Slashdot Mirror

the optimal compression of a fixed source is well known.

you're an ignorant hypocrite.

cower behind your chosen pseudonym some more, feeb.

you're completely pathetic.

expression image

where

expression image

is the length of the codeword for block .

expression image

where

expression image

is the length of the codeword for block .

expression image

Since both upper and lower bounds of approach the entropy rate, H, as n goes to infinity, we have

expression image

Thus, the theorem established that the entropy rate is the rate of an optimal lossless data compression code. The limit exists as long as the source is stationary.

you're an ignorant hypocrite.

cower behind your chosen pseudonym some more, feeb.

attempt to spread your lies and ignorance while taking no responsibility for it.

you're completely pathetic.

expression image

Since both upper and lower bounds of approach the entropy rate, H, as n goes to infinity, we have

expression image

Thus, the theorem established that the entropy rate is the rate of an optimal lossless data compression code. The limit exists as long as the source is stationary.

you're an ignorant hypocrite.

cower behind your chosen pseudonym some more, feeb.

attempt to spread your lies and ignorance while taking no responsibility for it.

you're completely pathetic.

All compression is based on basically the same idea - a model of the process that created the data. The model makes somewhat less error in predicting what will come next compared to a random model / no model, and hence needs less information to correct those predictions. For instance, in speech compression it is normal to start with a model of the human vocal tract. Even general compression algorithms like gzip work this way, making basic assumptions, such as real-world data tends to have values which repeat, a weak model but useful nonetheless.

OK Found one. Look at the texture of the monkey fur here: http://www.data-compression.com/image.shtml

Crikey, that was hard.

If you're smart enough to come up with the next great compression algoritm, I encourage you to do so!

I would prefer more browsers to use gzip for retrieving web pages.

(I should check this out by timing various downloads, but I'm too lazy. Somebody else can prove me wrong!)

So why do JPEG files with "more" compression download faster? Because JPEG is a lossy format: when you increase the "compession" you're not encoding data more efficiently, you're throwing data away. Depending on the image, you can do this and still end up with something that looks the same. But push it far enough and you end up with crap.

Actually, there is such thing as "lossless" compression.

For example, dictionary-style compression (what .zip uses) compresses data by developing a small dictionary of byte sequences that recur in a file, and representing those byte sequences as a single byte, thereby saving space. You develop a large enough dictionary of this type, and you're saving file space.

Zip is living proof that lossless compression exists - you COMPRESS your text files, without LOSING any of the data in it when you DECOMPRESS.

That's what lossless compression is.

For more info, look into the entropy of data, which helps to determine the lossless compressability.

An example of LOSSY compression is mp3 or JPEG, where you (usually) sacrifice some quality for increased compression. Part of what makes mp3 work so well, is that it throws out the parts of the audio signal that are out of the human range of hearing.

--

In essence, is not this the same as file compression? The amount of information is the same (for those, who remember, what Bit is).

It is more than merely compression. The received data is compressed, which saves transmission time, but this technology is already well known (and the company isn't claiming a compression rate better than entropy, or anything else silly). The innovation here is the elimination of acknowledgement or ARQ packets. I'm speculating here, but it looks like they are encoding the data by transforming a file into a huge "codeword" -- when the codeword is transmitted, the receiver waits for enough packets to correctly decode the codeword, which results in the recovery of the file. There's no need for ARQ or TCP because transmitting extra codeword elements will automatically correct any errors incurred in transmission.