The misunderstanding of image resolution is something I come across from time to time from my clients. Some people tend to have a basic understanding of this subject but let me try and put it in clear and simple terms to help.
What do we mean by image resolution?
Resolution refers to the number of pixels in an image. Resolution is sometimes identified by the width and height of the image as well as the total number of pixels in the image.
Resolution units can be tied to physical sizes such as pixels per inch (PPI) or dots per inch (DPI). DPI is normally referred to in the print process and PPI more common for screen resolution. This helps us design folk to work out if an image is high enough resolution for print or to be viewed clearly on a screen.
Why is knowing the resolution important?
We have all probably seen an image which is, what we call, pixelated. This means we can see the pixels the image is made up with by the naked eye. Sometimes this can be the desired effect for style but often it is a common mistake. Here is an example
The first image is 400 x 400 pixels. The second image is 100 x 100 pixels scaled up to the same size. Both are 72 DPI
In very simple terms this is what you should be looking for:
300 DPI for print used at 100%
72 DPI or PPI for screen used at 100%
So, what does the 100% thing mean?
This simply means at the physical size. If you import your image in to a design software or Microsoft Word and don’t scale up the image is it said to be used at 100%. It is ok to reduce the size of the image but if you enlarge the image the quality will degrade, detail will be lost, and you will start seeing the pixels with the naked eye. E.g., An image for print should be 300 DPI. If scaled up to 200% the image is only 150 DPI.
So how do we get to 300 DPI for print? Most print material is printed at about 150 screen. Screen, in printing terms, is the little dots that make up the image or colours out of the Cyan, Magenta, Yellow and Black plates. The higher the screen number the better the quality. Newspapers are typically printed at about 85 screen whereas magazines, books and brochures are printed at 150-200 screen. To work out the DPI you simply double the screen number. If you are printing at 150 screen the DPI needs to be 300 at 100% size.
How will you know if you image is fit for purpose?
If your image has been professionally produced, you shouldn’t have to worry. Your image maker or photographer will supply you with a high-resolution image with size constraints. If you have some kind of image software, such as PhotoShop, you can find out that way. Don’t just go off the memory size of the image. I’ve been told, many times by clients, “Well the image is 2mb, that should be good enough.” No, sometimes it’s not depending on the size it will be used at. If you have swiped the image off a Google search then it probably isn’t going to be good enough for print, plus you need to watch out for copyright laws. Not all images on the internet are free to use.
What do I do if the image isn’t high enough resolution and I don’t have anything else?
Your designer should be able to scale up the image a little using image software. I recommend 25% to my clients. You can go larger, but the image will start to lose detail and soften. This, however, is a much better option than doing nothing and seeing those awful telltale pixels. You may have to source another image. There are loads of great royalty free images for very little cost. Your designer should be able to help here or have a look for yourself. Always keep a note of the source of your image. You may be able to go back to the source and ask for a higher resolution.
Using images for screen
This is far easier. The image only needs to be 72 DPI at 100%. Simply, if it looks ok on screen to you it is probably ok. You can always check on-line if you are using images for social media for a recommended size. Such as 2000 x 2000, 72 DPI for Instagram.
I hope you have found this useful and easy to understand. If you do have any questions, please do not hesitate to drop me a line. I’d be happy to help.