Hello, dear!
Good day to you!
In this post, I will introduce some basic video knowledge: pixel, resolution, color space, video format, and frame rate.
Let's begin!
What is video
When we slow down the playback speed of the video, we can see that the video is actually made up of still images. This is because, when continuous images are presented at a speed of more than 24 images per second, we can see that the continuous images present a smooth and continuous visual effect according to the human visual persistence principle. We call this continuous picture a video.
Because a video consists of images, the definition of the image determines the definition of the video. So what determines the sharpness of the image? Here, we need to understand the concept of pixel and resolution first.
Pixel
The pixel is the number of photosensitive elements on the CCD/CMOS. After a photosensitive element undergoes the steps of photosensitive, photoelectric signal conversion, and A/D conversion, a point is formed on the output image. If we magnify the image several times, You will find that these continuous tones are actually made up of a number of small dots of similar colors, which are the smallest unit of pixel (Pixel) that makes up the image. That is, a pixel is the smallest unit that constitutes an image.
Resolution
Resolution refers to the number of pixels expressed or captured per unit length. Resolutions are divided into many types, including image resolution, print resolution, display resolution, etc. In a video conference system, the resolution we refer to generally refers to the image resolution and the display resolution.
The maximum resolution of a photo output by a digital camera refers to the resolution of the image, in the unit of Pixel per Inch (PPI). The monitor resolution is the size of the Windows desktop. Common settings are 640x480, 800x600, 1024x768, etc.
Resolution vs Pixel
The pixels are proportional to the resolution. The more pixels, the higher the resolution.
For example, a typical 2-megapixel digital camera has a maximum image resolution of 1600 x 1200 = 192 megapixels. The maximum image resolution of a 3-megapixel digital camera is 2048 × 1536 = 3.14 megapixels. As you can see, the higher the pixel, the higher the resolution of the maximum output image.
Color space
We know that a video is made up of a continuous digital image, and a digital image is made up of pixels, so how are these pixels obtained? Here, we need to introduce another concept: color space.
A color space is a set of colors. Each color is described by a set of parameters. These parameters are called color components. Different industries use different methods to describe the color of an object. The following describes the common color space.
RGB
RGB (Red, Green and Blue) is a commonly used color standard in the industry and can represent most colors. The model is mainly used for color monitors and a large class of color video cameras. However, scientific research generally does not use RGB color space because its details are difficult to adjust digitally. It puts hue, brightness, and saturation together and is difficult to separate. It is the most versatile hardware-oriented color model.
As shown in the preceding figure, a digital image is actually composed of three components: red (R), green (G), and blue (B).
YUV
In YUV space, each color has one luminance signal Y and two chrominance signals U and V. The luminance signal and the chrominance signal are disconnected so that the intensity can be changed without affecting the color.
YUV uses RGB information, but it produces a black-and-white image from a full-color image, then extracts three main colors into two additional signals to describe the color, and combines the three signals to produce a full-color image.
Advantages of YUV
YUV is more consistent with the visual characteristics of human eyes.
YUV is better compatible between black-and-white and color images.
YUV facilitates compression.
Common Video Formats
Video formats are also gradually updated as the technology continues to iterate. Early video formats include CIF (resolution: 352 × 288), 4CIF (also known as D1, resolution: 704 × 576).
Currently, the mainstream video formats are HD or higher, such as:
HD: 720p; resolution: 1280 x 720
Full HD: 1080p; resolution: 1920 x 1080
Ultra HD: 4K; resolution: 3840 × 2160
Frame rate
Before we know the frame rate, we first need to understand what a frame is. As we have mentioned earlier, a video is composed of successive images, and each image is considered a frame. The only difference is that the frame is in RGB format, and the video frame is in YUV format.
The frame rate is actually the number of frames transmitted per second, or the number of frames displayed per second. It is called Frames Per Second in English.
Generally, the frame rate affects the smoothness of the picture. The higher the frame rate, the smoother the picture. The smaller the frame rate, the more jittery the picture is. In other words, frame freezing occurs. The video is coherent only when the frame rate is not lower than 24 fps.
Certainly, although the video presented with a higher frame rate is smoother, the computing and transmission resources consumed by the video are higher. Therefore, in many actual application scenarios, it is sufficient that the frame rate is ensured to be 24 fps or higher. For example, in a video conferencing system, the frame rates commonly used include 5 fps, 15 fps, 30 fps, and 60 fps.
That is all, thanks!
