KR20020072052A - Clamp level automation compensation method - Google Patents

Abstract

PURPOSE: A method for automatically correcting a clamp level is provided to automatically adjust a clamp level to the black level to stabilize color and brightness of a picture. CONSTITUTION: A default value of a clamp level decided by a specification is set. A clamping section and a plurality of points in the clamping section, at which clamp level values are read, are set. When power is on or a source format is changed, clamp level values are read from the plurality of points in the clamping section and a representative value of the clam level values is determined. The representative value is compared with the default value to calculate a difference between the two values, and the difference is compared with a predetermined reference value. When the difference is larger than the reference value, the difference is subtracted from the default value to newly set the default value. When the difference is smaller than the reference value, the difference is added to the default value to newly set the default value.

Description

CLAMP LEVEL AUTOMATION COMPENSATION METHOD}

TECHNICAL FIELD The present invention relates to a DTV system, and more particularly, to a clamp level automatic correction method.

In general, as shown in the block diagram of FIG. 1, a digital TV system includes a tuner unit 110 that receives a high frequency signal (RF) and detects a broadcast signal desired by a user, and in the tuner unit 110. Y / C separation unit 120 that separates the detected broadcast signal into luminance / color (Y / C), and demodulates the luminance / color (Y / C) signal in the Y / C separation unit 120. One of a color demodulator 130 for outputting a chroma signal RY (BY), video signals from an external device AV1, AV2, DVD, HD / STB, PC, and video signals from the color demodulator 130; A switch unit 140 for selecting a video signal, an analog-to-digital converter (ADC) 150 for converting the video signal in the switch unit 140 into a digital signal based on the clamp signal CLP, Temporarily stores the digital video signal from the analog-to-digital converter 150 in the memory 161 and performs video data processing to output the primary color video signals R, G, and B. A video data processing unit (VDP) 160, a video amplifying unit 170 for amplifying the primary color image signal from the video data processing unit 160 to a CPT 180, and a control program. It is composed of a CPU (CPU) 190 for controlling the operation of the switch unit 140 while adjusting and adjusting the setting values of the analog-to-digital converter 150 and the video data processing unit 160 during the clamp operation.

Referring to the operation of the digital TV system as follows.

When the tuner unit 110 receives a high frequency signal (RF) and detects a broadcast signal desired by the user, the Y / C separator 120 separates the broadcast signal into luminance / color (Y / C) and the color demodulator ( 130 demodulates the chroma signal RY (BY) using a demodulation carrier.

At this time, the chroma signal R-Y (B-Y) is input to the switch unit 140 together with the luminance signal Y.

However, not only an output signal from the color demodulator 130 but also image signals from the external devices AV1, AV2, DVD, HD / STB, and PC are input to the switch unit 140.

Accordingly, by the user's key input, the CPI 190 controls the switch unit 140 to output image signals from the external devices AV1, AV2, DVD, HD / STB, PC and the output of the color demodulator 130. One of the signals is selected.

In addition, the CPI 190 determines the format of the video signal selected by the switch 140 and sets the ADC value of the analog-to-digital converter 150 and the VDP value of the video data processor 160 to match the format. do.

In this case, the analog-to-digital converter 150 sets a sampling period based on the clamp signal CLP to convert the image signal selected by the switch unit 140 into a digital image signal.

Here, the analog-to-digital converter 150 sets a reference section for converting an analog signal into a digital signal. The method generally sets the clamp section in a black level section without a signal as shown in the waveform diagram of FIG. do.

Accordingly, the video data processor 160 temporarily stores the digital video signal from the analog-to-digital converter 150 in the memory 161 and then performs a video data processing operation to reproduce the primary color signals R, G, and B. FIG. The video amplification unit 170 amplifies the video signal from the video data processing unit 160 by a predetermined level and outputs it to the Citi 180 to display an image on the screen.

However, conventionally, as shown in Fig. 2, the clamp section is set and the value that sets the level is collectively applied to all sets (SET) so that the deviation between the ICs or the deviation caused by the temperature progression is not taken into account. There will be slight quality deviation (brightness, color, etc.).

Therefore, there is a problem in that a clear image cannot be displayed when an image quality deviation occurs due to the deviation between ICs or the progression of temperature.

In particular, when processing a non-standard signal, such as a VCR, there is a problem that the image quality deviation occurs severely.

Accordingly, the present invention provides a method for automatically correcting a clamp level, which is designed to correct a phenomenon in which brightness and color are distorted due to a clamping level change caused by an IC deviation or temperature during an analog / digital conversion process in order to improve the conventional problem. There is a purpose.

1 is a block diagram of a typical digital TV system.

2 is a waveform diagram showing a conventional clamp level setting.

3 is an exemplary view showing waveforms of normal / abnormal clamp levels.

4 is an operational flowchart for clamp level automatic correction in an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

110: tuner portion 120: Y / C separation portion

130: color demodulation unit 140: switch unit

150: analog / digital converter 160: video data processing unit

170: amplifier 180: CPT

190: CPI

In order to achieve the above object, the present invention sets a stable point as a clamping section, filters a plurality of values in the section, and then compares the filtered value with a value designated as a default value. By adjusting the value to provide a stable clamp level.

