JP2002225342A - Method and circuit for correcting shading - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a circuit for correcting shading in which the shading characteristics of an image recorder can be corrected in a short time with high accuracy and a desired shading-free image can be obtained. SOLUTION: A mesh % variation rate due to variation in the quantity of light is determined as a function of scanning position Xi and set, as mesh % quantity of light coefficient data K(Xi), in a mesh % quantity of light coefficient data memory 76. Reference quantity of light data P0(Xi) is corrected using measured shading characteristics, i.e., mesh % correction quantity data ΔS(Xi) and the mesh % quantity of light coefficient data K(Xi) to determine corrected quantity of light data P'(Xi) according to a formula; P'(Xi)=(ΔS(Xi)/K(Xi)+1).P 0(Xi).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a shading correction method and a correction circuit in an image recording apparatus for two-dimensionally recording an image by scanning a recording medium with a light beam in a main scan and a sub-scan.

[0002]

2. Description of the Related Art FIG. 1 shows a schematic configuration of an image recording apparatus 2 for recording an image two-dimensionally. In the image recording apparatus 2, a laser beam L output from a laser light source 4 is modulated by a modulating means 5 such as an acousto-optic modulator (AOM) according to image information, and guided to a light deflecting means 6 such as a galvanometer mirror. By deflecting in the main scanning direction (arrow X direction) and guiding the recording medium F conveyed in the sub-scanning direction (arrow Y direction) via a scanning lens 8 such as an fθ lens, an image is two-dimensionally recorded. You.

When an image is recorded in this way, for example, there is a problem that the beam spot shape of the laser beam L applied to the recording medium F varies depending on the main scanning position due to the influence of the aberration of the scanning lens 8. . FIG.
Shows the fluctuation characteristics (shading characteristics) of the dot% of the image caused by the aberration. In addition, the light quantity of the laser beam L with respect to the recording medium F varies depending on the scanning position due to flare or other unnecessary light in the image recording apparatus 2 or an error in the flatness of the recording medium F. May occur.

[0004] If the light amount of the laser beam L fluctuates on the recording medium F, an image having a desired quality cannot be recorded. So, conventionally,
After obtaining the shading characteristics of the image recording apparatus 2, light amount correction is performed so as to obtain a constant target dot% indicated by a dotted line. Hereinafter, a conventional shading correction method will be described.

[0005] First, after setting a light amount data of the laser beam L to P and recording a test image, halftone% data S of the image is measured. Next, the laser beam L is changed by the light amount data ΔP, a test image is recorded with the light amount data (P + ΔP), and the dot% data (S + Δ
Measure S). From these results, halftone light quantity coefficient data K (= ΔS / (ΔP / P)), which is a halftone rate of change due to a change in the light quantity of the laser beam L, is obtained. FIG.
The halftone light quantity coefficient data K obtained as described above is shown.
Conventionally, the dot% light quantity coefficient data K is set to be constant regardless of the scanning position.

Next, based on the shading characteristics of the image recording apparatus 2 shown by the solid line in FIG. 2 obtained by the measurement, the halftone correction amount data ΔS (Xi) with respect to the target halftone data S0 shown by the broken line at the scanning position Xi is expressed by ΔS (Xi) = S0−S (Xi) (1), and in order to set the halftone correction amount data ΔS (Xi) to 0, the halftone correction amount data ΔP (Xi ) Is obtained as ΔP (Xi) = P0 (Xi) · ΔS (Xi) / K (2) Note that P0 (Xi) represents reference light amount data in which light amount fluctuations with respect to the scanning position Xi on the recording medium F due to fluctuations in the main scanning speed of the laser beam L by the light deflecting means 6 are corrected in advance.

By the way, the dot% correction amount data ΔS (Xi)
Does not always change at a constant rate with respect to the light amount correction amount data ΔP (Xi). That is, when the light amount correction amount data ΔP (Xi) is obtained as described above and the test image is recorded again with the corrected light amount data (P0 (Xi) + ΔP (Xi)), shading cannot be completely corrected. There are cases.

Therefore, it is necessary to repeat the operation of measuring the shading characteristics again to obtain the light amount correction amount data ΔP (Xi), thereby gradually bringing the data to the target dot% data S0. In this case, it has been pointed out that a considerable processing time is required until a desired image without shading can be recorded.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is possible to correct shading characteristics in an image recording apparatus with high accuracy and in a short time. An object of the present invention is to provide a shading correction method and a correction circuit capable of obtaining a desired image.

[0010]

In order to solve the above problems, the present invention provides a method for two-dimensionally recording an image by performing main scanning and sub scanning of a light beam on a recording medium. First, a change rate of a pixel area ratio due to a change in light amount of the light beam on a recording medium is obtained as a function of a scanning position.
And a second step of recording an image on the recording medium using the light beam set to a predetermined light amount, and measuring a pixel area ratio at each of the scanning positions of the image,
A third step of correcting the predetermined light amount of the light beam for each of the scanning positions based on a change rate of the pixel area ratio due to the light amount change, so that the pixel area ratio has a desired value corresponding to the scanning position; , Consisting of

The present invention also relates to a shading correction circuit in an image recording apparatus for two-dimensionally recording an image by performing main scanning and sub scanning of a light beam on a recording medium. A first holding unit that is set as a function of a scanning position of the light beam and holds a change rate of a pixel area ratio due to a change in light amount of the light beam on the recording medium; A second holding unit that holds shading data obtained by measuring a pixel area ratio at each of the scanning positions of an image recorded on the recording medium, and a change rate of the pixel area ratio due to the light amount change, Correction means for correcting the predetermined light amount from the shading data.

In this case, since the change rate of the pixel area ratio due to the change in the light amount of the light beam on the recording medium is set as a function of the scanning position, high-precision shading correction can be performed for each scanning position. . Also, since shading correction can be completed quickly with one process,
For example, the shading correction can be easily performed at an arbitrary time in response to a temporal change of the image recording apparatus. Therefore, it is possible to record an image while maintaining the accuracy of the image recording apparatus sufficiently.

[0013]

FIG. 4 shows a plate making system 30 to which the image recording apparatus of the present invention is applied. The printing plate preparation system 30 is a device (CTP (computer) for directly preparing printing plates for each color of Y, M, C, and K on which an image for preparing a color print is recorded without using a film.
to plate) device).

The plate making system 30 includes a plate feeder 34 for supplying a recording medium 32 before image recording, and an image recording apparatus for recording an image by scanning the recording medium 32 with a laser beam L corresponding to an image signal. 36 and a developing device 38 for developing the recording medium 32 on which the image is recorded. As the recording medium 32, for example, a photopolymer printing plate, a thermal printing plate, a silver salt diffusion transfer printing plate, or the like can be used.

The plate feeding device 34 holds a plurality of recording media 32 and pushes the recording media 32 to the image recording device 36 in the direction of the arrow.
Supply one by one.

The image recording device 36 conveys the recording medium 32 supplied from the plate supplying device 34 in the sub-scanning direction (the direction of the arrow Y) by the recording stage 40 and modulates the recording medium 32 according to the image signal from the image recording unit 42. By scanning the laser beam L in the main scanning direction (the direction of arrow X), a two-dimensional image (here, a halftone image) is recorded on the recording medium 32 by the area modulation method.

The developing device 38 develops an image recorded on the recording medium 32 supplied from the image recording device 36 and outputs a printing plate.

FIG. 5 shows an image recording unit 42 and its control circuit in the image recording device 36 shown in FIG.

The image recording unit 42 includes a laser light source 46 for outputting a laser beam L for recording an image on the recording medium 32, and an acousto-optic modulator (AOM) for modulating the laser beam L in accordance with image data. 48, an optical deflector 50 such as a galvanometer mirror and a resonant scanner for deflecting the modulated laser beam L in the main scanning direction (arrow X direction), and a scanning lens 52 such as an fθ lens. The laser beam L deflected in the main scanning direction (arrow X direction) by the optical deflector 50 is guided to the recording medium 32 conveyed in the sub scanning direction (arrow Y direction) via the scanning lens 52.

A control circuit for controlling the image recording unit 42 includes a shading correction circuit 54 (correction means) for correcting shading of the image recording device 36 by correcting the amount of the laser beam L output from the laser light source 46.
AOM that drives and controls the AOM 48 in accordance with the corrected light amount data corrected by the shading correction circuit 54 and the image data supplied from the image data memory 56.
It basically comprises a driver 58.

The AOM driver 58 includes an oscillator 60, a gain controller 62, a multiplier 64, and an amplifier 66. The drive signal output from the amplifier 66 is AOM driver 58.
48. The gain controller 62 is supplied with a gain control signal based on the corrected light amount data from the shading correction circuit 54, and the multiplier 64 is supplied with an image signal based on the image data from the image data memory 56.

The shading correction circuit 54 inputs the measured dot% data S (Xi) obtained by measuring the dot% (pixel area ratio) of the test image recorded on the recording medium 32 by the measuring device 68. An input unit 70, a measurement network% data memory 72 (second holding unit) for storing the measurement network% data S (Xi), a target network% data memory 74 for storing the target network% data S0 (Xi), % Light coefficient data K
(Xi) for storing halftone light amount coefficient data memory 76 (first holding means), light amount data memory 78 for storing light amount data P (Xi), and scanning speed fluctuation correction data ΔQ (Xi) for reference light amount data P0 And a D / A converter 82 for converting the corrected corrected light amount data P '(Xi) into an analog signal. Note that Xi represents a scanning position in the main scanning direction (the direction of the arrow X).

Although the target net% data S0 (Xi) has been described as a constant value independent of the scanning position Xi in FIG. 2, it may be set to a desired value corresponding to the scanning position Xi. The subtractor 84 calculates the halftone correction amount data Δ which is the difference between the measured halftone percent data S (Xi) and the target halftone percent data S0 (Xi).
S (Xi) is determined as ΔS (Xi) = S0 (Xi) −S (Xi) (3)

The dot% light amount coefficient data K (Xi) is light amount correction amount data ΔP which is a light amount change of light amount data P (Xi).
K (Xi) = ΔS (Xi) / (ΔP (Xi) / P (Xi)) (4) represents halftone correction amount data ΔS (Xi) for (Xi), and is a function of scanning position Xi. Is required. FIG. 6 shows an example of halftone light quantity coefficient data K (Xi). The divider 86 divides the dot% correction amount data ΔS (Xi) by the dot% light amount coefficient data K (Xi).

The light amount data P (Xi) is set as reference light amount data P0 in a state before being corrected, and is set in the light amount data memory 78 as a value independent of the scanning position Xi. Light intensity data P '(X
i). Note that the reference light amount data P0 is
The setting is made in accordance with the machine difference of the image recording device 36, the variation between lots of the recording medium 32, and the like.

The scanning speed fluctuation correction data ΔQ (Xi) is
It is data for correcting the reference light amount data P0 with respect to the fluctuation of the main scanning speed of the laser beam L by the optical deflector 50,
It is set according to the reference light amount data P0. The scanning speed fluctuation correction data ΔQ (Xi) is supplied to the adder 94 via the switch 92 only at the time of the first correction, and is added to the reference light amount data P0 from the light amount data memory 78. The output of the adder 94 is multiplied by ΔS (Xi) / K (Xi), which is the output of the divider 86, in the multiplier 88, and then added to the output of the multiplier 88 in the adder 90.

The printing plate preparation system 30 of this embodiment is basically configured as described above, and the operation thereof will be described next.

First, an operation of recording an image by the plate making system 30 will be schematically described.

Recording medium 32 supplied from plate feeding device 34
After being positioned on the recording stage 40, is transported to the image recording device 36. Next, the image recording unit 42
Accordingly, the recording medium 32 is scanned, and a desired image is recorded.

That is, the corrected light amount data P '(X) corrected by the shading correction circuit 54 shown in FIG.
i) is supplied from the light quantity data memory 78 to the D / A converter 82 and is converted into a gain control signal which is an analog signal, and then supplied to the gain controller 62 constituting the AOM driver 58. Further, an image signal which is turned on / off according to image data is supplied from an image data memory 56 to a multiplier 64 constituting the AOM driver 58.
Accordingly, the high-frequency signal output from the oscillator 60 is gain-adjusted by the corrected gain control signal in the gain controller 62, is controlled to be turned on / off by the image signal in the multiplier 64, is amplified by the amplifier 66, and is amplified by the amplifier 66. Is supplied to the AOM 48.

The laser beam L output from the laser light source 46 is modulated and controlled to a desired light intensity by the AOM 48, and is guided to the recording medium 32 via the optical deflector 50 and the scanning lens 52. As a result, the laser beam L is scanned in the main scanning direction (arrow X direction) on the recording medium 32 conveyed in the sub scanning direction (arrow Y direction), and an image is two-dimensionally recorded.

The recording medium 32 on which the image is recorded is again
After being conveyed in the sub-scanning direction (the direction of the arrow Y) by the recording stage 40, it is supplied to the developing device 38 and subjected to a developing process, whereby a plate is created. This process is performed on the printing plates of each color Y, M, C, and K.

Incidentally, in the image recording device 36 for recording an image as described above, the fluctuation of the dot% due to the fluctuation of the light amount of the laser beam L on the recording medium 32 depending on the scanning position Xi (shading (FIG. 2) )) Must be corrected in advance. Therefore, next, this shading correction method will be described in detail.

First, a method for setting the dot% light quantity coefficient data K (Xi) will be described with reference to the flowchart shown in FIG.

In the image recording device 36, the test image is recorded on the recording medium 3 based on the image data which should be 50% halftone%, for example, by gradually changing the light amount of the laser beam L.
2 (step S1), and the dot% at each light amount is measured for each scanning position Xi (step S2).

Next, the difference of each light amount at the scanning position Xi with respect to the reference light amount data P0 (Xi) (= P0 + ΔQ (Xi)) obtained by correcting the reference light amount data P0 with the scanning speed fluctuation correction data ΔQ (Xi) is shown. ΔP1, ΔP
2,..., ΔPn, and the differences in the measured dot% at each light amount with respect to the target dot% data S0 (Xi) at the scanning position Xi are ΔS1, ΔS2,. Xi), ΔP2 / P0 (Xi),
.., ΔS1, the difference of halftone dot from ΔPn / P0 (Xi),
... ΔSn are approximated by a straight line, and the slope of the straight line is obtained as halftone light quantity coefficient data K (Xi) at the scanning position Xi. This processing is performed for each scanning position Xi (step S3).

The halftone light quantity coefficient data K (Xi) obtained as described above is set in the halftone light quantity coefficient data memory 76 (step S4).

Next, a shading correction method using halftone light quantity coefficient data K (Xi) will be described with reference to the flowchart shown in FIG.

First, the initial setting of the shading correction circuit 54 is performed (step S11). In this initial setting, the measurement network% data memory 72 and the target network% data memory 7
4, setting of the scanning speed fluctuation correction data ΔQ (Xi) in the scanning speed fluctuation correction data memory 80, setting of the reference light amount data P 0 in the light amount data memory 78, and the image data memory 56.
Is set for test image data for generating shading correction data. Then, the switch 92 is set to the ON state.

Next, the image recording device 36 is driven to record an image for creating corrected light amount data P '(Xi) subjected to shading correction (step S12).

In this case, the target network% data S0 is stored in the measurement network% data memory 72 and the target network% data memory 74.
Since (Xi) is stored, the halftone dot correction amount data ΔS (Xi), which is the output of the subtractor 84, becomes 0. Therefore, the data supplied to the multiplier 88 via the divider 86 also becomes 0. On the other hand, the reference light amount data P0 output from the light amount data memory 78 is added to the scanning speed fluctuation correction data ΔQ (Xi) output from the scanning speed fluctuation correction data memory 80 in the adder 94, and the reference light amount data P0 ( Xi) (= P0 + ΔQ (Xi)) as an adder 9
0 is supplied. Then, the reference light amount data P0 (X
i) is corrected light amount data P ′ (Xi) (= P0 (X) in which only the scanning speed fluctuation correction data ΔQ (Xi) is corrected.
i)) is supplied to the D / A converter 82. After the correction light amount data P '(Xi) is calculated, the switch 9
Turn 2 off.

The D / A converter 82 outputs the corrected light amount data P '
After converting (Xi) into an analog signal, it is supplied to a gain controller 62 constituting the AOM driver 58. A
The OM driver 58 adjusts the gain of the high-frequency signal output from the oscillator 60 in the gain controller 62 based on the correction light amount data P ′ (Xi), which is a gain control signal. Next, the high-frequency signal whose gain has been adjusted is turned on / off in accordance with the test image data from the image data memory 56 supplied to the multiplier 64, and then amplified by the amplifier 66, and the acousto-optic modulator (AOM) 48.
Supplied to

The light quantity of the laser beam L output from the laser light source 46 is controlled by the acousto-optic modulator (AOM) 48 controlled as described above,
Then, the image is guided to the recording medium 32 via the scanning lens 52, and an image for shading correction is recorded. In this case, the recorded image is scanned in the main scanning direction (arrow X direction) according to the scanning speed fluctuation correction data ΔQ (Xi).
The shading due to the scanning speed fluctuation with respect to is corrected, but, for example, the shading caused by the aberration and flare by the scanning lens 52 is not corrected.

