JPH10161045A - Method for recording image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily correct shading without reducing the number of expressible gradation by correcting exposure data so as top indicate a certain exposure for the picture element of a peripheral part so as to show the exposure of specified times and obtaining it form the total of the exposure of plural times in the case than corrected exposure exceeds the maximum exposure of one time. SOLUTION: Recording light L is modulated for each picture element based on the exposure data by a spatial modulation element 13, and photosensitive material is exposed by the recording light L, so that a multilevel image is recorded. When exposure values made by the picture element obtaining a maximum exposure value and other specified picture elements at the time of modulating the recording light L based on the same exposure data out of the plural picture elements of the spatial modulation element 13 are respectively made as E and E/S, the exposure data showing the exposure (n) for a specified picture element at the time of recording the multilevel image is corrected so as to show the exposure of nearly nS. In the case that the exposure value corrected exceeds the maximum exposure per one exposure, the exposure corrected is obtained from the total of the exposure of the plural times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image recording method using a spatial light modulator, and more particularly, to an image recording method capable of correcting shading of a spatial light modulator or the like.

[0002]

2. Description of the Related Art Conventionally, a recording light is modulated by a spatial light modulator having a plurality of pixels arranged one-dimensionally or two-dimensionally, and the recording light is used to expose a photosensitive material to give gradation to the photosensitive material. 2. Description of the Related Art An image recording apparatus for recording an image is known.

In this type of image recording apparatus, when recording light is modulated by different pixels of the spatial light modulator based on the same exposure data, different portions of the photosensitive material exposed by each recording light are originally different from each other. Sometimes it should be the same concentration, but not so. This phenomenon is generally called shading, and is caused by non-uniform characteristics between pixels of the spatial light modulator, and non-uniform characteristics of an optical system that projects an image generated by the spatial light modulator onto a photosensitive material. ing.

Conventionally, in order to correct this shading, so-called solid exposure is performed by giving the same exposure data to each pixel of the spatial light modulation element, and the light exposure is performed based on the density distribution in the photosensitive material at that time. The exposure data is corrected for each pixel so that the amount of exposure received by the material is constant in any part thereof.

For example, when the exposure amount at the central portion of the image is 10 and the exposure amount at the peripheral portion of the image is 5 when the solid exposure is performed, if it is desired to obtain a uniform exposure density at both portions, the exposure at the peripheral portion is required. Exposure data of the central part
If the correction is made so as to be double the level, the exposure densities of both portions become equal.

Basically, when the exposure data is corrected in this way, not only when a uniform exposure density is obtained, but also when ordinary image exposure is performed, shading is corrected, and an appropriate image without density unevenness is recorded. Will be done.

[0007]

However, in such a correction method, there is a difference in the number of gradations that can be expressed between the central portion and the peripheral portion of the image. That is, in the above example, assuming that the resolution of the light exposure of the spatial light modulator is originally 256 levels, the central part can express 256 gradations as it is, while the peripheral part has a half of 128 gradations. Only the number of gradations can be expressed.

Therefore, it is conceivable to use a spatial light modulator having sufficient exposure amount resolution in advance in consideration of the shading correction amount. That is, in the above example, 51
If a spatial light modulator having a two-level exposure resolution is used, 256 gradations can be expressed even in the peripheral portion of the photosensitive material.

However, in this case, when a D / A converter is used to output digital image data from the image data storage means or the like to the spatial light modulator, the number of bits is large and the D / A converter is very expensive. A problem arises that an A converter is required. When a spatial light modulator of a type that can drive each pixel directly with digital image data is used, a D / A converter is unnecessary, but the problem of a large circuit scale due to an increase in the number of bits still remains. Will be.

Further, if the shading characteristics change significantly during repeated use of the image recording apparatus, there arises a problem that the circuit must be largely changed.

The present invention has been made in view of the above circumstances, and has as its object to provide an image recording method capable of easily correcting shading without reducing the number of expressible gradations.

