JPH0830146A - Color image forming device - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain optimum visual characteristics according to the transfer material and to optimize the amount of toner to be transferred onto the transfer material. [Structure] The optical sensor 6 determines whether it is a normal transfer material or an OHT sheet. In the case of a normal transfer material, γ ₁ is selected from the γ conversion table. On the other hand, in the case of an OHT sheet, the bias voltage value applied to each of the suction roller 38 and the transfer drum 25 is set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus capable of adjusting the image quality of an output image.

[0002]

2. Description of the Related Art In a color image forming apparatus for forming a color image on a transfer material by superposing toner images of a plurality of colors, (a) an electrostatic latent image is formed on an image carrier and successively formed. A method of developing with a toner agent and transferring to a transfer material each time to superimpose a plurality of color toner images on the transfer material, or (b) superimposing a plurality of toner images on an image carrier or an intermediate transfer body, There is a method of collectively transferring these onto a transfer material.

Of these, the method (a) is German DE2.
It has the structure described in Japanese Patent Laid-Open No. 607727, Japanese Patent Laid-Open No. 50-50935, etc., and is put to practical use. on the other hand,
The method (b) has problems such as color mixture at the time of development and image quality deterioration at the time of retransfer, but it has advantages such as a simple structure, and is a technique that is currently attracting attention.

In any of the systems, finally, as shown in FIG. 6, the toner images T of plural colors are mixed by heating and fixing the toner images T of plural colors formed on the transfer material 15. It is possible to obtain a full-color image.

An example of a fixing device of the heat roller type will be described with reference to FIG.

In FIG. 6, 20 is a fixing roller for melting and fixing the toner T on the transfer material 15 by heating and pressurizing, and 21 is a pressure roller for pressing. Normal,
In many cases, the fixing roller 20 is heated from the inner surface using a heater 22 such as a halogen lamp. Therefore, it is general that the surface temperature of the fixing roller 20 is monitored by a temperature detecting element 19 such as a thermistor, and the heater 22 is turned on / off to adjust the temperature. As the color toner T, four colors of yellow, cyan, magenta and black toner are generally used. The oil applying device 23 applies silicone oil 24 onto the fixing roller 20 to improve releasability and prevent toner offset onto the fixing roller 20.

In the case of fixing the color toner T, unlike the case of ordinary black-and-white printing, not only the fixability but also the melt-mixing property of each color is an important factor for proper color reproduction. Therefore, the color toner T is designed not only for chromatic colors but also for black toner so that the melting point thereof is slightly lower than that of black toner of a commonly used black-and-white copying machine. For example, a method of shifting the molecular weight of a material such as a styrene-acrylic resin or polyester used as a binder resin to a low molecular side, or a method of distributing a wax having a low melting point as a release material is generally used.

Next, using such a device, the OHT
A method of forming an image on a transparent transfer material such as (overhead transparency) will be described. In this application,
Since the purpose is to project the image on the OHT sheet onto the screen, unless the above-mentioned color toners are sufficiently melted on the OHT sheet and not spread into a smooth state with less unevenness, good color reproduction and No image can be obtained.
For this reason, as an OHT sheet for a color printer, a transparent sheet such as PET (polyethylene terephthalate), which is usually used in black and white printers, is coated with a resin similar to that used for a binder of toner such as polyester or styrene / acrylic. In general, the toner particles are buried in the surface during fixing.

At the same time, in order to provide sufficient melting heat, the temperature of the fixing roller 1 is often set higher than that of a normal transfer material, or the fixing roller 1 is rotated at a low speed to perform fixing.

[0010]

However, in the conventional apparatus, although the transparency and color of the OHT image have been improved as described above, the impression of the image at the time of projecting the OHT image is discussed much. Never happened. However, comparing the image actually formed on the white transfer material and the one formed by projecting the image formed on the OHT by the same image data on the screen, the image on the white transfer material is compared. It was found that the image obtained by projecting the image on the OHT on the screen gives a lighter impression than when viewed in room light. In particular, this tendency becomes strong in the halftone density portion. Also, even when reproducing the same halftone, it does not matter so much when a halftone with rough pixels is reproduced in a conventional binary image by using dithering or an error diffusion method, but the density per dot is divided into multiple stages. , When a method of reproducing halftone while making pixels fine, for example, when using a pulse width modulation method or a brightness modulation method,
It was found that this tendency became remarkable.

