JPH01136110A - Image detecting method - Google Patents

Abstract

PURPOSE:To decide whether an image exists or not in a short time and with high accuracy by comparing a frequency value of a histogram for showing the number of picture elements to an output signal of an image sensor, with a prescribed value, and also, comparing the number of times of a polarity inversion obtained by binarizing the output signal of the image sensor, with a prescribed value. CONSTITUTION:When an expanse in the axis-of-abscissa direction of a histogram derived from an image signal of a narrow area, namely, the overall length L1 in the axis-of-abscissa direction in which the histogram exceeds a set value exceeds a set value, it is decided that an image exists, and by using this area. Also, when the overall length L becomes below the set value and it is decided that no image exists, this histogram derives binarization levels (a), (b) by using a histogram whose crest is high and whose width is narrow. Thereafter, while changing a focus zone, an output signal of a line sensor is binarized in a real time, and with respect to the focus zone in which the number of times of its polarity inversion exceeds a prescribed value, it is decided that an image exists. In such a way, whether the image exists or not can be decided in a short time and with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image detection method for an autofocus device that determines focus using an image sensor such as a COD line sensor.

(Technical Background of the Invention) Various autofocus methods using image sensors such as COD line sensors have been proposed. However, this autofocus operation presupposes that projection light of an image area suitable for the operation is input to the image sensor. For example, in an image area with a single brightness or in an area where the density changes infrequently, correct autofocus operation cannot be performed, resulting in malfunction.

Therefore, a method has been proposed that determines whether the image area is suitable for autofocus prior to the autofocus operation. In other words, there is a method that calculates the number of black and white inversions and if it is a predetermined number or more, it is determined that an image exists. However, this method requires changing the binarization level depending on the background density of the image and the negative/positive polarity of the original film. Therefore, it is necessary to calculate the background density in advance.For example, in the previous scan (
There is a method in which a histogram of the entire image is obtained by pre-scanning, and the background density is determined using this hilt gel. However, when the histogram is obtained by pre-scanning the entire image, a problem arises in that the operation time is long. In order to shorten the operation time, it is conceivable to create a histogram based on image signals of only a small area, but in this case, a problem arises in that the accuracy decreases.

In particular, when the background density is determined in an image portion with high image density, such as a character string, and the slice level for binarization is determined based on this background density, the accuracy decreases significantly.

(Object of the Invention) The present invention was made in view of the above circumstances, and even if the negative/positive polarity of the original film is unknown,
It is an object of the present invention to provide an image detection method for an autofocus device that can determine the presence or absence of an image with high precision in a short time using an image signal in a narrow area.

- (Structure of the Invention) According to the present invention, this purpose is to improve the image quality of an autofocus device that controls a projection lens to a focused position using an output signal of an image sensor obtained by scanning image projection light with an image sensor. In the detection method, the total length of the range of the output signal in which a frequency value of a histogram indicating the number of pixels for the output signal of the image sensor is equal to or greater than a set value is determined;
This total length is compared with a certain value, and if the former is greater than or equal to the latter, it is assumed that there is an appropriate image and autofocus operation is performed.If the former is less than or equal to the latter, the binarization level is determined using this histogram, and this binarization level An autofocus device characterized in that it binarizes the output signal of an image sensor using , integrates the number of polarity inversions, and performs an autofocus operation by treating a focus zone where the number of polarity inversions exceeds a certain value as an image. This is achieved by an image detection method.

(Principle) N-1 and P-1 in Figure 5 show the changes over time t in the output signal V of the CCD line sensor in a microleague printer, and N-2 and P-2 in the same figure show their respective histograms. There is.

Here, N-1 and N-2 are P if the original is a negative film.
-1 and P-2 are for positive films.

Generally, the blackening rate of originals is about 6%, and at most 20~20%.
The limit is 30%. Therefore, on the line sensor, the number of pixels corresponding to the background becomes overwhelmingly large. Further, the density of this background is relatively stable with little variation within one sheet or one film. Therefore, the number of pixels N for the output signal V (corresponding to density)
The histogram (N-2, P-2) showing the background density has large maximum values A and B at 01.02. If a suitable image is not included, the maximum value will be extremely high, and if an image is included, the maximum value will become lower and wider. Therefore, if the spread of this histogram in the horizontal axis direction (corresponding to the output signal and density) is above a certain level, it can be determined that an image exists, and if it is below a certain level, it can be determined that there is no image. Here, the area of each histogram is constant corresponding to the number of pixels of the line sensor.

