file and images sizes in photography...

• All computer-generated information creates a file
• File size = number of bytes, kilobytes, megabytes, etc.
• 1 kilobytes (kb) = 1,000 bytes (actually 1,024 bytes)
• 1 megabyte (mb) = 1,048,576 bytes (1,024 kilobytes)
• 1 gigabyte (Gb) = 1,073,741,824 bytes (1,024 megabytes)
• 1 terabyte (Tb) = 1,099,511,627,776 bytes (1,024 gigabytes)

• A digital camera is a little computer that produces digital files
• A camera file can be a jpg (acronym for Joint Photographic Experts Group) or RAW (apparently not an acronym, but usually shown in all-caps. Nobody knows why...)

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• Photo file: more pixels = more bytes in the file = bigger file size
• Picture resolution is measured in Pixels Per Inch (ppi)
• DPI and PPI are sometimes erroneously used interchangeably, but they are NOT the same
  • PPI = photo resolution = pixels per inch (ppi), e.g 300ppi
  • DPI = PRINT quality = dots per inch = how many dots per inch a printer can produce
• Photo size = number of pixels per side of a rectangular image, e.g 2000x2500

• Stock photos are usually 300ppi
• Websites like Amazon prefer photos that are at least 1000 pixels (px) on the long side with a 300ppi resolution
• For photo editing ("Photoshopping") the best size is at least 1400px on the long side

​Photo Prints:

• To determine ppi, multiply the desired print size in inches by the resolution ppi (dpi)
• 8" x 10" image @ 300ppi resolution =2400 px by 3000 px ( (8x300=2400 and10 x 300=3000). 
• 4" x 6" @ 300ppi = 1200x1800 ppi.
• Amazon, eBay, etc., prefer at least 1000 ppi on the longest side

• Magazines, books and most other high quality publications are typically printed at a 133 or 150 LPI (Lines Per Inch).
• 150 LPI x 2 = 300 ppi image resolution 
  • 2" x 3" @ 300  = 600x900ppi
• Newspapers typically use a lower 85 LPI = 170 ppi
  • 4" x 6" @ 170ppi = 680x1020ppi

TV and Video Displays:

• TV – High definition (HD) are usually 4:3 size ratio or 16:9 for wide screen
• It is impossible to resize an image from 4:3 to 16:9 evenly without adding a border at the top and bottom or cropping the top and bottom. ​