This is thought to be caused by the following. First. A projected image by the OHT projector will be described with reference to FIG.

In general, the projector 104 transmits the light of the white light source 101 including a lens through the platen glass 102, the OHT document 106, the reflection mirror 103, and the screen 10.
It has a structure in which a light source is projected on 5. Therefore, the color toner T absorbs the light only once. If the color of the toner is red (that is, if three color toners of yellow, magenta, and cyan are used, two colors of yellow and magenta are mixed).
, The transmittance of the red component of the white light is σ _R ,
Assuming that the transmittance of the complementary color of red is σ _C , the proportion of red in the light component after transmission is σ _R / σ _C.

On the other hand, when a similar red toner image is formed on the white transfer material, the visible light is the light that has been absorbed twice by the toner T due to the surface reflection of the transfer material, as shown in FIG. Becomes Therefore, of these, the proportion of red is (σ
_R / σ _C ) ² . (Σ _R / σ _C ) >> 1, so
In comparison, the OHT projection image is a weak red image (in this example). Of course, in addition to this, it goes without saying that when transmitting light through the OHT sheet itself, the influence of equipment such as PET and the resin coat layer is added. The same applies to the other arbitrary colors. It should be noted that this tendency is not so noticeable in a halftone dot image (binary dither image or the like) having a coarse grain or a high density image, because the human sense of the gradation change becomes relatively dull on the high density side. It seems to be because.

In addition to this, there is also a case where the electrostatic capacity of the OHT sheet itself is different from that of a normal transfer paper, and the transfer efficiency is worse than that of the normal transfer paper, and the image itself becomes thin. In such a case, the above-mentioned phenomenon is added and the OHT projection image becomes a more blurred image.

An object of the present invention is to solve the above-mentioned problems and obtain optimum visual characteristics according to the transfer material.
An object of the present invention is to provide a color image forming apparatus capable of optimizing the amount of toner to be transferred onto a transfer material.

[0016]

[Means for Solving the Problems]

1) A color image forming apparatus according to the present invention includes a developing unit that develops a latent image formed on an image carrier based on color image data with toners of a plurality of colors, and a toner obtained by the developing unit. In a color image forming apparatus having a transfer means for transferring an image onto a transfer material and a fixing means for fixing the toner image transferred onto the transfer material by the transfer means, a determining means for determining the type of the transfer material. And a setting unit for setting the image processing parameter and the transfer condition by the transfer unit according to the result of the judgment by the judgment unit.

2) A color image forming apparatus according to the present invention is obtained by developing means for developing a latent image formed on an image carrier based on color image data with toner of a plurality of colors, and developing by the developing means. The type of the transfer material is input in a color image forming apparatus having a transfer means for transferring the formed toner image onto a transfer material and a fixing means for fixing the toner image transferred onto the transfer material by the transfer means. And an setting unit for setting image processing parameters and transfer conditions by the transfer unit according to the type of transfer material input by the input unit.

3) In the color image forming apparatus described in 1) or 2) above, if the transfer material is an overhead transparency sheet, the overhead
It is characterized in that the image processing parameters are changed so that the amount of toner adhered to the transparency sheet at least in the halftone density range is larger than that of normal paper.

4) In the color image forming apparatus described in 1) or 2), the image processing parameter is related to a γ correction process for correcting the halftone of each color.

5) In the color image forming apparatus described in 1) or 2), the image processing parameter is related to color masking.

6) In the color image forming apparatus described in 1) or 2), the image processing parameter is related to the undercolor removal processing.

7) In the color image forming apparatus described in 1) or 2) above, the setting means further sets a transfer material suction condition in multiple transfer.

8) In the color image forming apparatus described in 1) or 2), the setting unit further sets the fixing processing time.

9) In the color image forming apparatus described in 1) or 2) above, storage means for storing a table having a plurality of image processing parameters for one transfer material, and image processing parameters from the storage means are stored. And a selection unit for selecting.

10) In the color image forming apparatus described in 1) or 2) above, there is provided humidity detecting means for detecting the humidity in the vicinity of the transfer means, and the setting means responds to the humidity detected by the humidity detecting means. It is characterized in that the transfer condition is set by setting.

