# Time Delay Optimization of Compressing Shipborne Vision Sensor Video Based on Deep Learning
## 2 SVSV Image Characteristics  
### Features of Shipborne Visible Light Camera Video Images  
The visible light camera is defined as a camera that can image light sensitive information in the wavelength range of 400 nm to 740 nm. Visible light cameras are one of the most commonly used perception devices for visual recognition in the marine field. The images captured by visible light cameras are characterized by rich color details and high image resolution, which facilitates target recognition and foreground segmentation. However, the visible light camera also has certain limitations. For example, in darkness or bad weather and other poor visibility weather conditions, the visible light camera imaging system will be subject to certain interference, making its detection ability reduced. It is difficult to filter out the noise of the collected video image data, affecting the accurate identification of the target. The application of vision sensors strengthens ship's ability to perceive surrounding targets and makes up for the shortcomings of traditional marine radar and AIS. The SVLC video image belongs to one of the ship video monitoring systems, and is mainly responsible for imaging the ship's external and cockpit environment, with the basic features of large sight distance, wide range, strong timeliness, high image resolution, continuous and uninterrupted, and easy to be influenced by the ship's attitude and climate within the video image. When the ship is sailing or anchored at sea, the SVLC continuously and uninterruptedly detects the environment around the ship, generating image content information that can show more visual details and texture. The brightness of the sky area will change with the intensity of light, the ocean and sky occupy most of the display area and data volume of the whole image, the different orientation of the camera arrangement will also lead to different sky-to-ocean ratio area in the image. As shown in Figure 1a, the ships are usually far away from each other when sailing. Therefore, the ship targets in the sea antenna area are small, and the targets may occupy only a few or tens of pixels in the whole image. In offshore, inland waterways or at anchor, the closer the target or the larger the target is, the larger the percentage of the image it occupies, and vice versa. The content information of the SVLC video image is variable, most of the area in the image is flat or changes more slowly in the background area of the sea and sky, and the pixel-to-pixel correlation is very strong. The targets in the images are different in shape but there is localization (mostly near the sea antenna), making more redundant data of the visible light image in the air domain. The grayscale histogram of the SVLC image is shown in Figure 1b, and it can be seen that the grayscale values exhibit a double-peaked  
Figure 1: Shipborne visible light camera video and grayscale histogram: (**a**) Shipborne visible light camera video; (**b**) Grayscale histogram. trailing feature with a very strong pixel-to-pixel correlation. The first peak with a small gray value corresponds to the sea background, the second peak with a larger gray value corresponds to the sky background, and the larger \"trailing\" part corresponds to the target in the image. In good weather conditions, restricted by the ship's own conditions, the movement of the target in the video content captured by the SVLC is generally slow, the target changes between video frames are limited, and the sea-sky background area does not even produce more obvious changes within a certain period of time, through these characteristics it can be inferred that there is a large amount of time-domain redundant data in the visible light video. To prove the above viewpoints, the average intra-frame pixel difference probability density \(p(d)\) and the average inter-frame pixel difference \(d_{k}(i,j)\) for 10 sets of SVLC videos are calculated using Equations (1) and (2) respectively.