A boy in Tiberias
Jacob Ziv was born on November 27, 1931, in Tiberias, on the shore of the Sea of Galilee, in what was then British-ruled Mandatory Palestine. He was the younger of two sons of Ben Tzion and Hannah Ziv, Jewish immigrants from Russia who had come to build a life in the Jewish community of the Land of Israel.
From childhood he was fascinated by electricity and gadgets. While supposed to be practising the violin, he turned his music stand into a lamp. He once tried to build a radio transmitter from the parts of a player piano; when he plugged it in, he blacked out the house. Those experiments pointed him toward engineering.
War, radar and the Technion
When the 1948 Arab-Israeli war broke out, Ziv was still in high school. He was drafted and served briefly at the front, until protests by mothers led the army to move its youngest soldiers to the rear. He was assigned to the Israeli Air Force and trained as a radar technician, his first serious encounter with the electronics of signals.
After the war he studied electrical engineering at the Technion, Israel Institute of Technology in Haifa, receiving his bachelor’s degree in 1954 and his master’s in 1957. From 1955 to 1959 he worked as a research engineer in the scientific department of Israel’s Ministry of Defense, developing communication systems. He described studying with a group of friends who would pick a book and work through it together, in the manner of religious Jews studying the Bible.
Information theory at MIT and Bell Labs
In 1961 Ziv went to the Massachusetts Institute of Technology, the world centre of information theory, the mathematical science of communication founded by Claude Shannon in 1948. He received his doctorate there in 1962, while also working as a research engineer at Melpar in Watertown, Massachusetts. He then returned to Israel to head the communications division of the defence ministry’s scientific department.
From 1968 to 1970 he worked at Bell Laboratories in Murray Hill, New Jersey, the most famous industrial research laboratory in the world, and he returned there for three later sabbaticals. With Aaron Wyner at Bell Labs he developed the Wyner–Ziv theory of compressing data when the receiver already has related information, and with Moshe Zakai he gave his name to the Ziv–Zakai bound in estimation theory. In 1970 he joined the Technion’s faculty of electrical engineering, where he would spend the rest of his career.
The Wyner–Ziv result, published in 1976, addressed a subtle question: how much must be sent when the person receiving the data already has something similar, such as a previous frame of a video. It showed that, in principle, the sender need not know what the receiver already has. The idea later influenced research on video coding and on networks of sensors.
The Lempel-Ziv idea
At the Technion in the 1970s Ziv teamed up with Abraham Lempel, a computer scientist. As Ziv recalled, he knew information theory and statistics, while Lempel brought expertise in algorithms, and the combination proved ideal. They set themselves an ambitious goal: a method of lossless compression, one that shrinks data and lets it be restored exactly, which would work on any kind of data without knowing its statistics in advance, and would still approach the theoretical limit Shannon had defined.
Their answer, published in 1977 in the IEEE Transactions on Information Theory as A Universal Algorithm for Sequential Data Compression, became known as LZ77. The encoder reads data in a single pass, and whenever it meets a stretch it has already seen, it replaces the repeat with a short pointer back to the earlier copy and the length of the match. The decoder simply follows the pointers to rebuild the original. A second method, LZ78, published in 1978, builds a dictionary of phrases as it goes. The older standard, Huffman coding, needed two passes and had to store a codebook with the data; Lempel-Ziv methods needed neither. Crucially, Ziv and Lempel proved that their methods approach the best possible compression for a very wide class of data.
An everyday example shows why the idea is so powerful. Ordinary text, computer code, web pages and many images are full of repetition: the same words, phrases, tags and patterns of pixels recur again and again. Lempel-Ziv methods find those repeats automatically, without being told what kind of data they are handling, and replace them with short references. A typical text document can often be shrunk to a fraction of its size, and restored exactly, bit for bit.
Everywhere and invisible
The Lempel-Ziv methods became the basis of much of the world’s data compression. A variant of LZ78 developed by Terry Welch, called LZW, powered the Unix compress program in the 1980s and the GIF image format. LZ77, combined with Huffman coding in the Deflate method, is used in ZIP archives, the gzip tool that compresses much of the web’s traffic, and the PNG image format. The Technion noted that the algorithm underlies formats such as PNG, GIF, ZIP and TIFF and played a major role in PDF and MP3.
Every time someone downloads a compressed file, loads a web page sent in compressed form or saves a PNG image, a descendant of Ziv and Lempel’s idea is at work, saving storage space, bandwidth, energy and money. Because the original papers were published openly and Bell Labs did not seek a patent on the theory, the ideas spread freely through computing.
The story also had a commercial side that Ziv did not control. Lempel’s employer, Sperry, patented a hardware implementation, and when the LZW variant inside the GIF format later became subject to patent licensing demands in the 1990s, software developers created the PNG format as a free alternative, itself based on LZ77. Either way, the ideas of Ziv and Lempel stayed at the core.
Building Israeli science
Ziv was also one of the builders of Israel’s scientific institutions. At the Technion he served as dean of electrical engineering from 1974 to 1976 and as vice president for academic affairs from 1978 to 1982, and he held the Herman Gross chair and the title of Distinguished Professor. From 1985 to 1991 he chaired the Planning and Grants Committee of Israel’s Council for Higher Education, which funds the country’s universities. He was a member of the Israel Academy of Sciences and Humanities from 1981 and its president from 1995 to 2004.
He received the Israel Defense Prize twice for work that contributed to the country’s security.
Colleagues remembered him as a teacher who loved to work through hard problems with students and younger researchers, and as a leader who believed that a small country could compete at the very top of world science if it invested in its universities. His years at the head of the Planning and Grants Committee and the Israel Academy came at a time when Israel’s research universities were growing rapidly and becoming internationally prominent.
Honours
Ziv received the Israel Prize for exact sciences in 1993, the IEEE Richard W. Hamming Medal in 1995 for contributions to information theory and the theory and practice of data compression, the Marconi Prize in 1995, the Claude E. Shannon Award in 1997 and the BBVA Foundation Frontiers of Knowledge Award in 2008. He was elected to the American Philosophical Society in 2003 and to the U.S. National Academy of Sciences in 2004.
In 2021 he received the IEEE Medal of Honor, the institute’s highest award, for fundamental contributions to information theory and data compression technology and for distinguished research leadership. He was the first Israeli scientist to receive it.
Jewish life and last years
Ziv’s life followed the arc of the Jewish community in the Land of Israel and then the State of Israel: born to immigrant parents in Tiberias, one of the four holy cities of Jewish tradition, a teenage soldier in the war of 1948, and then one of the scientists who built the new country’s universities and research. His own image for learning, a small group studying a book together like religious Jews poring over the Bible, came from that world.
In old age glaucoma took most of his sight, but he kept working. His last paper, completed in January 2021 with his Technion colleague Yuval Cassuto, dealt with quickly transmitting the very large files produced by DNA sequencing. Ziv died on March 25, 2023, at the age of 91, a few weeks after his long-time collaborator Abraham Lempel. Technion president Uri Sivan called his work a beacon of scientific excellence.
Legacy
Jacob Ziv belongs to the small group of theorists whose mathematics became infrastructure. The Lempel-Ziv algorithms made it practical to store and send the vast and varied data of the digital age, from documents and images to software and web pages, at a fraction of its raw size.
His name also lives on in the Technion, where he spent more than half a century, and in the textbooks of information theory, where the Lempel-Ziv algorithms and the Wyner–Ziv and Ziv–Zakai results are standard material for every student of the field.
Most of the billions of people who benefit from his work every day have never heard his name. But each ZIP file, each PNG image and each compressed web page carries, in its letters LZ, the initials of a boy from Tiberias and his colleague.
Sources & further reading
From WinZips to Cat GIFs, Jacob Ziv’s Algorithms Have Powered Decades of Compression, IEEE Spectrum · Dist. Prof. Jacob Ziv 1931–2023, Technion · Jacob Ziv, Wikipedia · Jewish Computer and Information Scientists, jinfo.org · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.