JPS5819184B2 - Image reading method and reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to photodiode arrays, CCDs (Cha
The present invention relates to an image halftone reading method and reading device using a multi-element reading device such as a rge Coupled Device, and in particular to correcting output fluctuations caused by sensitivity differences between multiple elements in the device and non-uniformity of illuminance. The present invention relates to an image reading method and a reading device that enable faithful reading of halftone images.

□ In conventional black and white binary image reading devices that use multi-element reading devices such as photodiode arrays and CCDs, there is usually a 10% variation in sensitivity between each element in the device. Ta.

However, in the case of binary reading, it is possible to appropriately set a threshold and determine black and white based on whether the output of each element exceeds this threshold, so variations in sensitivity have not been much of a problem.

However, when trying to read an image with halftones without losing any halftones, such a method cannot be adopted, and it becomes necessary to correct the sensitivity difference between each element in the device. .

The present invention satisfies these needs, and not only makes it possible to correct sensitivity differences easily and inexpensively, but also
The present invention proposes an image reading method and a reading device that can simultaneously correct non-uniformity in illuminance caused by an original illumination device.

In the image reading method of the present invention, in an image reading device that reads halftone images using a multi-element reading divider, by sequentially reading images of a uniform halftone pattern in advance, variations in sensitivity of each element of the device and illuminance can be eliminated. The degree of non-uniformity of the image is measured, this variation information is encoded and stored in memory, and when reading the image,
The present invention is characterized in that the variation information stored in the memory is read out in synchronization with the reading, and the gain of the amplifier is controlled based on the read variation information, thereby correcting sensitivity differences and the like.

Next, the image reading method of the present invention will be explained in detail with reference to the drawings.

As already explained, in the image reading method of the present invention, before reading an image, the sensitivity difference of each element in the device is measured in advance, and this is encoded as variation information and stored in the memory.

To this end, first, an image of a uniform halftone pattern is read using a multi-element reading device to measure output fluctuations caused by variations in sensitivity, non-uniformity in illuminance, and the like.

FIG. 1 is an example of this, in which the image signal voltages V for images of a uniform halftone pattern are not at the same level.

Therefore, it is determined in which level range the image signal voltage V corresponding to each element falls by comparing it with a reference voltage.

FIG. 2 shows the relationship between the image signal voltage and the reference voltage when five reference voltages L1 to L5 are set and the level range is set to four levels.

By determining the peak voltage Vp of these image signal voltages and coding them according to the relationship shown in Figure 3, it is possible to obtain information on variations caused by differences in sensitivity of each element within the device and non-uniformity of illuminance. It will be done.

When encoding a four-level level range like this, two bits (bt and b2) are sufficient.

Then, the encoded variation information is stored in memory.

Next, when actually reading an image, the encoded variation information may be read out from the memory in synchronization with the image reading, and the gain of the image signal amplifier may be controlled.

FIG. 4 is a block diagram showing an embodiment of the image reading device of the present invention.

In the drawing, 1 is a multi-element reading device, 2 is a selector switch, and 3 is a multi-element reading device.

is a level comparator, 4 is a variable amplifier, and 5 and 6 are encoders.
1', 7 and 8 are memories such as shift registers, 9 is a decoder, 10 is a clock oscillator, and 11 and 12 are circulation circuits of shift registers 7 and 8.

First, the changeover switch 2 is switched to the contact C side in order to measure the four variations due to differences in sensitivity of each element in the device, code it, and store it.

In response to a clock pulse from a clock oscillator 10 whose driving is started by a read start signal or the like, a multi-element read device 1 such as a photodiode array or COD,
Images of a uniform halftone pattern are sequentially read, and the level comparator 3 sequentially determines which level range the output falls within.

The determination result by this measuring means is encoded by encoders 5 and 6 provided as encoding means in the relationship shown in FIG. 3.

Each bit b1 and b2 of the code is input to and stored in shift registers 7 and 8, respectively.

The shift registers 7 and 8 are memory means having a capacity capable of storing the same number of codes as the number of elements, and can store variation information.

During this time, circulation circuits 11 and 12 are open.

Next, in order to proceed to actual image reading, the switch 2 is switched to the contact d side.

This switching of the switch 2 is performed electronically after measuring the sensitivity of each element, but manual operation is also possible.

The clock generator 10, whose driving is started by a read start signal or the like, generates the same number of clock pulses as the number of elements of the device 1, and drives the device 1.

The device 1 sequentially reads images and inputs the image signal V to the variable amplifier 4.

At the same time, the clock pulses are also applied to the shift registers I and 8, so that the codes indicating the previously measured and stored variation information are sequentially read out and decoded by the decoder 9 provided as decoding means.

The output of the decoder 9 controls the gain of the variable amplifier 4.

In this case, the image signal output of the element read by the device 1 and the code output of the decoder 9 of the variation information indicating the sensitivity difference of the element are simultaneously input to the variable amplifier 4.

Therefore, considering the non-uniformity of illuminance, when a highly sensitive element is reading, the gain of the amplifier 4 is reduced, and when a less sensitive element is operating, the gain is increased. The image signal (■) is an image signal V that has been corrected for differences in sensitivity of each element.

The output is closed.

During actual image reading, a portion of the output of each shift register 7 and 8 is sent to the circulation circuit 11 and 12, respectively.
Since it is re-inputted to the input side by
Once one cycle of reading is completed, the next image can be read immediately.

As explained in detail above, according to the image reading method and reading device of the present invention, it is possible to correct the sensitivity difference between each element in the reading device, and also correct the illuminance difference caused by the lighting device at the same time. As a result, many excellent effects can be achieved, such as being able to read halftone images faithfully and making it possible to construct the device inexpensively and easily.

[Brief explanation of the drawing]

Fig. 1 is a time chart showing an example of the image signal voltage of a uniform halftone pattern, Fig. 2 is a time chart showing the relationship between the image signal voltage and the reference voltage, Fig. 3 is an example of encoding, and Fig. 4 is FIG. 1 is a block diagram showing an embodiment of an image reading device of the present invention. In the drawing, 1 is a multi-element reading device, 3 is a level comparator, 4 is a variable amplifier, and 7 and 8 are shift registers.

Claims (1)

[Scope of Claims] 1. In an image reading device that is equipped with a multi-element reading device and reads halftone images, the output fluctuations of each element of the device are measured by sequentially reading images of a uniform halftone pattern in advance. These are encoded and stored as variation information, and when actually reading an image, the variation information is read out and decoded in synchronization with image reading, and read using the decoded variation information. An image reading method characterized by correcting an image signal. 2. A multi-element reading device, a measuring means for measuring its output fluctuation, a variable amplifier, a changeover switch for switching the output of the multi-element reading device and inputting it to one of the measuring means and the variable amplifier, and to the measuring means. a decoding means connected to the coding means; a memory means connected to the coding means; and a decoding means connected to the memory means and controlling the gain of the variable amplifier by the output thereof. An image reading device characterized by: