JP3304896B2 - PAL color frame detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PAL color frame detection circuit for detecting the order of color fields in a color frame from a composite video signal of a PAL color television.

In general, a video signal of a color television is transmitted by modulating a color subcarrier with color information. In order to provide the reference phase of the color subcarrier, several cycles of the color subcarrier having the reference phase are cut out in a burst during the horizontal retrace period and transmitted. This is called a color burst signal.

Incidentally, the frequency F of the color subcarrier
The ratio between SC and the frequency FH of the horizontal synchronization signal is not an integer. In the PAL system, FSC / FH = 284-１ ／ + 1/625 (1) is defined. In the PAL system, the ratio of the frequency FH of the horizontal synchronizing signal to the frequency FV of the vertical synchronizing signal is set to FV / FH = 625/2 (2) because of horizontal sweep interlace.

FIG. 3 is a schematic diagram showing a state of interlacing in accordance with the proportionality of the equation (2). FIG. 3A shows a state of a horizontal scanning line in an odd field, and FIG. 3B shows a state of an even field. This shows the status of the horizontal scanning line. However, to simplify the drawing, the number of scanning lines is set to 312.5 (# 0 to # 31) on the assumption that horizontal scanning is performed even during the vertical blanking period.
2). For odd fields, scan line # 0 starts at the upper left corner. At the center of the scanning line # 312, a vertical synchronizing signal enters, where the odd field ends and the relationship of the equation (2) in the odd field is satisfied, and the operation shifts to the even field. Scanning line # 0 of the even-numbered field is continued as it is, and the scanning line # 0 at the upper end of the even-numbered field starts from the center point in the horizontal direction. In the even field, a vertical synchronizing signal is input when the scanning line # 312 reaches the lower right corner, where the even field ends, and the relationship of the equation (2) in the even field is satisfied, and the process returns to the next odd field. As described above, actually, for example, in an odd-numbered field, an image is displayed from the center of the scanning line # 22, and a vertical retrace period starts from the right end of the scanning line # 309, and is not displayed on the screen.

In the PAL system, the color subcarrier is modulated by inverting the phase of the RY signal for each scanning line in order to compensate for the transmission distortion of the color difference signal. For this reason, the phase of the color subcarrier is a 1/4 line offset method so that the phases of the RY signals are not aligned between the scanning lines, and the color subcarrier frequency FSC is set so that the dots are inverted between the fields. And the horizontal synchronizing signal frequency FH is defined as in the above equation (1). Therefore, from the horizontal scanning shown in FIG. 3 and the relationship shown in the equation (1), the relationship between the horizontal synchronizing signal and the color subcarrier is different from the 0th field to the 7th field, and the 8th field is the 0th field. It has the same relationship as the field. The range from the 0th field to the 7th field where the relationship between the horizontal synchronization signal and the color subcarrier is different from each other is called one color frame. In the case where the color video signal is switched, if the switching is not performed while maintaining the continuity of the color frames, the switching will be accompanied by unnaturalness. For these reasons, it is necessary to detect a color frame of the composite video signal.

FIG. 4 shows a part of the relationship between the phase of the horizontal synchronizing signal and the phase of the color subcarrier in the PAL system. In FIG. 4, X is the number of the horizontal scanning line, and one field has scanning lines # 0 to # 312 (including a vertical blanking period). In FIG. 4, only # 0 to # 7 and # 312 are shown. Is omitted. A indicates whether the field is an odd field (logic "1") or an even field (logic "0"). If the phase of the color subcarrier at the starting point of the first scanning line X = 0 of the first odd field (first color field) of a certain color frame is 0 °, the next scanning line X =
At the starting point of 2 (left end), from equation (1), the phase of the color subcarrier is 0 ° (starting phase of X = 0) + 360 ° × (284−1 / 4 + 1/625) × 1 (3) Among them, the term of 360 ° × 1/625 × 1/2 is smaller than the other terms, so that it is approximately omitted, and the equation (3)
Is represented as 270 ° when expressed in a modulo of 360 °. Up to about X = 7, since the accumulated error due to the omission of the 1/625 term can be tolerated, the phase of the color subcarrier as shown in FIG. 4 is similarly obtained.

For the final scanning line X = 312, from equation (1), 0 ° + 360 ° × (284−1 / 4 + ／ 625) × 312 (4), which is also expressed by a modulo of 360 °, 180 °
Since this scan line ends at the center of the horizontal axis, the phase at the end point is 135 °, which is the X of the next even field.
= 0 is the phase of the starting point of the scanning line. Since the scan line of X = 0 starts from the center point of the horizontal axis, the phase of the end point is 135 ° −45 ° = 90 °, which is the scan line of the scan line X = 1 of the second color field (CF = 1). It becomes the phase of the starting point. In FIG. 4, the mark * indicates the phase of the color subcarrier at the starting point of the scanning line starting from the center of the horizontal axis. Similarly the second
Last scanning line X of color field (CF = 1) = 312
From the equation (1) is 90
° + 360 ° x (284-1/4 + 1/625) x 31
1 = 0 °. Thus, from equation (1), P shown in FIG.
The relationship between the phase of the color subcarrier in the AL system and the horizontal synchronization signal FH is obtained. That is, the phase of the color subcarrier signal at the horizontal scanning start point is 90 ° for each line.
The phase of the color subcarrier signal at the start of the field shifts by 135 ° for each field. The values in parentheses in FIG. 4 will be described separately.

[0008]

2. Description of the Related Art A color frame detecting circuit for a PAL color video signal is disclosed in, for example,
-101194, "Synchronous signal generator", JP-A-63-40518, "Color frame detection device", and JP-A-9-33158, "PAL system" These conventional circuits detect the order of color fields in a color frame by constantly observing the phase of the color subcarrier that shifts line by line or field by field as described above. Therefore, there is a problem that the circuit scale becomes large.

[0009]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a color frame detecting circuit which can detect the order of a color field in a PAL color frame with a simple circuit.

[0010]

According to the present invention, the phase relationship between the color subcarriers shown in FIG. 4, the presence / absence of color burst superposition at a specific scanning line number, and the burst phase at the beginning of the frame (odd field) are shown. To detect a color frame.

That is, the PAL color frame detection circuit according to the present invention comprises a vertical synchronization signal, a horizontal synchronization signal, a field OE signal indicating an odd / even field state, and a burst extracted by a burst control oscillator from a composite video signal. A synchronization / burst signal extraction circuit for outputting a signal, a line counter for counting the number of scanning lines from the vertical synchronization signal and the horizontal synchronization signal, and first detecting a line number on which the burst signal is superimposed; An O / E detection circuit for generating a changing pulse and detecting an odd or even field from the field OE signal; and detecting the phase of the burst signal at the beginning of each frame from the vertical synchronization signal, the field OE signal and the burst signal. A burst phase detection circuit for performing level detection; And a decoding circuit for decoding the output of the O / E detection circuit and the burst phase detection circuit, and specifying which of the eight color fields in the color frame is present in the color frame. .

One preferred embodiment further includes a burst appearance detection circuit for detecting the appearance of the first burst signal in each field from the burst flag signal and the vertical synchronization signal, and a color frame detection circuit,・
The burst signal extraction circuit further outputs the burst flag signal indicating the appearance of the burst signal, and the decoding circuit outputs, for each field, code data for specifying which of the eight color fields is present in the color field, The color frame detection circuit detects the order of the color field by capturing the code data in accordance with the output timing of the burst appearance detection circuit.

In this case, the code data output from the decoding circuit is obtained by superimposing a 1-bit logical signal indicating whether the field is an odd field or an even field, and a first burst signal of the field. 1 indicating whether or not the line number is a specific line number
It is characterized by being 3-bit code data composed of a combination of a bit logical signal and a 1-bit logical signal indicating the polarity of the phase of a burst signal at the beginning of a frame including the field.

In another embodiment, the apparatus further comprises a color frame detection circuit comprising a 3-bit octal counter for counting the vertical synchronization signal, wherein the decoding circuit determines whether the field is an odd field or an even field. An output logic of the O / E detection circuit indicating another, an output logic of the line counter indicating whether or not a line number on which the first burst signal of the field is superimposed is a specific line number; When the three types of eight output logic combinations of the burst phase detection circuit, which indicate the polarity of the phase of the burst signal at the beginning of the included frame, become one specific logic combination,
A reset signal for resetting the bit octal counter is output.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of an embodiment of a color frame detection circuit according to the present invention. Referring to FIG. 1, a color frame detection circuit according to the present embodiment receives a video signal, which is a PAL analog composite signal, and outputs a horizontal synchronization signal, a vertical synchronization signal, and a field OE signal indicating an odd / even field state. A synchronization / burst signal extraction circuit 1 for outputting a burst signal extracted by a burst control oscillator and a burst flag signal indicating the appearance of the burst signal, and the first burst in each field based on these signals. A burst appearance detection circuit 2 for detecting the appearance of a signal, a line counter 3 for counting the number of horizontal scanning lines and outputting a line number on which a burst signal is superimposed first in the field, and a level at an intermediate point of one line O / E (Odd / Even) that generates a pulse that varies and detects an odd or even field Number) detection circuit 4, a burst phase detection circuit 5 for detecting the level of the phase of the burst signal at the beginning of each frame (odd field), a line counter 3, an O / E detection circuit 4, and a burst phase detection circuit 5. A decode circuit 6 that decodes the output and generates code data indicating which of the eight color fields in the color frame are present, and code data generated by the decode circuit 6 based on the output of the burst appearance detection circuit 2 And a color frame detection circuit 7 that outputs a color field signal of the field by latching

As described above, in the PAL system, the color subcarrier is modulated by inverting the phase of the RY signal for each scanning line in order to compensate for the transmission distortion of the color difference signal. In accordance with this, the phase of the burst signal is ± 13 with respect to the phase of the BY signal, which is the reference phase of the color subcarrier, for each scanning line.
Changes 5 °. As shown in FIG. 4, in the PAL type composite signal, the phase of the color subcarrier shifts by about 90 ° for each line, so the phase of the burst signal with respect to the horizontal synchronizing signal is 360 ° / 625 in the equation (1). Is ignored, the polarity changes every two lines with the same phase of the two lines, resulting in the opposite phase.

That is, for example, assuming that the phase of the color subcarrier shown in FIG. 4 is the reference phase, when the phase of the color subcarrier is 0 °, 270 °, 180 ° or 90 °, the phase of the burst signal is 0 ° + 135 ° = 1
35 °, 270 ° -135 ° = 135 °, 180 ° + 1
35 ° = 315 ° and 90 ° -135 ° = 315 °. For example, if the phase 135 ° of the burst signal is represented by polarity 0 and the polarity of 315 ° is represented by polarity 1, the polarity becomes as shown in FIG.

Here, looking at the polarity of the burst signal at the beginning of each frame (odd field), every two frames (4
(For each field). Further, in the PAL system, a burst blanking period in which a burst signal is not superimposed by a meander gate signal before and after the vertical synchronizing signal is provided, and the burst signal is actually superimposed as shown in FIG. When defining line numbers, the first, second, fifth and sixth color fields (CF = 0, 1,
4 and 5), scanning line # 6 and thereafter, third and seventh color fields (CF = 2, 6), scanning line # 5 and later, and fourth and eighth color fields (CF = 3, 7). # 7 and later. Furthermore, the output of the O / E detection circuit 4 indicating whether the field is an odd field or an even field changes alternately for each field.

Therefore, the O / E that changes for each field
The output of the detection circuit 4 is logic A, the logic B indicates whether the line number on which the burst signal is first superimposed is a specific line (for example, X = 6) or the burst signal at the beginning of a frame which changes every field. Is represented by logic C, eight types of color fields in a color frame can be specified by three-bit status signals A, B, and C as shown in FIG.

In this manner, the decoding circuit 6 of this embodiment outputs the signal A indicating the distinction between the odd field and the even field output from the O / E detection circuit 4 and the burst signal first in each field output from the line counter 3. A logical combination of a signal B indicating whether or not the line on which is superimposed is the scanning line # 6 and a signal C indicating the polarity of the burst signal at the beginning of the frame output from the burst phase detection circuit 5 are decoded. Output the field number CF.

