Digital photography printing - understanding resolution
To get good results in digital photography printing it helps to know how pictures are made up. Every digital image is made up of individual dots called pixels.
. . . ok, back to your computer screen . . .The resolution of any image is a way of saying how many pixels go across, and how many pixels go from top to bottom. If you were to count the dots (or “pixels” as we’re now calling them!) from left to right on your monitor and find there are 1024 of them, then you count how many are up and down and you find there are 768 pixels from top to bottom.
Now for a little bit of maths. The resolution of your screen is:
in our example above it is:
- This is then divided by 1 million (makes 0.786432)
So that's megapixels, but what's "ppi" all about?Resolution is often expressed in another way – by stating how many pixels there are per inch (or "ppi"). This is important in digital photography printing because it determines print quality. The more pixels you can cram into every inch, the better the print will be.
Lets go back to our computer monitor. If your monitor has 1024 pixels across, and the width of the screen is 12 inches (that’s a standard 15” monitor – 15” is the diagonal screen size). The maths:
The more ppi you have, the smaller the dots are. Lets say we make each pixel on our screen half size. We can then fit twice as many of them into the same space:
The picture on the screen would look much sharper and you would have to get a lot closer to your monitor screen before you could make them out individually.
NB: this is what High Definition TV does
How many ppi is enough?The holy grail for good digital photography printing is 300ppi. With 300 pixels crammed into every inch of your image the naked eye cannot make out the individual pixels. The image appears beautifully crisp!
Suppose you’re getting into digital photography and buy a digital camera with 0.8 megapixels. It would be perfect for taking pictures to view on your monitor. But what about printing . . . hmmm sadly not enough ppi. The biggest print you would be able to produce would be (maths again - last time, I promise!):
So our print would be 3.4 inches wide. Not very big, is it?
NB: Prints are determined by the number of “Dots Per Inch”, or “DPI”. Printers use small dots of ink to make their pictures up. The difference between dots and pixels is meaningless. For now just consider a “dot” to be the same as a “pixel”.