Resampling images

Changing the pixel dimensions of an image is called resampling. Resampling also affects the display size of your image. When you downsample, meaning that you decrease the number of pixels in your image, information is deleted from the image. When you resample up, or increase the number of pixels in your image, new pixels are added based on color values of existing pixels.


Resampling pixels that make up the dog's eye A. Downsampled B. Original C. Resampled up (Selected pixels displayed for each image.)

Keep in mind that resampling can result in poorer image quality. For example, when you resample an image to larger pixel dimensions, the image will lose some detail and sharpness.

Applying the Unsharp Mask filter to a resampled image can help refocus the image's details.

To avoid the need for resampling, scan or create the image at a high resolution. If you want to preview the effects of changing pixel dimensions on-screen or print proofs at different resolutions, resample a duplicate of your file.

Resampling affects not only the size of an image on-screen but also its image quality and its printed output--either its printed dimensions or its image resolution.

If you're preparing images for the Web, it's useful to specify image size in terms of the pixel dimensions.

To resample an image:

1. Choose Image > Resize > Image Size.
2. Make sure that Resample Image is selected, and choose an interpolation method:
• Bicubic is the slowest but most precise method, resulting in the smoothest tonal gradations.
• Nearest Neighbor is the fastest but least precise method.This method can result in jagged effects, which become apparent when distorting or scaling an image or performing multiple manipulations on a selection.
• Bilinear is the medium-quality method.
3. To maintain the current proportions of pixel width to pixel height, select Constrain Proportions. This option automatically updates the width as you change the height, and vice versa.
4. In Pixel Dimensions, enter values for Width and Height. To enter values as percentages of the current dimensions, choose Percent as the unit of measurement.

The new file size for the image appears at the top of the Image Size dialog box, with the old file size in parentheses.

5. Click OK to change the pixel dimensions and resample the image.

For best results in producing a smaller image, downsample and apply the Unsharp Mask filter. To produce a larger image, rescan the image at a higher resolution.