TV tuning table. Horizontal color stripes

It is safe to say that almost every one of our readers more than once watched incomprehensible splash images at the end of TV programs. During prophylaxis, they can be found even in the daytime. What are these "funny pictures", and what are they for? ..

Fig. 1 Table 0249

Fig. 2 EIA Resolution Chart

Fig. 3 BBC table

Fig. 4 Table from Philips test generator

Fig. 5 Chess field

The problem of evaluating and comparing the quality of various electronic equipment arose, perhaps, before the appearance of this equipment itself. With regard to television technology, this problem is solved with the help of special measuring and test tables... So what are the most important types of test images we know? The first type is the so-called Resolution Charts or resolution tables. Their main purpose is to evaluate the resolution of TV or video cameras, displays, televisions, television / cinema sensors and the entire transmitting and receiving path as a whole. A typical example is the well-known table 0249 (Fig. 1), which has long been used by domestic television as a screensaver. Another example is the EIA Resolution Chart (Fig. 2), which is the de facto standard for evaluating resolution, developed by the Association of Electronic Engineers in 1956 for the same purpose.
It is this table that we use to assess the resolution in tests of video cameras and video recorders. With the help of a vertical target located symmetrically above and below the center of the table, it is possible to measure the resolution of the camera directly in the TVL.
The horizontal quality of the aperture corrector can be assessed using a horizontal wedge. For a more accurate hardware assessment of the signal level corresponding to a frequency of 200 TVL, the table contains a number of special zones filled with vertical and horizontal strokes, with a resolution corresponding to 200 TVL. To assess geometric distortions and resolution at the edges of the image, four combined targets are used, inscribed in concentric circles located at the edges of the table. Evaluation of dynamic range and system performance automatic installation It is very convenient to conduct expositions on the fragments of the gray wedge inscribed in the central circle of the table. The electronic version of the table can be downloaded at: http://www.bealecorner.com/trv900/respat/EIA1956-v3.zip
Arising at the very beginning of television broadcasting (naturally, black and white), when the problems of correct focusing and geometric distortions were in the foreground, these tables were focused on controlling and adjusting these particular parameters. The circles in the center and at the edges of the screen, filled with vertical and horizontal wedges, allow for a fairly accurate assessment and adjustment of the deflection and focusing systems of the transmitting camera and television receiver. From other parameters of the path, they can be used to evaluate the transmission of the so-called gray wedge - the ability of a camera or TV receiver to correctly reproduce the full dynamic range of a scene and the accuracy of setting gamma correction schemes.
With the advent and massive distribution of color television, it turned out that the capabilities of traditional black-and-white tables are completely insufficient. First of all, this is due to the much more complex structure of the full color signal and the need to evaluate and adjust a much larger number of specific parameters. In addition, it became obvious that it is practically impossible to solve the problem of quality control of the equipment and receivers of color television by simply filming a table printed on paper or film. It's time for electronic test sheets.
Let us explain. The test signal, which creates the image of the table, is not filmed by the transmitting television camera, but is synthesized electronic device(generator). Such test signals do not suffer from the specific distortion introduced by the transmitting television cameras. They allow not only subjectively assessing the image quality directly on the TV receiver screen, but also using special equipment to measure the characteristics of the video channel. Electronic test charts contain elements that allow control and adjustment of individual components of a color TV. There are many variations of test charts developed by associations of radio engineers, radio electronics firms, and television broadcasters. Naturally, the table format is determined by the standard of the transmitted TV signal, therefore appearance tables used for NTSC, PAL or SECAM systems will differ slightly from each other. For example, in fig. 3 you can see the test chart used by the BBC, and in fig. 4 is a table obtained from a PHILIPS test generator; it is this table that is used by most of the broadcast TV channels around the world. The universal table (UEIT), shown in Fig. 6 is well known to most of our readers. We see it on our screens during broadcast breaks. In addition, there are many more highly specialized measuring signals, such as a grid field for checking the convergence of beams, a checkerboard field (Fig. 5), etc.
And now, using the example of the familiar “our” universal table, let's see what can be seen and understood with its help. For the convenience of notation individual elements tables are designated horizontally by letters and vertically by numbers. So, what parameters of video equipment can be assessed using a measuring table, just by eye, without any measuring devices.

1. Image size

Fig. 6 UEIT

As an attentive reader may remember, a few years ago, one curious advertisement quite lucidly explained that on the TV receiver screen we see much less of what is actually transmitted. In reality, the image on the screen is cropped by 10-15% compared to the transmitted signal. The standard frame size is set according to the reference lines available in the table, which are aligned with the edges of the picture tube frame. The accuracy of setting the aspect ratio can be assessed by the squares and circles in the table.

2. Geometric distortion

Geometric distortions of the image are caused by the nonlinearity of the signals generated by the line and vertical scan generators. Let's say right away that most modern TVs, thanks to the proven circuitry, practically do not have any problems with this. The nonlinearity of the sweeps can be assessed by the type of circles included in the table, which, in the presence of distortions, take the shape of an ellipse. The amount of nonlinearity can be quantified if desired. To do this, it is enough to measure the aspect ratio of a square, which, due to nonlinear distortions, can turn into a rectangle.

3. Convergence of rays

The correctness of the static convergence of the rays of the color kinescope can be checked by the white cross shown on the gray background in the center of the table. In the presence of static convergence of rays, the image of a white cross does not contain colored borders. The white grid areas in the corner areas of the table are used to control dynamic convergence across the entire screen margin.

