Adobe Photoshop DPI photo editing photo sizes PPI

Photo image & file sizes

A digital camera is a little computer that produces digital files. All computer-generated information creates a file.

A camera file can be a JPG (acronym for Joint Photographic Experts Group). Your cell phone camera usually produces JPGs. DSLR cameras can be set to produce JPGs or RAW files. (“RAW” is apparently not an acronym, but usually shown in all-caps. Nobody knows why…)

  • 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)
  • 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 = how the picture is displayed on your screen
    • 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 2000×2500

Photo Prints:

  • Stock photos are usually 300ppi
  • For photo editing (“Photoshopping”) the best size is at least 1400px on the long side
  • 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 ( (8 x 300=2400 and 10 x 300=3000). 
  • 4″ x 6″ @ 300ppi = 1200×1800 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, e.g. 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. ​

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