JPS61222375A - Copying machine - Google Patents

Abstract

PURPOSE:To similiarly correct record density by detecting the reading characteristic of an image sensor by reading the densities of two reference density plates and providing variably a threshold that identifies the record density according to the reading characteristic. CONSTITUTION:Two densities with different values of two density plates are read by an image sensor 12 and a reader 18. According to the result of the reading, the reading characteristic of the image sensor 12 is detected at a reading characteristic detection circuit 19. And based upon the detected result of this reading characteristic, the threshold that identifies the record density of an original picture image is set variably. Therefore, the correction of the record density including half tone is similiarly executed through all density area even with the secular change of an optical system, such as the image sensor 12 etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses an image sensor to read a document image,
The present invention relates to a copying device that copies onto recording paper.

[Prior Art] As is well known, in a copying machine, an image sensor reads an original image, and by comparing the read output with a predetermined threshold value, the density of the original image is identified, and the image is recorded according to the identification result. Determines the recording density recorded on paper.

By the way, in this case 1. The characteristics of the output density relative to the input density, that is, the reading characteristics of the image sensor change due to changes in the ambient temperature, changes over time, changes over time in the light source, and the like. Therefore, even if the input density is constant, the recording density changes.

Therefore, before starting to read the original image, an image with a reference density is read, and depending on the reading result, the reference voltage when converting the read image signal to omega elements is varied, or the bias level of the image sensor output signal is varied. Conventionally, methods have been implemented to correct variations in the input S degree.

[Problems to be Solved by the Invention] However, since each correction method uses only one reference density, it is not possible to grasp the reading characteristics of the image sensor over the entire density range, and it is difficult to correct the recording density. There was a problem in that it could not be performed uniformly over the entire concentration range. Further, since the read image signal is corrected before determining the recording density, there is a problem that the relationship with the threshold value of the intermediate wing changes, resulting in a difference in the recording density of the intermediate tone.

SUMMARY OF THE INVENTION An object of the present invention is to provide a copying apparatus that can uniformly correct recording density including halftones over the entire density range.

Means for Solving Problem F] The present invention provides two reference density plates having different densities arranged within the field of view of an image sensor, and reading the densities of these two reference density plates by the image sensor,
a detection means for detecting the reading characteristic of the image sensor based on the output signal of the image sensor for one reference density; and a threshold value for identifying the recording temperature of the document image read by the image sensor based on the reading characteristic detected by the detection means. The apparatus is provided with processing means for variably setting the recording density and determining the recording density accordingly.

[Operation] By reading the densities of the two reference density plates, the reading characteristic of the image sensor within the density range of these density plates is detected. In the processing means, threshold values such as halftones are varied according to this reading characteristic, and the recording density is determined based on this new threshold value.

[Embodiment] FIG. 1(a) is a side sectional view showing an embodiment of the optical system of a copying apparatus according to the present invention. It has mirrors 13 and 14 and a lens 15 that take in the reflected light of the original image from the slit 16 and form an image on the image sensor 12. The scanner 1 moves at a predetermined speed in the direction of arrow A when reading a document, and sequentially reads images of a document placed on a platen glass 2. When the scanner 1 reaches the end of the document, it returns to the standby position shown in the figure. In this standby position, the upper part of the slit 16 is covered by the platen cover 3, and the light sources 10 and 11 are turned off, so that no light enters the image sensor 12 from the outside. On the surface of the platen cover 2 above the slit 16, a first density reference plate 17A made of a black film or black plate and a second density reference plate 17B made of a white film or plate are arranged (see FIG. 1). b) It is attached as shown in the top view.

Therefore, light having black and white densities is incident on the image sensor 12 at its standby position.

FIG. 2 shows an image sensor 12 based on image signals of a black image and a white image read at the standby position of the scanner 1.
12 is a diagram illustrating an embodiment of a circuit that detects the reading characteristics of the image sensor 12 and determines the recording density based on the detection result. The image signal read by the image sensor 12 is input to the reading circuit 18, where, for example, the 128th floor After being quantized into a digital image signal of
It is input to 0.

Then, the reading characteristics detection circuit 19 detects the reading characteristics (that is, the photoelectric conversion characteristics) of the image sensor 12 based on the digital image signals of the black image and white image read at the standby position of the scanner 1. That is, if the black image is the first reference density and the white image is the second reference density, then
As shown in the density-image signal output characteristic diagram of FIG. 3, the reading characteristic of the image sensor 12 is detected to be a characteristic indicated by a straight line A, B, or C, for example.

, this detection data of the reading characteristics is input to the processing device 20. The processing device 20 receives the read image signal of the original image and determines the recording density of the pixel of interest using a 4×4 dither matrix as shown in FIG. At this time, the recording density when recording based on the initially set threshold values for each division number "1" to r16J' of the dither matrix has the characteristics as shown in FIG. 5, and the input original image Assuming that the recording density with respect to the density is set to the characteristics shown in FIG. 6, the processing device 20 adjusts the recording density according to the reading characteristics of the image sensor 12 so that the recording density with respect to the input document density has the characteristics shown in FIG. The threshold value initially set for each section of the dither matrix is variably set, and the recording density of the pixel of interest is determined based on this new threshold value.

In this case, since the processing device 20 needs to know the relative value position of the pixel of interest in the main scanning direction and the sub-scanning direction, the scanner 1
Position information PD1. which indicates the moving position of the image sensor 12 in the sub-scanning direction and the scanning position of the image sensor 12 in the main scanning direction, respectively. P
D2 is input from a control section (not shown). Furthermore, in order to variably set the threshold value of the dither matrix for the recording density characteristics shown in FIG.
RD and WRD are input. And this processing device 20
The density of the pixel of interest determined in is sent to the recording device 21 pixel by pixel as recording data.

Note that the reference density plates 17A and 17B are arranged parallel to the sub-scanning direction of the platen 2 as shown in FIG. By reading the density of 17B, variations in the recording density due to fluctuations in the illuminance of the light [R10, 11 when the scanner 1 moves in the sub-scanning direction can be greatly reduced.

[Effect of the invention] As explained above, according to the present invention, two
The density of the two standard density plates is read, the reading characteristics of the image sensor are detected based on the reading results, and the threshold value for identifying the recorded density of the original image is variably set based on the detection results of the reading characteristics. Even if the optical system changes over time, correction of recording density including halftones can be uniformly performed over the entire density range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an optical system in a copying apparatus according to the present invention, and FIG. 2 is a block diagram showing an embodiment of a circuit that detects the reading characteristics of an image sensor and roughly determines the density of a recorded image. Figure 3 is a graph showing an example of detection of the reading characteristics of an image sensor, Figure 4 is a pattern diagram showing an example of a dither matrix for expressing halftones, and Figure 5 is an initialization of the dither matrix shown in Figure 4. FIG. 6 is a graph showing an example of the recording density characteristics depending on the set threshold value. FIG. 6 is a graph showing the setting characteristics of the recording density for the input original image. DESCRIPTION OF SYMBOLS 1... Scanner, 2... Platen, 12... Image sensor, 17A, 17B... Density standard plate, 18...
...Reading circuit, 19...Reading characteristic detection circuit, 20
... Processing device, 21... Recording device. Figure 1 (a) Figure 1 (b) Figure 3

Claims (1)

[Scope of Claim] A copying apparatus that uses an image sensor to read a document image and copy it onto recording paper, comprising: two reference density plates each having a different density arranged within the field of view of the image sensor; a detection means for reading the density of the density plate with the image sensor and detecting the reading characteristics of the image sensor based on the output signals of the image sensor for two reference densities; A copying apparatus comprising processing means for variably setting a threshold value for identification in accordance with the reading characteristics detected by the detection means and determining recording density.