In the security screening industry, centralized image review is replacing the traditional local image review model, allowing one image reviewer to simultaneously process images from multiple devices. However, many people find this system more complex than local image review when they first encounter it. In fact, the simplest three steps of centralized image review security screening have only three core steps: view the image, identify the object, and handle the situation. Below, from principle to practice, we explain these three steps clearly.
1. First Understand the Principle: How X-rays "See" Prohibited Items
When X-rays emitted by a security scanner pass through luggage, different materials absorb the rays to varying degrees. Traditional single-energy imaging can only show density differences, and the image is black and white. However, the current mainstream dual-energy imaging can simultaneously collect high-energy and low-energy data sets, calculate the effective atomic number of an object, and thus classify materials into three categories: organic (orange), inorganic (blue), and mixed (green).
Organic materials typically include plastics, paper, clothing, food, and most explosives and drugs; inorganic materials include metals, glass, ceramics, and various knives and firearms. The colors seen by the image reviewer are the intuitive result of material classification.
CT-type security equipment goes further, providing density and tomographic slices of objects, with stronger identification capabilities for liquids and powders. But no matter how advanced the equipment, the workflow of the image reviewer remains unchanged—only the information is richer and the basis for judgment is greater.
2. The Simplest Three Steps of Centralized Image Review Security Screening (How to Use)
Step 1: Quickly scan the overall outline. After the image pops up, first spend 1 to 2 seconds looking at the whole. Focus on whether there are abnormal large shadows, whether there are outlines that clearly do not belong to luggage categories, such as gun shapes, knife shapes, or densely arranged bottles and cans. This step does not delve into details, only performs a preliminary screening of "is there anything suspicious."
Step 2: Locate suspicious items by color and density. If high-density blocky objects appear in orange areas, be alert to explosives or drugs; if slender strips with sharp angles appear in blue areas, think of knives, scissors, or metal tools. Pay attention to overlap and occlusion: two harmless objects stacked together may form a shape similar to prohibited items in the image. At this point, rotate the view or switch channels to look again.
Step 3: Combine image with bag opening and handling. After the image reviewer determines something is suspicious, they mark the location through the centralized image review system and notify the on-site bag opener. The bag opener finds the item at the marked location and confirms whether it is prohibited. If confirmed, handle according to procedures; if it is a false alarm, provide feedback to the image reviewer to help with subsequent adjustments. After these three steps, one image review cycle is complete.
3. Common Pitfalls: Why You Always Feel Uncertain
The first pitfall is over-reliance on color. Color is only a reference for material classification, not an absolute conclusion. For example, some chlorine-containing plastics appear green and are easily misjudged as prohibited items in the mixed category. The correct approach is to judge comprehensively based on color, shape, and density.
The second pitfall is ignoring image angles. Centralized image review usually only shows fixed-angle images generated by the equipment, unlike local image review where luggage can be rotated at any time. If occlusion is found in the image, actively use the system's multi-view function or have the on-site staff re-scan the bag.
The third pitfall is fatigue in image interpretation. Centralized image review is efficient, but after continuously viewing dozens of images, the reviewer's attention will noticeably decline. A common industry practice is to rotate every 30 to 40 minutes, or use system-assisted alarms to remind of suspicious images. Do not push through; missed detections often occur during fatigue periods.
The fourth pitfall is ignoring equipment differences. Different brands and models of security scanners may have different color mappings and density thresholds. After switching equipment, first test with known items several times to familiarize yourself with the image characteristics before formal image review.
4. Applicable Scenarios and Boundaries
Centralized image review is suitable for scenarios with high luggage flow and limited number of image reviewers, such as subway stations, large event entrances, and logistics sorting centers. However, it is not omnipotent: for the identification of liquid explosives, ordinary dual-energy equipment still has limitations and requires CT-type equipment or liquid detectors to assist. For scenarios with poor image quality and severe luggage stacking, the false positive rate of centralized image review will also increase.
In summary, the simplest three steps of centralized image review security screening—scan the outline, determine the color, and handle the situation—are essentially a standardized interpretation logic. Understanding the material identification principle of X-ray imaging and avoiding pitfalls such as color dependence, angle neglect, and fatigue interpretation will significantly improve image review efficiency and accuracy.