Since the code data output from the decoding circuit 6 changes according to the output of the line counter 3 monitoring a specific line in the field, it changes so as to indicate the color field in the middle of the field. Therefore, the color frame detection circuit 7 synchronizes with each frame by latching the output of the decoding circuit 6 with a signal indicating the appearance of the first burst signal in the field output by the burst appearance detection circuit 2 and synchronizes with each frame. Output a signal.

As described above, in this embodiment, the hue information is detected by a simple circuit by monitoring the change in the polarity of the burst signal in a specific line of each field using the periodicity of the PAL video signal. be able to.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, the signal A indicating the distinction between the odd field and the even field is logic 1, and When the signal B indicating that the line on which the burst signal is superimposed first is the scanning line # 6 is logic 1, and the signal C indicating the polarity of the burst signal at the beginning of the frame is logic 0, the reset pulse , And a octal (binary 3 bit) counter that counts the vertical synchronizing signal and is reset by the reset pulse to output the order of the color field.

[0024]

As described above, according to the present invention, P
By using the periodicity of the video signal of the AL system, the line on which the burst signal is superimposed first in each field is monitored, and a stable PA can be obtained with a simple circuit configuration.
L-type color frame detection becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of input / output logic of a decoding circuit 6 of FIG. 1;

FIG. 3 is a schematic diagram showing horizontal scanning lines in an odd field and an even field of the PAL system.

FIG. 4 is a diagram showing a change in polarity of a burst signal and a phase of a color subcarrier of each line in each field of the PAL system.

[Explanation of symbols]

 Reference Signs List 1 synchronization / burst signal extraction circuit 2 burst appearance detection circuit 3 line counter 4 O / E detection circuit 5 burst phase detection circuit 6 decoding circuit 7 color frame detection circuit

Claims (4)

(57) [Claims] 1. A P detection method for detecting the order of a color field in a color frame of a PAL-type composite video signal.
In the AL system color frame detection circuit, a vertical synchronization signal, a horizontal synchronization signal, and a field OE indicating an odd / even field state are output from the composite video signal.
A synchronization / burst signal extraction circuit that outputs a signal and a burst signal extracted by a burst control oscillator, counts the number of scanning lines from the vertical synchronization signal and the horizontal synchronization signal, and first detects a line number on which the burst signal is superimposed. Line counter, generates a pulse whose level changes at the midpoint of one line,
An O / E detection circuit for detecting an odd or even field from the field OE signal; a burst phase detection for detecting a phase level of a burst signal at the beginning of each frame from the vertical synchronization signal, the field OE signal and the burst signal Circuit, and a decoding circuit for decoding the output of the line counter, the O / E detection circuit, and the burst phase detection circuit, and specifying which of the eight color fields in the color frame is present. A PAL color frame detection circuit characterized by the above-mentioned. 2. The apparatus according to claim 1, further comprising: a burst appearance detection circuit for detecting an appearance of a first burst signal in each field from the burst flag signal and the vertical synchronization signal; and a color frame detection circuit. Further, the burst circuit outputs the burst flag signal indicating the appearance of the burst signal. The decoding circuit outputs, for each field, code data for specifying which of the eight types of color fields is present in the color frame. 2. The PAL color frame detection circuit according to claim 1, wherein the PAL system detects an order of the color field by capturing the code data in accordance with an output timing of the burst appearance detection circuit. 3. The code data output from the decoding circuit is superimposed on a 1-bit logic signal indicating whether the field is an odd field or an even field, and a first burst signal of the field. 3 bits consisting of a combination of a 1-bit logical signal indicating whether or not the line number is a specific line number and a 1-bit logical signal indicating the polarity of the phase of the burst signal at the beginning of the frame containing the field 3. The PAL color frame detection circuit according to claim 2, wherein 4. A color frame detecting circuit comprising a 3-bit octal counter for counting the vertical synchronizing signal, wherein the decoding circuit indicates whether the field is an odd field or an even field. O / E
The output logic of the detection circuit, the output logic of the line counter indicating whether the line number on which the first burst signal of the field is superimposed is a specific line number, and the output logic of the line counter at the beginning of the frame containing the field A reset signal for resetting the 3-bit octal counter is output when the eight types of logic combinations of the three types of output logic of the burst phase detection circuit that indicate the polarity of the phase of the burst signal become one specific logical combination. 2. The PAL color frame detection circuit according to claim 1, wherein: