Resizing an Image
Photoshop CS6 Tutorial
How to Resize an Image in Photoshop
Images from the camera are rarely the correct size for your projects. Resizing an image allows you to change the dimensions, resolution or both.
With an image open, choose Image > Image Size.
In the Pixel Dimensions section you can resize based on pixel size or a percentage of the original image.
In the Document Size area you can change to overall Image Size and Resolution.
To keep from distorting the image, make sure that Constrain Proportions is checked.
If you are enlarging your image, use Bicubic Smoother.
Bicubic Sharper works better with image reductions.
Maintaining the Resolution
If you can resize the image by changing the resolution and retaining the same pixel dimensions, there is no re-sampling. Resolution is generally set in Pixels Per Inch (ppi).
Web images are usually 72 ppi and print images are 300 ppi. Images are defined as a series of little colored squares called pixels. To see your image on a pixel level, zoom in real close.