4. Image resolution

Fig. 7 VHS VCR

Fig. 8 S-VHS VCR

The resolution of the image is easy and convenient to estimate from strip 13 (Fig. 5), in which 7 groups of strokes are formed. These dashed stripes are created by bursts of sinusoidal voltages with frequencies approximately corresponding to 200, 300, 400 and 500 lines. At the same time, the section of the highest frequency is located in the center, and groups low frequencies... With their help, the resolving power of the luminance channel is estimated. To assess the clarity of the image along the edges of the raster in small circles, there are groups of vertical strokes corresponding to 300 and 400 lines. Look at what remains of the resolution after recording this table on a VHS video recorder (Fig. 7) and S-VHS format (Fig. 8).
In lane 9 of the table, from column f to column u, there are three groups of paired color strokes - magenta-green, yellow-blue, and red-cyan. The color fidelity is evaluated with these colored strokes. It should also be noted that the strokes in stripe 13 on a color TV screen can acquire a color called moire.

5. Setting brightness, contrast and white balance estimation

This is perhaps the most popular part of the measurement table. It is on it that you can set the correct brightness and contrast of the received image.
In line 8 of the table, there is a gray scale containing fragments with different brightness. This area is for setting the contrast and black level. Adjust the brightness and contrast controls so that all parts of the gray scale are visible in the image. In an extreme case, it is considered acceptable to merge two adjacent fragments in the area of black and dark gray colors. The gray scale is also used to control and adjust the white balance. When the balance is adjusted correctly, all grayscale tones remain neutral gray and do not acquire any color.

6. Evaluation of reflected signals

7. Correctness of reproduction of the color of the image

Fig. 9 Color distortion when detuning the matrixing scheme

The correctness and accuracy of color reproduction is ensured by setting the signal matrixing circuit and the color burst system in the television receiver. To control color rendering, two rows of colored rectangles (stripes 6-7 and 14-15) are intended in sequence: white, yellow, cyan, magenta, red, blue and black.
The rectangles in the top row (lane 6-7) should have a color saturation of about 75%, and the bottom row (lane 14-15) should have a saturation of 100%. The colors of the rectangles can be distorted when the matrixing scheme is detuned ( possible variant in fig. nine). Loss of color sync can cause loss of color. In the same area, the clarity of color transitions is assessed. The transition between green and magenta is particularly problematic.

8. Interlaced scanning

Fig. 10 One of the possible types of interlaced scanning distortion

The accuracy of interlaced scanning can be judged by the type of oblique lines located in sections 11, g – j and 10, q – u of the table. The presence of kinks means that the lines of adjacent frames are partially overlapped. As an example, Fig. 10 shows one possible type of interlaced operation distortion.

9. Multi-contour and trailing continuations

To assess this type of distortion, contrast marks (narrow stripes; white on black and black on white) are used in zones 10 and 11 f – u of the table. Interference arising from, for example, poor antenna matching is clearly visible against the contrasting background of these areas; in the absence of interference, the marks remain clear and single.

10. Evaluation of the linearity of the chromaticity channel characteristics

A signal that creates a wide line in the 12 f – u bandwidth of the table, smoothly changing color from green to magenta, serves to evaluate the linearity of the chroma channel response. The absence of any visual distortion or additional tint indicates good linearity.

Of course, in one small note it is impossible to tell about the great variety of television measurements. Today we have casually touched this huge interesting world... Now, in connection with the rapid spread of systems with compression, the question of assessment rises again to its full extent. And here our good old static measuring tables and signals are already bad helpers. New transmission technologies require new assessment and measurement techniques. And there is no end to this circle. But that's a completely different story.

A test picture with several test zones is used here. With this image, you can adjust the five basic parameters of the image on your TV or monitor. The Ladies image is in the set of test images, the link to the sweep will be at the bottom of the article.

Before adjusting, you must turn off all enhancers and other functions on the TV that affect the image. The image can be connected via USB from a flash drive, if you use another source, for example, a computer, then look at the correspondence of the signal parameters at the source output and at the TV input. The size, scan and frame rate must be the same. You also need to install the TV in the place where it will constantly work and turn on the light source that will work when watching the TV set.

This test has several zones that can serve as a visual reference for the image. To get the best picture quality on your TV, you only need to make these five settings:

Aspect ratio, screen boundaries.
Brightness.
Contrast.
Color.
Clarity (focus).

Adjusting the borders of the image (overscan)

In the picture, you can see tips (arrows) at the edges, so these arrows should be fully visible and the tips just touch the edge of the screen. If not correct setting size, not only will the image be cropped, but the clarity will also decrease. On the TV, the menu items affecting the picture boundaries (Zoom) can be called: pixel to pixel, Full Pixel, Just Scan, Pixel-to-Pixel, Original, Overscan, etc.

Below are pictures of how an incorrectly selected scaling can affect the clarity of the picture:

Brightness

With the correct brightness setting, look at the grayscale at the top of the Ladies picture. All 32 shades should be visible and have a clear border.

In the figures below, the areas where the incorrect brightness setting is visible are outlined in red. Or the brightness is too low, then the black grayscale merges into one. Or the brightness is large and the grayscale in the light areas merges.

Contrast

After adjusting the brightness, we look at the same gray scale. If in the light areas we see the merging of individual areas into one, then adjust the contrast in the TV. With the correct settings, we should see all 32 grayscale sections. As you can see, an incorrect contrast setting affects the display of human skin. When the contrast level is too high, areas with a negative appear on the skin.

Sometimes it happens that after adjusting the contrast, you need to go back to adjusting the brightness and then check the contrast again.

The following picture shows too low level contrast ratio of the TV.

Color

The quality of display of human skin is very indicative for the correct color adjustment. It is necessary to find a balance when everything is correct with the color in the dark areas and the light areas will not be dull. Sometimes for image quality it is better to set a lower color saturation, it will be more natural. Of course, too low color should be avoided.

When adjusting the color, you still need to make sure the quality of the white color. The areas of the test pattern where there is white should be white. If there is any color cast, then it is wrong.

Also notice the small contrasting areas on the color bar. You should see them, they are controlled by color saturation. These squares should stand out against the background.

Definition

The clarity of the image can be checked well in the area where the two stripes intersect. These lines should appear without halos or shadows. Typically, the factory defaults are already correct and rarely need to be adjusted at home.

Gamma

This adjustment parameter is not found in every TV. But if it is, then you need to check its correct setting. To check the gamut, use a color strip and an image of girls.

Conclusion

It is necessary to carry out such settings immediately after purchasing the TV. Still, there are situations when the device is so bad that any adjustments cannot improve the image quality.

Examples of

Universal Electronic Test Chart (UEIT)

Designed for testing color TVs operating in the SECAM standard with a screen aspect ratio of 4: 3. UEIT was developed by the candidate of technical sciences N.G.Deryugin and the engineer of the State Research Institute of Radio (NIIR) V.A.Minaev. The informal name is "color prophylaxis table" (TCP). Experimental broadcasts from the Ostankino television tower (at that time - the All-Union Radio and Television Transmitting Station named after the 50th anniversary of October, ORPS) began in 1970. Based on their results, the table was finalized, and since 1971, the second version, UEIT-2, was broadcast on the air and via communication lines. Main parts:

The grid field is the background of the table. Allows you to customize the convergence of rays, and also visually breaks the table into rows and columns. In the center of the large circle there is an additional crosshair for centering the image and also for adjusting static convergence, and in small ones - as a reference point for adjusting dynamic convergence;
Table border - fiducial marks for setting the image size;
Circles to control the geometric distortion of the raster. To check the accuracy of the aspect ratio adjustment, you can measure the side lengths of the square in the center;
Color bars at 75% saturation (lines 6-7) and 100% (lines 14-15) for color control. With an oscilloscope with selection separate lines it is possible to adjust by them instead of a separate generator of color stripes;
Gray scale (8th line) - to set brightness, contrast, white balance and black level;
Contrasting color stripes (line 9) to adjust the clarity of color transitions;
Smooth color transition (12 lines) to check the linearity of the chroma channel. In some implementations there is a full spectrum, in others there is a transition from green to magenta;
Vertical strokes on the 13th line, as well as in the small circles (lines 3,4,17,18) for evaluating the resolution and dynamic focusing. They are formed by bundles sinusoidal signals frequencies 2,3,4 and 5 MHz, correspond to the resolution of 220, 330, 440 and 550 lines.
Oblique stripes in 10-11 lines for control of interlaced accuracy;
Contrast marks in the same lines to control stretching continuations (caused by a malfunction of the TV outlines and also when several TVs are connected via a video output via a low-quality cable) and repetitions (caused by an unsuccessful design or antenna location);
Alternating black and white squares (line 16) - for evaluating the frequency response of the video path for all channels;

TIT-0249

A black and white test chart designed in 1949. There were two ways of transmitting TIT-0249: shooting with a TV camera from a graphic original or reproduction using a monoscope. Currently, it is practically not used by TV channels, but sometimes it is used to assess the resolution of video cameras.

TIT-0154

This table was created in 1954 specifically for the then experimental color television system with sequential color transmission. It is described in and. The use of this table, as well as the experimental system itself, was soon discontinued.

EIA Resolution Chart

Developed in 1956 and has become a kind of test chart standard

Notes (edit)

TV test chart- 143. Television test pattern Test pattern D. Fernsehtestbild E. Television test pattern F. Mire de télévision Normalized image, the elements of which are used to control and evaluate the parameters and characteristics of the image ... ... Dictionary-reference book of terms of normative and technical documentation

A special image reproduced on a picture tube screen for adjusting television equipment and assessing the quality of a television image. Represents a slide, a drawing (for example, on the target of a monoscope) or formed electrically ... encyclopedic Dictionary

TV test chart- tikrinamoji televizijos lentelė statusas T sritis radioelektronika atitikmenys: angl. television chart; television test pattern vok. Fernsehtestbild, n rus. TV test chart, f pranc. mire de télévision, f ... Radioelektronikos terminų žodynas

The test table is used to control the parameters that characterize the quality of the television image. T. and. so it is performed on a special card, on a transparency, in the form of a frame on film or applied to an aluminum plate of the Monoscope. ... ... Great Soviet Encyclopedia

- (test table), an image of a drawing, as a rule, having the form of various geometric shapes of a known shape, brightness and color placed in a certain order, which serve to assess the quality television channel(including TV) and ... ... Encyclopedia of technology

TV test chart- 1. Normalized image, the elements of which are used to control and evaluate the parameters and characteristics of the image of the broadcast television path or links of the broadcast television path Used in the document: GOST 21879 88 Television ... Telecommunication vocabulary

digital TV test chart- Normalized image, the elements of which are used to assess the parameters and characteristics of the television image at the output of the digital channel of broadcast television or its parts. Note The table can be electronic, optical and ... ... Technical translator's guide

On a color TV screen, a black and white image should be reproduced with the same quality as on a black and white TV screen with the same size screen. If a black and white image on a color TV screen is reproduced with distortion and turns out to be colored in any colors, then these distortions will necessarily worsen the parameters of the color image. Therefore, before evaluating the performance of a color TV when receiving a color image, you must first make such an assessment when receiving a black and white image. Monitoring the quality of a black and white picture allows you to avoid errors that arise when evaluating the parameters of a TV when receiving real color images containing many color shades and often transmitted with different color effects.

