What is a high-definition camera?

Abstract: HD camera has high sensitivity, high signal-to-noise ratio and minimal vertical tail level. Even in harsh environments, they can ensure the reproduction of realistic images. The specific technical conditions of HDTV itself determine the special requirements of HDTV lighting, which is characterized by soft light, uniform light distribution, small light ratio and strong perspective.

What is a high-definition camera? Solutions to technical problems of hdtv cameras.

What is a high-definition camera?

A high-definition camera is a digital camera that can shoot high-quality and high-definition images. The picture can reach the 720-line progressive scanning mode with the resolution of 1280*720 or the 1080 interlaced scanning mode with the resolution of 1920* 1080.

Hd concept

Maybe many people can only vaguely know 1080P or something. When I saw digital TV in advertisements, I always said that I supported the standard 1080i/ 1080P. Let's see what 1080i and 1080P mean. 1080i and 720p are internationally recognized standards for digital HDTV. Where the letter I stands for interlaced scanning and the letter P stands for progressive scanning. And 1080 and 720 represent the resolution that can be achieved in the vertical direction. 1080P is the highest standard home HD signal format at present.

High definition standard

With the development of society, high-definition video surveillance has developed rapidly, mainly to solve the problem that people can't see the details clearly in the normal monitoring process. High definition means high resolution. The definition of high definition first comes from the field of digital TV. HDTV, also known as HDTV, is the standard format of high definition television determined by the American Society of Motion Picture and Television Engineers. The definition of TV is measured by the number of horizontal scanning lines, and its centralized HD is divided as follows:

(1) 1080i format is a standard digital TV display mode, 1 125 vertical scanning line, 1080 visible vertical scanning line, 16:9, and the resolution is190.

(2)720p format is a standard digital TV display mode, with 750 vertical scanning lines and 720 visible vertical scanning lines, with a resolution of 16:9, progressive /60Hz and a line frequency of 45KHz.

Characteristics of high-definition camera

1, high image definition

High-definition IP network camera, using 5 million pixel progressive scanning CMOS image sensor, can achieve full real-time broadcast quality of 720P( 1280*720 resolution)/1080p (1920 *1080 resolution), which is much higher than the traditional CCD analog camera.

2. The system has strong environmental adaptability.

The system has an adaptive intelligent adjustment mode, which can automatically adjust the camera's aperture, gain, noise reduction and other parameters according to different light environments, and always maintain the most perfect picture effect. Because the system realizes the full digitalization of monitoring from acquisition to storage, the traditional phenomenon that the camera is directly affected by light changes will no longer exist. At the same time, the common video signal interference in line transmission will also disappear completely.

3, color reproduction is realistic

The video capture and compression chip used in the system is a world-famous brand from the United States, and it is also a provider of professional broadcast video capture chips such as Sony Panasonic. Color display is comparable to the color reproduction of professional 3CCD camera, and it has absolute advantages in image color fidelity, color information processing, wide dynamic range and system noise reduction.

4. Long system life

Because the system adopts CMOS image sensor, the power consumption and heat generation of the camera are low. The stability is also much higher than that of traditional analog cameras. At the same time, because the components are relatively simple, the failure rate is relatively low. POE power supply will be supported, and the power supply will be directly through the network cable, which solves the problem of on-site power supply.

Solutions to technical problems of HDTV cameras

For a cameraman who is already familiar with standard definition TV camera technology, in order to shoot high-quality HDTV programs, we must first understand the technical standards of HDTV and the characteristics of HDTV cameras, and then have superb HDTV camera technology and the ability to solve some technical problems in HDTV camera shooting. Such as: exposure problems, focusing problems, lighting problems, composition problems, etc. These technical problems are not very demanding in standard definition TV shooting, but they must be treated with caution and solved seriously in high definition TV shooting, otherwise the quality of high definition TV pictures will be affected.

First, the characteristics of high-definition cameras

The main difference between HD camera and SD camera lies in the scanning format, and others, such as appearance structure, switch setting and operation, are similar. Here are some features of Sony HDW-750CE HD camera.

HDW-750CE digital camera is a new member of SONYHDCAM HD program production series. As the pre-production equipment of 1080/50i HD programs, HDW-750CE is a brand-new pre-production equipment after HDW-F900 of 1080/24P, which is especially suitable for the requirements of China radio and television users. Its main features are as follows.

HDW-750CE adopts the most advanced 2.2 million pixel CCD, high quality 10 digital-to-analog conversion and the latest digital circuit processing technology (DSP), so they have higher sensitivity, better signal-to-noise ratio and minimal vertical tailing level. Even in harsh environments, they can ensure the reproduction of realistic images.

HDW-750CE can provide many advanced image processing functions such as multi-point color correction matrix, enhanced color temperature balance function, enhanced contrast control, enhanced brightness control and three-channel skin detail adjustment. These means enable the cameraman to fully reflect the director's intention through simple adjustment.

HDW-750CE has built-in HD-SDI output interface, which can meet the requirements of live playback of high-definition signals of camcorders. If optional down-conversion boards are used, they can also provide SDI and composite video signal output to meet the needs of many existing users.

Second, the definition of HDTV and standard definition TV is compared.

The definition of TV refers to the ability of the picture to reproduce the details of objects, that is, the ability to distinguish tiny adjacent areas and extremely detailed parts of objects of different colors. Clarity directly affects the picture quality of TV. The definition of TV picture is not only influenced by TV system equipment, but also by many factors such as illumination, contrast between light and dark, nature of light, direction of light and so on.

Whether it is high definition or standard definition TV, the most commonly used camera device in modern TV cameras is charge coupled device (CCD), which is a limited pixel camera device, so its definition is limited by the number of pixels. At present, the horizontal CCD pixels used by high-definition cameras are about 2000 (actually 1920 pixels), and those used by standard-definition cameras are about 1000 (actually, 980 pixels). Therefore, the horizontal resolution that the high-definition camera can achieve is 2K, and the standard-definition camera is1k. However, due to the limitation of transmission bandwidth, the resolution of the output signal of the high-definition camera is only 1.55K, while that of the standard-definition camera is only 0.64K Due to the limitation of technical level, the current practical high-definition video recorder adopts bandwidth limiting technology, and the actual horizontal resolution of the TV signal recorded by the high-definition TV camera is about1.25k..

Third, exposure technology.

The cameraman stands in front of the camera, facing the photographed scene, observes the reflected brightness and its distribution range of the photographed scene under certain lighting conditions, and then determines measures such as exposure, aperture size and gamma characteristics, and captures the most effective part of the brightness range of the scene on the interface of CCD to form a video image with saturated chromaticity and moderate brightness.

In actual shooting, the brightness range of the scene is sometimes very large, which exceeds the brightness range that CCD can accommodate. At this time, the correct exposure is the key to determine the image quality. Over-exposure, the picture becomes white or even limited, resulting in the loss of layering in the highlighted part of the picture. Insufficient exposure, less picture levels, especially the level of dark parts can not be actively reflected. For high definition photography, I think the correct exposure should be controlled within the range of 0.5 aperture.

The exposure value of a camera is generally determined by the zebra crossing and the automatic aperture in the viewfinder. However, in practical work, we found that the aperture detection value in the viewfinder of the camera is not completely consistent with the scale of the lens, which can not reflect the change of half-way aperture. Therefore, in terms of exposure accuracy, it is suggested to add standard monitors and oscilloscopes at the shooting site. Especially when shooting on location with high illumination, attention should be paid to keeping highlights.

1, adjustment of gamma characteristics

When shooting, highlights sometimes appear in the scene, which will exceed the dynamic range of CCD. The shot picture cannot reflect the texture of the scene at the highlights, so it is necessary to adjust the gamma characteristics to obtain the best exposure effect.

In the normal brightness range, CCD presents ideal linear photoelectric conversion characteristics, as shown in figure 1. The straight line in the figure represents the photoconductive characteristics. In a limited photoconductive range, the brightness of the scene is directly proportional to the output level, which can faithfully reproduce the brightness of the scene, and the reproduction value is always directly proportional to the brightness and tone of the subject. When the upper clipping level (0.7V) or the lower clipping level (0V) is exceeded, the brightness and tone of the scene will suddenly be blank or darkened again. The linear part of the photoconductive curve rises steeply, which means that the brightness range of the subject is narrow and the dynamic range (film tolerance) is limited or low.

The arc represents the gamma characteristic. The gamma characteristic is a curve characteristic formed after being processed by a nonlinear circuit (gamma correction circuit), and the photoconductive characteristic after being processed by the gamma correction circuit presents a nonlinear characteristic, especially the highlight part of contrast compression enhances the photosensitivity (from dotted line to dotted line), and the slope processing of the highlight part is called inflection point processing in high-definition camera technology. The high-definition camera adopts precise digital processing circuit, and the cameraman can accurately adjust the gamma characteristics of the camera by setting the menu to realize different exposure intentions, thus controlling the tone level and high-definition degree of the picture.

2. Determine the reference tools of exposure value.

We can observe and adjust the exposure value through the color monitor and oscilloscope, so as to make accurate exposure at the shooting site. This is an effective measure to ensure the picture quality of HDTV. Therefore, it is very important to adjust the parameters of the monitor and oscilloscope.

Adjustment of display. In order to adjust the color, we must first input the color bar signal into the monitor. As we all know, the blue component is distributed in the four bars of white, yellow, blue and green on the left side of the color bar signal. In the standard 75% color bar, the amplitudes of the corresponding blue signals in these four color bars are exactly the same. Generally speaking, there is only one blue button on the display. When we press it, only the blue signal will be displayed on the screen. We only need to adjust the chromaticity so that the corresponding four bars have the same brightness. In this way, the display can accurately reproduce the color and tone of the picture.

Adjustment of brightness and contrast. Brightness level is to adjust the black level, and contrast adjustment is to turn on the brightness level. When the brightness level is adjusted, the brightness signal rises or falls as a whole. If we don't adjust the brightness correctly, the signals may overlap in bright or dark areas, and the details can't be distinguished. On the contrary, if we enlarge or reduce the contrast, the base point of the dark part is fixed and the brightness of each color bar changes.

In order to adjust the brightness signal, it is necessary to input three-level adjustment signals (PLUGE), including -3% black, 0% black and +3% gray. When adjusting, we make the two stripes of -3% black and 0% black relatively the same, but we must see the gray stripe of +3%, which is the correct brightness signal.

Contrast adjustment, in fact, there is no corresponding strict standard, we can adjust it to a suitable degree according to the environment and feeling. However, high contrast may reduce the corresponding clarity. Each monitor has a corresponding preset contrast value. Just adjust the contrast value to this position.

Oscilloscope provides a series of images of narrow-angle exposure meter readings, which accurately expresses the brightness of the corresponding objects. It is relatively easy to install an oscilloscope. We set the black level to 7.5IRE on the oscilloscope. This indicates that the darkest main tone is 7.5IRE instead of 0.0IRE.

Secondly, exposure value decides the scene. We arrange the brightness signal of 18% gray board at 50IRE unit, and realize it by setting the aperture of the camera to ensure that the illumination intensity is appropriate to the aperture value of the camera. To set the aperture, we can use the gray board or calculate the exposure coefficient equivalent of the camera in advance according to the incident light exposure meter. So we get the black level of 7.5IRE and the aperture value of the scene. For the highlight part of the scene, you can set the inflection point of the camera to be at 100IRE. In short, to set up an oscilloscope, you must first set the black level to 7.5IRE and expose the gray to 50IRE. Then through illumination or inflection point processing, the important high brightness falls on the 100IRE unit of the oscilloscope.

Fourth, focusing technology.

It is a common problem that the focus of high-definition camera is not easy to focus. In fact, the focus problem of HD is caused by the high definition of HD, because the resolution of HD is high, the horizontal field of view is larger than that of SD, the picture contains many scenes, and the depth of field is much smaller than that of SD, so you should be extra careful when focusing.

When shooting on location, the viewfinder of a high-definition camera is the same as that of a standard-definition camera, and it is indeed more difficult to find an accurate high-definition focus than a standard-definition camera. If the cameraman is not sure, it is recommended to use a standard monitor, the bigger the better.

In order to get the best clear image when shooting HDTV, the focusing technology of HD camera is different from that of SD camera. The correct focusing method is as follows:

When shooting a high-definition still lens, the zoom lens should be zoomed to a certain focal length (that is, a suitable scene) and used as a fixed focal length lens. Then, what kind of focal length should be used for shooting, and the focus should be directly focused on the appropriate focal length until the image of the subject in the viewfinder is the clearest, or until the scale value indicated by the focus baseline is just equal to the focal length value directly measured with a tape measure.

When shooting a still lens in standard definition, the zoom ring is often used to zoom the lens to the maximum focal length and focus it accurately, and then switch to a preselected short focal length for shooting. This method is not suitable for the focusing requirements of high-definition camera technology, because there is a small amount of image surface drift when the zoom lens zooms, and the best focusing position under different focal lengths is not necessarily the same. In addition, when using the push-pull zoom lens, it is easy to accidentally touch and change the focus position during the zooming process after focusing. Therefore, in order to get the clearest image of the subject when shooting in high definition, it is necessary to focus on the used focal length directly and accurately, otherwise the focus of the picture will become soft and affect the clarity of the picture.

Verb (abbreviation of verb) lighting technology

The clarity of TV pictures is not only affected by the aperture and depth of field caused by illumination, but also by the contrast between light and shade and the nature of light.

It is worth noting that the clarity of the picture does not depend on the brightness of the whole picture and the use of a lot of illumination light. The key is to use moderate contrast between light and shade and corresponding light properties.

1, contrast and clarity

The ratio of the brightness of the brightest part to the darkest part on the TV screen is called contrast. When the contrast is large, the image is black and white, and the contrast between light and dark is large. The clarity of TV pictures is related to the contrast of lights. The contrast of lighting is not only the contrast between the subject and the background, but also the contrast of the subject itself in different light directions. If lighting makes the picture more gray (the number of different levels that can be distinguished from the brightest to the darkest), then the TV has stronger ability to display image details, higher definition and better quality.

The contrast between the subject and the background is handled by lighting. In general, the subject is brighter than the background. Because too bright background will not only distract people's attention, but also darken the subject, and the three-dimensional sense and details of the dark area will be poor, and the clarity will inevitably decrease. The contrast between light and shade should also be controlled correctly against the light irradiation in different directions on the subject, so that the tone levels of the brightest and darkest parts can be fully reflected. Any transition between dark and bright will hide the details of the image and blur the picture. For HDTV, the contrast between light and shade is more important.

2. Influence of light characteristics on image clarity

The clarity of objects on HDTV screen is not only related to the contrast of light, but also related to the nature of light. The softness and hardness of light properties also have a great influence on the clarity of object appearance. It is worth noting that the choice of lighting properties is determined by the surface structure of the object, that is, the light properties used by the object are different with different surface structures. Generally speaking, the surface of rough objects should be irradiated with strong light; Smooth surfaces should be illuminated with soft scattered light. When shooting on TV, we will find that the scenery shot on cloudy days looks dull because there is no shadow, and the surface texture disappears. Once an object is reversely illuminated by sunlight, the outline of the object will immediately stand out. The nature of visible light has a great influence on the clarity of the picture.

As far as the overall effect of the picture is concerned, because hard light can outline the scene and the texture is very obvious, we feel a strong sense of space. However, soft lighting tends to produce dull images without three-dimensional sense, so it can't provide the best definition.

However, judging from the local effect of the picture, it may be that the contrast between light and dark caused by strong light is too large, which reduces the ability to reproduce the details of the object. On the contrary, the delicate tone levels caused by soft light can improve our ability to distinguish the details of objects, so we feel the picture is clear. High-definition camera lighting should use soft light, which is very beneficial to improve the clarity of the picture.

In short, there are many factors that determine the clarity of the picture. The choice of light, hardness and lighting direction should be based on the key points and scenes we want to highlight to improve the clarity of the picture.

3. Lighting characteristics of HDTV

The specific technical conditions of HDTV itself determine the special requirements of HDTV lighting, and its characteristics are as follows:

The light should be soft. Soft light should be used for lighting, and strong light should be used as little as possible. Especially the human face, it is best to use soft scattered light. You can add a soft light sheet or gauze in front of the spotlight to soften the light.

The light should be evenly distributed. Is that the light in the performance area should be uniform. When lighting, the light from different directions shines on the performance area, and the illumination of the light from the same direction should be consistent, so as to ensure the consistency of the color tone of the front and rear images when the camera changes position for continuous shooting. Therefore, the uniformity of TV lighting refers to the consistency of illumination and contrast in the performance area.

The light ratio is small. Small light ratio is to adjust the relative brightness ratio between the object and the background, the object itself in different directions, and the relative brightness ratio between different objects in the picture. The light ratio of HDTV lighting is generally 2: 1 ~ 3: 1, but it will increase or decrease with different light angles and the key points we need to highlight. The light ratio of HDTV lighting is smaller than that of movie lighting.

Strong sense of perspective. In other words, the perspective of the picture is strong. Of course, the perspective is related to many factors. However, high-definition TV lighting must pay attention to the change of color tone and color tone, and pay attention to the expression of three-dimensional, layered and spatial sense, which is the remarkable feature of high-definition lighting different from standard-definition lighting.

Sixth, the characteristics of picture composition

In terms of picture composition, HDTV and SDTV are basically very similar, with only a few small differences, one of which is the difference of frames, that is, the frame problems of 16:9 and 4:3. If you want to shoot HD and broadcast HD, you must pay attention to the frame structure of the composition. When HDTV is down-converted to standard definition TV (16:9 frame changes to 4:3 frame), there are three modes: mailbox mode (black edges will appear on the upper and lower parts, and the effective picture range will be narrowed), compression mode (horizontal compression will deform the picture, but the whole information will appear on the screen), and cropping mode (information on the left and right sides will be removed, and the picture content will be incomplete). China audiences are used to the mailbox mode.

