Binary run length encoding example
You can read and write RLE data in one pass, using almost no memory. Given a vector V compressed with RLE, you can apply any scalar function f to its component in time O V where V is the compressed size of the vector. Some RLE formats have worse complexity bounds. Any downsides to RLE? Random access is slower. Sometimes, only sequential read from the beginning is possible. Updating an RLE-compressed array can be difficult. You need long runs of identical values. Thus, if the compression rates are modest, it could actually take longer to process an RLE-compressed array.
What is the RLE format? Here are some common variations: Instead of using a counter for each run of characters, you only add a counter after a value has been repeated twice. Thus, if many characters are not repeated, you will rarely use an unnecessary counter. You can use a single bit to decide whether a counter is used. Again, this may avoid many unnecessary counters if values are often not repeated. Instead of a counter, you may store the location of the run in the array.
On the previous example, this would give the following:. This would be interpreted as a run of twelve Ws, a B, a run of twelve Ws, a run of three Bs, etc. In data where runs are less frequent, this can significantly improve the compression rate. One other matter is the application of additional compression algorithms. Even with the runs extracted, the frequencies of different characters may be large, allowing for further compression; however, if the run lengths are written in the file in the locations where the runs occurred, the presence of these numbers interrupts the normal flow and makes it harder to compress.
To overcome this, some run-length encoders separate the data and escape symbols from the run lengths, so that the two can be handled independently. Run-length encoding schemes were employed in the transmission of television signals as far back as The ITU also describes a standard to encode run-length-colour for fax machines, known as T.
From Wikipedia, the free encyclopedia. Not to be confused with run-length limited. Proceedings of the IEEE. The ITU also describes a standard to encode run-length-colour for fax machines, known as T.
From Wikipedia, the free encyclopedia. Not to be confused with run-length limited. Proceedings of the IEEE. Compression formats Compression software codecs. Multimedia compression and container formats. See Compression methods for methods and Compression software for codecs. Retrieved from " https: All articles with unsourced statements Articles with unsourced statements from December Views Read Edit View history. This page was last edited on 18 December , at