From this histogram, the background concentration DI, D?
And when determining the binarization levels a and b, the maximum value A
, when the peak of H is high and its width is narrow, in other words, when the spread of the histogram in the horizontal axis direction is small, this means that the histogram is obtained in an area with a large amount of background, which is desirable from the viewpoint of improving accuracy. .

The present invention focuses on such points, and when the spread in the horizontal axis direction of the histogram obtained from the image signal of a narrow area, that is, the total length L+ in the horizontal axis direction at which the histogram exceeds the set value, is equal to or larger than the set value LO. It is assumed that there is an image, and by performing an autofocus operation using this area, it is possible to significantly shorten the operation time.

In addition, the total length indicating the spread of the histogram is set, and the set value Lo
When it is determined that there is no suitable image in the following conditions, the histogram at this time has high peaks and a narrow width, which is suitable for determining the background density with high accuracy, and the binarization level is set to a.

Find b. For example, FIG. 5 (N-3).

As shown in (P-3), when it is a negative original, the image is on the darker side than the density DI where the histogram is maximum, and on the other hand, when it is a positive original, the image is on the side where the density is lighter than the density D2.

Therefore, the density a obtained by adding a fixed value α to the density of the larger point of the two points where the peak of the maximum value of the histogram intersects with a fixed set value χ0 is the negative binarization level, and the fixed value β is determined from the density of the smaller point. The density obtained by subtracting can be used as the positive binarization level.

In the present invention, the total length indicating the spread of the histogram is the set value L.
o or less and it is determined that there is no image, this histogram has high peaks and a narrow width, and the binarization levels a and b are obtained as described above using the first histogram. From then on, the focus zone is changed. At the same time, the output signal of the line sensor is binarized in real time, and a focus zone where the number of polarity inversions is a certain number or more is determined to be an image.

(Embodiment) Fig. 1 is an overall schematic diagram of a league printer that is an embodiment of the present invention, Fig. 2 is a block diagram of its autofocus control device, Fig. 3 is a flowchart of its operation, and Fig. 4 is a diagram of each part. FIG.

In FIG. 1.2, the symbol 1O is the original image of a microphotograph such as microfiche or microroll film. 12 is a light source, and the light from the light source 12 is transmitted to the original image 10 via a condenser lens 14, a heat shielding filter 16, and a reflecting mirror 18.
guided to the underside of

In the reader mode, the transmitted light (image projection light) of the original image IO is guided to the transmissive screen 28 by the projection lens 20 and the reflecting mirrors 22, 24, 26.
8, an enlarged projected image of the original image 10 is formed. In the printer mode, the reflecting mirror 24 is rotated to the imaginary line position in FIG.
The projection light is guided to a PPC type slit exposure type printer 34 by reflecting mirrors 22, 30, 32. printer 34
The reflecting mirrors 22 and 30 move in synchronization with the rotation of the photosensitive drum 36, and a latent image is formed on the photosensitive drum 36. This latent image is made visible by toner charged to a predetermined polarity, and this toner image is transferred onto the transfer paper 38.

Reference numeral 50 denotes a focus control optical system, which includes a semi-transparent mirror 52 disposed on the optical axis of image projection light, a projection lens 54, a CCD line sensor 56 as an image sensor, and a servo motor 58.

A portion of the projection light that has passed through the projection lens 20 is guided by a semi-transparent mirror 52 to a line sensor 56 through a projection lens 54 . The line sensor 56 is movable by a motor 58 in a direction perpendicular to the optical axis. Furthermore, when the projection lens 20 is placed at a position where the projection light is focused on the screen 28 or the projection surface of the photosensitive drum 36,
The focal length of the line sensor 56 is determined so that the image is accurately formed on the light receiving surface of the line sensor 56.

The autofocus mechanism includes a servo motor 60 that moves the projection lens 20 forward and backward in the optical axis direction, and the focus is controlled by the control means 48 so that the projection light is correctly focused on the screen 28 or the projection surface of the photosensitive drum 36.

The control means 48 is constructed as shown in FIG. In other words, in synchronization with the clock pulse output by the clock 62, C
The OD driver 64 drives the line sensor 56. This line sensor 56 outputs a pulse voltage that changes in voltage in accordance with the amount of light incident on each pixel for each scan. This pulse voltage varies from pixel to pixel even if the same amount of light is projected due to variations in the characteristics of each pixel. The signal processing circuit 66 corrects this variation in characteristics of each pixel and shapes the waveform to produce output signals V shown in FIG. 5 N-1 and P-1.

The output signal V processed in this way is sent to the A/D converter 6.
8 is converted into a digital signal, and input interface 7
0 to the CPU 72. In FIG. 2, 74 is a ROM that stores control programs for the CPU 72, and 76
is RAM, 78 is output interface, 80 and 8
2 is a D/A converter, 84.86 is a motor 58.
This is a driver that drives 60.

In Figure 2, 100.102 is a comparator, and each comparator io
The output signal V is input to the non-inverting input terminal of 0.102,
The inverting input terminal is connected to the CPU 72 as described later.
The negative and positive binarization levels a and b determined in are input (see FIG. 5), so these comparators 100,
The output of 102 is V>a, V> as shown in Fig. 4c and d.
It becomes H level in the range b. Reference numerals 108 and 110 designate monostable multivibrators, which output polarity inversion pulses e and f of a constant time width in synchronization with the rise of the waveforms of the outputs c and d of the comparators 100 and 102.

These polarity inversion pulses e and f are integrated by counters 112 and 114 every time the line sensor 56 scans. These count values Nn and Np each indicate the number of times of polarity reversal, and are each a constant value M set by the setting device 116 and 118.
n and Mp in comparators 120 and 122.

When each count value Nn, Np reaches a certain value Mn, Mp, the comparators 120, 122 output signals g, h which become H level indicating that an image is present. Signals g and h are from the CPU 72
If either signal g or h becomes H level, the CPU 72 determines that there is an image. At this time, it is determined whether the original image is negative or positive in accordance with the signal g or h which is at the H level, and an autofocus operation is performed using the corresponding binarization level a or b.

Next, the operation of this embodiment will be explained. The control means 48
The servo motor 58 is controlled so that the projection light in the area corresponding to the zone set in U72 is incident on the line sensor 56. The user selects the reader mode with the reflecting mirror 24 positioned at the solid line position in FIG. 56.

The control means 48 then reads and stores the output signal V of the line sensor 56 (step 102), and measures the exposure amount based on this output signal V (step 104).
. That is, the output signal V of the signal processing circuit 66 is read into the CPU 72 via the interface 70, and
Exposure amount control is performed in . If the exposure amount is not appropriate (step 106), the amount of light should be changed (step 108), then the exposure amount is measured again. This exposure amount adjustment is performed, for example, by selecting the voltage of the pixel corresponding to the background area from among the output signal voltages of each pixel of the line sensor 56, and adjusting the light amount of the light source 12 so that this becomes a predetermined voltage. be exposed.

Next, the control means 48 determines whether or not the projection light input to the line sensor 56 includes an image suitable for autofocus. That is, based on the output signal V, N-2 in FIG.
Obtain the histogram shown in P-2 (step 110),
The total length of the range on the horizontal axis, that is, the range of the output signal or concentration, in which the frequency N on the vertical axis is equal to or greater than the set value % is determined. If this total length is greater than or equal to a certain value Lo (step 112)
Assuming that there is a proper image (step 114), the control means 4
8 performs autofocus control (step 116).

Various methods can be used for this autofocus control. For example, the position of the projection lens 20 at which the contrast is maximized is determined from the output signal V, and that position is determined to be in focus (step 118).

If you switch to printer mode in this focused state (step 12)
0), the reflecting mirror 24 is rotated to the position shown by the imaginary line in FIG. 1, and the image is transferred onto the transfer paper 38 to obtain a hard copy.

