To confidently import images into software programmes at the correct resolution for printing can be a little tricky…
When the resolution is wrong, very often the images will become blurry or pixelated or at the opposite end of the scale your file will suddenly become enormous and eat up memory.
Importing images into some software programmes can be very deceptive. Images at different dots per inch will be imported at the same size and you will be unable to judge how they will print. An image at 300 dpi has much more detail and has denser ‘dots’ than an image at 72 dpi which will subsequently appear almost a quarter of the size.
Pixels per inch is ‘ppi’ – however it is always referred to as ‘dpi’
The resolution of a photo is described in pixels but by width and height, its size is only relevant when compressed to either 300 or 72 dpi. etc.
The resolution of a printed image is described in ‘pixels per inch’ which is usually 300dpi.
An image created at 300 x 300 pixels will be 1 inch square (@300 dots per inch). However if you create an image 72 x 72 pixels and save it as 72dpi it will also be and inch square. But opening it in a 300 dpi document it will measure 0.24 inches (0.61cm) as the width and height of the 72 pixels will be matched to the ratio of the 300 dpi document. (approx a quarter of the size)
Programmes such as Adobe Illustrator which generates ‘vector’ graphics imports files in their native dpi, which can be disastrous if outputting a large file that you think will be scaleable. The images you use in those files must be 300dpi at full size.
Microsoft Word is the same, it displays the files at 96dpi and files generated are only 220dpi which is too low for professional printing successfully.
Programmes such as Adobe Photoshop and Microsoft Paint indicate the dpi and allow you to manipulate the images and image sizes.
Jpeg images imported into Quark are imported at 100% but indicate the dpi so you can check the resolution depending on what output you require – i.e. screen or print.
Using a windows pc you can find the pixel size of your images by a ‘right click’ on your image file then go to ‘properties’ and ‘advanced’ to find your dpi.
On a mac ‘get info’ ‘apple + i’
Read the previous article Size Matters! where we looked at images sizes in 72 dpi and 300dpi and compared sizes between screen and print, also in Why is my picture printing badly? gives further information on resolution and quality of printed images.
To successfully use a picture at 300 dpi you need to know the actual size required. To print an image at 10 inches you will need it to be 10 inches actual size at 300dpi.
If you have an original image scanned at 300 dpi, size 2 inches square, the image you will obtain will be 600 dpi when used at 1 inch square, 300 dpi at 2 inches square and 150 dpi at 4 inches square.
A useful trick to be able to know quickly how large a picture roughly can be printed in inches divide your pixel width/height by 300 to determine how many inches in size it will print. If on screen divide by 72.
Just a final note, we know an image is made up of pixels (dots) per inch which generates the size of the image depending on where it is presented, i.e. printed at 300 dpi or on a screen. This can be misleading as not all screens are standard. If your screen is 1024 x 768 pixels an image of 512 pixels in width will take up half the screen, if your screen is only 512 pixels wide the image will take up the whole screen. The resolution your screen is set at will alter the size you see images.
Different screen resolutions and different printing criteria will affect your projects and how they appear. Checking the correct formats and requirements from your printer or output device can make all the difference to your final result. The quality of the images printed in a newspaper will not the be as good a quality as you will find in a book.
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