JP2005096197A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly reproduce density gradation of an image without making a step height great enough to be visually recognized between adjacent levels occur in the density gradation of the image to be reproduced, in terms of an image forming apparatus and an image forming method, wherein the amount of light emitted from a light-emitting device such as an organic EL device is controlled by using the image input signal, so that an image can be exposed and recorded. <P>SOLUTION: A first light-amount control signal V<SB>1</SB>for controlling the amount of the light emitted by the organic EL device is generated from the image input signal. An ON/OFF control signal V<SB>2</SB>for controlling an ON/OFF state of exposure by the organic EL device, and a second light-quantity control signal V<SB>3</SB>for controlling the amount of the emitted light for the exposure are generated from the image input signal. A light-emission control signal of the organic EL device is generated by performing signal switching among the signals V<SB>1</SB>, V<SB>2</SB>and V<SB>3</SB>, depending on the amount of differences of image formation density between a control level of the amount of the light to be emitted by the organic EL device in accordance with the image input signal, and a control level adjacent to the above control level. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image forming method for controlling the amount of light emitted from a light emitting element such as an organic electroluminescence element (hereinafter referred to as an organic EL element) by using an image input signal to record an exposure image.

  A color printing system that prints out an image such as a photograph exposes a photosensitive material with modulated light to record the image as a latent image, and then processes and develops the latent image to print out the image. .

Today, various proposals have been made to use an organic EL element as a light source for exposing a photosensitive material in this color printing system.
The organic EL element has a cathode electrode that forms an electron injection electrode, an anode electrode that forms a hole injection electrode, and an organic layer of a thin film containing a fluorescent organic compound disposed between these electrodes. Composed. Then, by passing a current (driving current) between these electrodes, electrons are injected into the cathode and holes are injected into the anode, and these holes and electrons recombine to generate recombination energy. Causes excitation of the organic layer. At that time, the organic layer emits fluorescence by emitting fluorescence when transitioning from the excited state to the ground state. Such an organic EL element has a dark spot where the light emitting portion has not emitted light, and a problem of luminance deterioration that decreases with use of the organic EL element. Realizing a long-life device is currently difficult.
In the following Patent Document 1, although a printer device using an organic EL element as a light source has been proposed, a practical color print system has not yet been provided.

By the way, in the case of an exposure recording apparatus that exposes and records an image on a photosensitive material using a light emitting element such as a laser light source, when an image input signal of the image is supplied, the density of the image to be formed on the photosensitive material from the image input signal The exposure amount to achieve this density, the light emission amount by the light emitting element, and the pulse control signal with the pulse width controlled to realize this light emission amount are generated, and exposure recording by the light emitting element is performed. A so-called pulse width modulation method is used.
When the organic EL element is used as a light emitting element in such an exposure recording apparatus, a method of exposing and recording an image on a photosensitive material using the pulse width modulation method is assumed from the viewpoint of easy control. In this case, an image is recorded by causing the organic EL element to emit light corresponding to the exposure amount required by the photosensitive material. In this case, the organic EL element is controlled by driving current as can be seen from the above-mentioned light emission mechanism. That is, the organic EL element is linearly controlled by the signal level of the driving current obtained by quantizing the light emission amount of the organic EL element. Will be performed.
However, in such control of the light emission amount of the organic EL element, it is assumed that the gradation reproducibility of the image is not appropriate depending on the characteristics of the photosensitive material, and an extreme step may be generated between the density gradations.

JP 2000-305191 A

  Accordingly, the present invention relates to an image forming apparatus and an image forming method for controlling the amount of light emitted from a light emitting element such as an organic EL element using an image input signal to expose and record an image. It is an object of the present invention to provide an image forming apparatus and an image forming method in which the density gradation of an image can be reproduced smoothly without causing a level difference that can be visually recognized in the gradation.

  In order to achieve the above object, the present invention provides an image forming apparatus that controls the amount of light emitted from a light emitting element using an image input signal to record an image on a photosensitive material, and emits light according to a supplied light emission control signal. A light emitting element that emits light and a control signal generation unit that generates the light emission control signal from an image input signal. The control signal generation unit emits the light so that an image is formed on a photosensitive material at a predetermined density. A first signal generation unit that generates a first light amount control signal for controlling a light emission amount by the element, and a portion of the photosensitive material to be recorded by ON / OFF of the exposure so that the exposure of the light emitting element is performed. A second signal generation unit that generates an ON / OFF control signal for controlling ON / OFF and a second light amount control signal for controlling a light emission amount of the light emitting element at the time of exposure, and an image input signal A light emitting amount of light emitted from the light emitting element is formed on the photosensitive material using a calculation unit that determines the light amount-density characteristics of the photosensitive material and a control level of the light emitting amount in the first light amount control signal determined by the light emitting amount. The first light quantity control signal, the ON / OFF control signal and the second control signal are determined according to the difference between the image formation density to be formed and the image formation density formed at the control level adjacent to the control level. And a signal switching unit that generates a light emission control signal by switching the signal to the light quantity control signal.

  Here, the second signal generation unit generates an ON / OFF control signal and a second light amount control signal corresponding to each exposure pattern so that the photosensitive material is exposed by exposure patterns having different sizes, The switching unit is selected from a plurality of exposure patterns so that a difference between an image formation density at a control level of light emission amount determined from an image input signal and an image formation density at an adjacent control level is equal to or less than a predetermined value. Preferably, the ON / OFF control signal and the second light quantity control signal corresponding to one exposure pattern are switched as signals to be controlled by the light emitting element.

Further, it is preferable that the control signal generation unit generates the ON / OFF control signal from an image input signal obtained by adding the first noise component.
The control signal generation unit further includes a determination unit that compares and determines the difference in image formation density between adjacent control levels with an addition value obtained by adding a second noise component to a predetermined value. It is preferable that the switching unit switches the signal and generates the light emission control signal according to the determination result.

  The light emitting element is, for example, an organic electroluminescence element.

  The present invention is an image forming method for controlling the amount of light emitted from a light emitting element using an image input signal and exposing and recording an image on a photosensitive material, wherein the image is formed on the photosensitive material at a predetermined density. A first signal generation step for generating a first light amount control signal for controlling a light emission amount by the light emitting element from an image input signal, and a portion of the photosensitive material to be recorded by exposure ON / OFF so that the portion of the photosensitive material to be recorded is exposed; A second ON / OFF control signal for controlling ON / OFF of the exposure by the light emitting element and a second light amount control signal for controlling the light emission amount by the light emitting element for this exposure are generated from the image input signal. A light generation amount to be emitted from the light emitting element is determined from a signal generation step and an image input signal using a light amount-density characteristic of a photosensitive material, and the light emission amount in the first light amount control signal determined by the light emission amount is determined. Generated in the first signal generation step according to the difference between the image forming density formed on the photosensitive material at the control level of the amount and the image forming density formed at the control level adjacent to the control level. The light emission control is performed by switching a signal between the first light amount control signal and the ON / OFF control signal and the second light amount control signal generated in the second signal generation step. And a control signal generation step for generating a signal.

  In the present invention, the control signal generation unit determines the light emission amount to be emitted from the light emitting element from the image input signal using the light quantity-density characteristic of the photosensitive material, and the light emission in the first exposure amount control signal determined by this light emission amount. The first light quantity control signal, ON / OFF according to the difference between the image formation density formed on the photosensitive material at the control level of the amount and the image formation density formed at the control level adjacent to the control level. A signal to be controlled of the light emitting element is switched between the OFF control signal and the second light amount control signal to generate a light emission control signal. For this reason, it is possible to finely set the density gradation so as not to cause a level difference that can be visually recognized between the control level of the first light quantity control signal and the adjacent control level. Can be reproduced.

  Hereinafter, an image forming apparatus and an image forming method according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

FIG. 1 is a block diagram of a color printer 10 that forms an image by exposing a photosensitive material as an example of the image forming apparatus of the present invention.
The printer 10 exposes and records a latent image on the photosensitive material P using the supplied image input signal, the photosensitive material supply unit 14 that conveys and supplies the photosensitive material P to the head unit 12, and the image. And a signal processing unit 16 for generating a drive signal for driving the head unit 12 for exposure recording on the photosensitive material P.

  The signal processing unit 16 in the printer 10 is connected to the image processing device 18 so that an image processed signal subjected to image processing by the image processing device 18 is supplied as an image input signal. Further, the conveyance path of the photosensitive material P in the head unit 12 is connected to the processor 13 so that the photosensitive material P exposed and recorded by the head unit 12 is guided to the processor 13.