[0012]

According to the image recording method of the present invention, as described above, the recording light is modulated for each pixel based on the exposure data by the spatial light modulator having a plurality of pixels. In the image recording method of exposing a photosensitive material according to and recording a gradation image on the photosensitive material, a maximum exposure when a recording light is modulated based on the same exposure data in a plurality of pixels of a spatial light modulator. Pixel p _MAX to get quantity
When the respective exposure amounts of the specific pixels p are E and E / S, the exposure data indicating the exposure amount n for the specific pixels p is substantially nS when a gradation image is recorded. If the corrected exposure value exceeds the maximum exposure amount per exposure, the corrected exposure amount is obtained as a sum of a plurality of exposures. It is characterized by doing so.

[0013]

According to the above example, if the pixel at the center of the image is the pixel p _MAX and the peripheral pixel is the specific pixel p, S = 2. Therefore, when a gradation image is recorded, the exposure data indicating the exposure amount n for the pixels p in the peripheral portion is indicated so as to indicate an exposure amount of approximately 2n, that is, the original exposure data. If the correction is made so that the exposure amount is about twice as high as the exposure amount, the shading is corrected. Of course, the exposure data indicating the exposure amount n may be corrected so as to indicate an exposure amount of exactly 2n, and this is most preferable.

In this case, if the exposure resolution of the spatial light modulator is originally 256 levels, the pixel p _{MAX in the} central portion can express 256 tones, while the peripheral portion can express 256 tones. Of the specific pixel p is 128
Only the number of gradations of can be expressed.

However, in the method of the present invention, if the value of the corrected exposure exceeds the maximum exposure per exposure, the corrected exposure is obtained by summing a plurality of exposures. _Therefore , the required number of gradations can be expressed by pixels other than the pixel pMAX. In other words, in the above example,
By performing exposure twice for the peripheral pixel p,
In this case, 256 gradations can be expressed.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of an image exposure apparatus that performs the image recording method of the present invention.
As shown in the figure, this image exposure apparatus is a color photosensitive material.
A light source 11 such as a halogen lamp that emits white recording light L for exposing the light source 10, and a light source 11 that is arranged so that the light source 11 is located near the focal position and parallelizes the recording light L emitted from the light source 11. An optical lens 12, a mirror array device 13 disposed at a position where the collimated recording light L is incident, and an imaging lens 14 disposed at a position where the recording light L reflected by the mirror array device 13 is incident And a filter plate 15 inserted in the optical path of the recording light L in front of the mirror array device 13.
And

Further, the mirror array device 13 and the imaging lens
A light absorbing member 18 is disposed at a position off the optical path of the recording light L between the light absorbing member 18 and the recording light L. And the photosensitive material 10 and the imaging lens
A paper mask 19 having an opening for defining the irradiation size of the recording light L on the photosensitive material 10 is provided between the paper mask 19 and the recording medium L.

The photosensitive material 10 is wound and held around the supply shaft 5, is fed out from the front end side, and is stretched between the nip rollers 16, 17. The above-described imaging lens 14 and other optical systems are disposed so that the recording light L enters the photosensitive material 10 in the stretched portion. Then, the photosensitive material 10 is pitch-fed by a predetermined length downward in the figure by rotating the nip rollers 16 and 17.

The mirror array device 13 includes a driver 30
Driven by The driver 30 is provided with an exposure controller that receives image data D indicating a color gradation image.
Drive-controlled by 31.

The mirror array device 13 has a plurality of micromirrors 20 arranged in a two-dimensional array on a silicon substrate 21 as shown in an enlarged view in FIG. Each micromirror 20 is formed of an aluminum alloy or the like into a square with one side of about 10 μm. Each micro mirror
The size a ′ of the 20 mirror arrangement directions X and the size b ′ of the mirror arrangement direction Y are respectively the mirror arrangement pitches a and b.
The length is close to.

