File Types: What's the difference between JPG, PSD, TIFF, and which do I use when?

I've had some good questions about file types and sizes...
I'll be breaking this topic into short bits over the next few posts, as it covers a lot of territory.

The basic issue is:
Where will the photo ultimately be used?
Print or Web?



Print Requirements:
(professional printing, office/home printing)

• Larger files in high resolution (300 dpi)
• Print files for professional printers must be CMYK* mode (I will do another post about color space.)
• Appropriate file types can be PSD, TIFF, a high resolution JPG, and sometimes PDF.
  (Which I'll discuss in more detail in another post.)

Web Requirements
(Computer viewed images websites, blogs, email, etc.)

• Smaller files in low resolution (72 dpi): this is so they load fast and it doesn't take ten minutes for your blog to show up with pictures.
• Color space for Internet images is RGB mode.
• The appropriate file type for photos of artwork is most commonly a low resolution JPG.

Tomorrow: 'Lossy' versus 'Lossless' file types

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