Image resolution for printing is the fineness of detail you can see in an image. It is measured in pixels per inch (ppi), or dots per inch (dpi)The more pixels per inch, the greater the resolution. You can think of this as similar to thread count in cotton sheets, or knots in handmade carpets: the higher the number per inch, the better the quality.
When you come to print, the pixels (ppi) are translated into dots (dpi). The image size of a file is a measure of the number of pixels along an image’s width and height. This is called the pixel dimensions and is measured in MBs. The document size of an image determines how large or small our image is going to print based on the image resolution.
As you change the resolution of a file, its physical dimensions change, and vice versa. Imagine the file as a flexible ball of data: rolled up tight there is a high resolution (pixel density) but low (linear) size. Rolled out flat, the resolution (density of pixels) is lower but the (linear) size has increased. It’s just like pastry!
Resizing is changing the size the image will print without changing the number of pixels in the image. Resampling changes the number of pixels in the image. Photoshop resamples images using interpolation methods to assign colour values to any new pixels based on the colour values of existing pixels.
You can read more about the different methods here. Information about how to use these elements in creating the best quality file for printing can be found in Using Photoshop to Resize and Resample. Understanding these basic terms will help you create better files, and in turn, better prints. To find out what resolution your file should be before printing, always use our ‘Technical Help Calculator’.