In FIG. 2, one micro mirror at the center is provided.
20 is omitted, and as shown therein, a drive unit for driving each micromirror 20 is provided.
The drive unit includes a yoke 22 for supporting the micro mirror 20 via a mirror support post (not shown), a pair of torsion hinges 23 for holding the yoke 22, and a pair of address electrodes 24 and 24.
And a bias bus (not shown) and the like arranged below these elements, and the direction of the torsion hinge 23 is changed by electrostatic force in accordance with the voltage applied by the bias bus and the address electrodes 24, 24. It is configured to change.
Each micromirror 20 is provided with a light non-reflective mask 25 for limiting its effective aperture.

The application of voltage to the address electrodes 24, 24 for each micromirror 20 is controlled by the driver 30 shown in FIG. That is, while no voltage is applied through the address electrodes 24, 24, the torsion hinge 23 (that is, the micro mirror 20
Is) parallel to the substrate 21, but when a voltage of a predetermined polarity is applied to one address electrode 24 and a complementary voltage of an opposite polarity is applied to the other address electrode 24,
The micromirror 20 has an angle −
When the state of voltage application to the address electrodes 24 and 24 is reversed from the above, the micromirror 20 is inclined at an angle θ with respect to the substrate surface as shown in FIG.

Therefore, in the case of FIG. 3, the recording light L reflected by the minute mirror 20 is deviated from the opening of the imaging lens 14, and in FIG. 4, the recording light L reflected by the minute mirror 20 passes through the imaging lens 14. Then, the photosensitive material 10 reaches the photosensitive material 10. In this way, the incidence of the recording light L on the photosensitive material 10 can be controlled for each micromirror 20. The recording light L reflected by the micromirror 20 in the OFF state is absorbed by the light absorbing member 18 shown in FIG.

The ON time of each micromirror 20 is modulated on the basis of image data D for each pixel within the frame time, so that a photosensitive material is provided for each micromirror 20.
The amount of light incident on the photosensitive material 10 is controlled, and the photosensitive material 10 is exposed to a gradation image.

In FIGS. 3 and 4, the imaging lens 14 is
It is shown only for indicating the opening angle range, and its size and position are different from actual ones. In the following, the states of the micromirror 20 as shown in FIGS. 3 and 4 are referred to as an OFF state and an ON state, respectively.

The above-mentioned filter plate 15 holds color filters of R (red) filter, G (green) filter and B (blue) filter, and a light shielding plate. Then, the respective color filters are sequentially inserted into the optical path of the recording light L,
During the color filter insertion period, the mirror array device 13 is driven based on each color image data corresponding to the color. During the switching period of each color filter, all the micro mirrors 20 are turned off.

The color light-sensitive material 10 is thus sequentially exposed by the modulated red, green and blue light, and a color photographic latent image is recorded thereon. Thereafter, the photosensitive material 10 is pitch-fed as described above, and undergoes a normal developing process in a developing unit (not shown). Thereby, the exposed image is visualized.

When the photosensitive material 10 is pitch-fed,
The light shielding plate of the filter plate 15 is inserted into the optical path of the recording light L. A nip roller 16 for feeding the photosensitive material 10 at a pitch,
The drive of the light source 17 and the light source 11 is controlled by the print controller 32. Further, the above-described exposure controller 31 is also controlled by the print controller 32. The print controller 32 operates upon receiving a command from a main CPU (not shown).

Here, the characteristics such as reflectivity are not uniform among the micromirrors 20 which become one pixel of the mirror array device 13, or the characteristics of the optical system such as the imaging lens 14 are uneven. If so, the shading described above occurs. Hereinafter, a description will be given of how to prevent the occurrence of density unevenness in an exposed image due to the shading.

FIG. 5 shows the exposure controller shown in FIG.
It shows the detailed configuration of 31. As shown here, for example, 8-bit image data D carrying a color gradation image is input to a table conversion section 40 of an exposure controller 31, where it is referred to a LUT (look-up table) to generate a 12-bit image data. It is converted into exposure data DE.

