Glossary related to video capture

1. SDL (similar to DirectX)

SDL (Simple DirectMedia Layer) is an open-source cross-platform multimedia development library written in C language. SDL provides several functions for controlling images, sounds, and outputs, developers can use the same or similar code to develop applications across multiple platforms (such as Linux, windows, and Mac OS X. Currently, SDL is mostly used for developing multimedia applications such as games, simulators, and media players.

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2. v4l (video4linux)

Video4linux (simple v4l) is the kernel driver for video devices in Linux. It provides a series of interface functions for Video device application programming, these video devices include popular TV cards, video capture cards, and USB cameras. For USB port cameras, the driver must provide basic I/O operation interface functions such as open, read, write, and close.

Implement interrupt handling, memory ing, and ioct1, the control interface function of the I/O channel, and define them in struct file_operations. In this way, when an application calls a device file such as open, close, read, and write, the Linux kernel accesses the functions provided by the driver through the file_operations structure. For example, when an application reads a device file, the kernel calls the READ function in the file_operations structure. To drive USB camera headers on the system platform, first compile the USB controller driver module into the kernel statically so that the platform supports the USB interface, and then use the camera to collect data, use insmode to dynamically load the driver module, so that the camera can work normally, and then proceed to the next step of Video Stream collection programming.

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3. UVC (USB video class)

Uvc is a protocol standard jointly developed by Microsoft and several other device manufacturers for USB video capture devices. It has become one of the USB org standards. Today's mainstream operating systems (such as Windows XP SP2 and later, Linux 2.4.6 and later, MacOS 10.5 and later) have provided UVC device drivers, therefore, hardware devices that meet the UVC specifications can be used normally on the host without any drivers. Devices using UVC technology include cameras, digital cameras, analog image converters, TV sticks, and static image cameras. The latest UVC version is UVC 1.1, which is defined by USB implementers Forum as the basic protocol and load format.

The Network Camera is the first UVC device that supports the most UVC devices. Currently, the operating system supports UVC only in Versions later than Windows XP SP2, not to mention Vista. Linux Kernel 2.4 and later versions support a large number of device drivers, including UVC devices. The advantage of using uvc usb has become a standard in the video field. After the hardware runs smoothly among various programs, the driver installation process is also omitted.

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4. YUV & RGB (two color encoding methods)

YUV is mainly used to optimize the transmission of color video signals, so that it is backward compatible with vintage black and white TVs. Compared with RGB video signal transmission, RGB requires three independent video signals to be transmitted at the same time ). "Y" indicates the brightness (luminance or Luma), that is, the gray scale value, while "u" and "V" indicate the color (chrominance or chroma ), it describes the image color and saturation, and is used to specify the color of a pixel. The "brightness" is established through the RGB input signal by overlapping specific parts of the RGB signal. "Color" defines two aspects of color-tone and saturation, expressed by Cr and CB respectively. Cr reflects the difference between the red part of the RGB input signal and the brightness value of the RGB signal. CB reflects the difference between the blue part of the RGB input signal and the brightness value of the RGB signal.

The importance of using YUV color space is that its brightness signal y is separated from the color signal u and v. If only the Y Signal component is used, but not the U or V component, the black and white gray images are displayed. The color TV uses the YUV space to solve the compatibility problem between the color TV and the black and white TV with the Brightness Signal y, so that the black and white TV can also receive the color TV signal.

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The RGB color mode is a color standard in the industry) the changes of the three color channels and their overlapping to obtain a variety of colors, RGB represents the colors of the red, green, and blue channels, this standard covers almost all colors that human vision can perceive and is one of the most widely used color systems.

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