Method and device for measuring brightness of display screen pixel points to eliminate crosstalk interference

Abstract

The present invention discloses a method and a device for measuring the brightness of display screen pixel points to eliminate crosstalk interference, belonging to the field of display screens. By means of different interval lighting modes, the number of intervals for pixel display is increased spatially, the brightness of pixel points under different interval lighting conditions is collected, and through comparison, the crosstalk change trend between pixel points with different intervals is obtained, so as to deduce the optimal acquisition interval. When the interval distance is less than the optimal interval, the crosstalk interference of pixel points cannot be ignored. When the interval distance is greater than the optimal interval, in order to traverse each pixel to be collected, the number of acquisition times needs to be increased exponentially, and the acquisition efficiency drops exponentially. The present invention avoids various stray light crosstalk interferences and improves the accuracy of the collected data; adopts the optimal interval scheme to efficiently measure the brightness data of LED display screen pixel points. For COB display screens with block differences, the brightness data can also be accurately collected, improving the correction uniformity of the display screen.

Description

Technical Field

[0001] The present invention relates to the field of display screens, and in particular to a method and device for measuring the brightness of display screen pixels for eliminating cross-light interference. Background Art

[0002] In recent years, with the rapid development of Mini-LED and Micro-LED technology, the resolution of LED displays has become higher and higher, and screens with resolutions of 4K, 8K and even higher are gradually appearing. Correspondingly, the LED pixel pitch is also getting smaller and smaller. Conventional displays have already occupied a large market with P1.25 and P0.95, and displays with smaller pitches such as P0.6 and P0.4 will be the mainstream of future industry development.

[0003] The development of smaller pitch display screens faces a very serious problem, that is, the phenomenon of cross-light interference between adjacent pixels. The so-called cross-light phenomenon means that when shooting a single pixel, the light emitted by the surrounding adjacent pixels will be superimposed on the light emitted by the former, making the data collected by the single pixel no longer accurate. As the product becomes more mature, the accuracy of LED display screen calibration has also increased, and industry standards have also increased the requirements for uniformity, and cannot tolerate slight deviations. The requirements for calibration accuracy of COB block differences are significantly higher than those of point differences. For LED display screen calibration, it is urgent to solve the problem of cross-light between LED pixels affecting the acquisition accuracy.

[0004] In the present invention, light emitted by non-tested LEDs on the LED display screen, that is, light emitted by adjacent LEDs that affects the tested LEDs themselves, is collectively referred to as stray light, and the interference of stray light on the tested LEDs is collectively referred to as cross-talk interference.

[0005] The degree to which stray light affects the pixels to be measured varies. The reasons for the difference in stray light are as follows:

[0006] 1. The same LED pixel to be tested will be interfered by the stray light emitted by multiple adjacent LED pixels. The farther the distance between them, the lower the intensity of the stray light interference.

[0007] 2. The light intensity emitted by the LED pixels themselves varies, and the intensity of the stray light generated by the LED pixels to be tested also varies. For LED pixel modules with the same spacing, the stray light of brighter LED pixels is stronger, and the stray light of darker LED pixels is weaker.

[0008] 3. Different LED pixel structures (chip / Top, etc.) will also produce stray light with different characteristics.

[0009] 4. Different arrangements of LEDs will also cause different characteristics of stray light.

[0010] 5. Different encapsulation processes. Compared with the traditional SMD soldering process, the potting glue on the surface of the lamp board in the COB and GOB processes with smaller pitch makes the display template an integral luminous surface. The surface of its transparent medium adds internal reflected light. The LED pixels are no longer individual entities in the SMD encapsulation method, making the phenomenon of light crosstalk more likely to occur and the light crosstalk interference more obvious.

[0011] Regarding the crosstalk interference phenomenon between LED pixels caused by stray light, there is currently no method in the industry to solve this problem. Summary of the Invention

[0012] To solve the above technical problems, the present invention provides a method and device for measuring the brightness of display screen pixel points to eliminate crosstalk interference, which can efficiently collect the pixel brightness of the LED display screen on the premise of avoiding various stray light crosstalk interferences.