The head unit 12 scans and exposes the photosensitive material P conveyed at a constant speed in a line shape in a direction (main scanning direction, X direction) orthogonal to the conveying direction (sub-scanning direction, Y direction). This is a unit for forming an image on the material P. The head unit 12 includes a moving unit 25 having a pair of rollers 20 and 22 and a driving motor 24 for conveying the photosensitive material P in the sub-scanning direction (Y direction) at a constant speed. It is mechanically connected to the drive motor 24, and the drive of the drive motor 24 is transmitted to the drive roller.
The head unit 12 includes a light emitting head 26 that exposes the photosensitive material P to light and exposes it, and a lens array 28 that includes a SELFOC lens that forms an image of light from the light emitting head 26 at a predetermined position of the photosensitive material P. Have.

In the present invention, the moving unit 25 fixes the light emitting head 26 and moves the photosensitive material P. However, the moving unit 25 may be configured to move the light emitting head 26 while the photosensitive material P is stationary.
The light emitting head 26 has a head length at least equal to or larger than the sheet width of the photosensitive material P. In the present invention, the head length is shorter than the sheet width of the photosensitive material P. It may be. In this case, the moving unit 25 is configured to move the photosensitive material P or the light emitting head 26 in the main scanning direction, and in the main scanning direction in accordance with the scanning exposure timing so as to perform exposure recording for the sheet width of the photosensitive material P. It is good to move.

  The light emitting head 26 is a head in which a plurality of light emitting element array lines in which a plurality of organic electroluminescent elements (organic EL elements) are arranged in a line are provided in parallel in a direction orthogonal to the arrangement direction. An image is recorded on the photosensitive material P by controlling the light emission of the element and performing scanning exposure. Specifically, the configuration is as shown in FIGS.

The light emitting head 26 includes 32 organic EL array lines formed by arranging 3520 organic EL elements in the X direction (main scanning direction) on a transparent glass substrate 26A in parallel in the Y direction (sub scanning direction). The R light emitting array portion 26R that emits R (red) light and the organic EL array line formed by arranging 3520 organic EL elements in the X direction are arranged in parallel in the Y direction. The G light emitting array 26G that emits G (green) light and the organic EL array line formed by arranging 3520 organic EL elements in the X direction were formed in parallel in the Y direction. A B light emitting array 26B that emits B (blue) light and driving ICs 26C, 26D, 26E, 26F, and 26H for supplying current to control these arrays to emit light are provided.
The driving IC 26C is an anode driving IC for injecting holes into each organic EL element of the R light emitting array 26R, and the driving IC 26E injects electrons into each organic EL element in the R light emitting array 26R. This is an IC for driving a cathode. The driving IC 26D is an anode driving IC for injecting holes into each organic EL element of the G light emitting array 26G and the B light emitting array 26B. The driving IC 26F is a cathode driving IC for injecting electrons into each organic EL element of the G light emitting array 26G, and the driving IC 26H is for injecting electrons into each organic EL element of the B light emitting array 26B. The cathode driving IC. An anode electrode and a cathode electrode are wired from these ICs.

  As described above, each organic EL element includes a cathode electrode that constitutes an electron injection electrode, an anode electrode that constitutes a hole injection electrode, and a thin film organic material containing a fluorescent organic compound disposed between these electrodes. And a layer. FIG. 2B shows eight organic EL elements provided on the glass substrate 26A. In the organic EL element, a thin-film organic layer containing a fluorescent organic compound is formed while the anode electrodes 40a to 40d and the cathode electrodes 42a and 42b intersect three-dimensionally, and the intersecting portion emits light. FIG. 2C is a schematic cross-sectional view of the organic EL element, and schematically shows the organic EL element provided at the intersection of the anode electrode 40a and the cathode electrode 42a.

As shown in FIG. 2C, in the organic EL element, a transparent anode electrode 40a made of ITO (Indium Tin Oxide) or the like is formed on a transparent glass substrate 26A, and a TPD is formed on the upper layer. The hole transport layer 44 is made of, and an organic layer 46 that forms a light emitting layer as a dopant by doping a small amount of, for example, aluminum quinoline (Alq ₃ ) or quinacridone or a laser dye as a light emitting material (dopant). Is formed. Further, an electron transport layer 48 is formed thereon, and a cathode electrode 42a is formed thereon. There is no restriction | limiting in particular about the material in each of these layers, It is good to use a well-known thing. Examples thereof include materials described in Japanese Patent Application Laid-Open No. 2000-305191 by the applicant of the present application.

  Further, a red, green, or blue color filter 50 is placed on the lower surface (the surface opposite to the surface on which the layer is provided) in FIG. 26R, G light emitting array 26G, and B light emitting array 26B are formed in respective regions. Therefore, the light emitted from the organic layer 46 which is a light emitting layer is transmitted through the hole transport layer 44, the anode electrode 40a and the glass substrate 26A, and the light having a wavelength corresponding to the color of the color filter 50 is shown in FIG. It is injected from the lower side of the glass substrate 26A in 2 (c).

  The light emitted from the R light emitting array 26R, the G light emitting array 26G, and the B light emitting array 26B is imaged at a predetermined position of the photosensitive material P by the lens array 28 to form light dots. As a result, the photosensitive material P is exposed and recorded as an image of one dot by light emitted from one organic EL element.

The photosensitive material supply unit 14 draws and cuts the web-shaped photosensitive material P wound in a roll shape by a predetermined length, and supplies the cut sheet-shaped photosensitive material P to the head unit 12. It is.
The processor 13 is a known device that develops the photosensitive material P on which an image is recorded as a latent image to develop the image. The processor 13 performs development processing, fixing processing, water washing processing, and the like.

The signal processing unit 16 includes a control signal generation unit 52 and a drive signal generation unit 54. The control signal generation unit 52 is a unit that generates a light emission control signal to be emitted from the organic EL element from the image input signal supplied from the image processing device 18.
FIG. 3 is a block diagram showing a schematic configuration of the control signal generation unit 52.
The control signal generation unit 52 includes a first signal generation unit 60, a second signal generation unit 62, a characteristic data storage unit 64, a light emission amount calculation unit 65, a determination unit 66, a switching unit 68, and a noise signal generation unit 70.

The first signal generator 60 generates a first light amount control signal V ₁ for controlling the amount of light emitted by the organic EL element for each pixel of the image so that an image is formed on the photosensitive material P with a predetermined density. stores the first light quantity control signal V _1, calls the first light quantity control signal V ₁ corresponding to the portion to be exposed and recorded in an organic EL device, switching the first light quantity control signal V ₁ section 68 is a part to be supplied to 68. The first signal generator 60 determines the density to be recorded determined from the image input signal by referring to a predetermined reference table, and uses the light quantity-density characteristic of the photosensitive material P so as to realize this density. The amount of light emitted from the organic EL element is determined, and the control level of the amount of light emission in the first light amount control signal V ₁ is determined from the amount of light emitted. The light emission amount control level is a pulse width of a pulse signal in which the pulse width is divided stepwise by 12 bits (0 to 4095 levels) in order to perform exposure by controlling the pulse light emission of the organic EL element according to the light emission time. The level. For example, when the exposure amount of the photosensitive material P is increased, in order to increase the light emission amount of the organic EL element, the pulse width is increased to increase the control level of the light emission amount. In this manner, a pulse signal having a predetermined control level is generated as the _first light quantity control signal V ₁ . Therefore, the first light quantity control signal V ₁ is a signal for controlling exposure by a so-called density modulation method in which the density of the image is determined by the density of the dot image to be exposed and recorded by the light emission amount of the organic EL element.

The second signal generation unit 62 controls ON / OFF of the exposure by the organic EL element so that the exposure is performed with a predetermined exposure pattern by switching ON / OFF of the exposure by the dot image formed on the photosensitive material P. / OFF control signal V ₂ and generates a second light quantity control signal V ₃ to control the amount of light emission of the organic EL element during the exposure for each pixel of the image, oN / OFF control signal V ₂ and the second stores the light quantity control signal V _3, the stored oN / OFF control signal V ₂ and the second light quantity control signal V _1, and sequentially calls to correspond to a portion to be exposed and recorded by the organic EL element, switching This is a part that is supplied to the unit 68.

ON / OFF control signal _{V 2} from the image input signal, an exposure pattern is defined, expressed by ON / OFF of an exposure of an image dot is the signal defining ON exposure by the image of each dot, the OFF . Second light quantity control signal V _3, when performing exposure by the exposure pattern, so that the image of the dot at a given concentration in the photosensitive material P is formed, a signal for controlling the light emission amount of the organic EL element. At that time, from the most significant bit of the image input signal is a digital signal, a second light quantity control signal V ₃ is generated, the ON / OFF control signal V ₂ from the lower bits are generated. That, ON / OFF control signal _{V 2} and the second light quantity control signal _{V 3,} the emission of ON by the exposure pattern, OFF is controlled, moreover, the light emission amount at the time of light emission is controlled. The gradation of the image is finely reproduced by ON / OFF of the dot image using the exposure pattern so as to interpolate between the gradations determined by the density of the dot image formed by controlling the light emission amount. . As a result, exposure is performed using both a so-called density modulation method and area modulation method that finely reproduces the density of an image to be recorded by the exposure pattern while roughly controlling the light emission amount of the organic EL element.

