Development and application of wide dynamic camera technology

Development and application of wide dynamic camera technology

1. Development process of wide dynamic camera

The security industry is a rapidly developing market. Video surveillance shows the broad prospects and growth of this market. The video surveillance market includes cameras, monitors, digital video recorders, audio and video matrices, image processors and other products. Recent events around the world have promoted the growth of demand for video surveillance products, especially the demand for products with high-quality video images.

In the application of surveillance cameras, scenes with large light-dark contrast or backlight often appear. For security reasons, CCD cameras are installed indoors and outdoors where surveillance is required. Because there are often multiple lighting conditions in the same location, the lighting conditions in many places are a mixture of daylight and artificial lighting, and there are very large light-dark contrasts and backlighting at different times, such as in bank savings offices and entrances and exits of important places. Because the strong light from the window and the soft light from the fluorescent lamps on the ceiling may cause difficulties in capturing the indoor and outdoor scenes at the time, it is impossible to clearly capture the indoor and outdoor scenes with large contrasts at the same time. However, for the security industry, it is required to capture clear images without losing details under complex lighting conditions. Due to the limitations of the CCD photosensitive characteristics, ordinary cameras will have the situation that the background is too bright and the foreground is too dark, or the background is clear and the foreground is too dark, or the foreground is suitable for the background and too bright. Traditional cameras generally use backlight compensation technology or place two cameras indoors and outdoors to adapt to the large light contrast, but the effect is not ideal. In response to this situation, wide dynamic technology was born.

In 1977, Panasonic launched the first generation of wide dynamic cameras, which had a wide dynamic range of 40 times. In 1999, Panasonic launched the second generation of super wide dynamic cameras, which had a wide dynamic range of 80 times (48dB). In April 2005, Panasonic's third generation of super wide dynamic cameras came out, with a wide dynamic range of 160 times (54dB). At present, wide dynamic technology is mainly mastered by some large foreign camera manufacturers. Although the technical methods of each company are different, the principle of using CCD to achieve wide dynamic is basically the same. The main technology of wide dynamic is to use a special DSP (digital signal processing) circuit to expose the bright part with the most appropriate shutter speed, and then expose the dark part with the most appropriate shutter speed, and then perform DSP processing and recombine the two images so that both the bright part and the dark part can be seen clearly. This requires very high technology to minimize the loss of color and clarity. However, due to the characteristics of CCD, the wide dynamic range of the camera can reach a maximum of about 60dB.

In October 2005, Chihshang Company launched the ultra-wide dynamic camera ISD-A10 using Pixim's DPS imaging technology, which has a dynamic range of up to 120dB and has very good color reproduction and clarity. It marks a huge breakthrough in wide dynamic technology, and the new generation of wide dynamic cameras has taken a big step forward from a higher starting point.

2. Pixim's DPS technology super wide dynamic camera is launched

At the ASIS International Security Exhibition in Orlando, Florida, USA in September 2005, a new CMOS-based technology, Pixim's DPS Digital Pixel System®, gave people a refreshing feeling. Ikegami, a manufacturer of professional broadcast and CCTV cameras, launched its first Pixim DPS camera, HyperDynamic ISD-A10, which became the highlight of the exhibition. After the exhibition, it was widely welcomed by the banking and financial institutions in the United States and Europe.

The images below show a comparison between a Pixim camera and a regular CCD camera in the same scene.

This time, Ikegami combined its leading low vertical spot, backlight compensation, color adjustment and other technologies in the camera field with Pixim technology to launch the super dynamic ISD-A10 camera.

Pixim's DPS chipset is tightly packed and easily shaped to capture very high quality images in any lighting condition, in normal or wide dynamic range scenes. The consistency and accuracy of Pixim's imaging technology overcomes the defects of poor object recognition and poor image color reproduction when capturing actual images due to the constant change of light and the limitation of accurate color reproduction of objects when existing analog technology is used. DPS image sensors convert light signals into digital signals at each pixel, so that each pixel has an independent and optimized exposure time to produce high quality, high color accuracy images.