In step 112, if the total length is less than a certain value Lo, it is assumed that there is no suitable image, and the control means 48 uses this histogram to set the binarization level a to negative and positive.
, b (step 122), that is, as mentioned above, the peak of the maximum value of the histogram intersects with the set value χ0.
A constant value α is added to the density of the larger point among the points to obtain a negative level a, and a positive level b is obtained by subtracting a constant value β from the smaller density. The CPU 72 moves the line sensor 56 by the motor 58 to select a different focus zone (step 124), and binarizes the newly scanned output signal (2) in real time using these binarization levels a and b. 126), and the counters 112 and 114 add up the number of polarity reversals Nn and Np (step 128). and count value Nn.

Np is a constant value M! 1. If it is larger than MP, comparator 120
．． 122 outputs an H level signal g or h indicating that an image is present to the CPU 72 (step 130). CPU72
If both signals g and h do not reach the H level, it is determined that there is no image and the line sensor 56 is moved to a new area and the operations of steps 126 to 130 are repeated. If either the signal g or h is at H level, it is assumed that there is a proper image (step 114), and the control means 48 performs autofocus control (steps 116, 118), and if the printer mode is set, a hard copy can be obtained (step 114). Step 120).

In the above embodiment, the binarization level a for negative and positive
, b are calculated, and the number of polarity inversions when binarized is calculated in parallel for negative and positive signals. Since either signal g or h becomes H level, it is the original image. It is also possible to distinguish between negative and positive images at the same time. However, the present invention includes a method in which the type of negative or positive is manually input and only one of the binarization levels a and b is determined accordingly.

Note that the image sensor is not limited to a CCD line sensor, but may be an MO3 type line sensor or an area sensor.

(Effects of the Invention) As described above, the present invention obtains a histogram of the output signal of an image sensor, and as a first step, calculates the range on the horizontal axis in which the frequency value on the vertical axis of this histogram is equal to or higher than a set value, that is, the output signal. The total length of the range or density range is determined, and if this total length is equal to or greater than a certain value, it is determined that there is an image suitable for autofocusing, and the autofocusing operation is performed, so the operating time can be greatly reduced. Also, if this total length is less than the set value, it is possible to determine that the histogram has been obtained in areas other than the character string and the high-density part of the image, so it is assumed that there is no image, and the histogram at this time has high peaks, so the background This histogram is suitable for determining density with high precision, and the binarization level is determined using this histogram.

Thereafter, the image sensor output signal is binarized in real time for each new focus zone, and if the number of polarity inversions is greater than a certain value, it is determined that an image exists. Therefore, there is no need to obtain a histogram for the entire image, and the presence or absence of an image can be determined in a short time and with high precision from the histogram for a narrow area. Further, after determining the binarization level, the number of polarity inversions is determined in real time for a new focus zone, so the operation time does not become long.

[Brief explanation of the drawing]

Fig. 1 is an overall schematic diagram of a league printer that is an embodiment of the present invention, Fig. 2 is a block diagram of its autofocus control device, Fig. 3 is a flow chart of its operation, Fig. 4 is an output waveform diagram of each part, FIG. 5 is a diagram showing an output signal of an image sensor and its histogram for explaining the principle. DESCRIPTION OF SYMBOLS 10... Original picture, 20... Projection lens, 56... -dimensional solid-state image sensor. N...Frequency value, χ...Setting value, L...Total length, Lo...Constant value, a, b...Binarization level, Nn Np...Number of polarity reversals. Patent applicant Fuji Photo Film Co., Ltd. Agent Patent attorney Yama 1) Yu Fumi (and 1 other person) Figure 1 Koj

Claims (1)

[Scope of Claim] An image detection method for an autofocus device that controls a projection lens to a focusing position using an output signal of an image sensor obtained by scanning image projection light with an image sensor, comprising: an output signal of the image sensor; Find the total length of the range of the output signal in which the frequency value of the histogram indicating the number of pixels for the signal is equal to or greater than a set value, compare this total length with a constant value, and if the former is equal to or greater than the latter, an appropriate image is assumed and autofocus operation is performed. On the other hand, if the former is less than the latter, use this histogram to find the binarization level, use this binarization level to binarize the output signal of the image sensor, accumulate the number of polarity inversions, and calculate the number of polarity inversions. 1. An image detection method for an autofocus device, characterized in that an autofocus operation is performed with a focus zone in which is equal to or greater than a certain value as an image.