Further, the second signal generator 62, the noise signal supplied from the noise signal component 70 is added to the low-order bits of the image input signal is ON / OFF control signal V ₂ is generated. The noise signal component unit 70 is a part that generates a noise component having a predetermined magnitude and supplies it to the second signal generation unit 62 and the switching unit 68.

For example, when generating a 12-bit second light amount control signal V ₃ and a 4-bit ON / OFF control signal V ₂ (4 × 4 exposure pattern) from a 14-bit image input signal, the signal information is 16 bits ( = 12 + 4) This is necessary, and the quantum number is excessive with respect to 14 bits of the image input signal. For this reason, a noise component is added to the lower bits (15, 16 bits) of 14 bits or less. Upon thus generated in the ON / OFF control signal V _2, the exposure pattern is defined noise component is added. Therefore, even if an image input signal is the same, since the type of the exposure pattern defined is changed by noise components, the image of the dots to be recorded using the ON / OFF control signal V ₂ exposure pattern is always the same pattern Therefore, the periodic density change due to the exposure pattern does not occur.

  The characteristic data storage unit 64 stores light quantity-density characteristics that define the correspondence between the amount of emitted light and the image forming density formed at this time in the photosensitive material P to be recorded. A density characteristic that defines the correspondence between the element control level and the image formation density formed at this control level is stored, and the density characteristic is appropriately called to the light emission amount calculation unit 65 and the determination unit 66.

The light emission amount calculation unit 65 is a part that determines the amount of light to be emitted from the supplied image input signal and supplies the determined amount of light to the determination unit 66. Specifically, the light quantity-density characteristic of the photosensitive material P is called from the characteristic data storage unit 64, and the light emission amount to be emitted from the organic EL element is determined using this, and supplied to the determination unit 66.

The determination unit 66 determines the control level of the light emission amount control signal V ₁ using the light emission amount supplied from the light emission amount calculation unit 65 and is determined using the density characteristic called from the characteristic data storage unit 64. The difference between the image formation density at the control level and the image formation density at the adjacent control level is compared with a predetermined threshold value and is determined. Here, the threshold value is an added value obtained by adding a noise component to a predetermined value. Therefore, the threshold value varies with each comparison.
Control levels, for example, when the light emission amount control signal V ₁ is assumed to be represented by 12 bits, is represented at the level of 4095, the difference in image forming density of the adjacent levels and the level is compared with a threshold value .

4 (a) is the concentration that represents the relationship between the concentration to be formed on the photosensitive material P control level at the control level when performing control in light emission amount control signal V ₁ of the 12-bit (0 to 4095 levels) It is a graph of an example of a characteristic. FIGS. 4 (a) curve S ₁ in represents the density characteristics of the conventional light-sensitive material P, the curve S _2, S ₃ shows the density characteristics when the sensitivity is changed by the temperature, humidity or aging deterioration . FIG. 4B shows a distribution of density differences in image forming density between adjacent control levels in such three types of density characteristics. A straight line T in FIG. 4B is a straight line at a density difference of 0.003. This density difference 0.003 is a limit value as to whether or not a person can visually recognize a level difference. If this limit is exceeded, it means that a person can visually recognize this level difference. Therefore, when the density characteristics change from the curve S ₁ in the curve S _2, as is clear from the relationship between the curve U ₂ and the straight line T representing the density difference in the curve S ₂ (see FIG. 4 (b)), the concentration A density step is visually recognized in the range of 0 to 1.5. Therefore, when the density characteristic of the photosensitive material P having the reference density characteristic changes due to environmental change or the like, the gradation of the image reproduced on the photosensitive material P is not smoothly connected.

For this reason, the determination unit 66 determines a portion where the gradation of the image reproduced on the photosensitive material P is not smoothly connected based on the difference in image formation density between the adjacent control levels. At that time, an addition value obtained by adding the noise component supplied from the noise signal generation unit 70 to a predetermined value is used as a threshold value for comparison and determination. Thus comparison, in the determination, for use as a threshold obtained by adding a noise component to a predetermined value, the switching section 68 to be described later, by using a fixed threshold, ON / OFF of the first light quantity control signal V ₁ switching uniformly to the control signal V ₂ and the second light quantity control signal V _3, there is a case where the gradation of the image switching unit content is not necessarily lead to smooth. Since the limit value of the density step that can be visually recognized by humans is 0.003, 0.002 is used as the predetermined value.
In this way, the difference in image formation density between the predetermined control level and the adjacent control level is compared and determined with respect to the threshold value obtained by adding the noise component to the predetermined value. Information on the determination result is supplied to the switching unit 68.

