Your time is valuable. It’s annoying when you receive an image which is too large, too small, or impossible to open.
And your customers, suppliers, or friends will hate you if you do it to them.
In this short article, you’ll learn how to send the right size image, in the right format. It’s surprisingly pretty simple, once you know how.
Image formats and sizes seem complicated at first, which is why people send images that are the wrong size or format. But once you understand a couple of basic principles, you’ll be able to easily size any image appropriately and send it by e-mail or upload it to a web site.
Begin with the end in mind
Take Stephen Covey’s advice - start by being clear about your goal. What is the person to whom you’re sending the image going to do with it? Is it just for them to look at on their computer, or will they need to print it? It makes a big difference (the reason is simple, and you’ll find out what it is in a minute). If the image is to be printed, how big?
Pixels and DPI
The answer to the sizing problem has to do with pixels. Unless you’ve been living in a bunker for the last five years, you’ve probably heard of them. You may even have an idea what a pixel is: the smallest element of a digital image - a single square (rectangle, actually) of a single colour.
The resolution of an image is expressed in PPI, or Pixels Per Inch. This is often confused with DPI (Dots Per Inch). Strictly speaking, DPI actually relates only to printers, but in practice, the terms are often used interchangeably.
Resolution essentially determines how large the image can be reproduced. This also depends on the output device (computer screen or printer). It’s important to understand the difference between size and resolution. The best way to do this is with an example…
Let’s say we have an image which is 300 pixels wide by 150 pixels high. This is the size or pixel dimensions of the image. Simple enough. But here’s the tricky bit (so pay attention):
The typical computer screen size, in pixels, is 1024×768 pixels. The resolution is usually 75 PPI (which means every square inch of screen ‘real estate’ is 75 pixels wide by 75 pixels high).
Therefore if we look at our 300 x 150 pixel image, it will be four inches (10 cm) wide and two inches (5 cm) high. Fine so far. But what if we now want to print that image?
Different printing devices can print at different resolutions. But generally, for an image to print well, it needs to have a resolution of at least 200 PPI, or preferably 300. Any less than this, and it will start to look chunky, fuzzy, or pixellated. Or all three!
You may have heard of printers which can print at 1200 DPI or more, but this is separate from the size of the image itself - there’s really no need to send a 1200 PPI image to your printer.
So you can see that our 300 x 150 pixel image will only print at a size of about 1 inch (2.5 cm) wide by half an inch high. Big difference!
By now you’re probably thinking, “OK, enough geeky explanations, how big should I size my image?!”
Here are some guidelines, then:
- On-screen viewing: height 500 to 700 pixels, width 700 to 900 pixels
- Print - 200 to 300 PPI. So for a 4×6″ (10×15 cm) print, the pixel dimensions should be 800 x 1200 at the smallest, or 1200 x 1800 at the largest. Obviously for a larger print, you need to increase the pixel dimensions accordingly.
The good news
Most imaging programs do all the calculations for you in the “resize” function. Here’s how to resize images in the most popular image editing applications:
In Photoshop (including Photoshop Elements), go to Image –> Resize –> Image Size, where you can either specify the new size in pixels; or in centimetres or inches. Don’t forget to set a suitable resolution for your end use (75 PPI for on-screen viewing, 200-300 PPI for print).
The procedure for PaintShop Pro is very similar: Go to Image –> Resize, where you can resize either as a percentage of the original size, specify the new pixel dimensions, or specify the absolute size in cm or inches and PPI.
If you don’t have either of these programs, you can even resize in Windows Paint. Choose Image –> Stretch, and then enter the new size as a percentage of the original size.
It’s also worth checking out Irfanview, a free image viewer which has been around for years. It supports every imaginable image format (and then some), and includes batch processing (allowing you to resize or otherwise adjust multiple images in one operation) as well as slide shows and a bunch of other features.
In Windows XP (and possibly some other versions) you can also check the size of your image without opening it, by hovering the mouse pointer over the file within Windows Explorer. A box soon pops up with all of the details.
Formats
OK, the last thing to think about is image format. Not only does this substantially affect the size of the file (in bytes), but also whether other people can open it!
You may have noticed that the most common format is JPEG (which stands for Joint Picture Experts Group, if you must know), often abbreviated to its three-letter Windows file extension, jpg.
Most likely your images are already in JPEG format if they have come from a digital camera, although some digital cameras can capture images in TIFF or RAW formats (which are beyond the scope of this article).
There are a couple of good reasons for the popularity of JPEG. The main one is size. A postcard-size, 300 DPI image takes up about 6 MB in it’s ‘native’ format. That’s one big e-mail! The same image saved as a JPEG takes up around one-tenth of that when saved as a JPEG at a decent quality setting.
(The other reason JPEG is a popular format is because it’s extremely widely supported - as well as digital cameras, every image editing or viewing application can handle it - which in turn ensures its popularity!)
So by ‘compressing’ the image, JPEGs take up a fraction of the space of most other formats. There must be a catch, right? Well, yes and no. Let’s explore a little deeper.
JPEG uses an algorithm (mathematical formula) to compress the image. And it does this essentially by “summarizing” parts of the image with less detail in them. In order to do this, and achieve the incredible ratio of compression which it does, it actually “throws away” some of the data (technically, it’s known as lossy compression - as opposed to lossless compression. An example of a lossless compression algorithm is zip).
Well, “throwing away” bits of your picture doesn’t sound too good, does it. Actually, it’s not as bad as it sounds. When you save an image as a jpeg, you’re presented with a choice of quality setting (exactly how this is presented varies from program to program). As you would expect, the higher the quality, the less compression is achieved, and vice versa. However, even at fairly high quality settings, the amount of compression is still substantial, yet the degradation (in the form of compression artifacts) is barely perceptible.
By the way, if you do need to send an image file which is larger than about 1 or 2 MB, a file transfer service like yousendit.com or megaupload.com is a much more elegant way to do it than e-mail. It saves clogging up both your own e-mail as well as the recipient’s. All you do is browse to the file on your computer and enter the recipient’s e-mail address, and the file transfer service does the rest.
Hopefully you’re now ready to give it a try! In summary:
1. Know your goal
2. Resize the image to the appropriate pixel dimensions, if required
3. Save in JPEG format with a reasonably high quality setting
Now go ahead and e-mail some pictures around the place!
Steven Pam is the founder of SmartShots Commercial Photography, based in Melbourne, Australia.
He specializes in photographing people, cars, and anything to do with aircraft.
