Design Note

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Below you'll find information specific to a link you clicked on in the Main Notes page.

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IMAGE SIZE BASICS

Resampling

Understanding resampling in Photoshop's
Image Size dialog box
What is Resampling?
Resampling refers to changing the pixel dimensions of an image. Downsampling or decreasing the number of pixels deletes information from the image. While this may sound bad, Photoshop actually handles downsampling very well and the loss of information is not noticable to the eye. Upsampling or increasing the number of pixels adds information to your image. This technique actually causes your image to appear blurry, not a good thing. There is a small amount of room for upsampling, but should be avoided most of the time. Bicubic interpolation is the highest q uality of adding or removing pixels that Photoshop uses.

Original Image
This Image Size dialog box illustrates an original image measuring 5" x 7" @ 300 ppi and a file size of 9.01 megabytes.

Downsampling
This Image Size dialog box illustrates a Downsampled image in which the resolution was changed from 300 ppi to 150 ppi.

Notice that when you downsample by changing either the Resolution or the Document Size that the Pixel Dimensions(File Size) changes to reflect the discarding of pixel information.

CROP TOOL

Another tool for adjusting the size and resolution of your image is the Crop Tool.

Pictured here is the Crop Tool and it's options. Use the Crop Tool with it's options blank and simply click and drag around the area of your image you want to retain.

Original image and image showing Crop Tool bounding box. Area outside selection is dimmed in order to highlight the area of the image which will be retained after cropping. If you're not pleased with the bounding box you can still resize it by dragging the corner handles or side handles indicated by the sample squares.

You can also enter dimensions and/or resolution in the Crop Tool Options.

IMAGE SIZE BASICS

Upsampling

This Image Size dialog box illustrates Upsampling an image from a resolution of 300 ppi to 600 ppi. The Pixel Dimension(File Size) has increased from 9MB to 36MB. Where does the additional pixel information come from? Photoshop tries to do its best job by looking at two pixel's colors and values and averages the needed pixel information between them. The result: a blurry image.

Lesson learned: Feel free to downsample an image, Photoshop does that very well. Beware of Upsampling because you will most likely end up with a poor quality image. This technique is particulary useful when preparing images for the web where small file sizes are all important.

Another option to consider if you're main intention is not to change file size(total number of pixels in an image measured in kilobytes, megabytes, etc) is to uncheck Resampling which I'll refer to as Resizing.