Most of your digital photos are going to be either viewed on your computer screen or printed on relatively small and standard photo paper sizes such as 4 by 6 and 5 by 7 inches. Every now and then however you would like to print bigger digital prints also known as enlargements
The digital photos that you take have a certain resolution associated with them. The digital photo resolution is determined at the time the digital photo is taken. Every digital camera supports a certain maximum resolution expressed in the number of mega pixels in a photo. Digital cameras can however be set to use lower resolution usually in order to save on disk space since lower resolution digital photos result in smaller photo files.
When printing digital photos on Snapfish or for that matter or any other photo printing service you must make sure that the paper size you are printing on is correct for the resolution of the digital photo that you are printing. If the digital photo resolution is too low for the paper size the result will be a printed photo that is pixelized. Pixelized digital photos prints are prints in which each pixel is big enough for the human eye to see. In other words when looking at the print instead of seeing a smooth photo the viewer can see each individual pixels as the pixels do not blend into each other as they should.
What the right resolution for each print is a function of a few factors. One is the paper size another one is the distance from which the paper print will be viewed. Usually the distance from which a paper photo is viewed correlates to its size so many times people quote the paper size as the sole factor for what resolution is needed for a good print.
Snapfish allows you to choose from many photo paper sizes and allows you to upload photos for printing in any resolution that you choose. It is really up to you to make sure that the prints you are making are correct for the photos that you upload.
So what is the method for determining the needed resolution? Printed resolution is measured in dots per inch or in other words in how many dots or pixels are printed on every inch worth of paper. The dots per inch can be calculated by dividing the total number of pixels in a digital photo by the paper size. So if you print a specific digital photo on few different papers every time you use a bigger paper the dots per inch number goes down and the print quality goes down too.
Usually as a rule of thumb 200 dots per inch and up result in a good print while 300 dots and up result in a very good quality print. Here is a table with some pre calculated minimum digital photo resolution needed for good and very good paper prints for different paper sizes:
page 4X6 1MP 2MP
page 5X7 1.5MP 3MP
page 8X10 3MP 7MP
page 11X14 6MP 14MP
page 16X20 12MP 28MP
page 20X30 24MP 54MP
This article and more are from Danette Mckay who is an expert in his field. snapfish printing provides more in depth information.