For this purpose, to test color televisions, you can use the black and white television test chart TIT 0249 (Fig. 1). According to the TIT 0249 test chart, you can control and adjust the parameters of a color TV and a black-and-white image displayed on its screen, such as, for example, synchronization stability, scanning frequency, geometric distortion, image size and linearity, centering, focusing, static and dynamic convergence of the kinescope beams , badan white.

Fig. 1. Television test table TIT 0249

The TIT 0249 test chart allows you to evaluate the clarity of the image in different parts of the screen, to detect stretching continuation and repetition, to identify the presence of frequency and phase distortions.

It is also possible to check the stability of synchronization, the operation of the sync pulse selectors and adjust the frequency of the master scanners during the transmission of real subject images. It is useful to check the frequency of the sweep master oscillators when receiving images transmitted by various telecenters and on various channels with different quality signal. At the same time, it is possible to adjust the natural frequency of the master oscillators of the TV so that, with their existing capture bandwidth, the images of all received television centers are well synchronized. Due to the poor performance of the sync pulse selectors, some of the lines in the TIT 0249 test table, on which its darkest details are transmitted in the BG and E squares, as well as in the upper edge of the table, may be shifted relative to the general image boundaries. For the same reason, frame synchronization stability may be reduced.

Fig. 2. Geometric distortions of the raster of the type: a - trapezoid; b - parallelogram; c - barrel; g - pillow

Geometric distortions such as trapezium, parallelogram, "barrel" and "pillow" (Fig. 2) are estimated from the image of the TIT 0249 test table with preliminary reduced dimensions so that all four corners of this table are visible. If the distortion is noticeable, then it (except for the distortion of the parallelogram type) can be corrected by the controls available on the TV. Pillow or barrel distortions are corrected by changing the inductance of the inductor and the resistance of the variable resistor in the pincushion distortion correction circuit. Distortions of the trapezoid type are corrected by changing the inductance of the halves of the coil, connected in series with the horizontal coils of the deflection system (OS), or by shunting one of the personnel coils of this system with a resistor with a resistance of 27-100 Ohm.

The aspect ratio and size of the picture must be adjusted so that the numbers 2-7 in the six squares A and E are visible and located at the top and bottom edges of the screen. At the same time, the letters BVGD in all squares 1 and 8 must be behind the side edges of the screen. This requirement must be observed due to the fact that the aspect ratio of the screen of the 59LKZTs and 61LK1Ts color kinescopes is 5: 4 (due to the technology of their manufacture), and according to the existing television standard, an image with an aspect ratio of 4: 3 is transmitted. After correct adjustment of the format of the size and linearity of the image, the dimensions of all the squares of the TIT 0249 test chart should be the same and they should not turn into rectangles in some parts of the screen, and the circles in the center and in the corners of the table should have the correct shape. If the distortions are noticeable, then the vertical linearity of the image is selected by the regulator, the knob of which is located on the rear wall of the TV, and the horizontal linearity - by rotating the magnet in the line linearity regulator (radar) located in the scanner.

The centering of the image should be made so that the top, bottom and side edges of the TIT 0249 test table are symmetrically located relative to the corresponding edges of the screen, and the center of the table - a small circle located in the corners of squares B4, G4, B5 and G5, is approximately in the center of the screen.

Centering the image vertically and horizontally is done by two regulators available in the scanner.

You can control the operation of the AGC system and approximately estimate the sensitivity of the TV by switching the antenna cable from the 1: 1 jack to the 1:10 or 1:30 jack. During normal operation of the AGC, the contrast of the image in this case should not change much, and with sufficient sensitivity of the TV, noise should only appear in the image in the form of swarming strokes and dots, similar to snow. The AGC system is configured by regulators located in the radio channel block.

Focusing of electron beams is considered good if the lines forming a raster are clearly visible, and the lines of concentric circles in squares B2, B7, D2, D7 and in the center of the test table have approximately the same thickness. In case of poor convergence of rays, the thickness of each of the routed lines is estimated. The focus control is brought out through a hole in the back of the TV.

With the correct adjustment of the APCG device on all received channels, the image clarity, even with poor convergence of the kinescope beams, is high and no interference appears on it in time with the soundtrack.

Checking device operation automatic shutdown the color channel is reduced to switching the TV from the reception of the TIT 0249 test chart to the reception of a color image on another channel and vice versa. With stable operation of this device, color interference should not appear on the TIT 0249 test table, while the color image should be reproduced steadily, without shutdowns, flickers, changes in brightness.

The static and dynamic convergence of the kinescope beams is considered satisfactory if the separation of the horizontal and vertical lines of the TIT 0249 test table at the edges of this table does not exceed 3-5 mm, and in the center of the screen is zero. Static convergence of the beams in the center of the screen is achieved by rotating the permanent magnets on the convergence regulator mounted on the tail of the deflection system and the lateral shift magnet of the blue beam. Dynamic convergence is performed by correcting the shape of the currents flowing through the coils of the convergence regulator using variable resistors and by changing the inductance of the coils in the convergence unit. After a large correction of the static convergence, the centering of the image may change slightly and the purity of the primary colors of the CRT may be disturbed.

Difficulties in the control and adjustment of static and dynamic information according to the TIT 0249 test table arise due to the small number of intersecting vertical and horizontal lines in it.

The primary colors, starting with red, are checked by extinguishing two of the three beams of the kinescope with switches on the chromaticity unit. In the image of the TIT 0249 test chart, each of the primary colors must have a uniform color throughout the entire field. The purity of the primary colors is adjusted by rotating the flat ring magnets located on the tail of the kinescope and by axially displacing the deflecting system. First, having achieved a pure red color across the entire screen, the purity of green and blue colors is checked. After adjusting the purity of the primary colors, the static convergence of the rays in the center of the screen is corrected.

The brightness adjustment, the setting of the black level and the estimation of the number of reproducible gradations of brightness are carried out according to the vertical and horizontal gradation bands located respectively in the squares VZ-GZ, V6-GB and B4-B5, D4-D5. Each of the stripes consists of ten rectangles with a stepped transition from white to black. An operational regulator on the front of the TV is used to adjust the brightness so that on the darkest strip the beams of the kinescope go out, and on the next strip they barely glow. The more rectangles in the gradation bands differ in brightness, the more halftones are reproduced in the image and the better it is in quality. Since usually in color TVs 6-8 gradations of brightness are viewed, it is permissible to set the brightness so that two rectangles of the tone strip are black. This makes it possible to obtain black when receiving different images, in the signal of which the black level is not strictly the same.

The correct black level should be set with the on-line dimmer in the middle position. This can be achieved by adjusting the dimmer setting in the chroma block. If this is not done, then it will not be possible to compensate for the drift of the black level arising from the drift of the parameters of the video amplifier, picture tube and instability of the incandescent voltage. If the black level is set incorrectly, so that black in the table is reproduced as gray, then the colors in the image will be diluted with white and appear low saturated. If black occupies three grades of brightness, then the reproduced colors will be oversaturated.

Checking and adjusting the static and dynamic white balance is carried out using the gradation stripes in the squares VZ-GZ, V6-GB and B4-B5, D4-D5. With a static white balance, as a result of the luminescence of three phosphors, the total white color is formed only for one combination of the intensity of three rays, that is, at the same brightness level, when only one of the rectangles of the gradation stripes is not colored. With good dynamic white balance, all tone bar rectangles from the darkest gray to the brightest whites have no noticeable coloration. To check the dynamic white balance, the operational regulator changes the contrast from minimum to maximum. With this dynamic of brightness change, the white balance must be maintained at all brightness levels.

The static and dynamic white balance is adjusted by changing the initial voltage on the modulators and the constant voltage on the accelerating electrodes of the kinescope using adjusted and variable resistors in the color and scan units. After adjusting the static and dynamic white balance with the adjusting brightness control in the color block, they ensure that the required black level in the image is achieved with the middle position of the operational brightness control located on the front of the TV. Difficulties in controlling and adjusting the static and dynamic white balance according to the TIT 0249 test chart arise due to the small size of the gray tones rectangles in the gradation bands in relation to the screen field.

It is possible to detect stretching continuations and repetitions that arise due to the reflected signals received by the antenna and generated in the antenna cable by the black rectangles located in the squares DZ, D6, E4-E5 and EZ-E6 of the TIT 0249 test table, When receiving reflected signals antenna or when they are formed in the cable, after the black rectangles, repeats (or shadows) will be visible. Repetitions and shadows are also noticeable near the numbers and letters located in the white squares and circles of the TIT 0249 test table.

In the presence of frequency and phase distortions in the TV brightness channel near the black rectangles in the squares DZ, D6, E4-E5 and EZ-E6 of the TIT 0249 test table, repetitions (shadows) from these rectangles are visible. In the formation of the end-to-end frequency and phase characteristics of the luminance channel, the video amplifier of the luminance channel and the intermediate frequency amplifier (IFA) are involved. Therefore, by changing the position of the spectrum of the received luminance signal relative to the frequency response of the UPCHI, it is possible to introduce predistortion into this spectrum, due to which the total distortion of the luminance signal will be corrected in one direction or another. It is possible to change the position of the spectrum of the luminance signal on the UPCHI characteristic by varying the frequency of the local oscillator of the channel selector in the manual setting mode.

If repetitions and shadows near the black rectangles of the TIT 0249 test chart are formed due to distortions in the brightness channel, then when the frequency of the local oscillator of the channel selector changes, these repeats and shadows will change their length and brightness. In the case when long and gray repetitions and shadows are observed, the bandwidth of the luminance channel is narrow, and the amplification of the lower frequencies of the luminance signal spectrum is insufficient (the local oscillator frequency is lower than necessary). When repetitions and shadows look like a white edging near the black rectangles of the TIT 0249 test chart, this indicates that the high-frequency part of the luminance signal spectrum is predominantly passing through the UPCI (the local oscillator frequency is higher than the optimal one). If, when the frequency of the local oscillator changes, the distance between the parts and their repetitions in the TIT 0249 test table does not change, then such repetitions are formed due to the reception of reflected signals by the antenna or due to the formation of these signals in the antenna cable.

Evaluation of the correctness of interlaced scanning is carried out using oblique lines in the squares BZ and B6 and along the horizontal wedges in the central circle of the test table TIT 0249. Due to poor interlacing ™, the oblique lines become jagged, and the diverging lines inside the horizontal wedges begin to bend up and down like a fan. Interlaced scanning can be poor due to the limitation of the vertical sync pulses in the UPCHI when the AGC is incorrectly adjusted, as well as due to inaccurate setting of the frame rate using the regulator displayed on the back of the TV.

