What Is CoaXPress?
CoaXPress, the standard for high data rates
The CoaXPress (or CXP for short) standard was originally launched by 6 companies from the industrial image processing industry. The aim was to develop a fast data interface that could also transfer a large amount of data over greater distances. The first CoaXPress interfaces were presented at the leading trade fair for industrial image processing: "Vision" in Stuttgart in 2008. After three more years of development, CXP 1.0 was officially released as a standard in 2011. Since then, the standard became established in industrial image processing, eventually advancing to CXP 2.0 in 2021.
An interface according to the CoaXPress 1.0/1.1 standard supports data rates of 6.25 Gbps (per channel). The current CoaXPress 2.0 standard specifies double the transfer rates of up to 12.5 Gbps (per channel).
Which application areas benefit from CoaXPress?
A major advantage of the CoaXPress interface compared to other standards is therefore the high data rate. But also the greater distances that can be bridged between the camera and the PC are valuable for many applications and offer possibilities even for very sophisticated image processing solutions. Especially in the semiconductor industry, CoaXPress is very popular. In 3D AOI systems (automated optical inspection), for example, large amounts of data must be realized with high resolution without significant latency. Other areas of application can be found, for example, in print inspection, food inspection, traffic technology (ITS) or medicine.
Interface comparison - CoaXPress vs. USB/GigE
Let's look at two well-known interfaces—USB and GigE—to illustrate a special feature of CXP.
The USB 3.0 interface has established itself as a reliable option in industrial image processing. The USB3 Vision standard relies on this interface, which is also gaining increasing mass market acceptance. Thus, all laptops, PCs, tablets, and smartphones now have a USB 3.0 interface.
Gigabit Ethernet (GigE) has been an established standard in industrial image processing since 2006. Based on the number of installed applications, GigE is currently the most widely used interface technology for industrial digital cameras.
USB 3.0 and GigE have the advantage of not requiring any additional integration of plug-in cards in the PC. By contrast, the CoaXPress standard relies on a corresponding plug-in card inserted in the PC for data transfer. This is because CoaXPress, unlike USB or GigE, is not already part of the standard PC. The plug-in card also saves CPU load: without a special plug-in card, the high data rates typical of CoaXPress would put a heavy load on the CPU just to transfer image data.
Upgrade to CoaXPress 2.0
After comparing the basic differences between individual interfaces, we will now take a closer look at the CoaXPress 2.0 standard. An interface according to the CoaXPress 1.0/1.1 standard supports data rates of 6.25 Gbps (per channel) while the CoaXPress 2.0 standard specifies transfer rates that are twice as high—up to 12.5 Gbps (per channel).
What distinguishes the interface card from the frame grabber?
While either option could be used as the plug-in card to connect a CoaXPress camera to the PC, each provides certain benefits based on your application needs.
The term “frame grabber” originated in a time when the analog video signal first had to be digitized in the PC. Nowadays, the image is already digitized on the camera sensor and then transferred to the PC in digital form. Therefore, the frame grabber only provides the digital interface (GigE, USB, Camera Link, CoaXPress) and stores the image data temporarily. Some frame grabbers can also perform pre-processing of the data, e.g., binning or scaling. The data is written directly to the main memory via Direct Memory Access (DMA) without going through the PC's processor, significantly reducing the load on the CPU. The image data from the frame grabber is usually accessed via special software for image processing (e.g., Halcon) or standardized interfaces such as GenICam. The configuration effort and costs for a frame grabber system are comparatively high but are worthwhile in applications requiring data pre-processing.
In contrast to the frame grabber, an interface card is fairly simple. It completely dispenses with pre-processing, instead it only accepts image data from the camera connection and stores it directly in the working memory. Again, this bypasses the CPU via DMA to reduce the load on the CPU. By omitting the image processing on the interface card, the costs and configuration effort for this are lower compared to a frame grabber.
Features | Interface card | Frame grabber |
|---|---|---|
Preprocessing of the image data (e.g. scaling) | No | Yes |
CPU relief via DMA | Yes | Yes |
Standard drivers/interfaces (e.g. GenICam) | Yes | Mostly |
Interfaces to image processing software (e.g. Halcon) | Yes | Mostly |
Installation and configuration effort | Low | Medium |
Costs | Low | Medium |
Заключение
Передача больших объемов данных на высокой скорости и на большие расстояния стала реальностью благодаря стандарту CoaXPress 2.0 в промышленной обработке изображений. Этот новый стандарт для систем компьютерного зрения был разработан как преемник широко распространенного интерфейса Camera Link и также требует установки дополнительной интерфейсной платы на ПК. Однако это не является недостатком: так предотвращается чрезмерная загрузка центрального процессора, что позволяет полностью освободить его ресурсы для решения задач обработки изображений. Кроме того, помимо передачи больших объемов данных, интерфейсная плата принимает на себя задачи предварительной обработки изображения.
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