Adobe Photoshop CS4 - Manual (Page 68)

61 USING PHOTOSHOP CS4
Opening and importing images
Last updated 1/10/2010
You can specify a default interpolation method to use whenever Photoshop resamples image data. Choose Edit >
Preferences > General (Windows) or Photoshop
> Preferences > General (Mac OS), and then choose a method from
the Image Interpolation Methods menu.
More Help topics
“ Sharpen recommendations ” on page 213
Change pixel dimensions of an image
Changing an image’s pixel dimensions affects not only its on-screen size but also its image quality and its printed
characteristics—either its printed dimensions or its image resolution.
1 Choose Image > Image Size.
2 To maintain the current ratio 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 finish setting options, click OK.
For best results when you produce a smaller image, downsample and apply the Unsharp Mask filter. To produce a
larger image, rescan the image at a higher resolution.
Change the print dimensions and resolution
When creating an image for print media, it’s useful to specify image size in terms of the printed dimensions and the
image resolution. These two measurements, referred to as the document size, determine the total pixel count and
therefore the file size of the image; document size also determines
the base size at which an image is placed into another
application. You can further manipulate the scale of the printed image using the Print command; however, changes
you make using the Print command affect only the printed image, not the document size of the image file.
If you turn on resampling for the image, you can change print dimensions and resolution independently (and change
the total number of pixels in the image). If you turn off resampling, you can change either the dimensions or the
resolution—Photoshop adjusts the other value automatically to preserve the total pixel count. For the highest print
quality, it’s generally best to change the dimensions and resolution first, without resampling. Then resample only as
necessary.
1 Choose Image > Image Size.
2 Change the print dimensions, image resolution, or both:
• To change only the print dimensions or only the resolution and adjust the total number of pixels in the image
proportionately, select Resample Image and then choose an interpolation method.
• To change the print dimensions and resolution without changing the total number of pixels in the image, deselect
Resample Image.
3 To maintain the current ratio of image width to image height, select Constrain Proportions. This option
automatically changes the width as you change the height, and vice versa.