It is possible to quantify the clarity of the image in the horizontal direction (the resolution when the kinescope beams move along the line) using vertical wedges in the central circle and in small circles in squares A7, A8, B7, B8 and D1, D2, El, E2 of the TIT 0249 test table. The numbers next to the section of the wedge, in which the lines begin to merge, characterize the clarity of the image.

The clarity of the image in the horizontal direction may be reduced due to poor focusing and poor convergence of the kinescope beams, due to inaccurate adjustment of the APCG system and local oscillator in the channel selector, as well as due to the presence of repetitions and stretching sequels. The clarity of the image vertically (the resolution when the kinescope beams move along the frame from top to bottom) can be estimated by the horizontal wedges in the large circle and in the small circles in the squares A1, A2, B1, B2 and D7, D8, E7, E8 of the TIT 0249 test table. Image clarity in the vertical direction may deteriorate due to poor focusing and convergence of the CRT beams and due to interlacing.

The signal of the TIT 0249 test table is taken from the photocathode of the transmitting television tube, onto which the image of the table is projected from the slide. Therefore, this signal contains nonlinear and geometric distortions due to the peculiarities of the scanning devices of the transmitting camera. In addition, due to imperfection of the focusing of the transmitting tube, finite resolution, different local sensitivity of its photocathode and uneven illumination of the slide, the image of the TIT 0249 test chart is characterized by uneven brightness and clarity.

To control and correct the parameters of a color TV and the image reproduced on its screen, it is better to use a test table formed from electrical signals - a universal electrical table UEIT (Fig. 3). This table does not really exist and is formed only on the TV screen. At the same time, a number of distortions arising from the transmission of real images using a transmitting camera are absent.

Fig. 3. Universal TV test table UEIT

The UEIT test chart can be used for subjective (visual) and objective (using instruments) control of the main parameters of color televisions and parameters of black-and-white and color (according to the SECAM system) television images. The UEIT test table provides the ability to control and correct the following parameters: image format; stability of synchronization and sweep frequency; geometric distortion; clarity of the image; reproduction of gradations of brightness; stretching sequels and repetitions; the correctness of the interlaced scan; setting the black level; image centering settings; convergence of rays; dynamic white balance; focusing the image.

In addition, the UEIT allows you to detect the presence of frequency and phase distortions of the brightness channel, as well as adjust the APCG device and the AGC system.

Along with this, UEIT makes it possible to control and correct such parameters of a color television image as color fidelity at different brightness levels, color clarity, setting "zeros" of frequency detectors, quality of color transitions, matching the levels of brightness and color-difference signals on the control electrodes of the receiving tube, time coincidence of luminance and color-difference signals.

The UEIT test table has a rectangular shape with a width to height ratio of 4: 3 and contains a frame of alternating black and white (respectively, black and white levels) rectangles in horizontal rows 1 and 20 and in vertical a and e of minimum and maximum brightness. They are used to control the operation of amplitude selectors of sync pulses (synchronization stability) in televisions and video control devices (VCU). Due to incorrect operation of the selector, vertical lines in the image become broken. The same phenomenon, accompanied by synchronization instability, is observed with an increase in the signal due to the limitation of synchronizing pulses in the UPCHI stages with poor AGC operation.

The UEIT test chart has a grid of 17 horizontal and 25 vertical white lines. The grid field is used to control the linearity of the sweeps, the convergence of the rays of the color kinescope and distortions in the form of multi-contour (repeats). A dark vertical line on a white rectangle (square 10e) and a light vertical line on a dark rectangle (square 11k) can also be used to check for distortions in the form of multi-contour. If the APCG device is incorrectly configured, the lines become fuzzy or become edged. Sections 10e - x and 11e - x are intended for checking distortions in the form of stretching continuations. Vertical grid lines are created by pulses with a duration equal to two elements of the decomposition of a television image. Horizontal white lines are caused by the flashing of two adjacent lines.

Most of the horizontal 13 - from b to u (Fig. 3) serves to check the horizontal clarity. It contains seven groups of black-and-white strokes, which correspond to signals of frequencies 2.8; 3.8; 4.8; 5.5; 4.8; 3.8; 2.8 MHz. Frequencies 2.8; 3.8; 4.8 and 5.5 MHz correspond to approximately 200, 300, 400 and 500 lines of definition, determined by the test chart TIT 0249. On a color TV screen, these black and white strokes can acquire additional coloration created by signals from them falling into the chrominance channel ...

Inside the large circle on the horizontals 10 and 11 in the sections e - c there are white, gray and black rectangles, which serve to control distortions in the form of stretching continuation and repetition. In the presence of such distortions, the brightness of gray in the sections 10l - m and 11l - m will not be the same and not uniform. If these distortions occur in the antenna and its cable, then when manually adjusting the local oscillator frequency in the channel selector, the stretching continuation and repetition do not change their appearance. If such distortions are due to the unevenness of the frequency and phase characteristics of the luminance channel, then when the frequency of the local oscillator is varied, the stretching continuation and repetition change in nature and intensity.

In sections 3, 4gg and cch; 17, 18gd and tsch are vertical black-and-white strokes, which correspond to signals with a frequency of 3 and 4 MHz. They are used to control the sharpness of the table corners and focus the electron beams.

