Computer Hacking Forensic Investigator (CHFI) Practice Exam

The JPEG compression algorithm divides images into blocks of 8x8 pixels. This choice is correct for several reasons related to how JPEG compression operates. The 8x8 pixel blocks are fundamental in the Discrete Cosine Transform (DCT) process, which is a key step in the JPEG compression. By using this block size, the algorithm is able to transform spatial data into frequency components more effectively, allowing for better compression while maintaining acceptable image quality.

Dividing images into these smaller blocks allows for the efficient quantization of frequency coefficients, minimizing redundancy by concentrating on the parts of the image that carry the most visual information. Consequently, the 8x8 block size strikes a balance between compression efficiency and image quality, as larger block sizes would not exploit the frequency characteristics as effectively and smaller sizes would increase overhead and potentially degrade performance.

The other block sizes, such as 4x4, 16x16, and 32x32 pixels, are not used in the JPEG compression scheme. Using these sizes would not align with the established JPEG standard that optimizes both the compression process and the resultant image clarity as seen in common JPEG images.