11) In the color image forming apparatus described in 1) or 2) above, there is provided a temperature detecting means for detecting the temperature around the transfer means, and the setting means responds to the temperature detected by the temperature detecting means. It is characterized in that the transfer condition is set by setting.

12) In the color image forming apparatus described in 9 above, the image processing parameters include a parameter for increasing the amount of toner adhered to the overhead transparency sheet at least in a halftone density region as compared with normal paper, and an intermediate value. It is characterized in that two kinds of parameters are provided, that is, a parameter for making a light range is light and a parameter for a dark range is dark.

[0028]

In the present invention, the type of the transfer material is discriminated by the discriminating means, and the image processing parameter and the transfer condition by the transferring means are set by the setting means according to the discrimination result.

In the present invention, when the type of the transfer material is input by the input means, the image processing parameters and the transfer conditions by the transfer means are set by the setting means according to the input type of the transfer material.

[0030]

Embodiments of the present invention will now be described in detail with reference to the drawings.

<First Embodiment> FIG. 1 shows a first embodiment of the present invention. This embodiment is an example of an electrophotographic laser beam printer. In FIG. 1, with respect to the heat fixing means, the same or corresponding parts as those shown in FIG. 6 described in the conventional example are designated by the same reference numerals, and a duplicate description will be omitted.

After the transfer material 15 is fed by the pickup roller 28 and conveyed by the conveying roller 29 and the registration roller 30, the normal transfer material is OH by the optical sensor 6.
It is determined whether the sheet is a T sheet. As the sensor 6, a transmissive or reflective optical sensor can be used. The determination signal is input to the controller 13 via the drive circuit 7. At this time, the processing according to the type of the transfer material will be described in detail later. On the other hand, as an image signal, for example,
A case where the signals 9 of Y, M, C, and K (K is black) are used and the signals are masked by the processing circuit 10 will be described. Here, a multi-value gradation signal is used as the signal 9 for the full-color image, and a binarized signal is input as the character signal of the document, but the binary signal becomes the multi-value maximum and minimum level signals. It is replaced (hereinafter, a full-color multilevel signal will be mainly described). This multi-valued signal is converted into a time-series pulse width modulation signal 11 by the processing circuit 10 and sent to the laser scanning optical system 5 via the controller 13. At this time, signals are exchanged by the controller 1
3 and the image processing circuit 10 and the M, C, Y and K signals are synchronized. In the laser scanning optical system 5, a laser diode (not shown) is driven via a drive circuit. After that, the laser light is converted into scanning light of 600 dpi (dots / inch) by a rotating polyhedron (polygon) mirror, and an electrostatic latent image is formed on the photosensitive drum 1. The photosensitive drum 1 is previously uniformly charged by a charging unit such as a charging roller 2, and is partially discharged by laser beam scanning to form the electrostatic latent image.

This electrostatic latent image rotates in the direction of the arrow while maintaining a predetermined fixed posture, and is sequentially contacted with the rotary developing means 4 of cyan, magenta, yellow and black.
Developed by C, 4M, 4Y, 4K.

As the toner, as an example, a polyester resin is used as a binder, the TG value (glass transition temperature) is about 60 ° C., and the MI value (melt viscosity at 100 ° C. heating) 4
An image was formed by a reversal phenomenon method using a non-magnetic one-component negative toner having a particle size of 6 to 8 μm and a particle size of ˜5 g / 10 min.
The OHT sheet used as the transfer material was a PET sheet coated with the same polyester resin as the binder of the toner.

First, the case where normal paper is used as the transfer material 15 will be described. When the sensor 15 detects that the paper 15 is opaque normal paper, the transfer drum 25
After being wound and held on a sheet of paper, a multi-color transfer for four colors is performed at a normal process speed to form a full-color image on the transfer material 15, and then fixing is performed by the fixing roller 20 at the same speed to complete the image formation. . At this time, the process speed is about 100 mm / sec, and the temperature of the fixing roller 20 is about 18 mm.
The temperature of the photosensitive drum 1 is 0 ° C. and the diameter of the photosensitive drum 1 is 40 mm.
A drum was used. Further, as the transfer drum 25, a conductive elastic sponge having a thickness of 5 mm is wound on an aluminum substrate, and the surface is covered with a conductive elastic sponge.
Using a sheet provided with a 5 μm PVdF (polyvinylidene fluoride) sheet, first, a bias voltage of −800 V based on the transfer drum is applied to the suction roller 38 by the high voltage power supply 39, and the transfer paper 15 is pre-sucked on the transfer drum 25. It was
Next, a high voltage power supply 41 is used to apply a transfer bias to the aluminum substrate of the transfer drum for the first color + 800V and the second color +1000.
Transfer was performed by applying V, third color + 1200V, and fourth color + 1400V, respectively.

