Photography Information

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:
This RSS feed URL is deprecated, please update. New URLs can be found in the footers at https://news.google.com/news


Fstoppers

Try to Master One Simple Thing in Your Photography
Fstoppers
To stop yourself from falling into this kind of routine, it's helpful to choose something in your photography that you can focus on improving and stick with it. It's difficult to fully dedicate yourself to learning numerous things at a time, because ...



Fstoppers

Is the Future of Smartphone Photography Bright?
Fstoppers
In fact, talk to a smartphone user and it's likely they will consider photography to be: point (often at one self), click, tap (to process) and Instagram or Snapchat it. That is photography. It may well be that the sheer exposure to a vast number of ...



Patch.com

Outdoor Photography Workshop On Nov. 3 In Sandy Springs
Patch.com
SANDY SPRINGS, GA — The Chattahoochee Parks Conservancy will partner with Tom Wilson to offer a one-day photography workshop on Saturday, Nov. 3. This class will be held from 9 a.m. to 5 p.m. at the Hewlett Lodge Visitor Center at Island Ford, which ...



FOX 13 News, Tampa Bay

Old school pics: Rediscovering the joys of film photography
FOX 13 News, Tampa Bay
While photography is not Berger's day job, the mountains of rolls of film in his home would make you think otherwise. Ironically, having a finite number of photos is another reason he enjoys film photography. He says having a limited amount of shots ...



New York Times

An Eye for Photography, but a Google Suite for Events
New York Times
I absolutely love what our photojournalists have been doing with drone video and photography. A few months ago, I worked with my colleague Josh Haner on a story about plans to make the Hoover Dam into a giant battery. Josh was able to capture stunning ...



The Eye of Photography

Collecting Photography: From Daguerreotype to Digital
The Eye of Photography
The V&A's new Photography Centre has opened with the major display Collecting Photography: From Daguerreotype to Digital, which explores photography as a way of 'collecting the world', from the medium's invention in the 19th century to the present day.



Fstoppers

A Refreshingly Honest Travel Photography Vlog
Fstoppers
Like the most popular Instagram profiles, a lot of Youtube photography vlogs have become incredibly formulaic. This video, by wedding and travel photographer Taylor Jackson, deliberately breaks from the successful formula to give the viewer some much ...



telegraphherald.com

Biz Buzz: Dubuque business rebuilds after fire; Lancaster photography studio opens; dog groomer changes locations
telegraphherald.com
Biz Buzz shares business tidbits from around the tri-state area. This week, we highlight developments in Dubuque, Lancaster, Wis., and Peosta, Iowa. Early on the morning of Feb. 8, Andy Link watched in disbelief as a massive fire raged at his Dubuque ...



WJTV

242 Creative Art showcases photography and painting
WJTV
Summer photography and paintings were featured, while 242 creative is celebrating its first year in business with the public. "We just needed more venues for the local vendors," said Gabe Porter. "There's a major demand for public assets. There's a ...



Fstoppers

Three Helpful Macro Photography Tips in Just Two Minutes | Fstoppers
Fstoppers
Interested in trying out macro photography? This quick and helpful video will give you three tips to keep in mind when you start shooting the small stuff.

and more »

Google News

home | site map | Seashell Photography
© 2006