JPS6146873B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a copying apparatus with high precision in original density versus copy density. It is often desired to correct the output voltage characteristic of a device having an output voltage characteristic in which the output monotonically increases (or decreases) with respect to the input as shown in FIG. 1 as shown in FIG. 1 or as shown in FIG. For example, there is a measurement device that requires a linear display for the output of a non-linear detection element to correct the output voltage characteristic, and a measurement device that requires multiple functions to correct the output voltage characteristic. There may be cases where it is desired to perform characteristic correction of a plurality of functions at once for each function whose input/output characteristics are non-linear. To give a specific example, there is a copying machine that uses a solid-state image sensor for the imaging section, a laser beam for writing and scanning, and a photoreceptor for the recording medium.
The input/output characteristics of each function are shown in FIGS. 2a to 2c. In FIG. 2, a represents the output of the image sensor relative to the original density, b represents the modulation characteristic of the optical modulator, and c represents the sensitivity vs. amount of incident light on the photoreceptor. In an actual copying apparatus, it is preferable to correct these characteristics so that the original density and the copy density have a 1:1 relationship as shown in FIG. A polygonal function signal generator is generally used for such characteristic correction. However, in conventional polygonal function signal generators that use diodes or Zener diodes, the circuit does not operate as calculated due to variations in element characteristics and temperature characteristics, making adjustment difficult and difficult to create with high precision. It was difficult. Furthermore, even if the circuit is constructed mainly of an idealized diode circuit consisting of operational amplifiers and diodes, as in Japanese Patent Publication No. 51-35336, the number of operational amplifiers and diodes required is equal to the number of broken lines, and it takes a long time to make adjustments. In view of these points, it is an object of the present invention to provide a copying apparatus in which there is little variation in original density versus copy density, almost no adjustment is required, and the original density versus copy density can be determined with high accuracy. Some copying apparatuses are constructed by combining an imaging device and a recording device. For example, the image signal from the imaging device is corrected by the circuit shown in FIG. 1:1
can be made into a relationship. That is, the imaging device captures a document image and outputs an image signal, and this image signal is converted from an analog value to a digital value by the A/D converter 1. In the read-only memory 2, an address is designated by the digital value, a code at that address is read out, and this code is converted from the digital value to an analog value by the D/A converter 3. The memory contents of the memory 2 are set so that the output signal of the D/A converter 3 becomes a desired corrected image signal with respect to the image signal from the imaging device. For example, if the copying density requires 16 gradations, the A/D converter 1 divides the image signal from the imaging device into 16 steps, or n times that number (16×n), and converts it into digital values. used. The memory 2 stores broken line functions in accordance with the content of image signal correction in a relationship of number of addresses versus content, and the input/output code thereof is, for example, as follows.

[Table] The output code of the memory 2 is converted from a digital value to an analog value by the D/A converter 3 to become a desired corrected image signal and provided to the recording device. This recording apparatus is, for example, one in which a laser beam from a laser is modulated by an image signal from a D/A converter using an optical modulator, and then guided to a photoreceptor to record an image using an electrophotographic method. If you use a large capacity memory 2 and create multiple types of broken line functions, that is, correction curves in memory 2, you can selectively use multiple types of correction curves as input by switching some of the input addresses of memory 2. be able to. For example, OFT can be used instead of a laser, optical modulator, etc. in a recording device.
When writing scanning is performed using an optical fiber tube, the correction curve can be changed by changing the switching input, and there is no need to change the circuit. Also transmits image signals,
If a high-quality image is required, it is conceivable to digitize the image signal from the imaging device, transmit it, return it to an analog value, and provide it to the recording device. In this case, the digitized image signal can be corrected in the memory 2, and the device itself can obtain an image output that matches the characteristics of the recording device.
On the sending side, multiple types of devices can be operated with one type of signal. In one embodiment of the present invention, as shown in FIG. 5 in the above-mentioned copying apparatus, the level of the image signal from the imaging device is judged by a level judgment circuit 4, and when the level is below (or above) a certain level, the image signal is The image signal is output to the recording device as it is through the switching circuit 5 as a signal that is not to be corrected, and when it is above (or below) a certain level, the image signal is given as a signal to be corrected to the A/D converter 1 for correction. D/
The image signal from the A converter 3 is outputted to the recording device through the switching circuit 5. In this case, the gradation division can be made finer than that of the above-mentioned copying apparatus, and the image signal can be corrected more precisely, and if the gradation division is made the same as that of the above-mentioned copying apparatus, the capacity of the memory 2 can be small. As described above, the copying apparatus according to the present invention converts the image signal from the imaging device into a digital signal, outputs the corrected image signal from the storage means using this digital signal, converts it into an analog signal, and sends it to the recording device. Since it is output, there is little variation in original density versus copy density, and adjustment thereof is almost unnecessary, and moreover, the original density versus copy density can be highly accurate. Furthermore, since the image signal is corrected only for those below or above a predetermined level, the correction range of the image signal is narrowed, so the image signal can be corrected finely by fine-grained tone division; This makes it possible to reduce the capacity of the storage means without reducing the storage cost.

[Brief explanation of the drawing]

1 to 3 are characteristic curve diagrams for explaining the present invention, FIG. 4 is a block diagram showing a polygonal function signal generation circuit in an example of a copying machine, and FIG. 5 is a diagram according to an embodiment of the present invention. FIG. 2 is a block diagram showing a polygonal function signal generation circuit. 1...A/D converter, 2...Read only memory, 3...D/A converter, 4...Level determination circuit.

Claims (1)

[Claims] 1. An imaging device that captures a document image, and a level that determines the level of an image signal from this imaging device and divides this image signal into image signals that should be corrected below or above a predetermined level and image signals that do not undergo other corrections. a determination circuit, an A/D converter that converts an image signal to be corrected from the level determination circuit into a digital signal, and a storage unit that outputs an image signal corrected by the image signal from the A/D converter; A D/A converter that converts the image signal from this storage means into an analog signal, and a recording device that records an image using the image signal from this D/A converter and the uncorrected image signal from the level determination circuit. Copying device equipped with