Changing the pixel dimensions of an image

When preparing images for online distribution, it's useful to specify image size in terms of the pixel dimensions. Keep in mind that changing pixel dimensions affects not only the size of an image on-screen but also its image quality and its printed characteristics--either its printed dimensions or its image resolution. 

To change the pixel dimensions of an image (Photoshop):

1. Choose Image > Image Size.
2. 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.
3. Under 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.
4. Make sure that Resample Image is selected, and choose an interpolation method. (
5. If your image has layers with styles applied to them, select Scale Styles to scale the effects in the resized image. This option is available only if you selected Constrain Proportions.
6. When you're done setting options, click the OK button.
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.

To change the pixel dimensions of an image (ImageReady):

1. Choose Image > Image Size.
2. To maintain the current proportions of pixel width to pixel height, select Constrain Proportions.
3. Under New Size, enter values for Width, Height, or Percent. The New Size text field displays the new file size for the image.
4. Select a interpolation method from the Quality pop-up menu