[0013] The technical solution provided by the present invention is as follows:

[0014] A method for measuring the brightness of display screen pixel points to eliminate crosstalk interference, including:

[0015] Step S100: Collect the brightness values of all pixel points when all pixel points in the selected rectangular area of the LED display screen to be measured are lit, and calculate the average value to obtain the brightness average value L0;

[0016] Step S200: Collect the brightness values of all pixel points when the pixel points in the rectangular area are lit in a way that every other pixel point is lit, and calculate the average value to obtain the brightness average value L1;

[0017] Step S300: Successively increase the number of pixel points with intervals, and so on, to obtain a series of brightness average values L t ; t is the number of pixel points with intervals, t = 1, 2,..., n, and n is the set maximum number of interval pixel points;

[0018] Among them, each pixel point is lit with the same brightness;

[0019] Step S400: Successively calculate the difference Δt between two adjacent brightness average values, where Δt = L t+1 - L t ;

[0020] Step S500: Obtain the minimum value of t when Δt / L t is less than ε, where ε is a positive number approaching 0;

[0021] Step S600: Collect the brightness values of all pixel points of the LED display screen to be measured in a way that every t pixel points are spaced apart.

[0022] Further, S200 includes:

[0023] S201: Light up the pixel points of the LED display screen to be measured at the same set brightness in a way that skips one pixel point, and collect the brightness values of the lit pixel points within the selected rectangular area;

[0024] S202: Replace the lit pixel points, repeat S201 until the brightness values of all pixel points within the selected rectangular area are collected, and calculate the average value to obtain the brightness average value L1.

[0025] Furthermore, the brightness values of the pixel points are collected by a luminance meter, a chrominance meter, an imaging luminance meter or an imaging chrominance meter.

[0026] Furthermore, the value of ε is less than one-thousandth.

[0027] A device for measuring the brightness of pixel points of a display screen to eliminate crosstalk interference, comprising:

[0028] A first acquisition module, configured to collect the brightness values of all pixel points when all pixel points within the selected rectangular area of the LED display screen to be measured are lit, and calculate the average value to obtain the brightness average value L0;

[0029] A second acquisition module, configured to collect the brightness values of all pixel points when the pixel points within the rectangular area are lit in a way that skips one pixel point, and calculate the average value to obtain the brightness average value L1;

[0030] A third acquisition module, configured to sequentially increase the number of skipped pixel points, and so on, to obtain a series of brightness average values L t ; t is the number of skipped pixel points, t = 1, 2,..., n, and n is the set maximum number of skipped pixel points;

[0031] wherein each pixel point is lit at the same brightness;

[0032] A calculation module, configured to sequentially calculate the difference Δt between two adjacent brightness average values, wherein Δt = L t+1 -L t ;

[0033] An acquisition module, configured to obtain the minimum value of t when Δt / L t is less than ε, where ε is a positive number approaching 0;

[0034] A fourth acquisition module, configured to collect the brightness values of all pixel points of the LED display screen to be measured in a way that skips t pixel points.

[0035] Furthermore, the second acquisition module includes:

[0036] The first acquisition unit is used to light up the pixel points of the LED display screen to be measured with the same set brightness in a way that one pixel point is skipped, and acquire the brightness values of the lit pixel points within the selected rectangular area;

[0037] The second acquisition unit is used to replace the lit pixel points, repeat S201 until the brightness values of all pixel points within the selected rectangular area are acquired, calculate the average value, and obtain the brightness mean value L1.

[0038] Further, the brightness values of the pixel points are acquired by a brightness meter, a chroma meter, an imaging brightness meter or an imaging chroma meter.

[0039] Further, the value of ε is less than one-thousandth.

[0040] The present invention has the following beneficial effects:

[0041] Through different lighting methods at intervals, the present invention increases the number of intervals of pixel point display in space, acquires the brightness of pixel points under different lighting conditions at different intervals. As the number of intervals increases, the intensity of adjacent crosstalk interference gradually weakens until the crosstalk interference can be ignored. By comparison, the changing trend of crosstalk between pixel points at different intervals is obtained, and thus the optimal acquisition interval is deduced. When the interval distance is less than the optimal interval, the crosstalk interference of pixel points cannot be ignored. When the interval distance is greater than the optimal interval, in order to traverse each pixel to be acquired, the number of acquisition times needs to be increased exponentially, and the acquisition efficiency decreases exponentially. The present invention avoids various stray light crosstalk interferences, improves the accuracy of acquired data; adopts the optimal interval scheme to efficiently measure the brightness data of pixel points of the LED display screen. For the COB display screen with block differences, the brightness data can also be accurately acquired, improving the correction uniformity of the display screen. Description of the Drawings