The image processing method was performed according to the procedure described below. FIG. 2 shows a black diagram in the image processing circuit 10. First, as the image signal 9, 8 of each color of Y, M, C and K
The multivalued signal of bits is input to the masking processing circuit 31.

As a masking processing method, generally, there is a method of forming a matrix I as shown in the following equation (1) and obtaining each processing by a function of another color.

[0038]

[Equation 1]

Using the formula (1), each color Y, M, C, K
As expressed by the following equations (2) to (5), Y ′, M ′,
Correct to C ', K'.

[0040]

[Number 2] _{Y '= a 11 · Y +} a 12 · M + a 13 · C + a 14 · f n (K) ... (2) M' = a 21 · Y + a 22 · M + a 23 · C + a 24 · f n (K) ... ( _{3) C '= a 31 ·} Y + a 32 · M + a 33 · C + a 34 · f n (K) ... (4) K' = a 41 · Y + a 42 · M + a 43 · C + a 44 · f n (K) ... (5) However, f (K) is a polynomial of degree n with respect to K data.

Next, in order to match the obtained Y ', M', C ', and K'image data with the gradation characteristics of the printer, γ correction is performed using the γ conversion table 32. FIG. 3 shows an example of this. Here, γ ₁ is a normally used γ table, and the signal 8 from the drive circuit based on the detection result of the sensor 6 in FIG.
When it is determined that the transfer material is plain paper, γ ₁ is selected by the determination signal 12.

The multi-level 8-bit signal Y ″ thus obtained,
M ″, C ″, and K ″ are converted into a time-series pulse width modulation signal 11 by the laser drive signal modulation circuit 33 and drive the laser drive circuit in the optical system 5. In this embodiment, sub-scanning is performed. For the density of 600 dpi, the main scanning density was switched to 600 dpi for characters and to 200 dpi for a full-color multi-valued image, and the pulse width of each laser ON time was modulated.

Next, a case where an OHT sheet is used as the transfer material 15 will be described. When the sensor 6 detects that the paper 15 is a transparent (or semi-transparent) OHT sheet, the paper 15 is wound around the transfer drum 25 and held, and then the multi-transfer for four colors is first performed at the normal process speed. O
A full color image is formed on the HT sheet. here,
When the OHT sheet is detected, the bias voltage value applied to each of the suction roller 38 and the transfer drum 25 is set to a value different from that of plain paper. Specifically, the controller 13 switches the suction bias control signal 40 and the transfer bias control signal 42 to values for OHT according to the transfer material determination signal, and inputs them to the respective high voltage power supplies 39 and 41. In this example, the suction bias value is -1000 V, and the transfer bias first color is +
1000V, 2nd color + 1200V, 3rd color +1400
V and the fourth color were set to + 1600V, and the bias values were changed to values larger than those for plain paper.

The degree of moisture absorption between the OHT sheet and the plain paper varies greatly depending on the environmental conditions. The bias is at room temperature and normal humidity, but since the state of moisture absorption and dehumidification of plain paper is larger than that of OHT sheets, the capacitance of OHT sheets is high under high humidity (mainly in absolute humidity). It is smaller than paper. On the contrary, under low humidity, the electrostatic capacity of paper becomes smaller. Therefore, the temperature sensor 43 and the humidity sensor 44 are added to the configuration of FIG. 1 to calculate the absolute humidity, and when the absolute humidity is high, the transfer bias value is paper <OHT sheet, and conversely, when the humidity is low, the paper is biased. It is preferable to properly control the transfer bias value so that the sheet is> OHT. Regarding the suction bias, a good result was generally obtained when the absolute value was set to paper <OHT. (Sometimes, the suction bias should be set to paper << OHT. In such a case, , The transfer bias is high and the paper <OHT at low humidity).

Also, both plain paper and OHT sheet are adsorbed,
Both of the transfer bias values tend to be set such that high humidity <low humidity. By thus controlling the transfer bias after optimizing the suction bias to stabilize the suction force, the difference in transfer efficiency between the plain paper and the OHT sheet can be minimized.

