JPS6059868A - Binary-coding circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a circuit that binarizes an analog signal obtained by scanning an image.

[Prior art]

By irradiating the microfilm with light from a light source, and using a lens to form an image of the light that has passed through the microfilm onto the light receiving surface of an image sensor (such as a COD image sensor, hereinafter referred to as CCD), photoelectric conversion is performed. It has been proposed to electrically process the microfilm image by extracting the microfilm image as an analog signal and converting the obtained analog signal into a binary video signal.

Here, when converting the analog signal obtained from the COD into a binary value, a method is generally used in which the analog signal is compared with a fixed potential to be used as a reference.

The fixed potential that should serve as a reference for this comparison is called a slice level. However, with this method, it is difficult to obtain accurate binary video signals for the reasons described below. That is, depending on the image, the range of change in the video signal is two or three times below the fixed potential, and the change may not be detected with the fixed potential. Furthermore, when a COD is used, the amount of light received by the CCD is generally determined by the product of the light amount of the light source and the irradiation time. Therefore, when the light source irradiation time is kept constant, the amount of received light and the amount of light are in a proportional relationship. Here, for example, large text portions on the negative film have high transmittance and therefore receive a large amount of light, while small text portions have low transmittance and therefore receive a small amount of light. Therefore, the dynamic range of the analog video signal photoelectrically converted and extracted by COD becomes large. Therefore, when the analog video signal obtained from COD is compared with a fixed slice level and binarized, the tips of large characters may become thicker or small characters may disappear. When played back, the image quality of the played characters deteriorates.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to provide a binarization circuit that can improve the image quality of reproduced characters, for example, by eliminating the conventional drawbacks and accurately binarizing images.

〔Example〕

FIG. 1 is a diagram showing the operating principle of the present invention, and FIG. 2 is a block diagram showing an embodiment of a binarization circuit based on the principle of FIG. 1. FIG. 1 will be explained. First, (1)
is an analog video signal waveform photoelectrically converted by the CCD. Next, when the slope of waveform (1) is subtracted, it becomes a waveform like (2). Therefore, the positive peak value (maximum value) of waveform (2) can be detected as shown in (5). Then, the analog video signal at the position corresponding to this peak value is stored.

This stored signal has a value approximately at the center of the variation range of the analog video signal. This is the signal ■ in waveform (3). In addition, signal [F] in waveform (3) is waveform (1)
shows the analog signal of On the other hand, when the absolute value of the signal of waveform (2) is subtracted from the analog video signal of waveform (1), signal O in waveform (4) is obtained. In addition, the signal of waveform (4) [F
] indicates an analog signal of waveform (1). Comparing this signal ■ with signal ■ and outputting ■≧■ as 1 and ■≧■ as O, the signal (6) is obtained. This is the binary video signal that should be used. In the signal (6), as will be described later, the binarization error at the point of change from a small amplitude signal to a large amplitude signal has been corrected. A signal obtained by comparing the conventional fixed slice level 0 signal and the original analog video signal (a) (the dotted line waveform shown in waveform (4)) is shown in (7). As is clear from signals (6) and (7), 2
It can be seen that the value width has become narrower. Therefore, it is possible to prevent characters with high transmittance from becoming thick.

Next, referring to FIG. 2, block diagrams showing embodiments of the present invention will be sequentially explained. IN is an N-bit digital signal obtained by analog-to-digital conversion of an analog video signal obtained from COD. This is stored by the latch circuit l. Next, a subtraction circuit 2 calculates the difference between the signal stored by the latch circuit 1 and the next input signal. The latch circuit 1 and the subtraction circuit 2 constitute a circuit for detecting the amount of slope of the video signal.

Next, the output of the subtraction circuit 2 is supplied to a peak position detection circuit 6 in order to detect the temporal position of the maximum value of the output calculated by the subtraction circuit 2. A storage circuit is provided for storing the input video signal at the time position using a pulse signal corresponding to the peak position of the slope amount of the video signal obtained by the peak position detection circuit 6. This circuit is a circuit for storing a video signal and a slice level serving as a comparison reference, and is the slice level memory circuit 5 in FIG. 2.

The subtraction circuit 4 is used to subtract the output of the latch circuit 1 by the output of the X-fold absolute value circuit 3, which multiplies the slope of the video signal output by the subtraction circuit 2 by X and calculates its absolute value. establish. The X times absolute value circuit 3 has a function of obtaining an appropriate binary output signal, preventing reproduced characters from becoming thicker, and adjusting image quality.

Then, the output signal obtained by the subtraction circuit 4 and the signal output stored in advance in the slice level memory circuit 5 are compared by the comparison circuit 7, and a binarized video signal is obtained as the output. I can do it.

9 is a slice level changing circuit, which input video signal 1
The area sentence excluding the section m from the minimum value of the input video signal l to the maximum number of the tilt amount signal 2 that appears next is detected as a valid slice level region, and the section from the minimum value of the input video signal l to the maximum number of the tilt amount signal 2 is detected as a valid slice level region. This is a circuit for correcting the slice level ■ of m to a fixed reference value regardless of the signal level (forcibly changing it to the fixed slice level G of waveform (4) in FIG. 1).

By providing such a circuit 9, it is possible to eliminate the error of the large amplitude signal due to the slice level at the small amplitude, which is caused by the peak of the slope appearing late in the part where the small amplitude signal changes to the large amplitude signal. This makes it possible to prevent the converted output (shaded portion in waveform 6). As a result, the output of the slice level memory circuit 5 in consideration of the change signal from the slice level change circuit 9 becomes a signal @ of waveform (4).

Note that jO is a delay circuit, which is a time adjustment circuit provided to synchronize the temporal phase with the output of the subtraction circuit 4 and store the input video signal in the slice level memory circuit 5. Further, 8 is a clock generation circuit that generates a clock signal for controlling the operation timing of the circuit.

Although this embodiment relates to microfilm, it can also be used for general film playback, facsimiles, copying machines, and the like.

In this way, in this embodiment, the maximum value of the slope amount of the analog video signal is detected, and the video signal corresponding to this maximum value is used as the reference signal for binarization. It can be set almost at the center of the signal, and there is no possibility that the reference value will exist outside the change range of the video signal, unlike when binarization is performed using the added base s value.

Further, since a peak value of the slope always appears in a changing video signal, by using this peak value, a reference signal for binarization that always corresponds to changes in the video signal can be obtained.

It is clear that in cases where the polarity of the analog signal is opposite, the minimum value of the slope amount may be detected and the video signal corresponding to this may be used as the reference signal.

〔effect〕

As explained above, according to the present invention, for example, in a region where a video signal changes from a small amplitude to a large amplitude, the inconvenience that a large amplitude video signal is binarized with a reference signal determined when the amplitude is small can be avoided. It is possible to remove this and achieve good binarization operation.

[Brief explanation of the drawing]

FIG. 1 is a detailed explanatory diagram of the present invention, and FIG. 2 is a block diagram showing an embodiment of the present invention.
4 is a subtraction circuit, 5 is a slice level memory circuit, 6 is a peak position detection circuit, 7 is a comparison circuit, and 9 is a slice level change circuit. Applicant Canon Co., Ltd.

Claims (1)

[Claims] In a binarization circuit that converts an analog video signal into a binary signal, it sequentially determines quasi-signals for binarization according to the video signal, and also determines the signal level for a specific video signal. A binarization circuit is characterized in that it performs a binarization operation using a fixed reference value regardless of the situation.