lossy file formats;

Audio:

• AAC - .mp4 .m4a .3gp

• ATRAC - .oma .aa3

• MP3 - .mp3

• MPEG-1 - .mp2

• Musepack - .mpc .mpp

• WMA - .wma

Still Image:

• CPC - .cpc

• DjVu - .djvu .djv

• JPEG - .jpg .jpeg

Video:

• DV - .dv .dif

• MNG - .mng

• MPEG-1 - .mpg .mpeg .mp2 .mp3 .mpa

• MPEG-2 - .mpg .mpeg .mp2 .mp3 .m2v

• Ogg Theora - .ogv

psychology & perception;

In methods of lossy compression, human psychology and perception is an important factor. This is because in lossy compressions, very little of the information from a file is still there. Without the deception of how the human eye perceives the difference of information, the file would be very noticeably different from the original. Without our minds to 'fill in the blanks', we would recognise the errors and inconsistencies in a lossy compression.

lossy vs lossless;

The method that offers the greatest compression ratio is lossy compression. The compression ratio of lossy video codecs are generally more superior to audio and still-image.
• The video can be compressed immensely at a 100:1 ratio with little visible quality loss.
• Audio can often be compressed at a 10:1 ratio with imperceptible loss of quality
• Still images are also often compressed at a 10:1 ratio.
The compression rate of lossy compression is about 5-6% while the rate of lossless compression ranges from 50 - 60%.

lossy & lossless;

Lossy and lossless compression are terms that describe whether or not, in the compression of file, all original data can be recovered when the file is uncompressed.

Lossy compression reduces a file by permanently eliminating certain information. When the file is uncompressed, only a part of the original information is still there (however, it usually goes unnoticed). Lossy compression is generally used for video and audio where a certain amount of information loss will not be detected.
The JPEG image file uses lossy compression.

With lossless compression, every bit of data that was originally in the file remains after the file is uncompressed. All the information is restored completely. Generally, this type of compression is used for text or spreadsheet files where the loss of data would pose a potential problem.
The GIF image file uses lossless compression.

data compression importance;

Data compression is very important for the 'online world'. When visiting a website, all the picture files that our browser downloads (file extensions like .png, .jpg and .gif) are all compressed. This also includes videos when online.
Files that are relatively large can be compressed so that they are smaller in size. For example, if an mp3 file is 20MB originally, it can be shrunken to around 3-4MB through compression. This makes it easier to transfer data across the Internet (whether by downloading or uploading).

data compression;

Data compression is the process of encoding information using fewer bits than the original representation would use. Like the compression of images, it reduces the size and quality of the data which could then degrade the quality. Essentially, it is the process of encoding large files in order to shrink them down in size.

Data compression ratio is a term used to quantify the reduction in data-representation produced by a data compression algorithm. The compression ratio is:
compressed size
uncompressed size
(compressed size over uncompressed size)