Digital photos can be viewed on computer screens or printed on paper. Most of the time you are most likely to print on standard paper sizes like 4X6 or 5X7. Every now and then however you might want to make enlargements of some photos that you specially care about. Print enlargements quality depends on your digital camera mega pixels figure, here is how.
Every digital photo that you take with your camera has a certain resolution normally expressed as the number of pixels in the photo or sometimes as two numbers depicting the number of pixels over the X axis and the number of the Y axis (multiplying these two numbers provides the total number of pixels in the digital photo).
When you print digital photos you are really printing those digital pixels on paper. If the paper size is very big relative to the digital photo resolution the result will be a poor quality print. One of the most noticeable results of such poor quality is your ability to actually see the individual pixels on the print also known as pixelization.
So how can you determine what is the maximum print enlargement that you can make from a certain digital photo? There is no one precise answer. In addition to the actual number of pixels in the photo there are other things that can influence the answer like how many details are in the photo, what were the lighting conditions and more. Even when considering the number of pixels the answer is not precise since different people would have different views about the quality of a photo print.
A rough estimation of what comprises a good print quality is based on the pixels density or in other words the number of pixels per inch on the printed photo. This is also known as PPI (pixels per inch) and it represents the number of pixels over an axis line.
Experiments show that the following qualities are usually associated with a specific PPI number:
PPI 100 - fair to bad
PPI 200 - good
PPI 300 and up - very good
The next logical step would be to figure out how many mega pixels are needed for good quality printing on a specific paper size. Fortunately calculating this number is very easy. To do that all you need to do is to simply multiply the page length by its width in inches. The result is the number of square inches on the page. Next multiply this number by the square of the PPI number and the result is the number of pixels on the page which is the number of pixels we want our source photo to have. Here are the numbers calculated for some common sizes (for 100,200 and 300 PPI respectively):
page 4X6 0.24MP 1MP 2MP
page 5X7 0.35MP 1.5MP 3MP
page 8X10 0.8MP 3MP 7MP
page 11X14 1.5MP 6MP 14MP
page 16X20 3MP 12MP 28MP
page 20X30 6MP 24MP 54MP
This table is just an estimation of what is considered suitable number of mega pixels for different paper sizes. There are many other factors to consider when making enlargements. Experimenting with different paper sizes is the best way to go but it can be expensive. In addition sometimes what is considered poor quality pixelization can actually be a nice artistic effect which strengthen the unfortunate fact that in addition to the above calculation some common sense and experience are needed in order to match a specific digital photo to a specific paper size enlargement.