A scale is located horizontally 8g - q, which is created by a step signal. It controls the reproduction of brightness gradations, dynamic white balance, as well as the installation of "zeros" of frequency detectors of color-difference signals. When correct installation"Zeros" the gray scale should not change its color shade when the color block is turned on and off. To install them, the red and green (and then blue and green) beams of the kinescope are covered. By adjusting the contour of the frequency detector of the blue (red) channel, the brightness of the sections of the horizontal 8 of the blue (red) color is equal

I am with the color block turned on and off.

Sections 8e and d are used to set the black level. The signal level corresponding to section 8d is 3% higher than the black level. First, by adjusting the brightness of the image, it is achieved that the difference in brightness is noticeable in sections 8d and 8d. Then it is reduced until both of these areas turn black.

The center of the UEIT test table is formed by the intersection of the horizontal white line at the border of the squares 10, 11n, o with the vertical line dividing the sections n and o. These lines serve for static convergence of the beams of a color kinescope and for centering the image.

To assess the quality of interlaced scanning, a diagonal light line is located in sections 10c - x and 11e - k.

Correctly interlaced, the line has no kinks or bends.

On a color TV screen in horizons 6, 7 and 14, 15, color bars of different brightness and saturation are reproduced. They are designed to assess color fidelity at different brightness levels and to control the primary colors of the TV (horizontal 14, 15). Less saturated color bars on horizons 6 and 7 can also be used to check the correction of predistortion, color-difference signals at video frequency (visually by reproducing transitions from one color to another).

On a color TV screen, in the horizontal 9 inside the circle, colored strokes are reproduced for visual verification of color clarity, which corresponds to a pulse frequency of 0.5 MHz. Green-purple strokes - section 8e-k, yellow-blue strokes - section 8l-r and red-blue strokes section 8c-x. The yellow-blue strokes control the operation of the luminance channel delay line and the temporal coincidence of the luminance and color-difference signals. If these signals do not coincide in time, a brown tint appears on the yellow strokes. It is also possible to control the adjustment of the high-frequency predistortion correction contour by color strokes. With the correct adjustment of this contour, the color of the yellow-blue and red-blue strokes approximately corresponds to the analogous colors of contours 6, 7. If the yellow and red strokes lose their color, this means that the specified contour is set to a higher resonant frequency, if the blue and cyan strokes lose their color, then - to a lower frequency.

On a color TV screen, a continuous color change from green to magenta with a transition through white (gray) in the middle of the strip is reproduced in the horizontal part of 10 from e to x. Using these signals, it is possible to control the drift of zeros and the linearity of the amplitude-frequency characteristics of detectors of color-difference signals. When the zeros leave, the gray is not in the middle of the strip: but with poor linearity, the color change is uneven and its saturation at the edges of the strip is not the same.

On sections 16b-u there are alternating black-and-white squares, which, together with sections 14, 15 b-u, serve to control and set the correspondence between the levels of the brightness and color-difference signals. The control is carried out with the chromaticity unit turned on by comparing the brightness of the luminous sections of the horizontal lines 16 and 14, 15 with the two beams of the kinescope turned off.

For control, turn off the "blue" and "green" electron beams of the picture tube. If the brightness of red in sections 16 and 14, 15 is the same from b to u, then the red signal level corresponds established level luminance signal. Compliance is achieved by changing the level of the red signal, increasing or decreasing the saturation of this color, or by changing the level of the luminance signal, increasing or decreasing the contrast.

Then turn on the blue and turn off the red beams of the picture tube. If the brightness of the blue color in sections 16 and 14, 15 is not the same from b to u, then the blue signal level does not correspond to the luminance signal level. The level of the blue signal is set by changing the saturation of that color while maintaining the level of the luminance signal. If, when the level of the blue signal changes, the necessary correspondence of the brightness of the blue color between sections 16 and 14, 15 does not work, then the level of the luminance signal is changed. However, after that, repeat the operation to set the red signal level.

To help you determine the resolution of video cameras, as well as to test other components of the video system, a special test chart has been developed.

We have tried to make it as accurate and informative as possible, and while it can be used to test broadcast equipment, it should not be considered a substitute for the various test charts designed for broadcast TV. This table should only be used for CCTV systems and as a guide for comparing different equipment and / or transmission media.

The table presented in this article has been modernized and has several differences from the table in the previous edition. The additions are mainly concerned with white lines, which will allow you to check if a person can be recognized at a certain distance. This procedure is based on the recommendations of the VBG (Verwaltungs-Berufsgenossenschaft): Installationshinweise fur Optische Raumuber-wachungs-anlagen (ORUA) SP 9.7 / 5.

Using this table, you can check many other parameters of the video signal, primarily the resolution, but also the bandwidth, linearity of the video monitor, gamma correction, color reproduction, load matching and reflection.

Before you start testing

The first thing you should do to improve the quality of your camcorder's image is to choose a very good lens (the resolution of which is much higher than that of the CCD itself). To control the optical resolution of lenses, fixed focal length lenses with manual iris are the best choice.

Short throw lenses with viewing angles over 30 degrees should be avoided as they can produce spherical distortion. Good choice for 1/2 "CCD camcorders there will be 8, 12, 16 or 25mm lenses. For 1/3" CCD camcorders, it is better to use 8, 12 or 16mm lenses.

A longer focal length will force you to mount the camcorder further away from the test chart. A photographic tripod is recommended for this purpose.

For testing the resolution of a video camera, it is better to choose a high quality black and white video monitor, since its resolution reaches 1000 TVL in the center.

Color videos monitors acceptable only if their quality matches or is close to the quality of video monitors broadcasting television. To meet this quality, a video monitor must have a horizontal resolution of at least 500 TVL. It is clear that black-and-white video cameras with a horizontal resolution of more than 500 TVL cannot be tested using such video monitors, but they are quite suitable for testing most color video cameras (with a resolution of up to 480 TVL).

Installation procedure

Place the chart perpendicular to the optical axis of the lens. The video camera must "capture" the table completely, exactly up to the yellow triangular arrows. To do this, you must switch the video monitor to "undescan" mode, and then you will see 100% of the image.

If you do not have such a video monitor, then dotted line along the perimeter of the table indicates a 10% narrowing of the view - this is close to what a regular video monitor would show. However, for permission checks, this is not entirely accurate. If you only have a standard video monitor, there is a little trick you can do.

Mount the camcorder on a tripod as close as possible to display the entire table. Set the V-hold control on the video monitor so that the vertical blanking pulse (horizontal black bar between the TV fields) is visible. You should set V-hold to such a position to get a stable horizontal bar somewhere in the middle of the screen. Then try to adjust the position of the camcorder on the tripod and / or lens so that the top and bottom positional triangles of the test chart touch the border of the black bar. Once you have adjusted the vertical position of the video camera, you can easily adjust the horizontal position as well, since the image of the test chart is in the middle of the video monitor screen. Now, and only now, can you take accurate data from the test table.

Light the table with two opaque incandescent bulbs (about 60W each) on both sides so that there is no glare on the table. It would be nice if the lamps have dimmers, since in this case you could check the minimum illumination of the camcorder. Naturally, in this case, this procedure should be carried out indoors without additional light. If you need to test the camcorder's performance at low light levels, you will need to purchase an accurate light meter. ( This method measuring the minimum illumination will not provide high measurement accuracy, since when you adjust the brightness of incandescent lamps, their emission spectrum changes. Approx. ed.)

Mount the camcorder on a tripod or bracket at a distance that allows you to clearly see the entire test chart. Make sure the tips of the arrows touch the edges of the full image or the black horizontal stripe if you are using the alternative method above.

Set the lens aperture to the middle position (F / 5.6 or F / 8) as this is the best optical resolution for most lenses, and then adjust the light to obtain the full dynamic range of the video signal. To do this, you need an oscilloscope. Do not forget to turn off all video processing circuits in the video camera under test, that is, AGC, electronic shutter, backlight compensation (BLC).

Make sure the load is matched, that is, the camcorder is loaded into 75 ohms at the end of the coaxial line.

What can you test?

To check the resolution of the video camera (vertically or horizontally), you must determine the point at which the four lines inside the circle, forming a sharp triangle, merge into three. This is the point that corresponds to the limit value of the resolution; it can be read from the table. A line-selectable oscilloscope is required to determine the horizontal resolution more accurately, as with broadcast equipment.

If you need to check the video bandwidth, read the megahertz value next to the last clear group of lines where you can see black and white lines.

The fine concentric lines in the center of the test chart square can be used to adjust focus and / or back focus. Before starting the adjustment, check exact distance between the video camera and the test chart. In most cases, this distance should be measured to the plane of the CCD. Although some lenses indicate the distance relative to the front of the lens.

Replaying a circle will only show you the linearity of the video monitor, since CCD cameras are not geometrically distorted by their design. Sometimes linearity is easier to check by measuring the vertical and horizontal length of the 6 x 6 squares to the left of the focus square.

The wide white and black stripes on the left side have a double function. First, they will show you if the wave impedance or there is a reflection of the signal, that is, white flooding into the black area (and vice versa) is a sign of signal reflection from the end of the line. These same strips can be used to test long cable quality, VCR playback, and other transmission or playback media. Second, you can determine if the camera / lens combination provides enough detail to recognize activity (intrusion or attack). To do this, the video camera should be positioned at such a distance that it can see a 3 m wide area in the plane of the test chart. If at the same time you can distinguish between the stripes, then the combination of video camera / lens you choose is good at detecting activity. It is clear that if it is possible to distinguish between the stripes near the number 1, then this is better than in the case of the stripes with the number 2.

White oblique stripes with right side have a purpose similar to that of the thinner stripes on the left side. If you can distinguish the lines next to the green letter C, or, even better, with the letters B and A, when the video camera is at a distance that allows you to see an area 1 m wide in the plane of the table, then you will be able to recognize a person at the same distance. A is better than B and B is better than C. This test can be used to determine if the selected camera / lens combination provides sufficient image detail. Even more valuable and informative is the evaluation of the playback quality of a hard disk recorder, since CCTV does not have objective methods for determining the quality of compression / decompression.

A color photograph of three kids will give you a good flesh color indicator, so if you are using a color camcorder, you can check the color temperature of the light source and the camcorder's auto white balance, if available. In this case, the color temperature of the light source must be taken into account, which in the case of an incandescent lamp is 2800 ° K.

For a more accurate color test of your camcorder, use the scale at the top of the test chart. The colors of this scale correspond to the color bars produced by a conventional TV test generator. If you have a vectorscope, you can check the color reproduction on a single scan line of color bars. As with any color reproduction system, the color temperature of the source is of great importance and in most cases it should be natural light.

The gray background exactly corresponds to 30% gray and, together with the grayscale at the bottom, can be used to check the gamma correction of the video camera / monitor system. The grayscale is linear, in contrast to some logarithmic scales. Linear scale was chosen because most modern camcorders have a linear response, making it easy to set up different levels on the oscilloscope. The grayscale can also be used to set the optimal contrast / brightness for the video monitor.

To achieve best setting video monitor, you need to do the following.