JPH0795609A - Image digital processing system - Google Patents

Abstract

PURPOSE:To improve the color regenerating performance for picture quality of images by placing a BPF at the precedent stage of an A/D converter to transmit a specific part of the frequency band of a low-band chroma signal. CONSTITUTION:A BPF 5 is placed at the precedent stage of an A/D converter 1 and therefore an input low-band chroma signal (a) is supplied to the converter 1 via the BPF 5. A fact that the duty ratio of the signal (a) is not equal to 50% means that the signal (a) contains a higher harmonic. Therefore a duty ratio approximate to 50% is secured when the higher harmonic is eliminated by the BPF 5. However the signal (a) has two information on the R-Y and B-Y signal components (c) and (d) undergone the orthogonal modulation. Therefore the picture quality is deteriorated if the components of a 2nd higher harmonic and subsequent ones are eliminated. In this respect, it is required to use the BPF 5 whose characteristic is sharply deteriorated immediately before twice of a subcarrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image processing system for digitally processing an image, which converts a low-pass color signal into a color difference signal for processing, and the processing is digitized.

[0002]

2. Description of the Related Art Among image data processing systems for digitally processing an image, those which convert a low-pass color signal into a color difference signal for processing, and the processing of which has been digitized have become mainstream recently. This is because the color difference signal can be treated like a luminance signal, so that processing such as noise reduction can be simplified. Therefore, the fact that this color difference signal conversion can be performed accurately determines the quality of the image quality.

FIG. 3 is a block diagram of an image data processing system according to a conventional example. In the figure, an input low-pass color signal a enters an A / D converter 1 and a burst section detection circuit 2 which is a hue reference. Then, an APC (auto phase control) clock generation circuit 3 generates a multiplied clock corresponding to the phase from the burst detected by the detection circuit 2, and the A / D converter 1 performs sampling and converts it into data. This data b is input to the color difference signal converter 4, and the RY signal component c and the BY signal component d, which are color difference signals, are extracted.

FIG. 4 is a waveform diagram showing each signal shown in FIG. 3, FIG. 4 (A) shows a signal waveform of the low-pass color signal a and the data b, and FIG. 4 (B) shows the R signal. FIG. 4C shows a signal waveform of the −Y signal component c, and FIG. 4C shows a signal waveform of the BY signal component d. In these figures, the horizontal axis represents the sampling points, and the sampled data are superimposed and shown as a bar graph. Now, in the color difference conversion, every other such bar graph-like data is rearranged into two columns, and the sign (positive / negative) is inverted every other one. Next, instead of the data arranged in the opposite column, data of 0 is inserted and a filter is applied so as to drop the sampling clock. Then, the data is smoothed to obtain the RY signal component c and the BY signal component d. You can take it out.

The color difference signal corresponds to vertical and horizontal coordinates in a vectorscope, which is a measuring device for monitoring the color phase, and the hue and the color level are determined by these coordinates. For the sake of explanation, color difference processing will be considered by taking as an example a signal in which R-Y and B-Y have the same level (here, 1 is represented as 1 unit) as shown in FIG.

The low-pass color signal corresponding to this hue is as shown in FIG. 6, and is a sine wave having an amplitude of 2 and a phase of + 45 °. Sampling was performed at a frequency four times as high as that of the subcarrier that is a carrier wave, and the points are indicated by vertical ruled lines.
The data sampled here are -1, 1, 1, -1, -1, 1 as can be seen from FIG. 1 more
If you place them every other row into two columns, you get "-1, (empty), 1,
(Vacant), -1, (vacant), 1, ... "" (vacant),
1, (vacant), -1, (vacant), 1, (vacant), ...
・ 」

Further, if the sign is inverted every other one and 0 is inserted in a vacant place, "1,
0,1,0,1,0,1, ... "" 0,1,0,1,
0, 1, 0, ... ”, and these are plotted in a graph as shown in FIG.

When this waveform is filtered and smoothed (each average value is taken), a constant value of 1/2 level is obtained. The level is halved because of the filter, and normally double amplification is performed. Therefore, it is taken out as a level 1.

[0009]

However, in the case of a color signal whose duty is not 50% as shown in FIG. 8, a sampling clock that is four times that of the subcarrier in the burst portion is generated, so this duty deviation is caused. Is output as it is as the difference of data.

Here, the case where the signals in FIG. 6 are shifted is considered. However, since the clock is generated so as not to shift once in four times, the signal shifts at the sampling timings of 0, 4, 8, ... However, at other sampling timings, 1 + ΔD ₁ , 1 + ΔD ₂ and 1 + ΔD _{3 respectively.}
It is assumed that the deviation of The data string at this time is "-
1, 1 + ΔD ₁ , 1 + ΔD ₂ , -1 + ΔD ₃ , -1,1
+ ΔD ₁ , 1 + ΔD ₂ , ... ”, and when the data sequence of RY and BY is made by the above method,“ ₁ , 0, 1
+ ΔD ₂ , 0, 1, 0, 1 + ΔD ₂ , ... ”“ 0, 1
_{+ ΔD 1, 0,1 + ΔD 3} , 0,1 + ΔD 1, 0, ··
・ ”

When this is filtered, as shown in FIGS. 9A and 9B in which the data b of the RY signal component c and the BY signal component d are graphed, the data b is not a straight line but is uneven. Will be taken out as a certain level. This is because interpolation is performed with data of 0. With such processing, when sampling is performed with a clock that is several times the number of carriers, unevenness of the level of the data b must occur. When this is shown on the vector, it becomes as shown in FIG. 10, which causes a phase variation and deteriorates the color image quality.

