JPH07162717A - Adaptive gamma correcting method - Google Patents

Abstract

PURPOSE:To determine the difference between the previous gradation frequency and the current gradation frequency and to control the switching time of a look-up table for gamma correction according to the difference. CONSTITUTION:This method is composed of an AD conversion part 1 converting a video signal 15 into digital data, a gradation frequency counting part 2 counting digital data according to gradation classes, a decision pattern generation part 3 comparing a reference frequency value and the frequency of each class and generating a decision pattern, a switch part 4 outputting a switch signal to a gamma correction part 9 based on the decision pattern, a memory 5 storing gradation frequency data classified by classes, the reference frequency value and the reference difference value, an arithmetic part 6 calculating a difference, a discrimination part 7 deciding the size of the difference, a counting part 8, an adaptive gamma correction part 9 selecting one pair of gamma correction data table from plural pairs of them by the switch signal of the switch part 4 and performing a gamma correction of digital data based on the data table, a DA conversion part 10 converting digital data after a correction into a video signal 16 and a control part 11 controlling each part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive gamma correction method applied to a liquid crystal projector for obtaining gradation reproducibility and color reproducibility similar to that of a CRT display when a television image signal or the like is input. .

[0002]

2. Description of the Related Art Originally, gamma correction is a correction performed on the sending side of a television signal in order to correct the light emission luminance of a CRT television. The relationship between the input voltage E of the cathode-ray tube and the light emission luminance L is not linear, and can be approximated by the relational expression of the above expression: L = K × (E to the power of γ). When L and E are plotted on a logarithmic scale, a straight line is obtained, and γ is its slope. In a color picture tube, γ is 2.2. Therefore, it is necessary to perform correction in order to reproduce the gradation and chromaticity of the image receiving screen in proportion to that of the subject. In the NTSC system, in order to reduce the load on the image receiving side, γ = 1 /
After applying the correction of 2.2, the display of the cathode ray tube is γ =
It is set to 1. Since the relationship between the input voltage and the light emission brightness of the liquid crystal projector device is different from that of the cathode ray tube, it is necessary to perform appropriate correction on the liquid crystal projector device side. As an example of the gamma correction method implemented in the conventional liquid crystal projector device, as shown in FIG. 2 and FIG. 3, all brightness gradations are expressed in 256 steps with 8 bits, and every 64 gradations are expressed. 0-63, 64-127 and 12
It is divided into four classes, 8-191 and 192-255. Then, the luminance of the image is divided into the four classes for each field to generate frequency distribution data, and the required frequency reference value is compared with the frequency of each class, and the result is used as a 4-bit determination pattern. 1 corresponding to each judgment pattern
Six types of gamma correction tables are provided, the table is adaptively selected by the 4-bit determination pattern, and the 8-bit full-luminance gradation image is gamma-corrected based on the selected gamma correction table. . However, when the frequency of each class is close to the reference frequency, the judgment value tends to change, and as a result, the judgment pattern changes and the gamma correction table that is selected changes, so the gamma correction value changes, and the final correction is made. There was a problem with flickering images.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a correction method in which the image flicker that has been caused by the conventional adaptive gamma correction is reduced.

[0004]

In order to achieve the above object, an AD converter for converting a video signal into digital data, and a gradation frequency counter for counting the digital data output by the AD converter for each gradation class. Unit, a judgment pattern generation unit that generates a judgment pattern by comparing the reference frequency value and the frequency of each class, a switching unit that outputs a switching signal to the gamma correction unit based on the judgment pattern, and the gradation frequency counting unit. A memory for storing the gradation frequency data for each class counted by the unit, the reference frequency value, and the reference difference value; a calculation unit for calculating the difference between the gradation frequency data for each class and that of the previous field; The difference calculated by the unit and the reference difference value stored in the memory to determine the magnitude of the difference, and the time to switch the switching unit based on the determination result of the determination unit. A digital data output from the AD converter based on the selected gamma correction data, which includes a timekeeping unit to measure and a plurality of sets of gamma correction data Is a gamma correction unit for performing gamma correction, a DA conversion unit for converting the corrected digital data into a video signal, and a control unit for controlling each unit.

[0005]

With the above configuration, when the discrimination unit compares the gradation frequency data for each class with the previous data and determines that there is a change of a predetermined magnitude or more, the determination pattern held by the switching unit. The data of is immediately changed to the currently generated judgment pattern. Further, when the discrimination unit compares the gradation frequency data for each class with the previous data and determines that the change is less than the predetermined magnitude, the data of the determination pattern held in the switching unit is retained as the previous data. To do.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The adaptive gamma correction method according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is an example of a block diagram for implementing the adaptive gamma correction method according to the present invention. As shown in the figure, 1 is a supplied video signal 1
A for converting 5 into 8-bit digital data, for example
It is a D converter. Reference numeral 2 is a gradation frequency counting unit configured to count digital data output from the AD conversion unit 1 for each gradation class, for example, provided with a counter for each gradation class. Reference numeral 3 denotes a determination pattern generation unit that compares the reference frequency value with the frequency of each class to generate a determination pattern.
Reference numeral 4 denotes a switching unit which outputs a switching signal to the adaptive gamma correction unit 9 based on the determination pattern, and which is composed of, for example, a 4-bit register (memory). Reference numeral 5 is a memory for storing the gradation frequency data for each class counted by the gradation frequency counting unit 2 and the reference numerical value and the standard difference value. Reference numeral 6 is an arithmetic unit for calculating the difference between the gradation frequency data for each class and that of the previous field. Reference numeral 7 denotes a discriminating unit that compares the difference calculated by the arithmetic unit 6 with a reference difference value stored in the memory 5 and determines the magnitude of the difference. 8 is a timekeeping unit that measures time, and 9 is, for example,
ROM that stores 16 sets of gamma correction data tables
(Read Only Memory), and one set is adaptively selected from the 16 sets in accordance with the 4-bit switching signal held by the switching unit 4, and is stored in the selected gamma correction data table. Based on this, the 8-bit digital data output from the AD conversion unit 1 is used as an address input, and the correction data stored in the corresponding address is output to perform the gamma correction. 10 is the digital signal after correction and the video signal 1
It is a DA conversion unit for converting into 6. Reference numeral 11 is a control unit that controls each unit.

The operation of the adaptive gamma correction method according to the present invention will be described with reference to FIGS. When the video signal 15 input by the AD conversion unit 1 is quantized by, for example, 8 bits, the gradation frequency counting unit 2 sets A as shown in FIG.
(0 to 63 gradations), B (64 to 127 gradations), C (12
(8 to 191 gradations) and D (192 to 255 gradations), the frequency distribution data is obtained by counting the frequencies for each luminance class. The judgment pattern generation unit 3 compares the reference frequency value with the frequency of each class, and when the frequency is higher than the reference frequency value, the data 1
(0), and when it is small, data 0 (1)
A data string corresponding to the D brightness class is generated, and the data string is called a determination pattern. As an example, the determination pattern generation unit 3 generates the determination pattern (0, 1, 1, 0) shown in FIG. 3 based on the frequency distribution data shown in FIG. Since the adaptive gamma correction unit 9 is preliminarily provided with 16 types of gamma correction data tables corresponding to the 4-bit judgment patterns, the judgment unit 7 compares the gradation frequency data for each class with that of the immediately preceding field. By comparing the difference calculated by the calculation unit 6 with the reference difference value and determining the magnitude of the difference, if the change in the tone frequency data for each class is equal to or more than a predetermined magnitude, it corresponds to the determination pattern. Then, a corresponding gamma correction data table is adaptively selected, and adaptive gamma correction is performed based on the data table.

The situation in which the gamma correction data table is selected according to the magnitude of the difference between the tone frequency data for each class will be described in more detail below. FIG. 4 illustrates one class of the determination pattern shown in FIG.
As shown in the drawing, when the classifying gradation frequency data is compared with the previous data, for example, the same data one field before, in the discriminating unit 7, it is determined that the difference ΔT2 is equal to or larger than a predetermined magnitude. In the case (FIG. (B)), the data of the determination pattern held in the switching unit 4 is changed to the generated current determination pattern (1). In addition, in the discrimination unit 7, the gradation frequency data for each class is compared with the previous data, and the difference ΔT
When it is determined that 1 is a change smaller than a predetermined magnitude ((a) in the figure), the data of the determination pattern held in the switching unit 4 is retained as the previous data and is not updated. For example, as another embodiment of the above operation, the calculation unit 6 calculates the percentage ratio of the frequency data to the frequency data at that time, and the determination unit 7 sets the reference percentage value stored in the memory 5 to 5%. 10% and 20%, the calculated percentage value is 5 by comparing with those.
If it is less than%, the data of the judgment pattern held in the switching unit 4 is kept as it is, and if it is 5% or more and less than 10%, it is changed after 2 frame times (2/30 seconds), and if it is 10% or more and less than 20%. It is changed after 1 frame time (1/30 second), and when it is 20% or more, it is determined to change immediately. Therefore, as described above, the difference Δ
When it is determined that T or the calculated percentage value is equal to or larger than a predetermined value, the determination data held in the switching unit 4 is updated for each corresponding class for the first time.
Update the judgment pattern so far. As a result, the gamma correction data table of the adaptive gamma correction unit 9 is switched to another type. When the difference ΔT is less than the predetermined size, the switching unit 4 holds the determination pattern so far for the predetermined time. As the gradation frequency data for each class which is the basis of the difference calculation, the first gradation frequency data for each class is continuously held.