The switching unit 68 performs signal switching between the first light emission amount control signal V ₁ or the ON / OFF control signal V ₂ and the second light emission amount control signal V ₃ in accordance with the supplied determination result information. This is a part that is generated as a light emission control signal.
That is, in accordance with information supplied determination result from the determination unit 66, the ON / OFF control signal V ₂ and the second light emission amount control signal V _3, or the first light emission amount control signal V ₁ is selected. For example, when the difference in image formation density is larger than the threshold value, the ON / OFF control signal V ₂ and the second light emission amount control signal V ₃ are selected, and in other cases, the first light emission amount control signal V ₁ is selected. It switches as follows. Thus, a light emission control signal is generated by the selected signal and supplied to the drive signal generation unit 54.

Thus, switch the signal at the switching unit 68 is performed at a concentration modulation system recording an image by using the first light emission amount control signal V _1, step a degree that can be visually recognized human between adjacent control level This is because there are cases where the gradation of density does not connect smoothly. Therefore, when there is a high possibility that the gradation of concentration does not lead to a smooth, first light emission amount control from signals V ₁ switches the signal to the ON / OFF control signal V ₂ and the second light emission amount control signal V ₃ concentration modulation scheme The exposure recording of the image is performed by the area modulation method.
In general, a human being can visually recognize a level difference when the density difference exceeds 0.003. Therefore, by setting 0.002 that is slightly lower than the density difference as a predetermined value and using a value obtained by adding noise components as a threshold value, signal switching can be made random within a certain range.
The light emission control signal generated in this way is supplied to the drive signal generation unit 54.

  The drive signal generation unit 54 converts the supplied pulse control signal into a drive signal for driving the light emitting head 26, and matches the timing of movement of the photosensitive material P by the conveying roller pair 20, 22. The light emitting head 26 is driven so as to expose a predetermined position.

Note that the second signal generation unit 62 in the signal processing unit 16 may be a second signal generation unit 62 as shown in FIG. That is, the size of the exposure pattern is different. For example, in the signal generation unit A (62A), the dot image is a 2 × 2 exposure pattern, and in the signal generation unit B (62B), the signal is a 3 × 3 exposure pattern. generating unit C (62C), with an exposure pattern of 4 × 4, and generates a plurality of oN / OFF control signal _{V 2} and the light emission amount control signal _{V 3} respectively different supplies it to the switching unit 72, switching unit In 72, the signal may be selected and switched according to the determination result in the determination unit 66.

In this case, a method of selecting from a plurality of different ON / OFF control signals V ₂ and light emission amount control signals V ₃ is, for example, 2 if the difference in image formation density between the control level and the adjacent control level is ΔD. A signal generated using an exposure pattern of dots × 2 dots is determined by using ΔD / (2 × 2) ^(1/2) to compare with the above-described threshold value. For a signal generated using an exposure pattern of 3 dots × 3 dots, a determination is made by using ΔD / (3 × 3) ^(1/2) and comparing with the above-described threshold value. A signal generated using a 4 dot × 4 dot exposure pattern is determined by using ΔD / (4 × 4) ^(1/2) in comparison with the threshold value described above. These comparisons and determinations are performed in order of increasing exposure pattern size. In the above example, ΔD / (2 × 2) ^(1/2) , ΔD / (3 × 3) ^(1/2) , ΔD / (4 × 4) It is preferable to perform switching in the order of ^(1/2) , and among these, it is preferable to switch to select a signal that falls below the threshold value first. Further, generation of different ON / OFF control signal _{V 2,} in addition carried out by changing the size of the exposure pattern to determine the exposure ON / OFF of the image dots, Froid type, the error diffusion using filters of different sizes Jariv type such as law may be generated ON / OFF control signal _{V 2} to determine the ON / OFF of the applied exposure.

