JPH09197893A - Image forming device - Google Patents

Abstract

Kind Code: A1 Abstract: The present invention relates to a gradation reproduction image such as a photographic image having a large number of isolated dot portions (macroscopic halftone density portions) in a binary digital image forming apparatus. It is an object of the present invention to provide an image forming apparatus capable of improving the fixability by changing the fixing conditions according to the ratio of In a digital image forming apparatus for binarizing image data, a signal value around a pixel of interest is set to 1 (a dot is printed when the image data is binarized by an image signal processing circuit. The density of the pixel of interest is estimated by calculating the number of pixels that are (meaning), and the density is estimated for all pixels or a specific area, and the ratio of the pixels whose density is less than or equal to a predetermined value to all pixels or the specific area From
The fixing conditions such as the fixing temperature of the fixing device 51 are changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus that forms an image by performing digital binary image processing using an electrophotographic system.

[0002]

2. Description of the Related Art Conventionally, in any of an image forming apparatus, an analog image forming apparatus, a digital binary image forming apparatus, and a digital multi-value image forming apparatus, the fixing temperature control temperature is controlled step by step depending on the number of copies or the number of outputs. Control the fixing temperature and the partial temperature of the fixing device according to the method and the size of the paper (transfer material) (for example, heat only the paper passage area for each size of the transfer material in the longitudinal direction of the fixing device). The following configuration is used.

The type of transfer material (thickness, basis weight, OHP
There is also used a configuration in which the fixing speed is changed by changing the fixing speed depending on the material of a special paper such as a sheet or a postcard, and the fixing time is lengthened for a transfer material which is unfavorable for fixing.

[0004]

However, in the above-mentioned conventional example, the fixing temperature is controlled stepwise or the fixing speed is changed depending on the number of output sheets, the size of the transfer material and the kind of the transfer material. The following phenomena occurred.

First, since the fixing control is not performed depending on the image density, the fixing property in the vicinity of the halftone density portion where the dots are dispersed in the case of a binary image has a high density portion where the dots are dense (solid portion). In some cases, the fixability of a gradation image such as a photographic image or a picture may be worse than that of a non-gradation image such as a character image.

Next, for fixing control depending on the number of output sheets and the type of transfer material, the fixing condition that should be obtained according to the actual apparent (macroscopic) image density is not set,
When there is a density change such as a γ correction from the outside or a change in the threshold value of the binarization process, a fixing failure may occur depending on the setting conditions.

Therefore, according to the present invention, the ratio of the halftone density portion of an image is determined for a gradation reproduction image such as a photographic image having many isolated dot portions (macroscopic halftone density portion) in a binary digital image forming apparatus. Accordingly, it is an object of the present invention to provide an image forming apparatus capable of improving fixing property by changing fixing conditions accordingly.

[0008]

According to a first aspect of the present invention, the above object is to develop image data into pixels in a matrix having a predetermined resolution, and convert the signal value of each pixel into a visible image. Means for binarizing into a value indicating that and a value indicating not to be visualized, and the image data processed by the means is visualized as a developer image to be formed on the transfer material. An image forming apparatus comprising a visible image forming means and a fixing device for fixing the developer image onto the transfer material by applying heat to the transfer material and the developer image while conveying the transfer material under pressure. , A means for estimating the image density of the specific pixel from the number of pixels having a signal value indicating that the image is to be visualized around the specific pixel, and the image density is estimated by the means in the matrix form. All pixels or all expanded to Performed for each pixel of a specific region of Motochu, estimated image density of the pixel is below a predetermined value,
This is achieved by increasing or decreasing the heat applied by the fixing device in accordance with the ratio of all the pixels or a specific area of all the pixels.

According to the second invention of the present application,
According to the first aspect of the present invention, a mask formed in a predetermined matrix is used in order to obtain the number of pixels having a signal value indicating that the image is to be visualized around a specific pixel. To be achieved.

Further, according to a third invention of the present application, the above object is the mask of the second invention,
This is achieved by forming the matrix in a 4 × 4 matrix for obtaining the number of pixels having a signal value indicating that the image is a visible image object other than the specific pixel.

According to the fourth invention of the present application,
The above object is achieved by switching the fixing temperature or the fixing speed or the pressure contact width of the transfer material pressing portion in order to increase or decrease the heat applied by the fixing device in any one of the first to third inventions. To be achieved.

Further, according to a fifth invention of the present application, the above-mentioned object is the fixing in order to increase or decrease the heat applied by the fixing device in any one of the first invention to the fourth invention. This is achieved by switching all of the temperature, the fixing speed, and the pressure contact width of the transfer material pressing portion, or by combining any two of them.

According to the sixth invention of the present application,
The above-mentioned object is, in any one of the above-mentioned first invention to fifth invention, that all pixels or pixels for which a ratio in a specific region in all pixels is to be calculated are determined by a plurality of image density standards. Achieved by

That is, in the first invention of the present application, regarding a binarized pixel, a signal value of pixels around a particular pixel of interest is detected,
The number of pixels having a signal indicating that the image is to be visualized is obtained, and the density of the specific pixel is estimated. Then, of the image densities obtained in this way, the proportion of isolated dots (halftone densities) is obtained by obtaining the proportion of pixels whose image densities are below a predetermined value and which are considered to be halftone densities.
Change the fixing conditions according to the obtained halftone density ratio,
An appropriate fixing condition is set for each pixel to perform a good fixing operation.

Further, in the second invention of the present application, by using a mask formed in a predetermined matrix shape, pixels around a specific pixel having a signal value indicating that the image is to be visualized. Since the number of
The concentration is estimated quickly.

Further, in the third invention according to the present application, the number of pixels having a signal value indicating that it is a visible image target other than a specific pixel is provided by a mask formed in a 4 × 4 matrix. Therefore, the amount of memory used for density estimation is reduced.

Further, in the fourth invention of the present application, the heat applied by the fixing device is increased or decreased by switching the fixing temperature or the fixing speed or the pressure contact width of the transfer material pressing portion. Appropriate fixing is performed.

Further, in the fifth aspect of the present invention, all of the fixing temperature and the fixing speed and the pressure contact width of the transfer material pressing portion are switched, or any two of them are combined. As a result, the heat applied by the fixing device is increased or decreased, so that appropriate fixing according to the image density can be performed while suppressing the temperature rise inside the apparatus.

Further, in the sixth aspect of the present application, since the pixels for which the ratio of all pixels or the ratio of the specific region in all pixels is calculated are determined by a plurality of image density standards, Appropriate fixing is performed on a high-definition image having a wide range of densities.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 shows an electrophotographic digital copying machine as an image forming apparatus in this embodiment. In FIG. 2, reference numeral 31 is a document to be copied, and the image of this document 31 is the lens 3
The image is projected onto the CCD device 61 by 2. CCD device 6
Reference numeral 1 decomposes the image of the original 31 into a large number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel. And this C
The analog image signal output from the CD device 61 is sent to the image signal processing signal 34, where it is converted into a pixel image signal having an output level corresponding to the density of each pixel and sent to the laser substrate 70. .

The laser substrate 70 forms and outputs a laser driving pulse having a width (time length) corresponding to the level of each input pixel image signal, and the laser driving pulse is supplied to the laser emitting device 71. The laser light emitting device 71 is caused to emit light for a time corresponding to the pulse width thereof, and electrostatic latent images having different dot sizes are formed on the photosensitive drum 40 corresponding to the density of the pixel.

That is, the laser light 36a emitted from the laser light emitting device 71 is swept by the rotary polygon mirror 37, and the lens 38 such as an f / θ lens and the laser light 36 are scanned.
A spot image is formed on the photosensitive drum 40 by the fixed mirror 39 that directs a toward the photosensitive drum 40. Thus, the laser beam 36a scans the photosensitive drum 40 in a direction (main scanning direction) substantially parallel to the rotation axis of the photosensitive drum 40 to form an electrostatic latent image.