Then, the worker uses the measuring device 68 to
The dot% at each scanning position Xi of the image recorded on the recording medium 32 is measured (step S13), and the obtained measured dot% is obtained.
The data S (Xi) (see FIG. 2) is set in the measurement network% data memory 72 via the input unit 70 (step S1).
4).

In the shading correction circuit 54, the subtractor 84 sets the target net% data S 0 (Xi) set in the target net% data memory 74 and the measured net% data S (set in the measured net% data memory 72). Xi) is obtained and supplied to the divider 86 as halftone correction amount data ΔS (Xi) (step S15).

Next, the divider 86 converts the dot% correction amount data ΔS (Xi) obtained by the subtractor 84 into dot% light amount coefficient data K set in the dot% light amount coefficient data memory 76.
(Xi), and the light amount correction coefficient data ΔS (X
i) / K (Xi) is calculated (step S16). Note that this light amount correction coefficient data ΔS (Xi) / K (Xi)
Corresponds to the correction amount data ΔP (Xi) for the light amount data P (Xi) from the relationship of the equation (4).

The reference light quantity data P0 (Xi) supplied from the light quantity data memory 78 is supplied to the multiplier 88 and the adder 9
At 0, correction is performed using the light amount correction coefficient data ΔS (Xi) / K (Xi) obtained as described above, and corrected light amount data P ′ (Xi) is obtained (step S1).
7). In this case, the scanning speed fluctuation correction data ΔQ (Xi) set in the scanning speed fluctuation correction data memory 80
Has already been added to the measurement network% data S (Xi),
The switch 92 is turned off. Therefore,
Reference light amount data P output from light amount data memory 78
Only 0 (Xi) is supplied to the multiplier 88 and the adder 90. As a result, the corrected light amount data P ′ (Xi) is obtained as P ′ (Xi) = (ΔS (Xi) / K (Xi) +1) · P0 (Xi) (5)

The corrected light quantity data P '(Xi) obtained as described above is set in the light quantity data memory 78 in place of the reference light quantity data P0 (Xi), and the D / A
After being supplied to the converter 82 and converted into an analog signal (step S18), it is supplied to the gain controller 62 as a gain control signal (step S19).

Therefore, the AOM driver 58 controls the oscillator 6
After the gain of the high-frequency signal output from 0 is adjusted by the gain control signal based on the corrected light amount data P ′ (Xi) in the gain controller 62, the multiplier 64 turns on and off in accordance with the test image data from the image data memory 56. Control and AOM4 via amplifier 66
8 The laser beam L output from the laser light source 46 is controlled by the AOM 48 driven as described above, and an image is recorded on the recording medium 32 again (step S20).

Then, the operator measures the dot% of the recorded image again using the measuring device 68 (step S2).
1). In this case, in the present embodiment, the reference light amount data P0
(Xi) is corrected using halftone light amount coefficient data K (Xi) set corresponding to the scanning position Xi to calculate corrected light amount data P ′ (Xi). The desired correction light amount data P '(Xi) can be obtained by one correction process. However, in consideration of an error at the time of measurement, a change with time, and the like, if necessary, the measurement net% data S (X
After setting i) again in the measurement network% data memory 72, the processing of steps S14 to S21 is repeated until it is determined that the desired shading state has been obtained (step S2).
2).

As described above, after the correction light amount data P '(Xi) capable of obtaining a desired shading state is set in the light amount data memory 78, an image is recorded on the recording medium 32 in accordance with the desired image data. I do. When recording the image after the shading correction, the gain controller 62 uses only the corrected light amount data P ′ (Xi) set in the light amount data memory 78.
Will be adjusted.

In the above-described embodiment, X-
The case where the present invention is applied to the image recording device 36 that records an image on the recording medium 32 set on the Y plane has been described. Is performed also by the influence of the eccentricity of the drum. Therefore, the present invention can also be applied to shading correction in a drum type image recording apparatus.

The present invention can be applied not only to an image recording apparatus 36 for recording an image on a printing plate, that is, a so-called plate setter, but also to a film setter for recording an image on a film as a recording medium. It is.