For the framing problems caused by 16:9 and 4:3 frames, if the cameraman can identify the range of 4:3 framing, he can shoot with 16:9 high-definition camera, which is more convenient to generate a complete 4:3 image. This problem is usually solved by adding a 4:3 logo frame in the camera viewfinder. In addition, due to the use of 16:9 mode, it is also quite different from the conventional 4:3 mode in lens processing. The larger the viewing angle in the horizontal direction, the longer the object that causes horizontal movement stays on the screen. Considering the visual experience of human eyes, the cameraman may be required to speed up the panning speed of the camera lens to speed up the lens rhythm.

Seven, TV movie picture quality adjustment technology

If you want to shoot the picture effect of a TV movie with a high-definition camera, you must first know what the picture effect of the movie is like. Compared with TV, the details of movie pictures are softer and more natural, and the gray transition is smoother, so the levels are richer. In the high-light part of the image, because the film is wider than the TV, the detail level of the high-light part is largely preserved, while in the low-light area, the compression range is larger. It seems that the whole picture is gloomy.

Through the comparative analysis of the film picture effect and the camera picture, we can purposefully use the powerful picture adjustment ability of the camera to create the film picture effect.

1, tone and contrast adjustment of the picture

You can improve the hue and contrast of the picture by adjusting the gamma menu. Adjust the parameters such as black level, black gamma, main gamma, inflection point, slope and white-cut level, and customize a most matching gamma curve for the scene brightness relationship of each lens, so that the brightness interval of the scene can be compressed or expanded to the full available dynamic range of CCD in the most appropriate proportion.

Adjust the main black level appropriately, and set it at around-10~- 15 when shooting outdoor scenes during the day, and set it at around 0~4 when shooting night scenes or indoor scenes. Of course, the setting parameters should be determined according to the specific requirements of the plot. Then adjust the main black gamma, reduce some black gamma levels appropriately, realize the local tone compression of dark areas, and increase the expressive force of dark areas. This setting can ensure that the dark part has enough density. Secondly, adjust the main gamma to -20~-50, and smooth the middle gray tone, so as to enrich the color saturation and gradation of the straight line area. After choosing the appropriate gray transition, you need to adjust the corresponding color reproduction, which can be done in the MATRIX menu item.

For the highlight part, properly adjusting the increase of inflection point and the decrease of slope, and adjusting the level of white cutting according to the requirements of the picture can expand the range of tone modulation and accommodate as many highlights details and levels as possible.

Through the above adjustment, the tone of the picture can be adjusted to a degree very close to the film effect. Especially the dark gray transition part of the picture is almost the same as the movie picture. The difference of highlights is obvious, but if the focal plane is used on the camera, the effect will be obviously improved. As for the difference in depth of field, we can make up for it by increasing the aperture of the corresponding gear or using a lens with a long focal length.

2. Adjustment of contour definition

Because the photosensitive unit on CCD is separated in the horizontal direction and the vertical direction, it transmits image information in two directions through sampling, so that when the image is reproduced, the black-and-white abrupt change in the horizontal and vertical directions becomes blurred, and at the same time, the image details become blurred due to the reduction of the amplitude of high-frequency signals, which is also called aperture distortion.

Aperture distortion is characterized by only high frequency amplitude reduction and no phase distortion. So it must be corrected by a special circuit, which is the contour enhancement circuit. By increasing the steepness of the rising edge and falling edge of the image signal, the contrast of the sudden change of black and white in the image can be enhanced, and even the edge of the image can be drawn, thus improving the clarity of the image outline. The contour enhancement circuit can obviously improve the contour clarity of the scene in the picture. The HD camera is equipped with detail switches and menu adjustment items.

When shooting HDTV, some people turn off the outline definition switch on the camera in order to soften the picture, so as to achieve the picture effect close to the film. We feel that if it is a close-up shot with people, HD is very prominent for people's faces and clothes, and it is easy to give people a stiff feeling. In this case, you should turn off the outline definition switch. But you don't have to do this for landscape pictures, because the focus of high-definition is soft, and then turn off the outline definition switch, the picture will appear more blurred than film. The necessary contrast enhancement of contour details is still necessary. The key is how to grasp the scale. Generally, the parameter value of contour definition is controlled between 30 and 75. Here's the rule. If you want to take a panoramic view or a sun scene, raise it a little. If you take close-ups or night scenes, you should turn it down. Especially in low illumination, we find that the contour definition value is improved and the clutter is also improved, which needs special attention.

We are still trying and exploring the application of high-definition camera technology. We believe that with the development and maturity of high-definition camera technology, TV cameramen will keep pace with the times with the progress of camera technology, accumulate experience in creative practice, and move towards a new realm of technology and art.