JP2672556B2 - Signal processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention mainly relates to a signal processing method of a signal output from a solid-state imaging device using a charge-coupled device (hereinafter referred to as CCD) or the like. Is applied to video cameras.

(Prior Art) FIG. 1 shows the relationship between the amount of light incident on the solid-state imaging device and the amount of signal output.

(Problem to be Solved by the Invention) The output with respect to a certain incident light amount A has an average value of a, but has noise ± Δa that changes with time. This noise a is a shot noise that incident light has, and there is no other way to suppress it than to obtain frame correlation in a two-dimensional image. This method adds many image signals and cannot be used for moving images.

[Configuration of the invention]

(Means for Solving the Problem) The present invention proposes a method for suppressing shot noise without taking frame correlation.

(Operation) FIG. 3 and FIG. 4 show the principle of the present invention with an example of the output signal. FIG. 3A shows a signal in which the average signal output S has a signal variation ΔS smaller than the noise n. It is considered that the signal change amount ΔS is buried in the noise n and cannot be detected. Therefore, the signal-to-noise ratio is improved from S / n to S / n 'by suppressing noise and signal variation as shown in FIG.

When the signal change ΔS is larger than the noise amount, the noise amounts n ₁ and n ₂ are ▲ n ^′ ₁ as shown in FIGS. 5 (a) and 5 (b).
Compressing to ▼ and ▲ n ^′ ₂ ▼ does not compress to ΔS.

(Example) FIG. 5 shows an example of a circuit that realizes this.

The signal train input from IN is delayed by one output by the delay circuit 1 and the difference signal Si ₋₁ −Si is taken by the differential amplifier 2. This signal is input to the suppression signal generation circuit 3, which is the point of the present invention, and at a certain value ai or more, a constant α times Si ₋₁ −Si (Si ₋₁ −S
When i) is less than ai, 0 is output. By adding this output to the signal Si, the noise suppression as described above becomes possible. The constant value ai is a constant representing the amount of noise depending on the signal Si, and in the case of shot noise, ai is proportional to the parallel vibration of Si. The relationship is shown in FIG. 2, where N is the number of photons in the input light. There is a relationship. The suppression signal generation circuit 3 has an example of input / output characteristics shown in FIG.

It has the characteristic. It is common sense that α is 1 or less. It is not necessary that the input / output characteristics have a tight relationship, and the characteristics shown in FIG. 6 (b) may be used.
FIG. 7 shows an example of a circuit for obtaining the characteristics shown in FIG. 6 (a).
It can be realized with a simple circuit.

In the above, noise is suppressed by using the signal one output signal before, but in the case of a two-dimensional sensor, if the pixels are arranged as shown in FIG. 8, the pixels adjacent to the pixel Sij are Si ₋₁ j, Sij ₋₁ , Sj. _There are four, ₊₁ j and Sij ₊₁ . It is possible to take the difference between the outputs of the four adjacent pixels and perform the above-described noise suppression between the output of the pixel having the smallest absolute value of the difference. It is not necessary to use all four, and the above description corresponds to the case of using one S j _-1 j.

[Effects of the Invention] The shot noise of incident light can be suppressed by performing the noise suppression as described above.

Moreover, this method is effective not only for shot noise but also for suppressing all noises that generally exist.

[Brief description of the drawings]

1 and 2 are characteristic diagrams, FIG. 3 is a diagram showing the principle of noise suppression when the signal change amount is smaller than noise, and FIG. 4 is a principle of noise suppression when the signal change amount is larger than noise. FIG. 5 is a diagram of an embodiment of the present invention, FIG. 6 is an input / output characteristic diagram of the suppression signal generator, FIG. 7 is a diagram showing a circuit example of the suppression signal generator, and FIG. FIG. 1: 1 pixel delay line, 2: differential amplifier, 3: suppression signal generator.

Claims (5)

(57) [Claims] 1. A plurality of photoelectric conversion storage means arranged in a two-dimensional array for storing signal charges obtained by photoelectrically converting incident light on a semiconductor substrate, and the signal charges stored in the photoelectric conversion storage means are sequentially read out. In the method of processing the electric signal output from the two-dimensional solid-state imaging device including the reading means, one electric signal read from one photoelectric conversion storage means is read by a plurality of photoelectric conversion storage means close to the photoelectric conversion storage means. If the smallest minimum absolute value among the absolute values of the differences obtained by subtracting the one electric signal from a part or all of the proximity signals of the plurality of issued proximity signals is smaller than a certain decision value, the difference giving the minimum absolute value. A signal processing method characterized in that a constant multiple of is added to one electric signal. 2. The signal processing system according to claim 1, wherein a part of the plurality of proximity signals is one electric signal read immediately before one electric signal. 3. The signal processing system according to claim 1, wherein the certain decision value is a value determined by a noise amount. 4. The signal processing method according to claim 1, wherein the noise amount is shot noise included in the one electric signal. 5. The signal processing method according to claim 1, wherein the constant multiple is 1 or less.