WHAT IS RESOlution?

 

What is resolution and dpi, and why should it matter to me? Often people will ask you to send your image to them in “hi res” or “300 dpi”. What does this mean? There is a lot of confusion about this, and hopefully my short  tutorial will  give you a basic understanding of the idea.


TWO TYPES OF RESOLUTION

There are two types of resolution, pixel resolution and embedded resolution. Pixel resolution and embedded resolution are different and independent of one another.

The confusion often comes in when people use the two interchangeably. Imbedded resolution is expressed in dpi, pixel resolution is not.


• Pixel Resolution is the total number of dots (pixels) that make up your image.

• Embedded resolution (dpi) is the number of dots per inch used in printing.


PIXEL RESOLUTION

When you shoot a picture with your digital camera, it records the image in an array of millions of pixels, tiny light sensitive photodiodes. The number of these pixels is the resolution. In digital cameras, this is expressed in megapixels, which means how many millions of pixels make up an image. A typical resolution from a 5mp camera might be 1920 pixels high by 2560 pixels wide, or 1920x2560. The resolution increases with pixel count. The pixel count also determines the file size of your image, the more pixels the larger the size of the file.


EMBEDDED RESOLUTION

Embedded resolution is used to tell the printer how far apart to place the dots. The higher the density of dots (higher resolution), the closer they are together for the same print size and the more detail an image can have. An image printed at 150 dpi (dots per inch), like in a newspaper, will not be as sharp and detailed as a glossy postcard printed at 355 dpi.


IMAGE SIZE AND INCHES

Your camera and computer measure images in pixels, while printers measure in inches. This is important, because in order to print an image, pixels need to get translated to inches.


The embedded resolution will affect how large (in inches) you can print your image.


For an image with the same pixel resolution:

A high embedded resolution (higher dpi) will print a smaller image (the pixels are packed tighter).

A low embedded resolution will result in a larger image (the pixels are more spread out).


If someone requests your image “at 300 dpi”, they also need to let you know the resolution and the size in inches. Ideally, they would ask for the exact pixel dimensions (i.e. 1920x1920 pixels) since pixel resolution and embedded resolution are independent of each other.

 

EXAMPLE

300 dpi is required by most commercial printing equipment, including that used by most publishers.


Your 5mp camera shoots a1920x2560 pixel image.

This would make:

a 6.4” x 8.5" magazine print @300 dpi

a 9.6” x 12.8" desktop print @200 dpi

a 12.8” x 17" newspaper print @150 dpi

a 26.7” x 35.6" monitor image @72 dpi (this is why sometimes an image won’t fit on your screen when viewing at actual pixel size)