JPH0681253B2 - Image forming condition control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming condition control device that detects an image density and controls an image forming condition according to the detected output.

(Background Art) As an example of a control device for this type of image forming condition, conventionally, a background portion of the document is calculated based on a light-receiving element output voltage obtained by irradiating a document with a predetermined amount of light and scanning and measuring the document with a light-receiving element. There is an automatic exposure adjusting device that detects the light amount of both the image area and the image area and obtains the appropriate value of the exposure amount or the developing bias as the image forming condition based on the detection information.

In such an apparatus, when the maximum value of the output voltage from the light receiving element is at the maximum level of the set voltage range, the minimum value of the output voltage from the light receiving element is a normal document and is a fraction of the maximum value set voltage range. Become. Therefore, if the level is set so that the minimum value can be accurately set, the maximum value may not be measurable. On the contrary, if the level is set so that the maximum value can be taken accurately, the accuracy of the minimum value will be poor. In particular, when a negative image such as microfilm is used as an original, it is generally caused by taking the maximum value in order to determine the exposure amount based on the minimum value of the light receiving element output voltage. However, there is a drawback that the accuracy of the automatic exposure adjustment function is lowered.

(Object) The present invention solves the above-mentioned drawbacks and provides a control device for image forming conditions capable of controlling the image forming means and accurately adjusting the density even if the dynamic range of the density of the film original is wide. With the goal.

(Embodiment) Hereinafter, a control device for image forming conditions according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. When light transmitted or reflected on a document is scanned by a light receiving element PD, the amount of light received by the light receiving element PD is converted into a current I by the light receiving element PD, and the current I Is further converted into a voltage by the feedback circuit including the operational amplifier OP1 and the resistor R1. Here, a capacitor C1 is connected in parallel with the resistor R1 to block undesired high frequency components and prevent oscillation.

The voltage converted by the operational amplifier OP1 is transferred to the operational amplifier OP2 and
Input to both OP3. Here, a resistor R2 and a capacitor C2 inserted in each input side of these operational amplifiers OP2 and OP3.
The resistor R3 and the capacitor C3 form an integral filter. Feedback variable resistor VR for the operational amplifiers OP2 and OP3
2 and the resistor R, and the feedback variable resistor VR3 and the resistor R are respectively connected to the (−) side terminal. Thereby, the operational amplifier OP
2 amplifies the output voltage of the operational amplifier OP1 by 1 + VR2 / R times. The operational amplifier OP3 outputs the output voltage of the operational amplifier OP1 by 1 + VR.
Amplify 3 / R times.

The respective outputs of the operational amplifiers OP2 and OP3 are supplied to the analog / digital converter AD as the maximum level output and the minimum level output. The digital output from the analog / digital converter AD is supplied to the central processing unit CPU for normal image processing, but the details thereof are not directly related to the present invention and therefore omitted here.

Here, when a negative image is used as the measurement target, the output of the operational amplifier OP3 is the analog / digital converter AD when the negative with the lowest background density is used within the normally used range.
Adjust the variable resistor VR3 so that it is close to the reference voltage of
Regardless of contrast, adjust the variable resistor VR2 so that the output of the operational amplifier OP2 is near the reference voltage of the analog / digital converter AD when the negative with the lowest image density is used within the normally used range. .

By adjusting in this way, the analog / digital converter AD used for both the negative image area and background area
It becomes possible to perform highly accurate photometry by fully utilizing the resolution of.

On the contrary, when a positive image is used as the measurement target, the output of the operational amplifier OP2 comes close to the reference voltage of the analog / digital converter AD when the document with the lowest background density is used within the normally used range. Adjust the variable resistor VR2 so that the output of the operational amplifier OP3 is close to the reference voltage of the analog / digital converter AD when the original with the lowest image density is used within the normally used range regardless of the contrast. Adjust the variable resistor VR3 so that it comes to.

Further, the analog / digital converter AD may be of a type having a built-in multiplexer, in which case the central processing unit CP
Depending on the signal from U, the output voltage MA from the operational amplifier OP2
X and the output voltage MIN from the operational amplifier OP3 are sequentially switched during photometry and input to the analog / digital converter AD. The duty ratio of the output voltage MAX to MIN does not have to be 50% as this input switching signal. Generally, the ratio of the image area that is difficult to pick up (the output voltage MAX in the case of a negative) is increased or the scanning position is changed. It is easy to program the central processing unit CPU to change the ratio of inputting the output voltages MAX and MIN.

As described above, the MIX and MIN voltages input to the analog / digital converter AD are converted into digital here and then input to the central processing unit CPU. At this time, the output voltage M
AX and MIN are sequentially compared with the maximum value and the minimum value, respectively, and the data finally left after the photometry is finished is the measurement data of the image area and background area on the negative. The measurement data of the image area and the background area obtained in this way are fed back to the exposure amount or the developing bias and the image forming conditions are adjusted so that an appropriate image can be obtained by a conventional calculation method.

In the example of FIG. 1, when the difference in gain between the operational amplifiers OP2 and OP3 is known in advance, as shown in FIG. 2, the feedback amount of the operational amplifier OP1 is set to the variable resistance V.
Adjustment may be made by R1 and resistors V1 and V2, and in addition, resistors γ3 and γ4 may be used instead of resistor R, and variable resistors VR2 and VR3 may be replaced by fixed resistors γ5 and γ6. In this case, the variable resistor VR1 is for adjusting the overall gain, and is provided for correcting variations in elements such as the light receiving element PD.

In the above two embodiments, the output voltages MAX and MIN are switched by the multiplexer for time-division input, but when the conversion speed of the analog / digital converter AD is slow, the number of samplings is small and the data accuracy is high. It can be worse. In such a case, a sample hold circuit may be used as shown in FIG. Light receiving element PD The amount of light received is converted into a voltage by a current-voltage conversion circuit 1 including an operational amplifier OP1 and then input to amplifier circuits 2 and 3 having operational amplifiers OP2 and OP3 and having amplification factors N and M, respectively. The above is the same as the above example, but in this example N
The voltages amplified by a factor of 2 and M are sampled and held by sample and hold circuits SH1 and SH2, respectively.

Here, the magnifications N and M are determined by the density range of the original document used as in the above example.

Incidentally, reset signals RS1 and RS2 and sampling signals S1 and S2 are supplied to the sample hold circuits SH1 and SH2 from the output port of the central processing unit CPU, as is well known.

Moreover, the peak hold of the sample hold circuit SH1 is the maximum value peak hold, and the sample hold circuit SH2
The peak hold of is the minimum value peak hold.

The voltages thus obtained by sample-holding are switched and input to the analog-digital converter AD with a built-in multiplexer as in the above example. Switching in this case is 1
Only once for each sampling.

Alternatively, sampling may be performed several times for each position, and the MAX and MIN values at each position may be averaged.

Further, in this case, the accuracy can be further improved by adopting a method of weighting the sampling data of each position and averaging it in order to correct the lens shading phenomenon.

(Effect) As described above, according to the present invention, it is possible to solve the above-mentioned conventional drawbacks and appropriately control the image forming condition without lowering the accuracy.

For example, according to the present invention, when configuring an automatic exposure adjusting device required as data for determining the image forming conditions of both the image area and the background area, two types of amplifiers having different gains are provided, and each of them receives light. By using at a level suitable for the measurable range of the maximum and minimum values of the element output, when a negative is used for an original such as microfilm, the background density becomes the minimum value of the light receiving element output, This is the standard, but you can adjust the level to the maximum value to reduce the accuracy of the minimum value, or adjust the level to the minimum value to prevent the maximum value from becoming unmeasurable. It becomes possible to measure with high accuracy.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a further embodiment of the present invention using a sample hold circuit. It is a block diagram shown. PD: Light receiving element, OP1 to OP3: Operational amplifier, R1 to R3, γ1 to γ6: Resistance, VR1 to VR3: Variable resistance, C1 to C3: Capacitor, AD: Analog-to-digital conversion with built-in multiplexer Unit, CPU ... Central processing unit, RS1, RS2 ... Reset signal, SH1, SH2 ... Sample hold circuit, S1, S2 ... Sampling signal, 1 ... Current-voltage conversion circuit, 2,3 ... Amplification circuit .

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takao Toda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kazuo Kashiwagi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Masaaki Yanagi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yoshihiro Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56 ) Reference JP-A-57-56843 (JP, A) JP-A-58-29219 (JP, A)

Claims (1)

[Claims] 1. An image forming unit for forming an image of a film original on a recording medium, a light receiving element for scanning the film original to measure the density of the scanned film original, and a scanning unit for scanning the film original. A signal sequentially output from the light receiving element is branched and input, and one of them is amplified with a gain such that a value obtained by exchanging the minimum density of the background portion of a film original within a normally used range with a digital value becomes a reference value. On the other hand, the other two amplifying circuits amplify the minimum density of the image area of the film original within the normally used range with a gain such that the converted value becomes a reference value. A converter for converting the output analog signal into a digital signal, and when the film original is irradiated with a predetermined amount of light in order to measure the density of the background portion and the image area of the film original. The outputs of the above two amplifier circuits are sequentially input, and the digital value of the maximum value of the output of one amplifier circuit and the digital value of the minimum value of the output of the other amplifier circuit are detected in parallel from these inputs. A control means for controlling the image forming means on the basis of the detected maximum digital value and the minimum digital value to adjust the density of the image formed on the recording medium. Control device for image forming conditions.