We often get asked by customers: “what size image do I need?”. Our initial response is usually: “are you using the image on screen, in print, or both? If in print, what are your quality expectations?”. Now this might sounds like we are trying to complicate things, but actually, image resolution is a reasonably simple concept once you “get it”.
In this article I will explain image resolution: what are pixels, DPI (dots per inch), screen size and print size? And how do they affect quality?
Pixels determine the image size on a screen
Digital images are formed from lots (tens of millions in some cases) of different coloured dots, known as pixels. The pixels are tiny and tightly packed, so when viewed on a screen, the individual dots are not noticeable, giving the illusion of a perfectly smooth yet sharp image.
It so happens that computer screens are made up of pixels too, so it is reasonably easy to predict how much space an image will take up on a screen.
Let’s use this picture of Archie. This is one of our free downloads, and is 300 pixels wide x 400 pixels high.
Example image 300 pixels wide x 400 pixels high
If we imagine a computer monitor that is 1300 pixels wide x 800 pixels high, this picture will take up this amount of space on the screen:
And here is our “medium” sized picture of Archie which is 480 pixels x 640 pixels:
Example image 480 pixels wide x 640 pixels high
See how this image takes up more space on the screen:
And what about our “high resolution” version of this image (3024 pixels x 4032 pixels)?
As you can see, the high resolution image is much bigger than this computer screen. So does this mean that you never need high resolution images for screen use? In many cases, that is correct, one of the smaller versions is likely to suffice. However if you were using an image for a full screen background, you may well need the high resolution version, but might want to reduce its size yourself.
DPI (dots per inch) determine the print size
In addition to the number of pixels, digital images have another resolution setting: DPI (dots per inch) which is important for printing images. Printed images are also formed from dots (the pixels from the image become the dots), but the user can decide the quality of the print by setting the appropriate DPI. This setting tells the printer how many dots to print per inch.
High definition printing (magazines, brochures etc.)
For high definition printing found in magazines or brochures, the recommended DPI is 240 – 350, with 300 DPI generally being the industry standard. This means the individual dots that make up the print will be so small and tightly packed they will be invisible to the human eye, even on very close inspection, and will produce the type of smooth yet sharp image one would expect in glossy magazines / brochures etc.
Therefore, to ensure best print quality, you are likely to need a high resolution image with plenty of pixels (dots). Using the high resolution image of Archie as an example, it is 3024 pixels x 4032 pixels. If we divide these dimensions by the 300 DPI we want for our glossy print, we find that this image will print out at 10 inches x 13.5 inches. Perfect to fill a full side of A4:
The high resolution version of this image gives a full A4 page high definition (300 DPI) print
But if we only wanted to print a small picture in the magazine, then we could use the 480 pixels x 640 pixels version which will give a 300DPI print size of 1.6 inches x 2.1 inches:
The 480 pixels x 640 pixels version will give a 300DPI print size of 1.6 inches x 2.1 inches
Low definition printing (posters, billboards etc.)
When an image is to be blown up to very large proportions, a much lower DPI is acceptable. Because this type of image is viewed from distance, it doesn’t matter if the print appears to have low definition when viewed up close, as that is not how it is intended to be seen. When viewed from afar, the individual dots will not be noticable.
So using the high resolution image of Archie, let’s say we were using it on a billboard, we could go as low as 25DPI. From that 3024 pixels x 4032 pixels image we would be able to fill a billboard measuring 120 inches (10 feet) x 161 inches (13 feet).
Low DPI image on billboard
Changing the DPI of an image
The DPI setting supplied with images can vary, but it is easily changed. For example, in Photoshop, open the Image Size information, uncheck “Resample Image” and type the DPI setting in “Resolution”. The width and height will change automatically so you can see how big the image will print at as you change the Resolution.
How to change the DPI in Photoshop
When choosing an image for your project, pay attention to the orientation:
“Landscape” orientation (sometimes known as “horizontal”)
Width / horizontal axis is longest:
“Portrait” orientation (sometimes known as “vertical”)
Height / vertical axis is longest:
Check the image you are interested in matches the orienation of the placeholder on which you are inserting it. Sometimes customers ask for help when they have chosen a portrait image for a banner on their website but the placeholder on their website is landscape. Sometimes we can fix this but it always means cropping the image quite severely, sometimes meaning it loses its impact or meaning.
Help choosing the right sized image from FreeDigitalPhotos.net
We help our customers choose the right sized image in a number of ways:
Image price / size guide
Each image has different dimensions because different cameras take different sized images, or the creator might have cropped some distractions out of an image … there are many reasons why they vary.
So we have created a size guide unique to each image. Look to the right of the image on our website and you will notice the link to “Price / size guide”:
Price / size guide
This gives more information about the size of a particular image. Here is a link to the size guide for Archie.
Sample images to download
We also allow you to download, free of charge, examples of all our sizes, including high resolution. Customers can use these example images to experiment with their designs to work out which size is best for their needs. Whilst the dimensions of the example image will not be identical to the image you are interested in, they still serve as excellent size guide.
Free resizing service
For purchased images only (sorry we cannot offer this service for free downloads) we will change the DPI setting to meet your needs. We will also try and help with cropping and resizing where an image does not exactly fit for you. Please note this service is on a best endeavours basis, and we cannot “upsize” images.
Upgrade an image
If a customer finds they have ordered too small a size, they can upgrade to a larger size and only pay the balance.
Contact us for help
We’re here to help so if you are still unsure which size you need please , explaining what you are using the image for, and we will do our best to help.
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