[0042] Figure 1 It is a flowchart of the method for measuring the brightness of pixel points of the display screen eliminating crosstalk interference of the present invention;

[0043] Figure 2 It is a schematic diagram of the changing trend of the average brightness acquired at different interval pixel points;

[0044] Figure 3 It is a schematic diagram of the light intensity cross-section distribution of the data acquired at the same pixel point with different step lengths affected by surrounding pixel points;

[0045] Figure 4 It is a schematic diagram of the light intensity plane distribution of the data acquired at the same pixel point with different pixel intervals affected by surrounding pixel points when the self-luminous brightness difference of the LED pixels of the display screen is small;

[0046] Figure 5Schematic diagram of the light intensity plane distribution of data collected at the same pixel point at different pixel intervals when the self-luminous brightness of the LED pixels of the display screen varies greatly, affected by surrounding pixel points;

[0047] Figure 6 Schematic diagram of the display method for traversing all pixels when the number of spaced pixels is 1;

[0048] Figure 7 Schematic diagram of the display method for traversing all pixels when the number of spaced pixels is 2;

[0049] Figure 8 Schematic diagram of the device for measuring the brightness of the display screen pixels to eliminate crosstalk interference according to the present invention. Detailed implementation manners

[0050] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0051] An embodiment of the present invention provides a method for measuring the brightness of display screen pixels to eliminate crosstalk interference, as Figures 1-7 shown, the method includes:

[0052] Step S100: Collect the brightness values of all pixel points when all pixel points in the selected rectangular area of the LED display screen to be measured are lit, and calculate the average value to obtain the brightness average value L0.

[0053] In this step, for the selected LED display matrix, each pixel is displayed with the same brightness, and the lit brightness of each pixel remains unchanged. A brightness meter, a chroma meter, an imaging brightness meter or an imaging chroma meter, etc. are used to collect the brightness of each pixel and take the average value.

[0054] Step S200: Collect the brightness values of all pixel points when the pixel points in the rectangular area are lit in a way of spacing one pixel point, and calculate the average value to obtain the brightness average value L1.

[0055] Compared with S100 in this step, the number of spaced pixel points (the interval is 1) is increased, and the LED matrix is displayed at spaced points to collect the brightness of each lit LED. In the same spaced point manner, each uncollected pixel is traversed until all LED pixels in the LED matrix are collected, and the average value is taken.

[0056] Step S300: Successively increase the number of spaced pixel points, and so on, to obtain a series of brightness average values L t ; where t is the number of spaced pixel points, t = 1, 2,..., n, and n is the set maximum number of spaced pixel points.

[0057] In this step, the number of spaced pixels is increased sequentially (the intervals are 2, 3, 4, …, n), the LED matrix is displayed at spaced points, the brightness of each lit LED is collected, and in the same way of spaced points, each uncollected pixel is traversed until all the LED pixels in the LED matrix are collected, and the average value is taken.

[0058] In S100 to S300, it is required to ensure that each pixel is lit with the same brightness.

[0059] Step S400: Calculate the difference Δt between the brightness means of two adjacent ones sequentially, where Δt = L t+1 -L t .

[0060] This step is used to compare the brightness changes of the LEDs under different conditions of the number of spaced points. As the number of spaced points increases, the stray light interference becomes weaker, the crosstalk interference becomes weaker, and the measured brightness value of the LED will gradually become smaller until the number of spaced points increases further and the degree of brightness reduction of the LED is too small to be negligible.

[0061] Step S500: Obtain the minimum value of t when Δt / L t is less than ε, where ε is a positive number approaching 0.

[0062] Exemplarily, the value of ε can be less than one-thousandth.

[0063] Step S600: Collect the brightness values of all pixel points of the LED display to be measured in the way of spacing t pixel points.

[0064] The strength of the stray light is inversely proportional to the interval between the pixels. The farther the pixel interval is, the weaker the influence of the crosstalk caused by the stray light on the accurate measurement is, and vice versa. To achieve accurate measurement, it is necessary to minimize the stray light crosstalk of adjacent pixels.

