# Talk:Data compression ratio

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## Definition

"The 10MB file that compresses to 2 MB would have ((10-2)/10)*100% = 80% compression ratio."

Is this formula really true? The table provided in http://www.7-zip.org/ doesn't complain to it at all. --riba 01:40, 7 February 2006 (UTC)

And what about compression ratios greater than 100

( (1000 - 1) / 1000 ) * 100 = 99,9% ?

so this sux

I agree. I've never seen a compression ratio expressed like this. Changing article.

Unfortunately, the formula used on the maximumcompression.com site, as well as the table at 7-zip.org, ignore the terminology used throughout many decades of data compression research and technology. Ratio means ratio, and a higher compression ratio means higher compression. I'll add some references. AndreasWittenstein 07:12, 27 March 2007 (UTC)BitJazz

NOTE: People confuse compression factor with compression ratio. See: [Data compression: the complete reference By David Salomon]. The correct formula is CR=output/input, and hence a lower value of CR is better. Please cite at least a peer-reviewed article before changing this formula again.

# Disputed

There seems to be no general concensus about the terminology even in the literature. In [Khalid Sayood: Introduction to Data Compression (Morgan Kaufmann, 2nd Ed., 2006)] the compression ratio is defined on page 5 like this:

Ratio of the number of bits required to represent the data before compression to the number of bits required to represent the data after compression.

So this leads to CR=input/output, the inverse of the definition by Salomon.

I believe that Sayood's definition is used more often than Salomon's, see the comments above. To me, a compression ratio of 4:1 (4 bytes are compressed to 1 byte) looks more natural than 1:4. I'm adding a dispute marker to the article. Voxelizer (talk) 11:23, 17 June 2010 (UTC)

# Other

needs clean up needs refs and soucres needs a link section as wellOo7565 20:16, 29 May 2007 (UTC)

There will be two things. Do not confuse with compression factor and compression ratio. The meaning of compression is to minimize the image.

Compression ratio=(total number of bits at input)/(total number of bits at output)i.e. 10:1,100:1,20:2 in this way.

Compression factor = (output bits/input bits) Compression Factor should be equal to or less than 1 and ratio should be grater than 0.

— Preceding unsigned comment added by 203.115.116.74 (talk) 10:10, 27 September 2011 (UTC)

## 1080i?

Why express the compression ratio of 1080i video, when you have to account for interlacing which muddies the waters? I say 1080p or 720p should be used to replace that little factoid, so it's easier to compute mentally and for users to understand. Bumblebritches57 (talk) 02:10, 31 August 2013 (UTC)

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