101 – Compression Explained

101 – Compression Explained
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There are 2 types of compression​

ORIGINAL IMAGE​

“Uncompressed”​

Loss·y​

Information is discarded in favor of small file size​

Loss·less​

Without loss of information while reducing file size

Lets talk compressing types

Loss·y

COMPRESSION

lossy compression or
irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size but will also degrade the image as the original pixel data is gone

None

50%

25%

None

Can be uncompressed

without data loss ◄

RLE Compression

Compressed down to 17%

Loss·less Compression

Run-length encoding (RLE) is a very simple form of lossless data compression in which runs of data are stored as a single data value and count, rather than as the original run.
This is most useful on data that contains many such runs. Consider, for example, simple graphic images such as icons, line drawings, and mostly black pixels. It is not useful with files that don't have many runs as it could greatly increase the file size.

Compression Examples

There are a few major Lossless compression methods. While they may compress differently the important similarity is they are all Lossless.
This option should always be used in working files. Only use compression when sending to the web where original image quality is less important then file size.
RLE, LZW, ZIPs and DEFLATE are a few examples.

When should you compress?

Any media being introduced into the workflow should always be data checked and if needed re-saved into a lossless format. Formats which contain proprietary formats ( PSD, Tiff, etc. ) should have a Master and production version.

CONVERT TO LOSSLESS ► ► ►

► ► ► ALWAYS LOSSLESS ► ► ►

NORMALLY LOSSY ► ► ►

LOSSY EXPORT

If your client is just viewing images then lossy is ok. This allows them to view it on websites and most computers quickly.

LOSSLESS EXPORT

Client should always receive a master version that is not lossy.
Lossless will allow compressing while not losing any data.

Basic Video Compression

Chroma sub-sampling

4 : 4 : 4

4:4:4
No compression and transports both luminescence and color data entirely

4 : 2 : 2

4:2:2
Half the sampling rate horizontally, but will maintain full sampling vertically.

4 : 2 : 0

4:2:0
Sample colors out of half the pixels on the first row and ignores the second row of the sample completely.