  In such a color printer 10, first, density characteristics as shown in FIG. 4A are stored in a memory or the like of the characteristic data storage unit 65. Since such density characteristics are specified by the type of the photosensitive material P, the density characteristics are stored for each type of the photosensitive material P, and the photosensitivity stored according to the type of the photosensitive material P used for exposure recording. You may make it read the density | concentration characteristic of the material P. FIG. Before recording on the photosensitive material P, a driving current is applied to the light emitting head 26 using a light emission control signal having a different pulse width quantized to 12 bits or 14 bits in the color printer 10 in advance, and the light emission control signal The density characteristics of the photosensitive material P may be obtained by causing the organic EL element to emit light at each control level and measuring the image forming density formed on the photosensitive material P using a known densitometer or the like. In this case, since the density characteristic of the photosensitive material P immediately before exposure recording is used, it is possible to finely control the light emission of the organic EL element in accordance with the change in density characteristic due to an environmental change or the like.

In the control signal generation unit 52, when an image input signal is supplied from the image processing device 18, the first light emission amount control signal V ₁ , the ON / OFF control signal V ₂ and the second light emission amount control signal are obtained from this image input signal. V ₃ is the first, is generated in the second signal generating unit 60, 62, these signals are first stored in a memory (not shown) each with a second signal generating unit 60, 62. Incidentally, ON / OFF control signal V ₂ and the second light emission amount control signal V _3, the noise component supplied from the noise signal generator 70 is generated using an image input signal added.

On the other hand, the light emission amount calculation unit 65 determines the light emission amount to be emitted by the organic EL element from the image input signal with reference to the light amount-density characteristic of the photosensitive material P, and this light emission amount is supplied to the determination unit 66.
In switching section 68 first uses the supplied light emission amount, control level for controlling the first light emission amount control signal V ₁ is determined. Next, the difference between the image formation density formed at this control level and the image formation density formed at the adjacent control level is compared with a predetermined threshold, that is, a threshold obtained by adding a noise component to a predetermined value. is, if the difference exceeds a threshold, ON / OFF control signal _{V 2} and the second light emission amount control signal _{V 3} is selected. If the difference is less than or equal to the threshold, the first light emission amount control signal V ₁ is selected. As described above, the switching unit 68 selects a signal. A light emission control signal is generated by the signal thus selected.

The generated light emission control signal is supplied to the drive signal generation unit 54, converted into a drive signal of an organic EL element that realizes control by the light emission control signal in the drive signal generation unit 54, and supplied to the light emitting head 26.
In the light emitting head 26, light emission of the organic EL element is controlled by this drive signal, and exposure by the density modulation method or exposure by the density modulation method and the area modulation method is performed. Of course, such a light emission control signal is supplied to each of the plurality of organic EL elements arranged in one direction, and is scanned and recorded in the main scanning direction (X direction). Further, since the photosensitive material P is conveyed in the sub-scanning direction (Y direction), the exposure recording is continuously performed by the light emitting head 26, whereby an image is recorded in a two-dimensional manner.
The photosensitive material P on which the image is exposed and recorded is supplied to the processor 13 and developed.

As described above, according to the present invention, the first light amount control signal V ₁ for forming an image by the density modulation method and the density modulation method according to the difference between the image formation density and the image formation density at the adjacent control level. and because the combination of area modulation scheme finely set the tone of the image to generate the emission control signals by switching the signal between the ON / OFF control signal V ₂ and the second light quantity control signal V ₃ to form an image, The density difference between the gradations of the image formed on the photosensitive material P becomes so small that the level difference is not visually recognized. Therefore, the gradation of the image is reproduced smoothly.

In the control signal generation unit 52, in each of the first signal generation unit 60 and the second signal generation unit 62, the first light amount control signal V ₁ , the ON / OFF control signal V _2, and the second light amount control signal of each pixel of the image. while previously produce the V ₃ is configured to store in memory, the determining unit 66, while the difference scanning of each pixel of the image on the image forming density in the control level adjacent to the image forming density in the control level, The first signal generation unit 60 or the second signal generation unit 62 generates a signal to be generated as a light emission control signal each time, comparing and determining the threshold value, according to the comparison and determination result. May be.

  The image forming apparatus and the image forming method of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

1 is a block configuration diagram of a color printer that forms an image by exposing a photosensitive material as an example of an image forming apparatus of the present invention. (A)-(c) is a block diagram which shows the head structure of the light emission head in the color print head shown in FIG. FIG. 2 is a block configuration diagram of a control signal generation unit that is a main part of the color printer shown in FIG. 1. (A) is a graph of an example of the density | concentration characteristic showing the relationship between the control level of the emitted light amount of an organic EL element, and the image formation density formed in a photosensitive material at this control level, (b) is three types of density characteristics. FIG. 6 is a diagram illustrating a difference in image formation density between adjacent control levels in density characteristics. It is a block block diagram in the other example of the control signal generation unit which is the principal part of the color printer shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color printer 12 Head unit 13 Processor 14 Photosensitive material supply unit 16 Signal processing unit 18 Image processing apparatus 20, 22 Roller pair 20,22
24 driving motor 25 moving unit 26 light emitting head 26A glass substrate 26R R light emitting array 26G G light emitting array 26B B light emitting array 26C, 26D, 26E, 26F, 26H driving 28 lens array 40a, 40b, 40c, 40d anode electrode 42a, 42b Cathode electrode 44 Hole transport layer 46 Organic layer 48 Electron transport layer 50 Color filter 52 Control signal generation unit 54 Drive signal generation unit 60 First signal generation unit 62 Second signal generation unit 64 Characteristic data storage unit 65 Light emission amount Calculation unit 66 Determination unit 68, 72 Switching unit 70 Noise signal generation unit

Claims (6)

An image forming apparatus that controls the amount of light emitted from a light emitting element using an image input signal and records an exposure image on a photosensitive material,
A light emitting element that emits light according to a light emission control signal supplied;
A control signal generation unit that generates the light emission control signal from an image input signal,
The control signal generation unit includes:
A first signal generation unit that generates a first light amount control signal that controls the amount of light emitted by the light emitting element so that an image is formed on the photosensitive material at a predetermined density;
An ON / OFF control signal for controlling ON / OFF of the exposure by the light emitting element and an amount of light emitted by the light emitting element at the time of exposure so that a portion of the photosensitive material to be recorded is exposed by ON / OFF of the exposure. A second signal generator for generating a second light quantity control signal to be controlled;
A calculation unit for determining a light emission amount to be emitted from the light emitting element from an image input signal using a light amount-density characteristic of the photosensitive material;
The difference between the image formation density formed on the photosensitive material at the control level of the light emission quantity in the first light quantity control signal determined by this light emission quantity and the image formation density formed at the control level adjacent to this control level. A signal switching unit that switches the signal between the first light amount control signal, the ON / OFF control signal, and the second light amount control signal according to the size, and generates the light emission control signal; An image forming apparatus comprising: The second signal generation unit generates an ON / OFF control signal and a second light quantity control signal corresponding to each exposure pattern so that the photosensitive material is exposed by exposure patterns having different sizes,
The switching unit is selected from a plurality of exposure patterns so that a difference between an image formation density at a control level of light emission amount determined from an image input signal and an image formation density at an adjacent control level is equal to or less than a predetermined value. The image forming apparatus according to claim 1, wherein an ON / OFF control signal and a second light quantity control signal corresponding to one exposure pattern are switched as signals to be controlled by the light emitting element.   The image forming apparatus according to claim 1, wherein the control signal generation unit generates the ON / OFF control signal from an image input signal obtained by adding a first noise component.   The control signal generation unit includes a determination unit that compares and determines an image formation density difference between adjacent control levels with an addition value obtained by adding a second noise component to a predetermined value. 4. The image forming apparatus according to claim 1, wherein the switching unit switches the signal to generate the light emission control signal. 5.   The image forming apparatus according to claim 1, wherein the light emitting element is an organic electroluminescence element. An image forming method for exposing and recording an image on a photosensitive material by controlling a light emission amount of a light emitting element using an image input signal,
A first signal generation step of generating a first light amount control signal for controlling the amount of light emitted by the light emitting element from the image input signal so that an image is formed on the photosensitive material at a predetermined density;
An ON / OFF control signal for controlling ON / OFF of exposure by the light emitting element, and an amount of light emitted by the light emitting element for this exposure so that a portion of the photosensitive material to be recorded is exposed by ON / OFF of the exposure. A second signal generation step of generating a second light amount control signal for controlling the image from the image input signal;
The light emission amount to be emitted from the light emitting element is determined from the image input signal by using the light quantity-density characteristic of the photosensitive material, and is determined on the photosensitive material at the control level of the light emission quantity in the first light quantity control signal determined by the light emission quantity. The first light amount control signal generated in the first signal generation step according to the difference between the formed image formation density and the difference between the image formation density formed at the control level adjacent to the control level. And a control signal generation step of generating the light emission control signal by switching the signal between the ON / OFF control signal and the second light quantity control signal generated in the second signal generation step. And an image forming method.

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