JPH04219066A - Image processor - Google Patents

Abstract

PURPOSE:To allow the outputting of copied images having optimum gradation characteristics by detecting the densities of a document and a copying device and making gradation conversion according to the respective densities. CONSTITUTION:The densities of the document images obtd. by scanning reading systems 103 to 105 in an arrow direction are detected by a density detecting circuit 113 and are converted respectively to C(cyan), M(magenta) and Y(yellow) of complementary colors according to the max. density and min. density of the document and the max. density value of a copying device detected by a copying density detector 124. The min. values K(black) of C, M, Y are extracted by a black extracting circuit 110 and are subjected to known color correction processing in a masking circuit 111 and a UCR circuit 112 to form images, by which the collapse of the gradations in the high-density parts is prevented without the aid of user's labor at the time of copying the document (mainly silver salt photograph) of the density above the reproduction range of toners.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus that detects the density of a read document and controls image gradation.

0002

2. Description of the Related Art Conventionally, a color image copying apparatus uses logarithmic transformation when converting an input luminance signal into a density signal, but the parameters used during the conversion are fixed. As a method for handling high-density continuous tone originals, several modes such as character mode 51 and photo mode 52 shown in FIG. 5 are set, gamma conversion data corresponding to each mode is prepared, and the user can copy the original A method is also used in which one of the modes is selected and set depending on the situation.

0003

[Problems to be Solved by the Invention] However, in the above conventional example, setting the mode is troublesome, and in the case of a document containing a mixture of text and photos, the user has to decide in which mode to copy. There was a problem that it could only be done. Also, when the text mode and photo mode are set separately, the gamma is intentionally raised in the normal text mode, and the middle tones are considerably delayed compared to the linear density in the photo mode, so the original document is There is also the problem that when a copy is made as a manuscript, the deterioration becomes severe.

[0004] When the range of logarithmic transformation is fixed,
If the range is too small, smearing will occur when copying high-density originals; if the range is set too high, the smearing will disappear, but the overall thickness will be thinner, so it is not suitable for copying originals that do not have high density (the limit of toner production). . Furthermore, if there is a density change in the copying apparatus itself, there is a problem in that unnatural images are copied.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image processing device that can output a copied image with optimal tonality depending on the density of the original and the copying device. shall be.

[0006]

Means for Solving the Problems and Operations In order to achieve the above object, an image processing apparatus of the present invention has the following configuration. That is, an image processing device that detects the density of a read original and controls the image gradation has a detection means that detects the copy density, and converts the density of the original image to match the maximum density that the device itself can reproduce. characterized by things.

[0007] Also, when reading a document, a calculation means for determining the maximum density and minimum density of the density data of the document, and a selection means for selecting an image processing parameter based on the maximum density and minimum density determined by the calculation means; The present invention is characterized by comprising a conversion means for performing gradation conversion according to the parameters selected by the selection means.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an image processing apparatus in this embodiment. Document table glass 1
The original 102 placed on the 01 is illuminated by a halogen lamp 103 for illuminating the original, and a rod lens array (for example,
An image is formed on a CCD line sensor 105 by SELFOC (registered trademark) 104 . The CCD line sensor 105 is coated with R, G, and B color separation filters dot-sequentially, and outputs the color separation of the original 102 at a pixel density of about 400 dpi. The reading systems 103 to 105 described above scan in the direction of the arrow, and the original image is sequentially read out line by line, and sampled and held by the S/H circuit 106 pixel by pixel. Then, it is converted into a digital signal by the A/D conversion circuit 107, and is converted into a digital signal by the shading correction circuit 108.
The output ram due to the variation between the 105 pixels is corrected.

The R, G, and B signals output from the shading correction circuit 108 are sent to a density detection circuit 113, which will be described in detail later, to detect the density in the document. Also,
The copy density detection device 124 also detects the maximum density value of the copying device. Here, the detected density and maximum density value in the document are sent to the CPU 113, and converted into complementary colors C (cyan), M (magenta), and Y (yellow) according to these values.

0010

[Math 1]

Here, the values of α and β are determined by the concentration detection circuit 113.
Maximum density value (Dmax) from and copy density detection device 1
Dmin is the value determined according to the maximum density value (Dcmax) from the density detection circuit 113, and Dmin is the minimum density value from the density detection circuit 113. Then, in the black extraction circuit 110, C, M,
The minimum value K (black) of Y is extracted, and well-known color correction processing is performed in a masking circuit 111 and a UCR circuit 112, resulting in C, M, Y, and K frame sequential signals. Here D/A
It is input to the conversion circuit 116 and becomes an analog signal again.
The output from the triangular wave generation circuit 117 synchronized with the image clock is compared with the comparator 118, and the laser driver 1
The semiconductor laser 120 is pulse width modulated through 19. The output from the semiconductor laser 120 is collimated by a suitable optical system, and the output is collimated by a polygon mirror 121 that rotates at high speed.
is scanned onto the photosensitive drum 122 by the drum 122.
form a latent image on the surface. The latent image on the drum 122 is
23, and then undergoes a transfer and fixing process (not illustrated)
, M, Y, and K planes are sequentially formed on the paper to complete the copying operation.

Next, the configuration of the above-mentioned concentration detection circuit 113 will be explained below with reference to the schematic block diagram shown in FIG. First, the digital image signal VD output from the shading correction circuit 108 is passed through the latch 201 to the latch 202, comparators 203, 206, latch 204,
207 in parallel.

The comparator 203 compares the image signal from the latch 201 with the image signal from the latch 202 one clock before, and if the new image signal from the latch 201 is smaller, outputs a comparison output to the AND gate 205. . This AND gate 205 is connected to the comparator 2
The comparator output from 03 is the sampling clock S.
It is sent to the latch 204 in synchronization with CL. However, the sampling clock SCL is a clock synchronized with the image data clock CLK for reading out image signals from the CCD 105.

On the other hand, the comparator 206, like the comparator 203, compares the image signal from the latch 201 with the image signal from the latch 202 one clock earlier. Here, if the new image signal from the latch 201 is larger, a comparison output is output to the AND gate 208. The AND gate 208 synchronizes the comparison output from the comparator 206 with the sampling clock SCL and sends it to the latch 207. And the latch 204,
At 207, when the comparator output is input from the AND gates 205 and 208, the image signal from the latch 201 is latched and sent to the CPU 114.

As described above, the maximum value and minimum value of the image signal input so far are latched in the latches 204 and 206, respectively. In addition to the comparator output and the sampling clock SCL, the AND gates 205 and 208 have
An enable signal EN indicating the valid section of each line of the image signal from the CCD 105 is input. That is, the configuration is such that the comparison results for the image signals in a predetermined section for each main scanning line are sent from the latches 204 and 207 to the CPU 114.

[0016] Therefore, C
The PU 114 can detect the lowest density level and the highest density level of each main scanning line by capturing the image signals from the latches 204 and 207 in synchronization with the synchronization signal MS for each main scanning line. Then, based on the low density and high density detected for each line, the CPU 114
The minimum density and maximum density of the original are respectively determined according to a program stored in the ROM 115 in advance.

FIG. 4 shows a tone reproduction curve (copy density relative to original density) when outputted using this method. In the figure, the standard curve 41 has a maximum print density of 1.6
5. Considering the density of the paper background to be 0.1, the difference is 1.55.
This value is used in all cases below. The difference between the lowest density and the highest density for 42 is 1.9, and for 43 it is 1.74.

Further, a density sensor 1 is installed at the developing device 123.
24, the sensor 124 measures the toner density on the surface of the drum 122, and the value is sent to the CPU 114, thereby performing logarithmic conversion that takes into account the maximum density that the copying machine itself can reproduce depending on the environment, specification status, etc. Is going. <Modification> Furthermore, as a modification, the signal from the CPU 114 may be sent to the black extraction circuit 110 via the logarithmic conversion circuit 109. This logarithmic conversion circuit 109 has n lookup tables, selects the most appropriate table based on the value of the difference between the highest density and the lowest density of the document detected by the CPU 114, and selects the most appropriate table, which is sent from the shading correction circuit 108. The image signals R, G, and B are converted into complementary colors C, M, and Y, respectively, according to the selected table.

Note that the selection of parameters for detection and conversion of the maximum density and minimum density described above is performed at the time of pre-scanning. As explained above, according to this embodiment, when copying originals (mainly silver halide photographs) with densities exceeding the reproduction range of toner, it is possible to reduce the gradation in high-density areas without bothering the user. This prevents the tone from becoming distorted.

Furthermore, when copying a high-density original, taking into account the maximum density of the copying machine, logarithmic conversion is performed according to the difference between the maximum density and the minimum density at the first time, and from the second time onwards, the maximum density is Toner reproducible limit value (approximately 1.5 to 1.65)
Therefore, logarithmic conversion is performed using a standard curve, and since the standard curve is much closer to linear than the curve used in conventional photo modes, it also prevents deterioration of generation copies.

[0021]

[Other Embodiments] Next, another embodiment according to the present invention will be described below with reference to the block diagram shown in FIG. Note that other parts not shown are the same as those in FIG. 1. The maximum density and minimum density of the R, G, and B signals subjected to shading correction by the shading correction circuit 501 are determined by the density detection circuit 506 according to the procedure described above. The same R, G, and B signals input to the density detection circuit 506, a code signal Cm indicating the highest density, and a code signal Cn indicating the lowest density are sent to the CPU 507. Thereafter, each RGB signal is logarithmically converted by the two methods described above (arithmetic operation within the CPU, LUT of the logarithmic conversion circuit).

On the other hand, C sent from the concentration detection circuit 506
The CPU 507 detects the maximum and minimum densities of the entire document from m and Cn (the maximum and minimum densities for each line of the document, respectively), calculates the difference value, and sends the code C
d to the masking circuit 504. The coefficients used in the calculation by the masking circuit 504 are
It is determined by this code signal Cd.

As described above, by changing the masking coefficient according to the maximum density and minimum density values, it is possible to prevent unnatural color reproducibility caused by changes in the dynamic range of logarithmic transformation.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
It is possible to output a copied image with optimal gradation depending on the density of the original and the copying device.

[Brief explanation of the drawing]

[Figure 1]

FIG. 2 is a block diagram showing the configuration of an image processing device in this embodiment.

FIG. 3 is a block diagram showing the configuration of a concentration detection circuit.

FIG. 4 is a diagram showing a tone reproduction curve of logarithmic transformation.

FIG. 5 is a diagram showing tone reproduction curves for each general mode.

FIG. 6 is a block diagram showing the configuration of an image processing device in another embodiment.

Claims (2)

[Claims] Claim 1: An image processing device that detects the density of a scanned original and controls the image gradation, comprising a detection means for detecting the copy density, and adjusts the density of the original image according to the highest density that the device itself can reproduce. An image processing device characterized by performing conversion. 2. Calculating means for calculating the maximum density and minimum density of the density data of the original when reading the original, and selecting means for selecting image processing parameters based on the maximum density and minimum density calculated by the calculating means, 2. The image processing apparatus according to claim 1, further comprising conversion means for performing gradation conversion according to the parameters selected by said selection means.