Section 86. About Size and Resolution

86. About Size and Resolution

BEFORE YOU BEGIN

78 Change Photo Resolution and Size

SEE ALSO

87 Change Image Size or Resolution

88 Change the Working Area Without Affecting Image Size

Two of the most common changes you'll make to an image are to adjust its size and to change its resolution. By size , I'm referring to an image's dimensions when printed, not its size onscreen. An image's resolution is determined by the number of pixels (dots) per inch.

To compute an image's print size, Paint Shop Pro looks at the number of pixels in an image and their relative size (the number of pixels per inch). Take a look at the first figure here, which depicts an image that's 10 pixels wide by 5 pixels high, using an imaginary scale of 16 pixels per inch. Based on the size of these pixels, the printed image will be about 1.6" wide by .81" high.

An image that's 10 pixels wide by 5 pixels high.

To compute the resolution of an image, you simply count the number of pixels per inch (ppi). Luckily, PSP does that for you, and you can view the print size and resolution of an image in the Image Information dialog box (choose Image, Image Information from the menu bar). The print size is listed as Dimensions and the resolution as Pixels per Inch . If you never plan to print a certain image, the image won't need a high resolution (a great number of pixels). But for you to print an image, you need the highest number of pixels you can getthe more the better. You must have an image resolution of 300ppi (pixels per inch) to create a high-quality print using an outside lab; for home printing, 200ppi usually does just fine.

NOTE

High resolution (over 200 pixels per inch) is unnecessary for an image destined to be displayed on a computer monitor or a television screen because NTSC standard TV resolution is 72 dots per inch and computer screen resolutions average 102 pixels per inch.

An image's print size and its resolution are interdependent; changing one without changing the other will affect the image's print quality. Reducing resolution while maintaining the same print size, for example, decreases the number of pixels per inch and, as you can imagine, inflates the size of each pixel. If the pixels become too large, a mosaic effect called pixelation might distract you from seeing the image as a whole. Look at the first figure showing the 10x5 rectangle. If you change the size of the pixels and make them twice as big (as shown in the second figure), you'll get a much larger rectangle, but the pixels will be much more apparent. When printed, the rectangle might look more like a mesh of dots than a solid rectangle, which is probably not the effect you're going for. The same is true of any graphic image: Make the image larger without increasing the number of pixels (resolution), and the pixels will become bigger and more evident in the final print.

Enlarging the pixels increases the image size while decreasing its quality.

Suppose that, instead of changing the size of the pixels, you maintain their relative size, but double their number. Once again, you'll also double the print size, although the print quality will remain the same, as shown in the third figure.

You can also enlarge an image without sacrificing quality by adding to the number of pixels.

NOTE

To increase the size of an image without changing its resolution, use the Image, Resize command to resample it. See 87 Change Image Size or Resolution .