CodeHS AP Computer Science Principles (CSP) Practice Exam

Lossless compression preserves every bit of the original data, so when you decompress you get exactly what you started with. That exact reconstruction is what makes it essential for things where any change would be problematic, like text files, code, or certain images. The examples PNG and ZIP illustrate this property: PNG uses a lossless method to compress image data so decompressed pixels match the originals, and ZIP compresses files in a way that allows them to be restored byte-for-byte. The other statements describe lossy behavior—reducing color depth or losing data—where information is discarded for smaller size, which isn’t guaranteed with lossless methods. And lossless techniques aren’t limited to text; they apply to images, executables, and other data too.