After that, the transfer drum 25 is about half the normal size.
Then, the OHT sheet 15 is conveyed to the fixing device. In the fixing device, the fixing roller 20 and the pressure roller 21 are rotated at a speed of about 1/2 of the normal speed to perform fixing, like the transfer drum 25. At this time, if necessary, the target of the temperature adjustment by the thermistor 19 is changed to a value (range of +10 deg to −10 deg) different from that of normal paper (on the basis of the temperature signal 18 of the thermistor, the controller 13 turns on the heater driver 16).・ Off signal 1
Send 7).

Now, an image processing method when the OHT sheet is passed will be described. In FIG. 2, the masking processing circuit 31 and the laser modulation circuit 33 are the same as those for plain paper, and therefore their explanations are omitted. The projected image of the OHT sheet tends to look faint visually as described above. Therefore, by using the γ conversion table 32, the density of the halftone portion corresponding to the reflection density of 0.3 to 1.3 (value in the image formed on the plain paper), which has particularly high detection ability with human eyes, is set. O
When HT is used, ΔD = 0.05 to 0.3 is made darker than in the case of normal paper (γ ₁ → γ ₂ in FIG. 3) to make a visual image of plain paper and OHT projection. It is possible to eliminate the difference in image impression.

As described above, after the OHT sheet is detected, the transfer bias value is optimized and the transfer efficiency is improved, so that the toner amount on the OHT sheet can be stabilized, and when the OHT sheet is used, γ can be stabilized. By changing the conversion table, it was possible to prevent the impression of the image at the time of projection from fading.

As a means for changing the image characteristic, a method of changing the developing characteristic by the developing devices 4C, 4M, 4Y, 4K may be considered, but such a method is generally applied to the developing device. There is a change in the bias voltage of DC and AC. However, when the bias voltage is changed, the densities of both the white background and the black background change, and it is not always possible to make a visually preferable correction. However, it goes without saying that the same visual improvement effect can be obtained by changing the developing bias and changing the image processing parameter.

Further, the transfer bias conditions described above are set so that the transfer amount of the toner on the plain paper is smaller than that on the OHT, and in combination with this, the image processing parameters described above are changed to optimum ones. May be.

In this embodiment, the sensor 6 or the like is used as the OHT sheet discriminating means, and the example in which the image processing parameters and the transfer conditions are automatically controlled based on the sensor 6 is described.
It is needless to say that the user may manually input the type of transfer material from a printer or a host computer as appropriate and generate the transfer material determination signal accordingly.

<Second Embodiment> In the first embodiment, an example of changing the γ conversion table has been described, but the masking processing circuit 3
The masking table 1 may be changed. That is,
By preparing the expression (6) together with the expression (1) and selecting the expression (1) or the expression (6) according to the type of the transfer material, the halftone is slightly darkened in the case of the OHT sheet. It can be adjusted to prevent the visual impression from fading when projected.

[0053]

(Equation 3)

Thus, the masking coefficient a ₁₁ ′-
In order to newly set a ₄₄ ′, it is necessary to set it in consideration of all the printing papers such as the characteristics of the toner, and more examination is required than changing the γ characteristics. On the other hand, it is possible to control the density and the saturation separately, and once set, more optimal image quality correction becomes possible. In particular, depending on how the masking coefficient is selected, the maximum amount of toner applied during full-color formation (for example, 100% to 40% in principle for a solid black image)
The amount of toner applied can be changed between 0%. In addition, 400%
Is a state in which all toners of Y, M, C, and K are piled up in a solid state, and 100% corresponds to the case of only K toner). There is an advantage that the amount of transmitted light can be controlled without changing.
As an example, the maximum toner loading is 200% for plain paper.
And when it was set to 250% for the OHT sheet, the OHT
The contrast of the projected image on the sheet is improved, and a clear image can be obtained.

<Third Embodiment> In the first and second embodiments, an example in which Y, M, C, and K signals are handled as image signals has been described, but R, G, B (red, green, blue). In a system in which the luminance signal of 1 is used as an image signal, the R, G, B signals are once converted into Y, M, C, K signals, and then the above-mentioned image processing is performed.