[0065] L t = The self-luminous brightness of the LED pixel + the sum of the stray light of the adjacent n-bit LED pixels + the sum of the stray light of the adjacent n - 1-bit LED pixels + the sum of the stray light of the adjacent n - 2-bit LED pixels + …… + the sum of the stray light of the adjacent n - t-bit LED pixels.

[0066] Among them, the LED interval distance without interval ≤ the LED pixel interval distance with interval of 1 ≤ the LED pixel interval distance with interval of 2 ≤ …… ≤ the LED pixel interval distance with interval of n.

[0067] The sum of the stray light of the LED pixels without interval ≥ the sum of the stray light of the LED pixels with interval of 1 ≥ the sum of the stray light of the LED pixels with interval of 2 ≥ …… ≥ the sum of the stray light of the LED pixels with interval of n.

[0068] There is the following rule:

[0069] 1) The more the number of spaced pixels, the more accurate the measurement result.

[0070] 2) When the number of spaced pixels is greater than a certain positive integer, the degree of improvement in precise measurement gradually becomes very small as the number of spaced pixels continues to increase, and the crosstalk of stray light between pixels can be ignored.

[0071] 3) The more the number of spaced pixels, the exponentially increasing the number of acquisitions required to traverse and measure each LED pixel to be measured. The larger the interval, the longer the time to collect data, which affects the acquisition efficiency. Therefore, it is necessary to find the number of spaced pixels that can achieve precise measurement and the highest efficiency.

[0072] 4) The method to obtain the optimal number of spaced pixels is to take the minimum interval value on the premise that the crosstalk of stray light between pixels can be ignored.

[0073] 5) After finding the optimal number of spaced pixels, based on this interval number, the LED matrix is displayed with spaced pixels spatially and data is collected time-divisionally. After multiple cycles, each LED pixel to be measured is traversed, and finally an accurate measurement result without stray light crosstalk interference is obtained.

[0074] 6) The acquisition method based on this number of pixel intervals is the method with the fewest acquisition times and the highest efficiency. Less than this interval number, there is crosstalk of stray light between LED pixels; greater than the interval number, the number of acquisitions increases exponentially and the efficiency will be greatly reduced.

[0075] Taking the COB screen as an example, the changing trend of the average brightness collected at different spaced pixels is shown in Figure 2 . As the pixel interval gradually increases, the average brightness gradually decreases, and the average brightness drop also continues to decrease. The brightness drop is the difference in the average brightness of different adjacent intervals, which is actually the stray light generated by the adjacent LEDs at the previous pixel interval. It can be seen from the figure that the brightness drop of this screen approaches 0 only when the number of spaced pixels is 5, and the adjacent pixels within the interval of 5 of this screen's pixels will generate non-negligible stray light to each other. Therefore, the acquisition is carried out with an interval of 5 points.

[0076] Taking the pixel with a luminous viewing angle of 160° as an example, the light intensity cross-sectional distribution of the data collected at the same pixel point with different step sizes affected by the surrounding pixel points is shown in Figure 3 . If the self-luminous brightness difference of the LED pixels on the display screen is small, the light intensity plane distribution of the data collected at the same pixel point with different pixel intervals affected by the surrounding pixel points is shown in Figure 4 ; if the self-luminous brightness difference of the LED pixels on the display screen is large, the light intensity plane distribution of the data collected at the same pixel point with different pixel intervals affected by the surrounding pixel points is shown in Figure 5 .

[0077] The display method of traversing all pixels with an interval pixel count of 1 is as follows Figure 6 , and the total number of traversals is (1 + 1) 2 = 4. It is necessary to display 4 times and collect 4 times to collect all the pixels of the LED display matrix.

[0078] When the interval pixel count is 2, the display method of traversing all pixels is as follows Figure 7 , and the total number of traversals is (2 + 1 = 3) 2 = 9. It is necessary to display 9 times and collect 9 times to collect all the pixels of the LED display matrix.

[0079] And so on. When the interval pixel count is n, the total number of traversals of the display method for traversing all pixels is (n + 1) 2 , and it is necessary to display (n + 1) 2 times and collect (n + 1) 2 times to collect all the pixels of the LED display matrix.

