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File Formats

An Explanation.
by

Tim Samoff

on 9 January 2014

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Transcript of File Formats

Industry standard graphic format for on-screen viewing through the Internet and Web. Not meant to be used for printing.
The best format for images with limited, solid colors (not photographic images, which should be saved as JPEG or PNG).
Can contain transparency.
GIF supports lossless LZW compression.
File Formats
Understanding
Different applications (programs) store data in different formats. Applications support some file formats and not others.
You can usually access these files by...
Open..., Save..., Save as..., Import..., Export..., Place...
In most cases, file formats appear as a three-letter suffix or “extension” after the name of the file:

.psd, .doc, .jpg, .png, .tif, .gif, .ppt,
etc.
Photoshop can save files in many file formats...
Save
Save As...
Save for Web...
.psd: Photoshop Document (its “native” format)
.pdf: Portable Document Format
.eps: Encapsulated PostScript
.tif: Tagged Image File Format
.gif: Compuserve Graphic Interchange Format
.jpg: JPEG, Joint Photographic Experts Group
.png: Portable Network Graphic
.bmp: Windows Bitmap
...Etc.
Photoshop can open many different image formats.
So...

What are the basic graphic file formats?
Which file formats should you use and why?
How does the format affect the file size?
How does the format handle compression?
EPS: Encapsulated PostScript
Preferred file format for importing into page layout programs such as InDesign, QuarkXPress, et cetera, for subsequent printing.
An object-oriented format.
Will only print to a postscript printer.
Uses lossy JPEG compression.
Only save your file as EPS if you need to import it into a page layout program.
TIF: Tagged Image File Format
Also seen as .tiff.
Widely used as a cross-platform file format designed for printing.
A bitmap image format.
TIFF supports lossless LZW compression which also makes it a good archive format for Photoshop documents.
GIF: Graphics Interchange Format
JPEG: Joint Photographic Experts Group
One preferred format for photographic images and for use on the Web (not meant for printing).
Not good for images with a lot of solid color, vector drawings, type, line art, or images with "Indexed" colors.
JPEG compression is lossy. Save and archive the original before converting to JPEG.
PNG: Portable Network Graphic
24-bit color depth (16.7 million colors).
Lossless compression.
Supports transparency.
Great for print and web (can yield higher file sizes than JPEGs).
How do you pronounce GIF anyway?!
CompuServe used to distribute a graphics display program called CompuShow. In the documentation for version 8.33 in the FAQ section, it states:

The GIF (Graphics Interchange Format), pronounced "JIF", was designed by CompuServe and the official specification released in June of 1987.
PDF: Portable Document Format
Developed to transfer and read documents without having to print them (the “paperless office”).
Cross platform format that can be read with the free download Adobe Acrobat Reader.
Can represent both vector and bitmap graphics.
Can also contain electronic document search and navigation features as well as hypertext links.
Can be created from almost any application, but the user cannot edit or modify the file except with Adobe Acrobat Pro (or other software).
Document formatting, fonts, colors, etc. are maintained and appear identical across platforms.
Excellent in the “prepress” process: can be sent to the printer, but can also be placed in other documents.
File format and size...
Vector-graphics files are memory conservative. You can easily work, save, transfer, print, and archive vector files.

To send vector files to a PostScript printer or place in a page layout program, they should be converted to an EPS or TIF file... But while TIF uses lossless compression, EPS uses lossy JPEG compression.
Bit-mapped images use a LOT of memory and, hence, a lot of disk space. The larger the file, the slower it is to edit, save, print, or send over the internet.
Lossless Compression
vs.
Lossy Compression

ILBM
JBIG2
JPEG-LS
JPEG 2000
JPEG XR
PGF
PNG
TIFF
Gifsicle
Jpegoptim

There are several lossless compression types for graphics:
There are even more lossy compression types, JPEG being the most widely used in the graphics world.
Let's take a look at another artifact of JPEG compression...
In Photoshop, when you Save as... a JPEG file, you can choose the level of compression and, therefore, the size and quality of the file.
PNGs on the other hand, don’t provide any compression options, because they are lossless.
So, why choose JPEG over PNG?
The reasons are becoming less and less, although often “photo” JPEGs still look great and result in much smaller file sizes than PNGs
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