Log space refers to a method for storing high dynamic range image data in a compressed space on a computer.
Since the human perceptual system has a lower sensitivity to changes in bright light, images encoded to log space discard some of the brightness detail in the highlights, allowing the entire image to compressed into a more modest file size.
The most common log format in use today is the DPX format, and its log space is designated as the Cineon color space. DPX is the successor to the older Cineon format, denoted with the file extension, .cin.
DPX files are most commonly stored with 10 bits of data precision, though it’s becoming more common to work with 12 or 16 bit DPX files, allowing for an even greater dynamic range.