The photosensitive drum 40 is an electrophotographic photosensitive drum that has amorphous silicone, selenium, OPC, etc. on its surface and rotates in the direction of the arrow. After being uniformly discharged by the exposure device 41, it is evenly charged by the primary charger 42. Be charged to. Then, the laser beam 36a modulated corresponding to the above-mentioned image information signal is exposed and scanned, whereby an electrostatic latent image corresponding to the image information signal is formed.

This electrostatic latent image is reversely developed by the developing device 43 using a developer such as toner particles to form a visible image (toner image). This toner image is stretched between two rollers 45 and 46, and is transferred onto a transfer material carrying belt 47 which is endlessly driven in the direction of an arrow shown in the drawing, and is a transfer material 48.
Is transferred by the action of the transfer charger 49.

Then, the transfer material 48 on which the toner image is transferred
Is separated from the transfer material carrying belt 47 and conveyed to the fixing device 51, and is conveyed under pressure by a fixing roller 52 having a heater 54 and a pressure roller 53, heated and pressed, and fixed on the transfer material 48 as a permanent image. It

The residual toner remaining on the photosensitive drum 40 after the transfer is removed by the cleaner 50 thereafter.

Next, a block diagram of the image processing circuit 34 and its peripherals in the image forming apparatus of the present embodiment as described above is shown. In the figure, reference numeral 61 is a CCD device for reading the above-mentioned document, and analog data of an image read by the CCD device 61 is converted into digital data by an A / D conversion circuit 62 and output to a shading (correction) circuit 63. Then, the CCD device 61, the lens 32, the illumination lamp (not shown), and the like are corrected. Then, the image data corrected by the shading circuit 63 is subjected to the scaling, movement, mirror image, italic,
The image data processed by the repeat processing, the folding processing, and the like, and further processed by the overall processing circuit 64 are processed by the pattern processing circuit 65 such as negative / positive inversion, trimming, and masking.

Here, the image data up to the pattern processing circuit 65 is luminance data having a linear characteristic with respect to the amount of light reflected from the original, whereas the density felt when the original is viewed. Is not linear with respect to the amount of reflected light, it is necessary to correct it and convert the luminance data into density data.

Therefore, in the LOG conversion (brightness density conversion or logarithmic correction) circuit 66, the image data up to the pattern processing circuit 65 is converted from brightness data to density data,
The γ correction (density correction or density processing) circuit 67 converts the image data thus converted into a density change (copy density key on the operation unit), AE measurement result, copy mode (photograph mode, character mode, etc.). And the like are corrected.

Then, the binarization processing circuit 68 converts the multivalued (for example, 256-valued) image data up to that point into binary data, and the binarized digital image data is analogized by the D / A conversion circuit 69. After being converted into data, the data is output to the laser substrate 70 described above, and based on the laser signal generated by the laser substrate 70, laser light is emitted to the surface (not shown) of the photosensitive drum 40 by the laser emitting device 71. , Form a latent image.

With respect to the image data binarized by the binarization processing circuit 68, a pixel density detection circuit 72 as a means for estimating the image density is used for each pixel or a plurality of pixels to detect the surroundings. The image pattern is detected and the image density is estimated.

The estimation of the image density is performed using each mask shown in FIG. The density detection mask 1 is used for central pixels except one line at the top, bottom, left and right ends of the image. At this time, the pixel of interest is indicated by diagonal lines. Similarly, the density detection mask 2 is used for the leftmost line of the image, and the density detection mask 3 is used for the rightmost line of the image.
Further, the density detection mask 4 is used for one pixel at the left front end of the image, the density detection mask 5 is used for one pixel at the right front end of the image, the density detection mask 6 is one line at the upper end of the image, and the density detection mask 7 is at the rear end of the image. 1 line, density detection mask 8
Is used for the left rear end pixel of the image, and the density detection mask 9 is used for the right rear end pixel of the image.

A method of estimating the density of each pixel of interest using such a mask will be described by taking the data shown in FIG. 4 as an example. For example, as shown in the density detection data A, if the data around a certain pixel of interest is as shown in the figure, the density estimation data of this pixel is 5. Here, 1 and 0 of the surrounding data are signal values (data) for each pixel, 1 indicates that a dot is printed, and 0 indicates that a dot is not printed. Similarly, the density estimation data of the density detection data B is 1. Further, in the case of a mask having 8 pixels around the target pixel as shown in data C or data D, the same data as in the case of mask 1 having 8 pixels around is performed by performing a simple calculation as shown in the figure. It becomes possible to consider the numerical value as.

Table 1 shows the relationship between the numerical values of the density estimation data thus obtained and the density.

[0036]

[Table 1]

As shown in Table 1, the numerical value calculated in this manner has a higher density (dots are denser), and a smaller value has a lower density (dots are independent). It is supposed to be.

Further, in the present embodiment, the density estimation of the target pixel as described above is performed only when the target pixel has data (when the data of dot 1 is included), the target pixel If there is no data in, the concentration estimation shall not be performed.

The ratio of the density estimation data in a certain area as shown in Table 2 is obtained using the thus calculated estimation data for each pixel, and the fixing temperature is changed accordingly.

Table 2 shows, in the first embodiment of the present invention,
Depending on the image ratio of the halftone density portion (or in the present embodiment, it is assumed that the density estimation data 3 or less is the halftone density portion) within the entire image area (or within the specific image area), Shows the relationship with the fixing temperature control temperature.

[0041]

[Table 2]

Considering, for example, a 400-dpi A4 size copy (or the same for a printer, FAX, etc.), one A4 size sheet has data of about 15 million pixels, and the density estimation data among them is 3 or less. %
In the case of (about 1.5 million pixels) or less, the proportion of the white portion or the high density portion (black portion) is high, and the proportion of the half tone density portion in which the fixing property is deteriorated is low, so that the fixing temperature control temperature is 190 ° C. .
Similarly, the ratio of data 3 or less is 10% to 20%.
In the case of (about 1.5 million to 3 million pixels), the fixing temperature control temperature is 200 ° C., and if it is 20% (about 3 million pixels) or more, it is 2
At 10 ° C., the higher the proportion of the image area estimated to be the halftone density, the higher the fixing temperature control temperature. For example, when the proportion of the halftone density is high, such as in a photographic image, the fixing temperature is raised and the character image When the halftone density is low, the fixing temperature is set to normal.

As described above, the density of each pixel of the digital binary image data is estimated, and the fixing temperature control temperature is made variable according to the ratio of the halftone density in a specific area.
It is possible to set an appropriate fixing temperature for each image. This makes it possible to prevent the fixing property from deteriorating even in the halftone density part where the fixing property changes greatly depending on the image density even at the same temperature, and the fixing property deteriorates in comparison with the low density part and the high density part. Become. Further, in order to improve the fixability in the intermediate density portion from the initial normal temperature control temperature, there is a risk that a high temperature offset or an excessive temperature rise in the machine adversely affects other parts. . Therefore, this method of changing the fixing temperature control temperature according to the image ratio of the halftone density portion is particularly effective. Further, as the fixing device using this method, a fixing device having a good thermal response is preferable in order to change the temperature control temperature for each sheet, and it is described in, for example, JP-A-63-313182. The film-type fixing device, etc., can be considered as an example.

In the present embodiment, for convenience, the detected concentration is set to 3
Hereinafter, the detection ratio is set to three levels of 10% and 20%, but it is also possible to change the detection density, the detection ratio, the number of switching steps, and the fixing temperature control temperature. For example, it is necessary to make the setting variable depending on the difference in conditions such as model and sales area, or to increase the number of switching in five steps or more to more finely control the temperature control temperature and the image density ratio. It is also a very effective means when it is improved and the harmful effect on the main body is considered. Further, if the determination area is limited to a certain specific area instead of all pixels, the effect of reducing the amount of used memory can be obtained.

Further, the concentration estimation according to this embodiment is
Since the correction is performed on the data after the γ correction process, the fixing failure can be surely prevented even if the density changes due to the correction.

Further, the contents described in the present embodiment and the contents described in the following embodiments mainly relate to the copying machine, but in the case of a digital binary image, such as LBP, FAX, file system and the like. It can be used for other devices.

(Second Embodiment) Next, a second embodiment of the present invention will be described. Note that description of common parts with the first embodiment will be omitted.

The basic structure and control of this embodiment are almost the same as those described in the first embodiment. However, in this embodiment, the fixing speed is changed by changing the estimated proportion of the halftone density portion, and the fixing is performed. Improve the sex. Hereinafter, the present embodiment will be described based on Table 3.

Table 3 shows the relationship between the ratio of the detected pixel density and the fixing speed, which represents the second embodiment of the present invention.

[0050]

[Table 3]

For example, in the density estimation data described in the first embodiment, the ratio of pixels of 3 or less is 1 for all pixels.
When it is 0% or less, fixing is performed at a fixing speed of 150 mm / sec, which is the same as the normal process speed. Similarly, 10
~ 20%, the fixing speed is 120 mm / sec, 2
If it is 0% or more, the image is fixed at 90 mm / sec, and as the ratio of the halftone density increases, the fixing speed is slowed down to increase the heat capacity per sheet and improve the fixability.

As described above, even if the method of changing the fixing speed is used, the fixing property can be improved by the image density as in the case of the first embodiment.

Further, since the fixing speed is changed, it is possible to further reduce adverse effects on other units such as offset and temperature rise in the machine, as compared with the case where the temperature control temperature is changed.

(Third Embodiment) Next, a third embodiment of the present invention will be described. Note that description of common parts with the first embodiment will be omitted.

The basic structure and control of this embodiment are almost the same as those described in the first embodiment. However, in this embodiment, the fixing nip width is changed by changing the fixing nip width according to the estimated ratio of the halftone density portion. Improve the sex. Hereinafter, the present embodiment will be described based on Table 4.

Table 4 shows the relationship between the ratio of the detected image density and the fixing nip width, which represents the third embodiment of the present invention.

[0057]

[Table 4]

For example, in the density estimation data described in the first embodiment, if the ratio of pixels of 3 or less is 10% or less with respect to all the pixels, the fixing nip width is 4.5 mm, and 10 is the same. If it is -20%, it is set to 5.5 mm, and if it is 20% or more, it is set to 6.5 mm to widen the fixing nip width as the ratio of the halftone density increases, thereby increasing the heat capacity per sheet and improving the fixing property.

As described above, even when the method of changing the fixing nip width is used, the fixing property can be improved by the image density as in the first embodiment, and the second embodiment can be performed. Since the temperature is not changed in the same manner as described in the embodiment, it is possible to reduce the adverse effect on other units due to the offset and the temperature rise in the machine.

In the present embodiment and the first and second embodiments, the method of making the fixing nip width (pressing force), the fixing temperature, and the fixing speed variable in order to change the fixing property has been described. It goes without saying that the same effect can be obtained if the fixing property can be changed by changing it.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 5 is a view showing a fourth embodiment of the present invention. In FIG. 5, 10 is a density detection mask for pixels in the central portion of the image except for the right side and 1 line at the rear end of the image, and 11 is 1 line at the right end of the image. 2 is a density detection mask of one line at the rear end of the image, and 13 is a density detection mask of one pixel at the right rear end.

FIG. 6 shows the mask, image pattern and density estimation data when the density detection is actually performed by the density detection mask shown in FIG. 5 in the fourth embodiment of the present invention. The maximum numerical value shown here is 3, and all three pixels around the pixel of interest (pixels indicated by diagonal lines) are filled with data (strike), and the density is high. Similarly, if the value is 0, there is no data around and the density is low.

In the above configuration, the basic configuration is almost the same as that described in the first embodiment, but in this embodiment, the size of the mask for halftone density estimation is changed to The ratio of the halftone density is easily obtained, and the fixing condition is changed to improve the fixing property.

A method of estimating the density of each pixel of interest using the mask shown in FIG. 5 will be described with reference to FIG. For example, as shown in the density detection data E, if the pixel data around a certain target pixel (the target pixel is shaded) is as shown in the figure, the density estimation data of this pixel is 2. At this time, as described before, the surrounding data of 1 and 0 represent the presence or absence of data for each pixel, and 1 is a dot and 0 is a dot. Similarly, the density estimation data of the density detection data F becomes 0. The maximum value of the density estimation data obtained in this way is 3 and the minimum value is 0. It can be estimated that the larger the numerical value is, the darker the density is, and the smaller the numerical value is, the darker the density is. If this masking process is performed when there is data (has data), when the numerical value is 0, it is the thinnest (even if the numerical value is 0, it is not white).

Table 5 shows the relationship between the ratio of detected image density and the fixing temperature control temperature, which represents the fourth embodiment of the present invention.

[0067]

[Table 5]

As shown in Table 5, the estimated data thus obtained is used to obtain the ratio of the density estimated data in a certain region, and the fixing temperature is changed accordingly. For example, if the density estimation data estimated to be halftone density is 1 or less, and if the proportion of the density estimation data of 1 or less in the entire image area is 10% or less, the proportion of the white portion or the black portion is high, The fixing temperature control temperature is set to 190 ° C. because the ratio of the halftone density portion where the fixing property deteriorates is low. Similarly, if the ratio of data 1 or less is 10 to 20%, the fixing temperature control temperature is 200 ° C., and if it is 20% or more, 210 ° C. is set. By increasing the fixing temperature control temperature, the fixing temperature control temperature is set high for images with many halftone images such as photographic images, and the fixing temperature control is performed for images with relatively low halftone density such as text images. Leave the temperature at the normal setting.

As described above, the density estimation mask for estimating the density of each pixel of the digital binary image data uses the masks 10 to 13 shown in FIG. 5 to estimate the density of one pixel. Data required for memory can be reduced, and memory cost can be reduced.

Further, instead of changing the fixing temperature control temperature described in the present embodiment, as described in the second and third embodiments of the present invention, the fixing speed, the fixing nip width, etc. The same effect can be obtained by using the method of changing the fixing conditions.

(Fifth Embodiment) Next, a sixth embodiment of the present invention will be described. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The basic configuration and control of this embodiment are almost the same as those described in the first embodiment, but in this embodiment, the estimated proportion of the halftone density portion is detected in a plurality of stages (this embodiment). However, the fixing temperature is changed according to the ratio of each estimated density to improve the fixing property. The present embodiment will be described below based on Table 6.

For example, according to the concentration estimation data described in the first embodiment, the estimated concentration is 2 or less, the case of 2 to 5 and the case of greater than 5 are classified into a high concentration and a high concentration of 2 to 5. In case of 5, halftone medium density, and in case of 2 or less, halftone low density (not a white background). Therefore, estimated density data is 2 or less, especially in the halftone density portion, as shown in Table 6 for 2 to 5. Change the fixing temperature control temperature in a matrix.

[0074]

[Table 6]

This method is not limited to fixing temperature control temperature, and fixing conditions such as fixing speed and fixing nip width can be changed in the same manner. Further, these conditions are not independent but are, for example, temperature and speed. Alternatively, all three conditions may be combined and changed. As a result, it becomes possible to set the fixing condition more finely according to the estimated image density, and the fixing failure,
It becomes possible to solve the problem of fixing due to image density such as offset and temperature rise in the machine.

This method is a particularly effective means when environmental conditions are deteriorated or the number of durable sheets of the main body is increased (when high durability is required).

[0077]

As described above, the first embodiment according to the present application is described.
According to the invention, the estimated density of the pixel of interest is detected from the image signal of the digital binary image data by the dot pattern of the pixels around the pixel of interest, and the ratio of the halftone estimated image to the image data in the entire area or the specific area is detected. By changing the fixing temperature control temperature according to the ratio of the halftone density pixels in the image area thus obtained, it becomes possible to change the temperature for each density with respect to the fixability that is changed by the image density (pattern), It becomes possible to improve the fixability.

According to the second aspect of the present invention,
By using a mask formed in a predetermined matrix shape, the number of pixels having a signal value indicating that the image is to be visualized is obtained around a specific pixel, so that the density can be estimated quickly. .

Further, according to the third invention of the present application, by the mask formed in the 4 × 4 matrix, pixels other than the specific pixel having pixel values having a signal value indicating that they are visible image objects in the surroundings are used. Since the number is obtained, it is possible to reduce the amount of memory used at the time of density estimation and to reduce the cost.

According to the fourth aspect of the present invention,
Since the heat applied by the fixing device is increased or decreased by switching the fixing temperature or the fixing speed or the pressure contact width of the transfer material pressing portion, it is possible to perform appropriate fixing according to the image density.

Further, in the fifth aspect of the present invention, all of the fixing temperature and the fixing speed and the pressure contact width of the transfer material pressing portion are switched, or any two of them are combined. As a result, the heat applied by the fixing device is increased or decreased, so that it is possible to perform appropriate fixing according to the image density while suppressing problems of thermal fixing such as temperature rise in the machine and offset.

According to the sixth invention of the present application,
The pixels for which the calculation of the ratio of all pixels or the ratio of a specific area in all pixels is determined by a plurality of image density standards, so that proper fixing is possible for a high-definition image with a wide image density. It can be carried out.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an image processing circuit and its periphery according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 3 is a diagram illustrating an image density detection mask according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of image density detection according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating an image density detection mask according to a fourth embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of image density detection according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1 to 13 Density detection mask 22 Pixel density detection circuit (means for estimating image density) 40 Photosensitive drum (visual image forming means) 43 Developing device (visual image forming means) 49 Transfer charger (visual image forming means) 51 Fixing device 68 Binarization processing circuit (means for binarization processing) 70 Laser substrate (visual image forming means) 71 Laser light emitting device (visual image forming means)

Claims (6)

[Claims] 1. The image data is expanded into pixels in a matrix having a predetermined resolution, and the signal value of each pixel is divided into a value indicating that the image is to be visualized and a value indicating that the image is not to be visualized. Means for performing a binarization process, a visible image forming means for visualizing the image data processed by the means as a developer image to form it on a transfer material, and a transfer material and a developer while conveying the transfer material under pressure. An image forming apparatus provided with a fixing device for fixing the developer image on the transfer material by applying heat to the image, having a signal value indicating a target of visualization around a specific pixel. A means for estimating the image density of the specific pixel from the number of pixels is provided, and the image density is estimated by the means for all pixels developed in the matrix or for each pixel in a specific area in all the pixels and estimated. The image density is An image forming apparatus, wherein the heat applied by the fixing device is increased or decreased according to a ratio of pixels having a value equal to or less than a constant value in all the pixels or a specific area in all the pixels. 2. The mask formed in a predetermined matrix shape is used to obtain the number of pixels having a signal value indicating that the image is to be visualized around a specific pixel. Image forming device. 3. The mask according to claim 2, wherein the mask is formed in a 4 × 4 matrix shape for obtaining the number of pixels having a signal value indicating a surrounding visible image object other than the specific pixel. Image forming device. 4. The fixing temperature or the fixing speed or the pressure contact width of the transfer material pressing portion is changed in order to increase or decrease the heat applied by the fixing device. The image forming apparatus described. 5. In order to increase or decrease the heat applied by the fixing device, all of the fixing temperature, the fixing speed, and the pressure contact width of the transfer material pressing portion are switched, or any two of them are combined. The image forming apparatus according to any one of claims 1 to 4. 6. The pixel for which the calculation of the ratio of all pixels or the ratio in a specific area of all pixels is determined by a plurality of image density standards.
The image forming apparatus according to claim 1.