3. Pixim’s DPS Technology Background

Pixim has developed a patented DPS imaging technology that is superior to traditional CCDs, marking a breakthrough in the basic principles of imaging technology. DPS technology was developed in 1993 by Abbasel Gamal, a professor of electrical engineering at Stanford University, and his doctoral student David Yang (Yang Xiaodong), and was later licensed to Pixim, which was founded by Dr. Yang Xiaodong in 1999. Since then, Pixim has applied for 56 patents for DPS concepts and technologies, 42 of which have been effective.

DPS imaging technology has a revolutionary significance in the process of video camera capture and image processing. The use of this technology to shoot high-quality moving and still images exceeds any other existing technology. The so-called DPS platform combines image capture and processing in an optimized system, and Pixim's imaging system has unparalleled capabilities. Pixim provides a complete digital imaging system including an image sensor, image processor, camera reference design method, software and key algorithms, making it easy to develop cameras and form high-quality, advanced performance cameras.

4. Basic principles of Pixim’s DPS technology

The core invention of DPS technology is to convert the light signal into a digital signal at each pixel when capturing an image - from analog to digital converter ADC (analog-to-digital converter), so that signal attenuation and chromaticity and brightness crosstalk are minimized, so that the sensor provides the best and independent exposure times for each pixel. Once the data is captured in digital form, a variety of digital signal processing technologies are used to reproduce the best image. Even in high dynamic range scenes under extreme lighting conditions, accurate low-noise images can be taken.

Pixim's DPS technology uses a technique called "multi-point sampling" to collect information to achieve high-quality images and wide dynamic range. In a single capture frame (typically 50 to 60 times per second in video), each pixel is independently and non-destructively sampled multiple times. The imaging system determines the best sampling time and stores the pixel information before the pixel is saturated and can no longer hold additional charge. In the following diagram, the bright pixel is stored at time axis T2, the last sample time before it reached 100% saturation.

Dark pixels accumulate charge more slowly and will take longer until they are sampled and stored at T6. The stored information values ​​captured by each pixel (intensity, time, noise compensation) are processed in parallel and then converted into a high-quality image. In contrast, other technologies set an exposure time per frame and sample each pixel simultaneously, resulting in some images with underexposed pixels (too dark) and some overexposed pixels (too bright).

Pixim's first DPS-based product, the D2000 video imaging system, consists of a digital imaging sensor and a digital image processor. The digital imaging sensor and the digital image processor are very much like the human eye and brain, interacting in real time to capture the highest quality images possible. Just as a person walks into a dark room, the brain directs the pupil of the eye to look for light, and the digital image processor loads new codes into the sensor to change not only the exposure time but also the actual image capture calculation method. The result is the best image under special image characteristics and lighting conditions.

Because each pixel has its own analog-to-digital converter, the information generated is captured and processed independently, and each pixel plays a role in its camera. At the pixel arrangement position of the image sensor, the exposure time of each pixel is adjusted to handle the unique light conditions. A camera built on the DPS system platform actually has thousands of independent camera units, each of which creates the best image possible. These images are then combined to create a high-quality video frame or picture. As imaging technology continues to move towards fully digital systems, Pixim's DPS technology will provide the image capture and processing foundation for high-quality video cameras and still cameras.

5. Performance comparison between traditional CCD cameras and Pixim cameras

The development of PIXIM technology relies on a large number of digital-to-analog conversions to reduce the amount of bright flicker in the image. Each pixel is matched with a digital-to-analog conversion, so bright pixels reduce the exposure, and low-light pixels increase the exposure.

PIXIM technology facilitates wide dynamic range digital video. What you see with your eyes is not what you can capture, at least not with digital video. The biggest problem with using CCD image sensors is that the captured image is not as good as what your eyes see. The eye can automatically adjust to continuously changing light to see the best image. When the eye sees a scene that contains both bright and dark light, it can reduce its sensitivity to the bright areas and increase its sensitivity to details in dark objects and shadows.

