JPH10257355A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a noise from being conspicuous by eliminating the timewise change of noise contained in a video signal. SOLUTION: A subtracter calculates a differential value between the pixel value of video signal at present inputted form an input terminal 1 and the pixel value of the video signal of a past frame held in a frame memory 7. A comparator 5 compares the level of a differential absolute value outputted from an absolute value circuit 3 with that of prescribed threshold value and applies the compared result to selector 6. The selector selectively outputs differential absolute value, when the differential absolute value is more than the threshold value. Moreover, when the absolute value is less than the threshold, it is judged to be a still image section, and the pixel of past of frame is outputted from the frame memory 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus which makes noise less noticeable by eliminating the time change of noise contained in a video signal.

[0002]

2. Description of the Related Art Conventionally, as a noise reduction circuit used to reduce noise contained in a video signal,
Japanese Patent Application Laid-Open No. 7-212628 is known. This circuit performs noise reduction only in still image processing, does not perform noise reduction in moving image processing, and obtains a large noise removal effect.

FIG. 2 is a diagram showing the basic configuration of a conventional frame cyclic noise reduction circuit. This noise reduction circuit includes an input terminal 9, a subtractor 10, a subtractor 11, a multiplier (coefficient generator) 12, a frame memory 1
3, including the output terminal 14.

This noise reduction circuit utilizes the correlation of video in the time axis direction. Since noise has no temporal correlation, it has an effect of reducing noise in a still image portion. When an input video signal is supplied to the input terminal 9,
An output video signal is taken out from the output terminal 14, and the output video signal is temporarily stored in the frame memory 13. Then, the video signal one frame before is taken out through the frame memory 13 and the current video signal input through the input terminal 9 is subtracted from the video signal by the subtracter 10.

In the case of a video signal having a correlation between consecutive frames, the output of the subtractor 10 becomes zero, and only noise having no correlation exists. The noise is multiplied by a multiplier coefficient K by a multiplier 12, and the multiplication result is provided to a subtractor 11.
Then, by subtracting the multiplication value from the input video signal,
Noise components can be removed.

[0006]

In such a noise reduction circuit, noise is reduced. However, noise cannot be completely removed. For example, when noise that changes with time occurs even in a still image, the noise is reduced. Noise cannot be removed.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and has as its object to realize an image processing apparatus that makes the time change of noise included in a video signal less noticeable.

[0008]

In order to solve such a problem, the invention according to claim 1 of the present application provides a frame for storing a video signal delayed for each frame with respect to an input video signal for each pixel. A memory, subtraction means for calculating a difference value between the pixel value of the input video signal and the pixel value of the frame memory, and comparison means for comparing the difference value obtained from the subtraction means with a predetermined threshold, When the difference value is equal to or larger than the threshold value in the output of the comparing means, a pixel value of the input video signal is selected.When the difference value is smaller than the threshold value, a pixel value held in the frame memory is selected. Selecting means for outputting to the frame memory by
Outputting the video signal held in the frame memory.

According to such a configuration, a difference value between the pixel value of the input video signal and the pixel value of the video signal delayed by one frame is calculated. It is determined that the pixel has changed due to the moving image. In this case, the input pixel signal is output as it is. If the difference value is less than the threshold value, it is determined that the input signal is a still image portion. In this case, the pixel signal held in the frame memory is output. In this way, the output pixel signal is controlled so as not to change even if there is noise that changes with time in the pixel signal. Therefore, an effect of making noise less noticeable in a video signal including a still image such as a background image is generated.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image processing apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of the image processing apparatus according to the present embodiment.
This image processing apparatus includes an input terminal 1, a subtractor 2, an absolute value circuit 3, a threshold setting device 4, a comparator 5, a selector 6, a frame memory 7, and an output terminal 8.

The subtracter 2 has a pixel value Vkn of the video signal Vk in the frame at the time Tk input through the input terminal 1.
This is a circuit for subtracting the pixel value Vjn of the video signal Vj in the frame at the time Tj held in the frame memory 7 from (n is the pixel number in one frame). The absolute value circuit 3 calculates the absolute value of the output of the subtractor 2 | Vkn−Vjn | = ΔVn
Is a circuit that converts the The threshold value setting device 4 is a circuit that sets the threshold value Th and outputs it to the comparator 5. The comparator 5 is ΔVn
And Th is compared, and a comparison result is given to the selector 6.

When ΔVn ≧ Th, the selector 6 selects the pixel value Vkn of the video signal given from the input terminal 1, and
When ΔVn <Th, the selecting unit selects and outputs the pixel value Vjn of the video signal held in the frame memory 7. The frame memory 7 is a memory that holds the pixel values Vkn or Vjn (n = 1, 2, 3,...) Of the input video signal V in frame units.

The operation of the image processing apparatus having such a configuration will be described. The video signal V in the frame at time Tk
At k, assuming that the noise superimposed on the pixel value Vkn is Nkn, the pixel value of (Vkn + Nkn) is supplied to the subtractor 2 and the selector 6 via the input terminal 1 at time Tk. Assuming that a pixel value of (Vjn + Njn) is held in the frame memory 7, the output ΔVn of the subtractor 2 for each pixel n is (Vjn + Njn).
kn-Vjn) + (Nkn-Njn).

If a still image continues for several frames, (V
kn−Vjn) = 0 (n = 1, 2, 3,...). Even if the entire screen is a moving image, the still image portion such as the background (V
kn-Vjn) = 0. In such a case, the absolute value circuit 3
Output ΔVn is | Nkn−Njn | = ΔNn. This Δ
Nn is a noise change portion in the pixel n. However, compared with ΔVn when the entire screen changes like a moving image, ΔN
n is a small value. Next, the comparison circuit 5 determines ΔNn and the threshold T
Compare magnitude with h.

As long as the noise does not change drastically, ΔNn <
Since it is Th, the comparator 5 instructs the selector 6 to select the pixel value (Vjn + Njn) held in the frame memory 7. Thus, the pixel value held in the frame memory 7 is output as a pixel value of a still image. Therefore, in a portion where the pixel value does not originally change, such as a background image, even if noise is added to the portion at times Tk, Tk + 1, Tk + 2,..., The pixel value of that portion is (Vjn + Njn) And is recognized as a noise-free image in terms of the psychology of the viewer.

Next, consider a pixel when the entire screen is a moving image or when a part of the screen includes a moving image. In this case, (V
kn−Vjn) ≠ 0. Therefore, the output ΔV of the absolute value circuit 3
n is substantially | Vkn-Vjn |. This ΔVn is a change in the pixel value at the pixel n, and is much larger than ΔVn of the still image. The comparison circuit 5 calculates ΔVn and the threshold T
Compare magnitude with h. Since ΔVn> Th, the comparator 5 instructs the selector 6 to select the pixel value Vkn input from the input terminal 1. Thus, the output terminal 8
Output the changed pixel value. These pixel values are held at the address n of the frame memory as pixel values at the time Tk.

Accordingly, in the case where the pixel value changes with time as in the case of a moving image portion, the time Tk, Tk + 1, T
Even if noise is added at k + 2,..., the image is a moving image, and is viewed as an image in which the noise does not matter because of the viewer's psychology.

[0018]

As described above, according to the present invention, when a video signal including a still image portion is input, it is possible to eliminate the temporal change of noise and to make the noise of the entire screen less noticeable. The effect is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a noise reduction circuit that is an example of a conventional image processing apparatus.

[Explanation of symbols]

 Reference Signs List 1 input terminal 2 subtractor 3 absolute value circuit 4 threshold value setting device 5 comparator 6 selector 7 frame memory 8 output terminal

Claims (1)

[Claims] 1. A frame memory for storing a video signal delayed for each frame by a frame unit with respect to an input video signal, and subtraction for calculating a difference value between a pixel value of the input video signal and a pixel value of the frame memory. Means, comparing means for comparing the difference between the difference value obtained from the subtracting means and a predetermined threshold value, and when the difference value is equal to or greater than the threshold value at the output of the comparing means, the pixel value of the input video signal is And selecting means for selecting the pixel value held in the frame memory and outputting the selected pixel value to the frame memory when the difference value is smaller than the threshold value, wherein the video signal held in the frame memory is selected. An image processing apparatus that outputs