American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

How many levels of brightness are in an 8-bit gray scale image?

1. 128

2. 256

3. 512

4. 1024

The correct answer is: 256

An 8-bit gray scale image can represent a total of 256 different levels of brightness. This is because in an 8-bit configuration, each pixel is allocated 8 bits of data, and since each bit can be either 0 or 1, the total number of combinations is calculated as \(2^8\). When you perform the calculation, \(2^8 = 256\), which translates directly to the number of gray shades that can be represented—from 0 (black) to 255 (white). This allows for a smooth gradient of gray tones, making 8-bit gray scale images capable of displaying subtle differences in brightness and contrast, which is essential for various applications in imaging and diagnostic purposes in cytogenetics and other fields. Other options like 128, 512, and 1024 represent different bit depth scenarios. For example, a 7-bit image would yield 128 levels, while an image with higher bit depth, such as 9-bit or 10-bit, would provide 512 or 1024 levels respectively. However, since the question specifically refers to an 8-bit gray scale image, the correct answer is 256.