A CCD sensor can adjust for both light and dark scenes, but not both at the same time. So when you carry the camera around the room, the exposure is good. But if you point the lens at a sunlit glass, the camera doesn't work very well. You can't see anything outside. Instead, bright objects in the foreground are drowned out by dark objects in the background. Everything in the shadows becomes black.

Limited light range does not affect the functionality of home video cameras and is often used in movies for artistic effect. But it makes this effect undesirable in the security camera market. If the bad guy hides in the shadows, you won't be able to identify him. If details in a brightly lit scene are lost, valuable clues may be lost.

PIXIM solves this problem with a new CMOS sensor technology, DPS. Even though the foreground is brightly lit, objects in the shadows are still clearly visible. Objects in brightly lit areas are not lost. The example of the dual-image comparison between PIXIM cameras and CCD cameras is vivid and convincing, and is considered reliable in the security camera industry.

In the photo below, you can see a PIXIM image sensor on the left and a Sony CCD sensor on the right. Since the CCD system is analog, it uses a crude three-phase assembly with many components. In contrast, the PIXIM system is digital and has a matching chip that sees and processes the image on a pixel-by-pixel basis. The included ARM-100 processor allows the camera manufacturer to choose PAL or NTSC output and dynamically adjust sensitivity.

Wide Dynamic Range (WDR)

Cameras based on Pixim can see the details of indoor images and outdoor environments, including pictures of bad guys. Cameras based on CCD cannot get any outdoor images, including people present.

Color Accuracy

Pixim-based cameras show better color fidelity and clarity. Note the difference in the color of the card table and cards, as well as the contrast of the text on the table.

Extreme lighting conditions

There is strong light in the jewelry store, but the Pixim camera is not affected by the strong light, and both indoor and outdoor images are clear.

White Balance

In any lighting situation, Pixim-based cameras produce images with higher color fidelity than cameras using other technologies. Even in typical (tungsten) lighting conditions, Pixim cameras display better image quality. CCD-based cameras have flaws in white balance and color accuracy. Notice how the Pixim camera captures all the details in the color image, the details on the shirt, and the color accuracy of the image on the wall.

6. Application of wide dynamic camera

There are many types of wide dynamic cameras in the surveillance camera market. Many products have developed from the first generation to the third generation. Their application scope is getting wider and wider and their use effect is getting better and better, such as the external business departments of banks and financial institutions, highway toll stations, hotels, office buildings and entrances and exits of important facilities and other places with large changes in light. However, many wide dynamic cameras now use synthesis technology. If the technology is not handled properly, it will cause poor image restoration ability, easy color distortion, double image, and unsatisfactory clarity. With the development of CCD wide dynamic technology and the application of new CMOS technology, camera manufacturers will bring more and better wide dynamic cameras to the market.

In CCTV monitoring systems, front-end cameras occupy a very important position. When choosing a wide dynamic camera, you should consider the following aspects:

1. Select the camera with parameters, indicators and functional requirements according to the actual application location and monitoring objectives.

2. Through sample demonstration, verify whether the marked product parameters, indicators, and functions are consistent with the product, and measure whether the clarity, wide dynamic effect, and color reproduction of the captured image are true.

3. Choose a camera with high reliability. After the monitoring system is built, if the quality and reliability of the camera cannot be guaranteed, and it needs frequent repairs and adjustments, or the image quality deteriorates or is damaged after running for a period of time, the loss to the user may exceed the cost of purchasing the camera.

4. A good camera should be equipped with a good lens to achieve the best effect.

The application of PiximDPS technology will undoubtedly bring vitality to the wide dynamic camera market, but whether the technology can be fully utilized depends on the technical strength of the manufacturer. Just like many manufacturers can use CCD devices to produce cameras, but the leading technology is still a few well-known brand manufacturers.

Pixim chip cameras, represented by Ikegami ISD-A10 camera, are not more expensive than traditional CCD cameras. Since its launch at the end of 2005, they have been widely recognized and praised after long-term use and observation by many users around the world.