In this embodiment, the exposure time of the photosensitive material 10 is controlled to 256 (including the case where the exposure amount is zero) by modulating the ON time of each micro mirror 20 within the frame time. Here, the 256 types of exposure amounts are defined as 0, 1, 2, 3 assuming that the unit exposure amount is 1 for convenience.
... 255. The above-mentioned exposure data DE specifies the micromirror ON time for obtaining one of the 256 exposure amounts.

The above exposure data DE is an exposure data correction unit.
The data is input to 41, where it is subjected to a process for correcting the shading, and is converted into exposure data DE '. Hereinafter, this correction processing will be described in detail.

FIG. 6 shows an example of the shading characteristics in one direction of the mirror array device 13. That is, when each micromirror 20 of the mirror array device 13 is turned on for the same time based on the same exposure data and the so-called solid exposure is performed, the exposure amount received by the photosensitive material 10 should be uniform regardless of its position. However, this is not the case, and a distribution of the exposure amount occurs as shown in FIG.

Here, the exposure amount (maximum exposure amount) by the micro mirror 20 at the position x _{0 in} FIG. 6 is represented by E, and the exposure amount by the micro mirror 20 at the position x is represented by E / S. In that case, the position x
The micromirror 20 of ₀ is driven based on the given exposure data DE as it is, while the exposure data DE of the micromirror 20 at the position x indicates an exposure amount S times the exposure amount originally indicated. If the micro mirror 20 at the position x is driven based on the corrected exposure data DE ′,
Shading is corrected, and the occurrence of density unevenness is suppressed. Note that S is referred to as a shading correction coefficient.

The exposure data correction section 41 converts the exposure data DE into exposure data DE 'according to the above principle. For example, if S = 1.6 for the micromirror 20 at the position x, assuming that the exposure data DE for the micromirror 20 indicates the aforementioned exposure amount “5”, that is, five times the unit exposure amount, the exposure data The correction unit 41 converts the exposure data DE into exposure data DE ′ indicating the exposure amount “8”. Further, assuming that the exposure data DE for the micromirror 20 at the position x indicates, for example, the exposure amount “3”, the exposure data correction unit 41 calculates the exposure data DE as 1.6 × 3 =
Exposure data DE ′ indicating an exposure amount “5” closest to 4.8
Convert to

In general, the above description indicates that the exposure data DE for the micromirror 20 at the position x is equal to the exposure amount “n”,
In other words, it indicates n times the unit exposure amount, and the shading correction coefficient for the micro mirror 20 at the position x is S
Expressing as (x), the exposure data correction unit 41 converts the exposure data DE into exposure data DE ′ indicating the exposure amount closest to nS (x) by applying rounding. Even if this rounding is performed, the fluctuation of the exposure amount due to the rounding is at most about half of the unit exposure amount, and this does not pose a practical problem not only in the high density region but also in the low density region.

The shading correction coefficient S for each position x
(X) can be properly determined by solid-exposing the photosensitive material 10 and measuring the exposure density at each position on the photosensitive material 10 at that time. In this example, the shading correction coefficient creation unit 42 that receives the measurement data on the exposure density creates a correction coefficient S (x) based on the measurement data, and inputs it to the exposure data correction unit 41.

The exposure data DE 'for each pixel (each micromirror 20) output from the exposure data correction unit 41 is temporarily stored in the divided exposure buffer memory 43. In the divided exposure buffer memory 43, the exposure data DE 'is stored separately for the first exposure data DE1 and the second exposure data DE2. That is, in this example, it is possible to handle pixels having the maximum shading correction coefficient S of 2, and the exposure amounts indicated by the exposure data DE ′ are 0, 1, 2, 3,.
It can take a value up to 0, but when the exposure amount is a value up to 255, all the exposure data DE '
On the other hand, when the value is 256 or more, the data indicating the exposure amount 255 is stored as the first exposure data DE1, and the data indicating the remaining exposure amount is stored as the second exposure data DE2.

At the time of image exposure, the exposure time control section 44 first reads out the first exposure data DE1 for each pixel from the divided exposure buffer memory 43, and drives each micromirror 20 with an ON time corresponding to the exposure amount indicated by the data. The drive control signal C1 to be driven is input to the driver 30 (see FIG. 1). Within the first frame time, each micromirror 20 is driven by controlling the ON time by the driver 30, whereby the exposure amount indicated by the first exposure data DE1 is obtained.

After the exposure in the first frame time is completed, the exposure time control unit 44 sets the divided exposure buffer memory 43
, The second exposure data DE2 for each pixel is read out, and a driver control signal C2 for driving each micromirror 20 is input to the driver 30 for an ON time corresponding to the exposure amount indicated by the second exposure data DE2. Each micro-mirror 20 is moved within the second frame time.
The driver 30 is driven by controlling the ON time, whereby the exposure amount indicated by the second exposure data DE2 is obtained.

As described above, the amount of exposure for each pixel can be controlled to only 256 types within one frame time. Therefore, if the above-described shading correction is performed, the pixel having the maximum 2 of the shading correction coefficient S is left as it is. Only half of the 128 gradations can be expressed. However, in this method, since the above-mentioned two exposures are repeated, a pixel having a maximum shading correction coefficient S of 2 can express 256 tones.

In the embodiment described above, the mirror array device 13 that controls the exposure amount by controlling the ON time of the micromirror 20 is used. The present invention is not limited to the spatial light modulation element that controls the exposure light, and can be similarly applied to a case where a spatial light modulation element that controls the exposure amount by intensity-modulating the recording light for each pixel, such as a liquid crystal display panel, is used. In such a case, the same effect can be obtained.

When such a spatial light modulator is used, the first exposure data DE1 and the second exposure data DE2 are converted to D / A signals in place of the exposure time control unit 44 shown in FIG.
For example, a unit that converts the signal and creates an analog signal for adjusting the degree of opening of each liquid crystal cell of the liquid crystal display panel may be used.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an example of an image exposure apparatus that performs a method of the present invention.

FIG. 2 is a partially cutaway front view of a mirror array device used in the image exposure apparatus.

FIG. 3 is a side view showing one state of a micro mirror of the mirror array device.

FIG. 4 is a side view showing another state of the micro mirror.

FIG. 5 is a block diagram illustrating a configuration of an exposure controller of the image exposure apparatus.

FIG. 6 is a schematic diagram illustrating shading characteristics of the image exposure apparatus.

FIG. 7 is an explanatory diagram illustrating division of exposure data in the image exposure apparatus.

[Explanation of symbols]

 10 Color photosensitive material 11 Light source 12 Condensing lens 13 Mirror array device 14 Imaging lens 15 Filter plate 16, 17 Nip roller 18 Light absorbing member 20 Micro mirror 22 Yoke 23 Torsion hinge 24 Address electrode 25 Micro mirror mask 30 Mirror array device Driver 31 Exposure controller 32 Print controller 40 Table conversion unit 41 Exposure data correction unit 42 Shading correction coefficient creation unit 43 Divided exposure buffer memory 44 Exposure time control unit L Recording light

Claims (1)

[Claims] 1. A spatial light modulating element having a plurality of pixels modulates recording light based on exposure data for each pixel, exposes a photosensitive material with the recording light, and records a gradation image on the photosensitive material. In the image recording method, among the plurality of pixels, when the recording light is modulated based on the same exposure data, each of the exposure amounts of the pixel p _MAX that obtains the maximum exposure amount and the other specific pixels p is E , E
When the gradation image is recorded, the exposure data indicating the exposure amount n for the specific pixel p is corrected so as to indicate the exposure amount of approximately nS. When the value of the amount exceeds the maximum exposure amount per one exposure, the corrected exposure amount is obtained as a sum of a plurality of exposures.