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Digital Image Files - Megapixels, Megabytes, or DPI?
When I promised readers that I was going to do an article on this topic I was scared. For two reasons - firstly, it's a HUGE subject. I get lots of questions about it, and I see a fair bit of misunderstanding about it. Secondly, there are already a lot of good articles about it on the web, like this one on luminous-landscape.com. But I know that trawling the internet for technical information is not your idea of fun. That's my job! So here's my attempt at summing this up quickly for you: DPI - Dots Per Inch The most common question I get on this topic is, "My client / boss / nephew has asked me to send an image at a size of 300 dpi. What does that mean"? The answer: Not much. You see, DPI stands for Dots Per Inch. It's a useful measure of image resolution (in other words, how much information is resolved in the picture). But if you don't know the image size in inches (or feet, miles, centimetres, millimitres, or some other measure of size), then the amount of dots per inch doesn't mean much. Using DPI to measure size is like using km/h to measure distance: "How far is it from here to the beach?" "Oh, about 60 miles per hour". For this to make sense the answer would need to be "about 10 minutes at 60 miles per hour". Likewise, the size of an image needs to be expressed as, say, "six by six inches at 300dpi". Different resolutions are used for different purposes. The most common are 72 or 75 dpi for screen viewing (Web use or PowerPoint presentations) and 300 dpi for printing. OK, so to give an example - 1 inch by 1 inch, 300 dpi image would be 300 pixels by 300 pixels in size. A 2 by 2 inch image at 300 dpi would be 600 by 600 pixels in size. Here's where megapixels and megabytes come into it. Mega! Megapixels The term megapixels is usually used to describe the output size of digital camera images. For example, the Canon Ixus 50 produces images which are 2592 x 1944 pixels in size. Multiply these numbers together and you get 5,038,848 - just over 5 million. Hence this is described as a "5 megapixel" camera. The last byte On a couple of occasions, I've sent an image of a certain size to someone and they've said, "that's no good, we need a 10 megabyte file". Now, this I'm sure they were well-intentioned but they were also a little misguided. The size in bytes (or megabytes - millions of bytes) represents how much storage the image takes up on your computer. This depends on all sorts of things, mainly the bit depth of the image and the file format - for example TIFF or JPEG. So what should I do? To avoid confusion, when specifying the file size you need, use pixels. How do you work out how many pixels you need? Well, that's why I started this discussion with DPI. Work out the largest size you're going to want to reproduce the image, in inches; and the resolution - for example 72 dpi for or 300dpi for most print applications. Then just multiply the size in inches by the DPI figure you came up with. Example: I want to reproduce the image A4 size in a printed magazine. A4 is 210mm x 297mm, or about 8.3 x 11.7 inches. The magazine needs artwork at 300dpi, so: 8.3 x 300 = 2490 and 11.7 x 300 = 3510 so I need an image sized about 2490 x 3510 pixels (about 8.7 megapixels) By the way: 1 inch = 2.54 centimetres. Did you know you can also do conversions on google? Try it yourself. Happy pixelling! Steven Pam is a digital commercial photographer based in Melbourne, Australia, specializing in people, aviation and music photography. http://www.stevenpam.com.au
MORE RESOURCES: The Face Magazine: Culture Shift review – rebellious fashion photography with a raucous sense of fun The Guardian Tale of Two Weegees at the International Center of Photography National Review The Street Photographer Who Captured New York’s Fabulous Unknowns The New York Times Meet the duo using hair and photography as a medium to consider Africa and the African diaspora Wallpaper* Is Photography Actually an Art Form? The Phoblographer Ethical Photo Editing: Maintaining Integrity in Yearbook Photography Walsworth Yearbooks Gallery to open annual photography show Bowie News - McBroom Wins Grand Champion at San Antonio Stock Show and Rodeo Photography Contest The Fayette County Record Works by Armineh Johannes Part of Chelsea Int’l Photography Competition The Armenian Mirror-Spectator Canadian Citizen Xiao Guang Pan Charged with Unauthorized Drone Photography of Cape Canaveral Defense Installations The Maine Wire Rania Matar’s “SHE” explores women’s resilience in new Middlebury Museum of Art photography exhibit The Middlebury Campus Photo Focus: The magic of photography Charleston City Paper Axel’s Shoot Out salutes three Vermont photographers Waterbury Roundabout Echoes of Beijing: Liu Shiming’s Sculptures and Lois Conner’s Photography in Dialogue, NYC Arte Fuse New photography exhibition launched at Stonehenge Yahoo News UK Grosby Group Celebrates 27 Years Covering the Academy Awards: A Legacy of Iconic Photography EIN News Ron Rosenstock remains in the picture at JCC Art Gallery, will be celebrated at gala - Worcester Mag Beyond the lens: S&T’s student photographer looks to the future Missouri S&T News and Research Photography Exhibit Chronicles Pandemic Time on the Island The Vineyard Gazette - Martha's Vineyard News Recovery and connection through art Homer News Minimalist Winter Photography Fstoppers Asheville photographer named 2024 Photographer of the Year, work displayed in Times Square Citizen Times Detroit photographer opens historical hip-hop exhibit Oakland Press John Blakemore obituary The Guardian Will Douglas photographs the Brentford Penguins – the football club that turns no child away It's Nice That Local Photographer Wins Major Award For Photos In East Palestine Wheeling Intelligencer Photos That Capture the Soul of San Francisco The New York Times 23 local artists recognized for their work during annual contest; reception is Saturday Times Reporter Are Photography Festivals Still Worth Your Time? The Phoblographer Documenting Black Seaside – past and present – has become a passion for one photographer. Monterey County Weekly After 15 Years, I Finally Got My Vision Back. Here’s How It’s Affecting My Photography The Phoblographer iPhone 16e specs show it’s missing 3 key camera features – including the latest Photographic Styles TechRadar B&H Photo Announces Bild Expo 2025 - A Two-Day Celebration of Photography, Content Creation, and Filmmaking PR Newswire The roots of American photography are firmly in Cincinnati, new documentary declares The Cincinnati Enquirer Through the Lens: Student Photographers on Campus The Dartmouth Photographers Stay Rooted At YUAG New Haven Independent Black and Baroque: The story of She Shoots 317 photography Indianapolis Recorder Paul McCartney announces Beverly Hills photography exhibit The Music Universe. What makes Bloomington unique? These European photographers plan to capture it on film. The Herald-Times Black history reimagined through a photographer’s lens BayStateBanner This photographer just broke the world record for the most headshots taken in an hour. Can you guess how many he captured? Digital Camera World A' Camera and Photography Equipment Design Award Announces Comprehensive Prize Package for 2024 EIN News ‘I want my photos’: Local bride in battle with photographer to get wedding pictures - Boston 25 News Designer Priya Ahluwalia and photographer Nick Sethi talk about their creative process and the need to innovate Harpers Bazaar India Hannibal Arts Council exhibits opening Feb. 28 feature photography, graphite drawings, oil and acrylic paintings Muddy River News Personal Focus: Former Southern Living photographers show their favorite images at Aldridge Gardens Over the Mountain Journal The American Dream, Through Foreign Eyes The New York Times 9th Xposure photography festival gets under way in Sharjah, UAE Digital Camera World "My images tell a story of art, science and culture all in one frame," says astrophotographer Josh Dury Digital Camera World BG Arts Council seeks entries for ‘Perspective: Photographers of NW Ohio’ BG Independent News How Huntsville-native + photographer Miles Whitmore is changing the creative scene in Huntsville Hville Blast |
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