[0080] In the present invention, through different interval lighting methods, the interval quantity of pixel point display is increased spatially, and the brightness of pixel points under different interval lighting conditions is collected. As the interval quantity becomes larger, the intensity of adjacent crosstalk interference gradually weakens until the crosstalk interference can be ignored. Through comparison, the change trend of crosstalk between pixel points with different intervals is obtained, and thus the optimal collection interval is deduced. When the interval distance is less than the optimal interval, the crosstalk interference of pixel points cannot be ignored. When the interval distance is greater than the optimal interval, in order to traverse each pixel to be collected, the number of collection times needs to be increased exponentially, and the collection efficiency decreases exponentially. The present invention avoids various stray light crosstalk interferences, improves the accuracy of collected data; adopts the optimal interval scheme to efficiently measure the brightness data of pixel points on the LED display screen. For the COB display screen with block differences, the brightness data can also be accurately collected, improving the correction uniformity of the display screen.

[0081] As an improvement of an embodiment of the present invention, the foregoing S200 includes:

[0082] S201: Light up the pixel points of the LED display screen to be measured at the same set brightness in a way of spacing one pixel point, and collect the brightness values of the lit pixel points within the selected rectangular area.

[0083] S202: Replace the lit pixel points, repeat S201 until the brightness values of all pixel points within the selected rectangular area are collected, and calculate the average value to obtain the brightness average value L1.

[0084] Due to dot-by-dot display, only some pixel points can be collected each time. Therefore, a method of multiple collections is adopted to traverse and collect each uncollected pixel. In terms of time, through time-sharing collection, and then cross-stitched and synthesized to obtain the collected data of each complete pixel, realizing accurate data collection.

[0085] An embodiment of the present invention further provides a display screen pixel point brightness measurement device for eliminating crosstalk interference, as Figure 8 shown, which includes:

[0086] The first acquisition module 1 is used to collect the brightness values of all pixel points when all pixel points in the selected rectangular area of the LED display screen to be measured are lit, and calculate the average value to obtain the brightness average value L0.

[0087] The second acquisition module 2 is used to collect the brightness values of all pixel points when the pixel points in the rectangular area are lit in a way that one pixel point is skipped, and calculate the average value to obtain the brightness average value L1.

[0088] The third acquisition module 3 is used to sequentially increase the number of skipped pixel points, and so on, to obtain a series of brightness average values L t ; t is the number of skipped pixel points, t = 1, 2,..., n, and n is the set maximum number of skipped pixel points.

[0089] Among them, each pixel point is lit with the same brightness.

[0090] The calculation module 4 is used to sequentially calculate the difference Δt between two adjacent brightness average values, where Δt = L t+1 -L t .

[0091] The acquisition module 5 is used to obtain the minimum value of t when Δt / L t is less than ε, where ε is a positive number approaching 0.

[0092] The fourth acquisition module 6 is used to collect the brightness values of all pixel points of the LED display screen to be measured in a way that t pixel points are skipped.

[0093] Through different interval lighting methods, the number of intervals for pixel point display is increased spatially, and the brightness of pixel points under different interval lighting conditions is collected. As the number of intervals increases, the intensity of adjacent crosstalk interference gradually weakens until the crosstalk interference can be ignored. By comparison, the crosstalk change trend between pixel points with different intervals is obtained, and thus the optimal acquisition interval is deduced. When the interval distance is less than the optimal interval, the crosstalk interference of pixel points cannot be ignored. When the interval distance is greater than the optimal interval, in order to traverse each pixel to be collected, the number of acquisition times needs to be doubled, and the acquisition efficiency is halved. The present invention avoids various stray light crosstalk interferences and improves the accuracy of the collected data; adopts the optimal interval scheme to efficiently measure the brightness data of pixel points on the LED display screen. For the COB display screen with block differences, the brightness data can also be accurately collected, improving the correction uniformity of the display screen.

[0094] As an improvement of an embodiment of the present invention, the second acquisition module includes:

[0095] The first acquisition unit is used to light the pixel points of the LED display screen to be measured at the set brightness in the manner of spacing one pixel point, and collect the brightness values of the lit pixel points within the selected rectangular area.

[0096] The second acquisition unit is used to replace the lit pixel points and repeat S201 until the brightness values of all pixel points within the selected rectangular area are collected, and calculate the average value to obtain the brightness average value L1.

[0097] Furthermore, the brightness values of pixel points are collected by a brightness meter, a chromaticity meter, an imaging brightness meter or an imaging chromaticity meter.

[0098] Exemplarily, the value of ε can be less than one thousandth.

[0099] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for measuring the brightness of display screen pixel points to eliminate crosstalk interference, characterized in that, Including: Step S100: Collect the brightness values of all pixel points when all pixel points in the selected rectangular area of the LED display to be measured are lit, and calculate the average value to obtain the brightness average value L0. Step S200: Collect the brightness values of all pixel points when the pixel points in the rectangular area are lit in a way of skipping one pixel point, and calculate the average value to obtain the brightness average value L1. Step S300: Sequentially increase the number of spaced pixel points, and so on, to obtain a series of luminance means L t ; t is the number of spaced pixel points, t = 1, 2, …, n, where n is the set maximum number of spaced pixel points; Wherein, each pixel point is lit with the same brightness. Step S400: Calculate the difference Δt between two adjacent average brightness values in sequence, where Δt = L t+1 - L t ; Step S500: Obtain the minimum value of t when Δt / L t is less than ε, where ε is a positive number approaching 0; Step S600: Collect the brightness values of all pixel points of the LED display to be measured in a way of skipping t pixel points.

2. The method for measuring the brightness of display screen pixel points for eliminating crosstalk interference according to claim 1, wherein S200 includes: S201: Light the pixel points of the LED display to be measured in a way of skipping one pixel point with the same set brightness, and collect the brightness values of the lit pixel points in the selected rectangular area. S202: Replace the lit pixel points, repeat S201 until the brightness values of all pixel points in the selected rectangular area are collected, and calculate the average value to obtain the brightness average value L1.

3. The method for measuring the brightness of display screen pixel points for eliminating crosstalk interference according to claim 1 or 2, characterized in that, Collect the brightness values of pixel points through a luminance meter, a chrominance meter, an imaging luminance meter or an imaging chrominance meter.

4. The method for measuring the brightness of display screen pixel points for eliminating crosstalk interference according to claim 1 or 2, wherein the value of ε is less than one-thousandth.

5. A display pixel brightness measurement device for eliminating crosstalk interference, characterized in that, Including: The first acquisition module is used to collect the brightness values of all pixel points when all pixel points in the selected rectangular area of the LED display to be measured are lit, and calculate the average value to obtain the brightness average value L0. The second acquisition module is used to collect the brightness values of all pixel points when the pixel points in the rectangular area are lit in a way of skipping one pixel point, and calculate the average value to obtain the brightness average value L1. The third acquisition module is used to sequentially increase the number of pixel points at intervals, and so on, to obtain a series of brightness means L t ; t is the number of pixel points at intervals, t = 1, 2, …, n, where n is the set maximum number of pixel points at intervals; Wherein, each pixel point is lit with the same brightness. A calculation module, configured to sequentially calculate the difference Δt between two adjacent average brightness values, where Δt = L t+1 -L t ; An acquisition module for acquiring the minimum value of t when Δt / L t is less than ε, where ε is a positive number approaching 0; The fourth acquisition module is used to collect the brightness values of all pixel points of the LED display to be measured in a way of skipping t pixel points.

6. The display pixel brightness measurement device for eliminating crosstalk interference according to claim 5, characterized in that, The second acquisition module includes: The first acquisition unit is used to light the pixel points of the LED display to be measured in a way of skipping one pixel point with the same set brightness, and collect the brightness values of the lit pixel points in the selected rectangular area. The second acquisition unit is used to replace the lit pixel points, repeat S201 until the brightness values of all pixel points in the selected rectangular area are collected, and calculate the average value to obtain the brightness average value L1.

7. The display pixel brightness measurement device for eliminating crosstalk interference according to claim 5 or 6, characterized in that, Collect the brightness values of pixel points through a luminance meter, a chrominance meter, an imaging luminance meter or an imaging chrominance meter.

8. The brightness measurement device for display screen pixel points for eliminating crosstalk interference according to claim 5 or 6, characterized in that The value of ε is less than one-thousandth.

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