That is, the present invention provides a method of setting a default value of a clamp level defined in a specification, setting a clamp section and a plurality of points to read the clamp level value within the clamp section, and clamping when power on or source format changes. Reading a clamp level value at a plurality of points set within a section to select a representative value, comparing the selected representative value with a preset default value, calculating a difference value and comparing the difference value with a preset reference value; And resetting the default value by subtracting the default value by the difference value if the difference value is larger than the reference value, and resetting the default value by adding the difference value to the default value if the difference value is smaller than the reference value.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Digital TV system for the embodiment of the present invention is the same as the general TV system of Figure 1 tuner unit 110, Y / C separation unit 120, color demodulation unit 130, switch unit 140, analog And a digital converter 150, a video data processor 160, a video amplifier 170, a CPI 180, and a CPI 190.

The CPI 190 sets a plurality of points N to read the clamp level value in the clamp section to be performed by the analog-to-digital converter 150 and the plurality of clamps read at the set points in the clamp section. The representative value MEAN is selected by filtering the level value, and the difference value DIFF is calculated by comparing the selected representative value MEAN with a default value DEF of a preset clamp level, and the difference value DIFF is a reference value ( If greater than REF, the default value DEF is reset by subtracting the difference value DIFF from the previous default value DEF. If the difference value DIFF is less than the reference value REF, the difference value is set to the previous default value DEF. It is configured to repeat the process of resetting the default value DEF by summing the difference values DIFF.

Referring to the operation and effect of the embodiment of the present invention configured as described above are as follows.

3 shows waveforms of the clamping level. FIG. 3 (a) shows a case where the clamping level is normally set, and FIG. 3 (b) shows a case where the clamping level is abnormally set due to IC deviation or temperature deviation.

4 is a flowchart illustrating an operation for automatic clamp level correction in an embodiment of the present invention.

First, set the default clamping level (DEF) according to the specifications of each signal (RF, A / V, DVD, HD / STB, PC, etc.) and set the clamping section internally for the analog-to-digital converter 150. After that, the number (N) to read the value in the clamping section and the point to read the value are set.

At this time, the clamping section is designated as a stable section without a signal, such as the back porch portion of the horizontal synchronization signal.

Thereafter, the CPI 190 checks the analog-to-digital converter 150 to read the value RDBK at a designated point in the clamping section, and to prevent N from malfunctioning due to the influence of noise in a non-standard signal such as a VCR. Select the representative value (MEAN) by filtering the read value.

In this case, the filtering method obtains an average value of all the values read from the designated points in the clamping section and selects the representative value (MEAN) or selects the average value of the remaining values except for the largest value and the small value and selects the representative value (MEAN).

Thereafter, the CPI 190 compares the representative value MEAN obtained above with the preset default value DEF, and returns the difference value DIFF to correct it.

That is, the CPI 190 obtains the difference value DIFF between the representative value MEAN and the default value DEF, and then compares whether the difference value DIFF is greater than the reference value REF.

At this time, if the difference value DIFF is greater than the reference value REF, the default value DEF is reset to the value obtained by subtracting the difference value DIFF from the previous default value DEF, and conversely, the difference value DIFF is the reference value REF. If it is smaller, the default value (DEF) is reset to the previous default value (DEF) plus the difference value (DIFF).

Thereafter, in order to determine whether the image is stable without any distortion of brightness or color of the image, the CPI 190 determines whether the default value is changed by comparing the currently reset default value DEF with the previous default value DEF. .

Therefore, if it is determined that the default value has been changed, the CPI 190 recognizes that there is a distortion of the brightness or color of the image, and repeatedly executes the process of reading the clamp level value (RDBK) at the designated position in the clamping section. do.

As described in detail above, the present invention has an effect of automatically satisfying the user by stabilizing the color and brightness of the image quality by automatically adjusting the clamp level with the black level against a change in the clamp level due to IC deviation or temperature deviation.

In particular, the present invention has the effect of always providing stable image quality even for non-standard signals such as VCR by filtering values read from a plurality of points designated in the clamping period.

Claims (4)

1. A method of correcting clamp levels in an imaging system, the method comprising: a first step of setting a default value of a clamp level specified in a specification; and a second step of setting a clamp section and a plurality of points at which the clamp level values are read in the clamp section. And a third step of selecting a representative value by reading a clamp level value at a plurality of points set in the clamp section when the power-on or source format is changed, and comparing the selected representative value with a preset default value to calculate a difference value. And a fourth step of comparing the difference value with a preset reference value, and if the difference value is greater than the reference value, subtracting the default value by the difference value to reset the default value, and if the difference value is smaller than the reference value, And a sixth step of resetting the default value by summing the difference values. The clamp level automatic correction method according to claim 1, wherein the representative value is selected as an average value of values read from a plurality of designated points. The method of claim 1, wherein the representative value is selected as an average value of remaining values except for the largest value and the smallest value among the values read from the plurality of points. The method of claim 1, further comprising: comparing the currently reset default value with the previous default value, and recognizing the change of the default value from the step of reading the clamping level value from a plurality of points designated in the clamping interval. Clamp level automatic correction method further comprising the step of.