention. It is a figure which shows the relationship between the image data Di, the correction data Dh, and the light emission amount data Do1. It is a figure which shows distribution of the light emission amount data Do1 with respect to image data Di. 3 is a block diagram illustrating a detailed configuration of a compression encoding unit 14. FIG. It is a figure which shows the relationship between the light emission amount data Do1 and the compression light quantity data Db. FIG. 4 is a diagram showing the contents stored in an LUT 22 on the optical head 20 side. It is a flowchart which shows the determination process of a quantization step. It is a figure which shows the light emission amount data quantized according to the determined quantization step. It is a figure which shows distribution of the light emission amount data at the time of encoding with a different compression method. It is a figure which shows distribution of the light emission amount data at the time of encoding with a different compression method. It is a figure which shows distribution of the relative quantization step at the time of encoding with a different compression method. It is a block diagram which shows the structure of the principal part of the light-emitting device which concerns on a modification. It is a figure which shows the example of the code | symbol which considers allocation. It is a figure which shows the generation frequency of the value of light emission amount data. It is a block diagram which shows the structure of the principal part of the light-emitting device which concerns on a modification. It is a block diagram which shows the structure of the principal part of the light-emitting device which concerns on a modification. 1 is a longitudinal sectional view of an image forming apparatus according to an embodiment of the present invention. It is a longitudinal cross-sectional view of another image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Host controller, 11 ... Correction value memory, 12 ... Correction calculating part, 14 ... Compression encoding part, 15 ... P / S conversion part, 20 ... Optical head, 21 ... Decoding expansion process , 22... LUT, 23... Constant current driver, 24... Light emitting element, 25.

Claims (12)

A data generation method for generating data to be transmitted between a control device and an optical head including a plurality of light emitting elements,
Based on correction data and image data for correcting variations in the amount of light of the plurality of light emitting elements, a predetermined calculation is performed to generate light emission amount data that can take M (M is a natural number) values,
Logarithmically convert the light emission amount data to generate logarithmically converted data;
The quantization step is determined so that the number of data obtained by quantizing the logarithmically transformed data can be N (N is a natural number, N <M), and the logarithmically transformed data is quantized to obtain quantized data. Generate
Assigning a code to each of the N values of the quantized data to generate compressed data;
A data generation method characterized by the above. The image data is i (i is a natural number) bit data,
The correction data is j (j is a natural number) bit data,
The data generation method according to claim 1, wherein the predetermined calculation is such that M satisfies M <2 ^{(i + j)} . When the number of bits of the compressed data is K (K is a natural number), 2 ^K > N,
Assigning the quantized data to N of the 2 ^K compressed data;
To 2 ^K -M pieces of the compressed data assignment is not the quantized data, including those frequency components higher than the bit pattern with the bit pattern of the compressed data with assignment,
The data generation method according to claim 1 or 2, characterized in that When the number of bits of the compressed data is K (K is a natural number), 2 ^K > N,
Assigning the quantized data to N of the 2 ^K compressed data;
Wherein the 2 ^K -M number assignment is not the quantized data to the compressed data, including those frequency components lower than the bit pattern with the bit pattern of the compressed data with assignment,
The data generation method according to claim 1 or 2, characterized in that   When N values that can be taken by the quantized data are arranged in the order of occurrence frequency, the compressed data code is assigned to the frequency data of the frequency component of the bit pattern of the corresponding compressed data as the quantized data has a lower occurrence frequency. The data generation method according to claim 1, wherein the data generation method is set so as to be away from the center of the data. A control device for controlling an optical head comprising a plurality of light emitting elements,
Correction for generating light emission amount data that can take M (M is a natural number) values by executing a predetermined calculation based on correction data and image data for correcting variations in light amounts of the plurality of light emitting elements. An arithmetic unit;
A logarithmic conversion unit for logarithmically converting the light emission amount data to generate logarithmic conversion data;
The quantization step is determined so that the number of data obtained by quantizing the logarithmically transformed data can be N (N is a natural number, N <M), and the logarithmically transformed data is quantized to obtain quantized data. A quantizer to generate;
An encoding unit that assigns a code to each of the N values of the quantized data, generates compressed data, and outputs the compressed data to the optical head;
A control device provided. When the number of bits of the compressed data is K (K is a natural number), 2 ^K > N,
The encoding unit includes:
Assigning the quantized data to N of the 2 ^K compressed data;
To 2 ^K -M pieces of the compressed data assignment is not the quantized data, including those frequency components higher than the bit pattern with the bit pattern of the compressed data with assignment,
The control apparatus according to claim 6. When the number of bits of the compressed data is K (K is a natural number), 2 ^K > N,
The encoding unit includes:
Assigning the quantized data to N of the 2 ^K compressed data;
Wherein the 2 ^K -M number assignment is not the quantized data to the compressed data, including those frequency components lower than the bit pattern with the bit pattern of the compressed data with assignment,
The control apparatus according to claim 6.   When the pre-encoding unit arranges N possible values of the quantized data in the order of occurrence frequency, the code assignment of the compressed data is such that the quantized data having the lower occurrence frequency has a bit pattern corresponding to the compressed data. The control device according to claim 6, wherein the frequency component is set so as to be away from the center of the frequency distribution. A control device for controlling an optical head comprising a plurality of light emitting elements,
Correction for generating light emission amount data that can take M (M is a natural number) values by executing a predetermined calculation based on correction data and image data for correcting variations in light amounts of the plurality of light emitting elements. An arithmetic unit;
A compression unit that converts the light emission amount data into compressed data that can take N (N is a natural number, N <M) values;
The compression unit includes a storage unit that stores each value of the light emission amount data and each value of the compression data in association with each other, and stores the storage unit based on the light emission amount data generated by the correction calculation unit. Generating the compressed data with reference to,
The compressed data stored in the storage unit generates logarithmically converted data by logarithmically converting the light emission amount data, and the number of data obtained by quantizing the logarithmically converted data is N. A quantization step is determined, the logarithmically transformed data is quantized to generate quantized data, and a code is assigned to each of the N values of the quantized data.
A control device characterized by that. A control device for controlling an optical head comprising a plurality of light emitting elements,
Compressed data that has been subjected to processing for correcting variations in the amount of light of the plurality of light emitting elements and processing for compressing the amount of data is performed on the image data that specifies the gradation to be displayed by each of the plurality of light emitting elements. A correction compression unit to be generated;
A correction data storage unit that stores correction data for correcting variations in light quantity of the plurality of light emitting elements,
The correction compression unit
The correction data read out from the image data and the correction data storage means, having a compressed data storage unit that stores each value of the image data and each value of the correction data and each value of the compressed data And generating the compressed data with reference to the compressed data storage unit,
The compressed data is
Based on the correction data and the image data, a predetermined calculation is performed to generate light emission amount data that can take M (M is a natural number) values, and the light emission amount data is logarithmically converted to logarithmically converted data. The quantization step is determined so that the number of data obtained by quantizing the logarithmically transformed data is N, and the logarithmically transformed data is quantized to generate quantized data. Generated by assigning a code to each of the N values of the data.
A control device characterized by that. A light emitting device comprising a control device and an optical head comprising a plurality of light emitting elements,
The controller is
Based on the correction data for correcting the variation in the light amount of the plurality of light emitting elements and the image data, a predetermined calculation is executed to generate light emission amount data that can take M (M is a natural number) values. A correction calculation unit;
A logarithmic conversion unit for logarithmically converting the light emission amount data to generate logarithmic conversion data;
The quantization step is determined so that the number of data obtained by quantizing the logarithmically transformed data can be N (N is a natural number, N <M), and the logarithmically transformed data is quantized to obtain quantized data. A quantization unit to be generated;
An encoding unit that assigns a code to each of the N values of the quantized data, generates compressed data, and outputs the compressed data to the optical head;
The optical head is
A decryption / decompression unit that decompresses the received compressed data and decrypts the light emission amount data;
A drive unit that drives the plurality of light emitting elements based on the decoded light emission amount data;
A light emitting device characterized by that.

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