If you use clip art or stock images in your media you will have come across this problem at some time. Your sharp and detailed picture from the web becomes pixelated and blurred when imported into a printable document!
How can a mouse be bigger than an elephant?
The difference is due to the resolution and size of the picture or photograph you have used.
The following diagrams should explain it, the images on computer screens and the internet are all displayed at 72 dpi (dots per inch), however for printing purposes the files required need to be 300 dpi. Converting a 72 dpi photograph or image can done but it reduces the size of the file.
To print an image at A5 size, 148 x 210mm you need an image 1748 x 2480 pixels at 300dpi.
For a screen image to display at the same size the image required is only 420 x 595 pixels (72 dpi)
If you try to print an image 420 x 595 pixels at A5 although it will look big enough it means that when printed the picture will only be 35.48 x 50.29 mm, or it will be so blurred and pixelated you will be disappointed with the quality. Enlarging will cause the degradation of the picture.
The mouse is 80mm square when looking at him on the screen and 227 x 227 pixels, but when added in to a document he will appear as only 19mm square – this can be a bit of a shock! Mice can often give you a bit of a shock – even elephants dont like them!
Images can always be made smaller but it is never recommended to stretch an imagevery much bigger than its original size. As a guide 200% is possible but I wouldn’t recommend enlarging an image by more than 150% and then I would test it.
Recently I needed large format images for an exhibition panel but was unable to find the sizes required at short notice. For good quality graphics the image needs to be actual size at 300 dpi. Half size is often acceptable and produces good enough results.
If you look at a pdf file at 100% and then magnify to 200% it should give you an idea of how your image will look.
When purchasing clip art or stock photos you are given a choice of sizes to download. Use this as a guide to work out what size picture you actually need for your purpose.
This problem occurs with photos used on web sites and also logos designed for web pages and then copied into documents that require printing.
TIP: Any file which is a ‘raster’ file is made up of pixels and cannot be enlarged larger than as stated above without degrading in quality. Always try to obtain a ‘vector’ file for your logo to ensure you are able to use it as varying sizes.
When buying images for your web site buy sizes that you will be able to use at a later date for any consistent media you may need.
Finally – resolution can be tricky and getting caught out is easy especially when obtaining images from the internet. What looks good on screen can be very frustrating when downloaded! Google gives you sizes in pixels for the images displayed and they will usually be at 72dpi. When downloading large stock photo images they will be received as 72dpi jpegs but the size will be huge to allow conversion to 300dpi.
Have you seen any resolution disasters in printed literature that has let down the overall quality of the document?