[0054]

As described above, according to the present invention, the rate of change of the pixel area ratio due to the change in the amount of light of the light beam is set for each scanning position, and shading correction of the amount of light is performed using this. High-precision shading correction can be completed by a single correction process. So, for example,
Even if shading correction is required due to a change over time of the image recording apparatus or the like, it is possible to quickly cope with the case.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image recording apparatus provided for explaining a conventional technique.

FIG. 2 is an explanatory diagram of shading characteristics before correction.

FIG. 3 is an explanatory diagram of halftone light quantity coefficient data set in conventional shading correction.

FIG. 4 is a schematic configuration diagram of a plate making system to which a shading correction method and a correction circuit according to the present invention are applied.

FIG. 5 is a block diagram illustrating a configuration of a control circuit in the image recording apparatus illustrated in FIG. 4;

FIG. 6 is an explanatory diagram of halftone light quantity coefficient data set in a shading correction method and a correction circuit according to the present invention.

FIG. 7 is a flowchart showing a setting procedure of halftone light quantity coefficient data set in the shading correction method and the correction circuit according to the present invention.

FIG. 8 is a flowchart showing a shading correction procedure in a shading correction method and a correction circuit according to the present invention.

[Description of Reference Numerals] 30 plate printing system 32 recording medium 34 plate feeding device 36 image recording device 38 developing device 42 image recording unit 46 laser light source 48 acousto-optic modulator (AOM) 54 shading Correction circuit 56 Image data memory 58 AOM driver 62 Gain controller 72 Measurement net% data memory 74 Target net%
Data memory 76: Halftone light intensity coefficient data memory 78: Light intensity data memory 80: Scan speed fluctuation correction data memory L: Laser beam

Continued on front page F term (reference) 2C362 AA20 AA22 AA31 AA55 AA57 AA63 CB18 2H108 GA00 JA00 5C074 AA07 AA09 BB03 DD04 DD05 DD08 DD13 DD16 EE04 EE11 GG19

Claims (6)

[Claims] 1. When a two-dimensional image is recorded by scanning a recording medium with a light beam in a main scanning direction and a sub-scanning direction, a change in a pixel area ratio due to a change in a light amount of the light beam on the recording medium. A first step of determining a ratio as a function of a scanning position; and recording an image on the recording medium using the light beam set to a predetermined light amount, and measuring a pixel area ratio of the image at each of the scanning positions. 2) correcting the predetermined light amount of the light beam for each of the scanning positions based on a change rate of the pixel area ratio due to the light amount change so as to set the pixel area ratio to a desired value according to the scanning position. A shading correction method, comprising: a third step; 2. The method according to claim 1, wherein the change rate of the pixel area ratio due to the light amount change is a pixel area ratio of each image recorded by changing the light amount of the light beam at each of the scanning positions. A shading correction method comprising: measuring and calculating a change rate of the pixel area ratio due to a change in the light amount. 3. The method according to claim 1, wherein the predetermined light amount corrected in the third step is:
A shading correction method, wherein the processing of the second step and the third step is repeated after replacing the predetermined light amount in the second step. 4. The method according to claim 1, wherein in the third step, the pixel area ratio is changed by changing the light amount so that the pixel area ratio is constant regardless of the scanning position. A shading correction method, wherein the predetermined light amount of the light beam is corrected for each of the scanning positions according to a rate of change of the rate. 5. A shading correction circuit in an image recording apparatus for two-dimensionally recording an image by performing main scanning and sub-scanning of a light beam on a recording medium, wherein the light beam scans the recording medium. A first holding unit that is set as a function of a position and holds a change rate of a pixel area ratio due to a change in light amount of the light beam on the recording medium; and performing the recording using the light beam set to a predetermined light amount. A second holding unit that holds shading data obtained by measuring a pixel area ratio at each of the scanning positions of an image recorded on a medium; and a change rate of the pixel area ratio due to the light amount change, and the shading data. And a correcting means for correcting the predetermined light amount from the shading correction circuit. 6. The correction circuit according to claim 5, further comprising: third holding means for holding scanning speed fluctuation correction data for correcting a scanning speed fluctuation of the light beam with respect to the recording medium; A shading correction circuit, wherein the predetermined light amount corrected by speed fluctuation correction data is corrected by a change rate of the pixel area ratio due to the light amount change and the shading data.