Canon OPTURA XI - Camcorder - 2.2 MP Manual de Instruções descarregar pdf (Página 22)

For CAP purposes, we need to realize whether or not our photos have been

compressed. If they were compressed, we need to know by how much so we can

determine if they still meet our customers' needs.

1.4.1 Compression

Lossless compression is similar to what WinZip or PKZip does. For instance,

if you compress a document into a ZIP file and later extract and open the

document, the content will be identical to the original. No information is lost in the

process. TIF and RAW are photo formats that can be compressed in a lossless

way.

Lossy compression reduces the image size by discarding information and is

similar to summarizing a document. For example, you can summarize a large

document into two-page document that represents the original, but you cannot re-

create the original out of the summary because information was discarded during

summarization. JPEG is an photo format that is based on lossy compression.

The table shows how, on average, a 5-megapixel photo (2,560 x 1,920 pixels)

is compressed using the various photo formats.

Photo Format

Typical file

size

Comments

Uncompressed TIF

14.1MB

Reference

Uncompressed 12-bit

RAW

7.7 MB

Reference

Compressed TIF

6.0 MB

Lossless compression

Compressed 12-bit

RAW

4.3 MB

Lossless compression

100% Quality JPEG

2.3 MB

Hard to distinguish from

uncompressed

80% Quality JPEG

1.3 MB

Sufficient quality for 4" x 6"

prints

60% Quality JPEG

0.7 MB

Sufficient quality for viewing on

a computer and on the Web

20% Quality JPEG

0.2 MB

Very low photo quality

1.4.2 Common Photo Formats

A. JPEG (also JPG)

JPEG (Joint Photographic Experts Group) is the preferred photo format for

CAP purposes because the quality is almost the same as RAW but results in

much smaller-size files; this significantly reduces the time it takes to save,

convert, adjust, download or upload files. With JPEG you can shoot hundreds of

photos at a time and the files are ready for release with no further processing.

JPEG is not a file format, but rather a method of data encoding used to

reduce the size of a data file. Its compression can produce very small files for

speedy downloads, and it is supported by all popular digital cameras and Web

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