resolution goldfish

On the left a Digital 72dpi image blown up 200% and on the right a Print based 300dpi blown up 200%

How many time have you heard that saying from a disappointed client. If that disappointed client has ever been you, then we at Creative Fabrik are here to make you happy again with some help to understand the differences between images you see on screen and images in print. One difference is resolution and the other is the chosen colour mode.
Resolution
Resolution is basically a measure of how much information is in a dot-based 'rastor' file. To clear this up straight away a 'rastor' file is made up of tiny dots, a vector file is made up of a mathematical path. Vectors are not resolution based and the same file can be printed on a stamp or on the side of a bus as you are only increasing the mathematical path.
Now in a more traditional dot-based printing (like a glossy magazine or newspaper) resolution is critical and is measured as dots per inch, or dpi. Newspaper printing uses a different way of printing and are normally printed at a much lower resolution than glossy magazines. If you take a look at a photograph in a newspaper you will be able to see the dots that make up the image. 
Now take a look at a glossy magazine and you probably can’t see the dots with the naked eye. With the help of a magnifying glass, you would see that they are still there, but they are much smaller than the dots in the newspaper photo, so, basically there is a condensed amount of dots in an inch. The glossy magazine photos have a higher dpi, probably about 300dpi, the newspaper has less dpi, probably about 120dpi... the higher the dpi, the sharper and clearer the image produced will be.
Digital images on the other hand are measured in pixels per inch, or ppi, which corresponds to dpi in printing. Now this is where the difference comes as a computer screen has very low resolution compared to print — most are only 72 ppi although the new Retina displays are 144ppi. The images don’t need to be any higher in resolution to look good on a monitor, and using a 300dpi image on a website will give the user no more clarity in viewing but will slow the website down... lower resolution make for smaller files that are faster to load, so it makes sense. The problem normally happens when you take, for instance, your logo from the website at 72dpi and expect it to look good on your business cards which needs a 300dpi image.
There are exceptions to this rule and it comes down to the actual physical size of the image and how small you are intending to print the said file. If for instance the image is huge on your web site, and really small on your business cards. For example, an image that is 900mm wide at 72 ppi it can be resized, keeping the total numbers of pixels the same, to be approx 200mm at 300 ppi.
Always remember you can do this resizing going down in resolution but once you have done this the information in the image has been lost so attempting the then stretch or enlarge the image will always give you a blurry, out of focus result.
Colour Mode
In printing terms we have decided that we need to have 300dpi images but the process of printing uses a colour mode known as CMYK, this is a 4 colour process using Cyan, Magenta, Yellow and Black inks that are printed on top of one another at different percentages to give you all the colours that you need.
Now Digital images, using 72ppi, are viewed in anything that is light based like a TV, computer monitor or mobile phone and these use a colour mode known as RGB, this is a 3 colour process using Red, Green and Blue and again this gives you all the colours in the spectrum when using the 3 colours as percentages.
Common 'Dot Based' Rastor File Types
For print you will need uncompressed .tif and .eps files
For digital you need .gif and .bmp files
For both you can use .jpg, .png and .pdf
Summary
Im summary keep as much resolution in your photos and images and if you are looking to resize... either small or large always go back to the original you have saved and make sure you save it at the highest resolution.
For Brand Identities always try to design and deliver these in a vector format, using Adobe Illustrator as you are not resolution based unless you really must have a 'rastor' image, using Adobe Photoshop in there, the KISS principle ;-) is always best for Brand Identites.
Always happy to help, just contact Creative Fabrik for more information.

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