Further, when the black (K) signal is generated, if the processing method is changed between the plain paper and the OHT sheet, the OH
It is possible to bring the impression of the T projection image closer to the image on the paper. This black signal generation is generally performed by removing undercolor (hereinafter, UCR
The image quality can be corrected by changing the UCR amount and changing the masking coefficient as necessary. Here, the amount of UCR specifically refers to the amount of K (black) that is the black portion. 100% UC
K at the time of R is calculated by the following equation (7).

[0057]

## EQU00004 ## K = min (Yi, Mi, Ci) (7) where Yi, Mi, Ci are the amounts of yellow, magenta, and cyan before undercolor removal, and the relationship with R, G, B. Can be obtained by equations (8), (9) and (10).

[0058]

## EQU00005 ## Yi = -logB (8) Mi = -logG (9) Ci = -logR (10) The relationship with Y, M, and C after undercolor removal is

[0059]

## EQU6 ## Y = Yi-K (11) M = Mi-K (12) C = Ci-K (13)

Therefore, UC before or after the masking process
The R amount may be different between the normal transfer material and the OHT sheet.

FIG. 7 shows an example of a processing circuit for changing the UCR amount before the masking process. The R, G, and B 8-bit image signals are subjected to logarithmic conversion and undercolor removal in the processing circuit 35. At the time of 100% UCR, the processing is performed according to the above-mentioned equations (7) to (13). here,
Based on the transfer material determination signal 12, the case of normal transfer paper and O
Change the UCR amount when using the HT sheet. As an example, for normal paper, the UCR amount is set to 100%, and the OHT
In the case of a sheet, the UCR amount is 50% to 80%. In this case, assuming that the UCR amount is α, instead of equation (7), equation (14)

[0062]

## EQU7 ## K = min (Yi, Mi, Ci) × α (14) However, 0 ≦ α ≦ 1 may be used.

Next, the masking coefficient of the masking processing circuit 31 is also changed according to the UCR amount. Depending on how the masking coefficient is selected, the amount of toner applied during black printing is 100
% -400% (400% is a state in which all toners of Y, M, C, and K are piled up in a solid state), but when the OHT sheet is passed, the UCR amount is reduced, while the toner amount is increased. It is better to adjust the image quality in each direction. Generally, the maximum amount of toner is 150% to 250% on plain paper, but it is good to increase it by about 50% for OHT sheets.

By performing such a processing, the amount of black (K) toner projected as a shadow when passing through the OHT sheet can be independently adjusted, so that the transparency of the projected image can be controlled.

Note that the above method is performed from R, G, B to Y,
An example of changing the UCR amount at the time of conversion into M, C, K is shown. In addition to this, the following process is simply performed after the masking process to perform Y ',
The data of M ′, C ′ and K ′ are converted into Y _T ′, M _T ′, C _T ′,
It can also be used by changing it to K _T ′.

[0066]

(8) Y _T ′ = Y ′ + β (15) M _T ′ = M ′ + β (16) C _T ′ = C ′ + β (17) K _T ′ = K′−β (18) , Β is a positive constant <Fourth Embodiment> In the first embodiment, the example in which the predetermined γ table is automatically selected when the OHT sheet is used is described based on the determination result of the transfer material. Furthermore, in the second and third embodiments, examples in which image parameters other than the γ table are changed have been described.

On the other hand, the transmission type projector shown in FIG. 4 has been described as an example of the OHT sheet projector. But OH
As a T-projector, recently, there is also a reflection-type portable projector in which a document is placed on a mirror, the projection light from the document surface is once reflected by the mirror, and the light that has passed through the document is projected again on the screen. The feature of this projector is that the projection light passes through the OHT sheet twice, so that the entire image becomes dark. Of course, since it passes through the toner layer twice at the same time, I see the image printed on white paper at this point, but in reality, it passes through the OHT sheet itself twice, resulting in a slightly dark image. , It tends to be a blurred projection image.

In the case of such a reflection type projector, for example, rather than the gradation correction of the characteristic such as γ ₂ in FIG.
It is better to perform gradation correction on a characteristic such as γ ₃ . For this purpose, it is desirable to prepare a plurality of image processing parameters in advance and perform image processing according to the OHT projector used. That is, as shown in FIG.
The T image selecting means 37 is provided, and the sensor 6 transfers the transfer paper to the OHT.
When it is determined that the sheet is a sheet, the image processing designated by the selection unit 37 may be executed. The determination of the transfer material is generally performed in the middle of a series of printing operations after the paper feeding operation is started. However, if the mode to be executed at the time of the OHT sheet can be set in advance, the printing operation can be interrupted. Absent.

In the first to fourth embodiments, an example of the solid transfer drum system has been described. In addition to this, a system of a hollow transfer drum in which only the insulating sheet of the similar multiple transfer system is kept hollow, Also in the transfer system using the intermediate, the same operational effect can be obtained.

[0070]

As described above, according to the present invention,
Since it is configured as described above, it is possible to obtain the optimum visual characteristics according to the transfer material and to optimize the amount of toner to be transferred onto the transfer material.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing an image processing circuit according to the first embodiment.

FIG. 3 is a diagram showing an example of γ characteristics.

FIG. 4 is an explanatory diagram for explaining light absorption of an overhead transparency sheet.

FIG. 5 is an explanatory diagram illustrating light absorption of plain paper.

FIG. 6 is a diagram illustrating an example of a heat fixing device.

FIG. 7 is a block diagram showing a processing circuit according to a third embodiment of the present invention.

FIG. 8 is an explanatory diagram for explaining gradation correction when a reflection type projector is used.

FIG. 9 is a block diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 1 Photosensitive Drum 6 Sensor 9 Image Signal 10 Image Processing Circuit 13 Controller 25 Transfer Drum 37 Selector 38 Adsorption Roller

Front page continuation (72) Inventor Takao Kume 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Toshiaki Miyashiro 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takehiko Suzuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Nobuaki Kaburaya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Invention Tatsuya Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akihiko Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (12)

[Claims] 1. A developing means for developing a latent image formed on an image bearing member on the basis of color image data with toners of a plurality of colors, and a toner image obtained by the developing by the developing means is transferred onto a transfer material. A color image forming apparatus having a transfer unit for fixing the toner image transferred onto the transfer material by the transfer unit, and a determination result by the determination unit for determining the type of the transfer material. A color image forming apparatus comprising: an image processing parameter and setting means for setting a transfer condition by the transfer means according to the above. 2. A developing means for developing a latent image formed on an image bearing member on the basis of color image data with toner of a plurality of colors, and a toner image obtained by the developing means is transferred onto a transfer material. In a color image forming apparatus having a transfer means for controlling the transfer material and a fixing means for fixing the toner image transferred onto the transfer material by the transfer means, an input means for inputting the type of the transfer material, and the input means A color image forming apparatus comprising image processing parameters and setting means for setting transfer conditions by the transfer means according to the type of the input transfer material. 3. The toner according to claim 1, wherein the transfer material is an overhead transparency sheet, the toner adhesion amount to the overhead transparency sheet is larger than that of normal paper at least in a halftone density range. A color image forming apparatus characterized in that the image processing parameters are changed so that 4. The color image forming apparatus according to claim 1, wherein the image processing parameter is associated with a γ correction process for correcting a halftone of each color. 5. The color image forming apparatus according to claim 1, wherein the image processing parameter is related to color masking. 6. The color image forming apparatus according to claim 1, wherein the image processing parameter is associated with undercolor removal processing. 7. The color image forming apparatus according to claim 1, wherein the setting unit further sets a transfer material suction condition in multiple transfer. 8. The color image forming apparatus according to claim 1, wherein the setting unit further sets a fixing processing time. 9. A storage means for storing a table having a plurality of image processing parameters for one transfer material, and a selection means for selecting an image processing parameter from the storage means. A color image forming apparatus further provided. 10. The humidity detecting means according to claim 1 or 2, further comprising humidity detecting means for detecting humidity in the vicinity of the transferring means, wherein the setting means sets a transfer condition according to the humidity detected by the humidity detecting means. Characteristic color image forming apparatus. 11. The method according to claim 1, further comprising a temperature detecting means for detecting a temperature around the transfer means, wherein the setting means sets the transfer condition according to the temperature detected by the temperature detecting means. Characteristic color image forming apparatus. 12. The image processing parameter according to claim 9, wherein the image processing parameters are such that the toner adhesion amount to the overhead transparency sheet in at least a halftone density region is larger than that of normal paper, and in the light region of the halftone region. A color image forming apparatus having two kinds of parameters, a parameter for darkening in a light and dark area.