X-ray scanners are complex machines. Not only do they have a generator and powerful imaging software, but they also have features some users are unfamiliar with, such as material discrimination. This blog article focuses on one such feature that x-ray personnel, both new users and experts, may not be intimately familiar with: bit imaging. We will discuss what bit imaging is, how it impacts x-ray scanners, and why it is important for security screening.
Pixels and Bits
Pixels and bitrate (or bit imaging) work together to determine how accurate images look to the human eye. This is especially true for x-ray images — the clearer the image, the more likely security personnel can quickly review the image and identify hidden threats.
Images are made up of many pixels and bits. Each pixel can only display one color at a time. The maximum number of colors a pixel can display is determined by the bitrate, and it is measured as a function of the number of bits. The higher the number of bits, the more colors a pixel can display.
Bits, like other data, can only exist in 2 states: as a 0 or a 1. 1-bit color means that a pixel can only display two color options – normally black or white – because the bit only has 2 possible states (identified as either 0 or 1). 2-bit color increases the color options exponentially by 2 to the 2nd power. This happens because there are now 2 bits that can each represent 0 or 1. Every possible combination of those values represents a new color. In this case, 00, 01, 10 and 11 are all different colors the pixel can show.
Every added bit increases the color options by a factor of 2. So 3-bit color has 8 color options, 4-bit color has 16 color options, etc. As the figure below demonstrates, each additional bit adds more color options to the image of the leaf, presenting truer and clearer depictions of its colors.
24-bit color is considered to be “True Color”. This is because the human eye can only perceive about 10 million colors. 24-bit color includes over 16 million colors – 16,777,216 to be exact – meaning it has more colors than the human eye can even perceive. Therefore, anything above 24-bit color tends to be unnecessary. Additionally, each extra bit means images have more data, and require increased storage capacity.
Bit Imaging and X-ray Security
Medical and security x-rays leverage bit imaging in different ways. Since medical x-rays are shown using gray-scale images, bit imaging shows the number of gray tones that a pixel can display. This allows medical personnel to see variations in shape, thickness and composition of objects, allowing them to better analyze images and diagnose possible health issues.
There are a wide range of colors security x-ray scanners are capable of showing, especially Astrophysics’ units that leverage 12- and 14-bit imaging. However, the ability to show all those colors does not directly impact the material discrimination and color imaging used in these scanners. That is because the colors displayed using Astrophysics’ 6- and 8-Color Imaging utilize object’s atomic (or Z) numbers for material discrimination.
Higher bit imaging in security scanners does have a larger impact on black and white (B&W) images. Just like with medical x-rays, higher bit imaging provides higher levels of contrast sensitivity. This allows security personnel to more clearly differentiate the shape, thickness and composition of objects they screen. This is extremely important when personnel are trying to identify threats. Increased image contrast allows for clearer images, helping ensure personnel can locate and isolate hazardous materials quickly and confidently.
Bit imaging is not the only feature found on security x-rays, nor is it the most important. It is however a critical component that helps users better understand the general functionality of these complex machines. A deeper understanding of how these features contribute to the overall final images they produce help personnel better understand how to leverage these tools to protect people, property and goods across the globe.
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