Understanding Resizing and resampling digital images. When you resize a raster image, you’re changing the pixels themselves, which can result in a “pixelated” or blurry image

1. Raster Images
Raster images are made up of a set grid of squares called pixels each pixel
is assigned a color. Unlike a vector image, raster images are resolution
dependent, meaning they exist at one size. When you resize a raster image,
you’re changing the pixels themselves, which can result in a “pixelated” or
blurry image. When you resample an
image larger (upsample,) your software
is essentially guessing at what image
data is missing based on the surrounding
pixels. This is called interpolation.

2. Resizing
Resizing will not change the original
number of pixels, the quality of the
image, or the file size. It only changes
the size of the pixel (resolution)
Image resolution for printing:
300 PPI (pixels per inch)
72 pixels per inch
144 px x 216 px
Print out = 2” x 3”
Image size: 91k
300 pixels per inch
144 px x 216 px
Print out = 1/2 inch x 3/4 inch
Image size: 91k
The image on the
right has been
downsampled
(interpolated)
Photoshop threw
away pixels to make
file size smaller.
24px x 36px
50ppi

3. 144 px x 216 px
Print out = 2.5 feet x 4 feet
5 pixels per inch
Image size: 91k
—Actual pixel size
Resizing

4. Resampling
Resampling means you’re changing the pixel dimensions of an
image. When you downsample, you’re eliminating pixels and
therefore deleting information and detail from your image. )
72 pixels per inch
144 px x 216 px
Print out = 2” x 3” Image size: 91k
300 pixels per inch
1200 px x 1800 px
Print out = 4” x 6” Image size: 6.1mb

5. When you upsample, you’re adding pixels. Photoshop uses
interpolation. Interpolation means Photoshop analyzes the colors of
the original pixels and “manufactures” new ones, which are added to
the existing ones. You can specify the interpolation method in
the Image Size dialog box Be sure to have “Resample” checked
72 pixels per inch
144 px x 216 px
Print out = 2” x 3”
Image size: 91k
300 pixels per inch
1200 px x 1800 px
Print out = 4” x 6”
Image size: 6.1mb
Note:
Upsampling
small files will
cause degrade in
Image Quality!