When graphic designers and printers start talking about image resolution, most people's eyes start to glaze over. However, understanding a few simple concepts about image resolution can make communicating with your web designer, graphic designer or printer a bit easier, and can make your next design project go more smoothly.

What is Resolution?
An image's resolution is measured by the number of pixels or dots per inch of printed size. When referring to screen images, resolution is stated in pixels per inch (PPI), and when referring to printed images, it's stated in dots per inch (DPI). Why? Computer screens use pixels. Printers use dots.

A pixel is simply a dot of color. When you put all of the pixels or dots of color together, you get the full image. A 100 x 100 pixel image is actually comprised of 10,000 individual pixels that, when viewed together as a whole, make up the image. The more pixels an image contains, the more detail that image will have and the sharper it will appear.

Web Images: 72 PPI
Most computer monitors display 72 DPI. Therefore, when preparing images for use on a website, 72 DPI is the norm. When it comes to web, you want your images to be as small in file size as possible so that your pages load quickly. Reducing the resolution to 72 DPI will help to get your images as small in size as possible. You CANNOT use web images for print projects because they will come out jagged and pixelated.

Remember when resizing your high-resolution images for the web, it's important not to overwrite your original files. Before resizing an image, make a duplicate of your image file first and amend the file name by adding 72 after it. This way you will have both your original high-res file and your new low-res file available for future use.

Print Images: 300 DPI
In print projects, high resolution is essential. If the images that you include in a print project do not have high enough resolution, they will appear fuzzy, jagged, or blurry. Most professional printers require a minimum of 300 DPI for all images at the final print size. Generally, the higher the resolution of your image is, the better the quality of the image will be when printed.

How to Check the DPI of an Image
If you're on a PC:
1. Right-click the image file. Select "Properties" from the context menu.
2. Click on the "Summary" tab in the top of the pop-up. If "Title," "Subject" or "Author" fields are displayed, click the button "Advanced" at the bottom.
3. In the Advanced properties view, the fields "Horizontal Resolution" and "Vertical Resolution" indicate the respective DPI.
4. Divide the DPI values by either 300 or 72, depending on whether you are checking for print or web resolution, and you will get the maximum size that you can use the image.

If you're on a Mac:
1. Right click on the image file. Select "Get Info".
2. Under "More Info: > Dimensions" you will see the DPI information displayed.
3. Divide the DPI values by either 300 or 72, depending on whether you are checking for print or web resolution, and you will get the maximum size that you can use the image.

Scanning Images and Digital Photos
You can either scan images or take photos with a digital camera for use in both website or print projects. The important thing to keep in mind is the physical size the images will need to be and the final resolution needed (for example, a 5"x7" photo @ 300 DPI in a print piece, or a 300 x 500 pixel image @ 72 DPI for a website, etc.).

If in doubt, don't know the final size, or think you'd like to use the image for both print and web, it's better to scan or photograph the image at a high resolution and downsize it later, if required.

Scan your images as large as possible; it's easy to resize them later. If you scan an image to small you may have to re-scan at a later date to get a larger print.

If you need an image that's twice the size of the original photo - scan it at 600 PPI. You can then enlarge it 100% and it will print at 300 PPI.

What Size Can I Use My Images?
To determine the size of images you have, simply divide the resolution required for your project into the pixel width and height of your image to get the maximum size you can use the image.

Example 1: A digital image that's 1500 PPI wide will print 15-inches wide if the print resolution is 100 PPI. If you change the same image to a print resolution of 300 PPI your final print size will becomes 5-inch wide.

Example 2: If your image file is 3000 PPI wide x 2400 PPI high with a print resolution 300 PPI, your final print size will be 10 x 8 inches. The same file with a print resolution of 150 PPI will give you a final print of 20 x 16 inches.

Cropping
When you are evaluating the image you want to use in your project, consider if you will be using the entire image, or if you will be cropping it. If you will be cropping the image, then the cropped portion will need to meet the resolution and size requirements.

Image Conversion
It is not possible to change a low quality image to a higher quality image simply by saving it with higher DPI settings. The image will have more dots per inch; but the quality will remain the same or even degrade the image further.

It is not possible to convert a low quality image into a vector file simply by saving it in a vector format. When this is attempted the low quality image is simply embedded in the vector file and NO conversion takes place.

When it comes to resolution and image size, you can't increase file resolution – you can only decrease it.

Download a PDF Version of this Article: