Resizing and Resampling
RESIZING AND RESAMPLING: Both of these terms refer to the same image manipulation. When you resize / resample you are specifying new pixel dimensions for that digital image. This action changes the pixel resolution of your digital image.

It is important to understand that when you resize an existing image's pixel resolution you aren't necessarily changing the originally assigned print resolution (document resolution), which is the PPI setting. Also, changing just the assigned PPI number after image creation does not change the pixel resolution of the image.

Changing only the assigned output resolution or PPI just scales the existing pixels to be larger or smaller on your photo paper and thus to a larger or smaller print size. You can change the pixel resolution of an image (resize) or its print size (PPI) independent of each other. You can also change both the image resolution and output resolution at the same time. Changing both image resolution and output resolution at the same time is known as resizing and rescaling the image.

See an example of Adobe Photoshop's image size dialogue box on the upper left. When the resample box is checked, you will be changing the pixel dimensions of your image when you insert new numbers in any of the tool's dialog boxes. When the resample box is not checked, you will only be allowed to change the print size to be made from the existing pixels. You can also use your imaging program's 'Image Size' dialog box to resize the pixel dimensions and rescale the new pixel resolution to a requested print size all in one operation. This combo resize and rescale is accomplished by selecting a new print size width and height and a new specified print resolution and keeping the resample box checked. The imaging program does the math to determine the new pixel dimensions necessary to print to the photo size and print resolution (ppi) you requested.