ISP processing chip technology and function analysis

HD monitoring requirements

High-definition monitoring means a greater amount of data, regardless of the enormous challenges brought to the coding chip, coding algorithms, network transmission, and storage systems. Thanks to continuous breakthroughs in these related fields, high-definition IP monitoring has been realized, and Develop and apply quickly.

According to SMPTE (American Society of Motion Picture and Television Engineers) standards, high-definition IP surveillance systems must meet the following requirements: Resolution requirements. That is, it needs to reach 1280×720/progressive or 1920×1080/interlaced/progressive. Frame rate can reach full frame rate. Better image color fidelity. 16:9 format.

Therefore, high-definition IP not only means a significant increase in the effective pixels of the sensor, but also real-time video, fidelity with high image color, and aspect ratio imaging with a 16:9 aspect ratio.

There are many design solutions for high-definition IPC, but from the architectural point of view, there are mainly two: First, the use of CCD / CMOS sensors as image acquisition equipment, supporting the provision of image processing and encoding SOC chip; Second, the use of front-end camera module The group is coded and transmitted as an image acquisition device and a general-purpose ASIC or DSP. Due to the flexibility of the first architecture, it is widely adopted by manufacturers. There are three implementations of image processing.

The first scheme adopts an integrated ISP coding chip. The flexibility of the scheme is inferior to the first scheme. The dedicated ISP processing chip has high stability, but the image quality is general and the cost is high.

The second scheme uses a dedicated ISP processing chip and an encoding processing section. The solution is more flexible. The dedicated ISP chip has good stability and can guarantee the quality of the image.

The third scheme adopts chips such as FPGA to realize signal processing and coding functions. This solution has the strongest flexibility, but has poor stability, high cost, and difficult to guarantee image quality.

The dedicated ISP solution is flexible in design, cost-effective, and can guarantee the quality of the image. It is suitable for the design of high-definition IPC.

ISP processing chip

ISP (imagesignalprocessing) refers to a video signal processing chip, which is generally implemented by a specialized ASIC or DSP. Usually, the sensor part is equipped with an embedded image processing chip to handle some simple functions, while the more complex 3A (ie, auto exposure, auto white balance and auto focus), WDR and other functions must pass through the back-end ISP. Processing to get a good image effect.

Take NXP2400 of Nextchip's high-definition multifunctional ISP chip as an example, this chip can be applied to the design of 1.3M/2M HD-SDI camera, high-definition analog camera and high-definition IPC. Its internal integrated 8-bit fast 8051MCU, 64MSDRAM and X-RAM on the chip. The chip has I2C, UART, SPI and other communication interfaces, and has timer, PWM, interrupt and other functions, and can be compatible with the standard 8051MCU.

The NVP2400 can directly receive raw video signals or LVDS signals. After preprocessing by the ISP, the chip can output composite analog signals and BT656/BT1120/YC16bits video data streams.

Analysis of chip characteristics

Unlike some dedicated ISP chips that only support a single Sensor, it can seamlessly connect with multiple Sensors, including Panasonic's MN34031PL, Sony's IMX036LQR/LLR, Aptina's MT9P031, and Omnivision's Ov2715 series CMOS.

The NVP2400 supports a variety of image preprocessing functions, including 3A processing, lens distortion correction (LSC) processing, brightness adaptive ACCE ie wide dynamic, 2D/3D digital noise reduction, dead pixel detection DPC, false color correction, color roll suppression, 64-times electronic zoom/picture-in-picture, day and night conversion, motion detection MD, privacy masking, custom OSD and other functions.

2D/3D digital noise reduction

Noise reduction is an important part of Camera's ability to obtain high-quality images. The 2D noise reduction function of the NVP2400 can effectively reduce the plane and edge noise. When expressing moving objects, the NVP2400 can effectively eliminate 3D noise, ghosting, and smearing through operations based on the comparison between the previous frame of image and the information between the current image pixels.

ACCE(adaptivecontrastandcolorenhancement)

ACCE (High Contrast Brightness/Color Adaptive Function) is a type of Wide Dynamic Technology (WDR). The NVP2400 can enhance the visibility of the entire screen by effectively adjusting the high contrast and brightness/color of the edge portion according to the visual characteristics of the human eye to the high-luminance area.

DEFOG defogging function

In a foggy or rainy environment, the camera may be blurred and the dynamic range may be degraded. Because under normal circumstances, the Sensor can receive multiple levels of brightness, but in the case of fog, the brightness level of the image is covered by fog. The NVP2400 improves brightness distribution by analyzing the luminance histogram of each region, which effectively enhances the wide dynamic range of the fogged image.

ColorInterpolation color algorithm

Because the color filter used by the Sensor is arranged in a Bayer arrangement, the color information in the acquired information is incomplete and must be guessed from the surrounding pixels to compensate for the lack of signal, which is called tween processing. Different from the general bilinear interpolation algorithm, the NVP2400 adopts a diagonal interpolation algorithm, which can eliminate the color distortion of the image generated by the linear algorithm and further improve the resolution of the image details.

Conclusion

High-definition IPC for video surveillance in security applications has more advantages than traditional analog cameras and ordinary network cameras, such as high-definition, megapixel sensors, more video information, and progressive scan CCD/CMOS Technology can make the picture-in-picture more clear, natural and smooth, without mechanical moving parts, more durable, greater visual coverage and so on.

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