An object of the present invention is to solve the above-mentioned drawbacks of the conventional system and to provide an image digital processing system capable of improving color reproducibility of image quality by efficiently performing color difference signal conversion. is there.

[0013]

In order to achieve the above object, according to the invention of claim 1, an A / D converter for A / D converting an input low-frequency signal, and the A / D converter In a digital image processing system having a color difference signal converter for converting the low band color signal digitized by the converter into a color difference signal, a frequency band of the low band color signal is provided before the A / D converter. It is characterized in that a filter for passing a specific band portion therein is provided.

According to the second aspect of the invention, the bandpass filter passes a frequency band less than twice the carrier of the color signal.

[0015]

According to the first aspect of the present invention, a filter (bandpass filter) provided in front of the A / D converter removes higher harmonics in the color signal in the low frequency range to reduce the duty to 5%.
Close to 0%.

In a second aspect of the present invention, a filter whose characteristic sharply drops (cuts frequency components higher than that) immediately before twice the subcarrier is used as the bandpass filter, and the second harmonic component is removed. Through, suppress deterioration of image quality.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an image digital processing system according to an embodiment. In the figure, 1 is an A / D converter, 2
Is a burst circuit detection circuit, 3 is an APC clock generation circuit, and 4 is a color difference signal converter.

In the present embodiment, the bandpass filter 5 is provided in front of the A / D converter 1. Therefore, the input low-pass color signal a is passed through the bandpass filter 5 to A /
It will be input to the D converter 1. Duty is 50
The reason why it is not% is that the signal contains harmonics to that extent, and if the harmonics are removed by the bandpass filter 5, the duty can be brought close to 50%.

However, the color signals are RY signal components c and B-
Since the two pieces of information of the Y signal component d are quadrature-modulated, if the components below the second harmonic are dropped, the image quality is rather deteriorated. Therefore, as the bandpass filter 5, a filter whose characteristic sharply drops just before twice the subcarrier is used (see FIG. 2).

By the way, when A / D conversion is performed by the A / D converter 1, aliasing noise is generated by sampling. Therefore, a low pass filter is usually used to remove this noise. However, in the present embodiment, as described above, since the bandpass filter 5 that passes the frequency band near the carrier is provided, this bandpass filter 5 can also be used for noise removal, and the circuit can be simplified. it can.

[0021]

According to the first aspect of the present invention, a filter (bandpass filter) that passes a specific band portion in the frequency band of the low-frequency signal is provided in the preceding stage of the A / D converter. Since the harmonics in the low frequency color signal are removed so that the duty is close to 50%, the color difference signal can be converted most efficiently and the color reproducibility of the image quality can be improved.

According to the second aspect of the present invention, a filter whose characteristic sharply drops (cuts frequency components higher than that) immediately before twice the number of subcarriers is used as the filter. Never drop. As a result, deterioration of image quality can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram of an image digital processing system according to an embodiment of the present invention.

FIG. 2 is a pass frequency band characteristic diagram of a bandpass filter used in the present invention.

FIG. 3 is a block diagram of an image data processing system according to a conventional example.

4A is a waveform diagram showing a signal waveform and data of a low-pass color signal shown in FIG. 3, and FIG. 4B is an R− shown in FIG.
Waveform diagram showing the signal waveform of the Y signal component, FIG.
FIG. 6 is a waveform diagram showing a signal waveform of a −Y signal component.

FIG. 5 is an explanatory diagram showing, on a vector, data of both signal components when the RY signal component and the BY signal component are at the same level.

6 is a low-pass color signal waveform diagram corresponding to the hue shown in FIG.

FIG. 7 is an R-Y, B-Y sampled from the signal of FIG.
It is explanatory drawing which made the data of the said into the graph.

FIG. 8 is a low-pass color signal waveform diagram in which the duty is not 50%.

9A is an explanatory diagram in which data of an RY signal component obtained by filtering the low-pass color signal of FIG. 8 is graphed,
FIG. 9B is an explanatory diagram in which the data of the BY signal component is graphed.

FIG. 10 is an explanatory diagram showing the data of the RY signal component and the BY signal component shown in FIGS. 9A and 9B on a vector.

[Explanation of Codes] 1 A / D converter 4 Color difference signal converter 5 Band pass filter (filter)

Claims (2)

[Claims] 1. An A / D converter for A / D converting an input low-frequency color signal, and a color difference signal for converting the low-frequency color signal digitized by the A / D converter into a color difference signal. An image digital processing system having a converter, wherein a filter for passing a specific band portion in a frequency band of the low-band color signal is provided in the preceding stage of the A / D converter. Image digital processing system. 2. The image digital processing system according to claim 1, wherein the band-pass filter passes a frequency band less than twice the carrier of the color signal.