[0009]

As described above, the present invention provides a correction method for reducing the flicker of an image generated by the conventional adaptive gamma correction. Therefore, there is an advantage that it is possible to realize a high-quality liquid crystal projector device having gradation reproducibility and color reproducibility similar to that of a CRT display.

[Brief description of drawings]

FIG. 1 is an example of a block diagram for implementing an adaptive gamma correction method according to the present invention.

FIG. 2 is a diagram showing an example of frequency distribution data for each luminance class of an adaptive gamma correction method.

FIG. 3 is a diagram showing an example of a determination pattern of an adaptive gamma correction method.

FIG. 4 is a diagram illustrating a method of updating a determination pattern held in a switching unit based on a difference of an adaptive gamma correction method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AD conversion unit 2 Gradation frequency counting unit 3 Judgment pattern generation unit 4 Switching unit 5 Memory 6 Calculation unit 7 Discrimination unit 8 Timing unit 9 Adaptive gamma correction unit 10 DA conversion unit 11 Control unit 15 Video signal 16 After gamma correction Video signal

Claims (10)

[Claims] 1. A for converting a video signal into digital data
A D conversion unit, a gradation frequency counting unit that counts the digital data output by the AD conversion unit for each gradation class, and a determination pattern generation unit that generates a determination pattern by comparing a reference numerical value and the frequency of each class. A switching unit that outputs a switching signal to the gamma correction unit based on the determination pattern; and a memory that stores the gradation frequency data for each class counted by the gradation frequency counting unit, the reference frequency value, and the reference difference value. , Comparing the difference calculated by the calculation unit with the reference difference value stored in the memory, and comparing the difference between the calculation unit that calculates the difference between the gradation frequency data for each class and that of the previous field A judging section for judging, a time measuring section for measuring the time for switching the switching section based on the judgment result of the judging section, and a plurality of sets of gamma correction data are provided, among which a switching signal of the switching section is selected. A group is selected, and based on the selected gamma correction data, a gamma correction unit that gamma-corrects the digital data output from the AD conversion unit, a DA conversion unit that converts the corrected digital data into a video signal, and controls each unit. The adaptive gamma correction method, wherein the control unit controls the length of time until the switching unit is switched according to the determination result of the difference determined by the determination unit. 2. The adaptive gamma correction method according to claim 1, wherein the gamma correction unit is configured by a look-up table using a ROM. 3. The adaptive gamma correction method according to claim 1, wherein the switching unit comprises a register. 4. The adaptive gamma correction method according to claim 1, wherein the gradation frequency counter is composed of a plurality of counters. 5. The calculating unit calculates a percentage ratio between the difference and the gradation frequency data of the field, and the discriminating unit changes the percentage based on the percentage ratio and a reference percentage value stored in a memory. The adaptive gamma correction method according to claim 1, wherein the size is determined. 6. A for converting a video signal into digital data
A D conversion unit, a gradation frequency counting unit that counts the digital data output by the AD conversion unit for each gradation class, and a determination pattern generation unit that generates a determination pattern by comparing a reference numerical value and the frequency of each class. A switching unit that outputs a switching signal to the gamma correction unit based on the determination pattern; and a memory that stores the gradation frequency data for each class counted by the gradation frequency counting unit, the reference frequency value, and the reference difference value. , Comparing the difference calculated by the calculation unit with the reference difference value stored in the memory, and comparing the difference between the calculation unit that calculates the difference between the gradation frequency data for each class and that of the previous field A judging section for judging, a time measuring section for measuring the time for switching the switching section based on the judgment result of the judging section, and a plurality of sets of gamma correction data are provided, among which a switching signal of the switching section is selected. A group is selected, and based on the selected gamma correction data, a gamma correction unit that gamma-corrects the digital data output from the AD conversion unit, a DA conversion unit that converts the corrected digital data into a video signal, and controls each unit. Based on the determination that the difference is small in the determination unit, the switching unit,
The switching data currently held is continuously held for a predetermined time, and the class-based gradation frequency data used for the difference calculation in which the difference is small is also continuously used for the next difference calculation. An adaptive gamma correction method characterized by the above. 7. The adaptive gamma correction method according to claim 6, wherein the gamma correction unit is configured by a look-up table using a ROM. 8. The adaptive gamma correction method according to claim 6, wherein the switching unit comprises a register. 9. The adaptive gamma correction method according to claim 6, wherein the gradation frequency counter is composed of a plurality of counters. 10. The calculating unit calculates a percentage ratio between the difference and the gradation frequency data of the field, and
7. The adaptive gamma correction method according to claim 6, wherein the determination unit determines the magnitude of change based on the percentage ratio and a reference percentage value stored in the memory.