Changing image dimensions, resolution, and paper size
You can change the dimensions and resolution of an image. You can also change the size of the paper border that surrounds an image.
In this section, you’ll learn about
• changing image dimensions
• changing image resolution
• changing the paper size
Changing image dimensions
You can change the physical dimensions of images by increasing or decreasing their height and width. When you increase image dimensions, the application inserts new pixels between existing pixels, and their colors are based on the colors of adjacent pixels. If you increase image dimensions significantly, images may appear stretched and pixelated.
You can change the height and width of an image without changing the resolution. The center image is the original, the first image has smaller dimensions, and the third image has larger dimensions. Noticethepixelation of the larger image.
To change the dimensions of an image
1 Click Image ` Resample.
2 Enable any of the following check boxes:
• Anti-alias — smooths the edges in the image
• Maintain aspect ratio — avoids distortion by maintaining the width-to-height ratio of the image
3 In the Image size area, type values in one of the following pairs of boxes:
• Width and Height — let you specify the image dimensions
• Width % and Height % — let you resize the image to a percentage of its original size
When you change the dimensions of an image, you produce better results using width and height values that are factors of the original values. For example, reducing an image by 50 per cent produces a better-looking image than by reducing the size by 77 per cent. When reducing an image by 50 per cent, the application removes every other pixel; to reduce an image by 77 per cent, the application must remove pixels irregularly.
Changing image resolution
You can change the resolution of an image increase or decrease its file size. Resolution is measured by the number of dots per inch (dpi) when the image is printed. The resolution you choose depends on how the image is output. Typically, images created only for display on computer monitors are 96 or 72 dpi and images created for the Web are 72 dpi. Images created for printing on desktop printers are generally 150 dpi, while professionally printed images are usually 300 dpi, or higher.
Higher resolution images contain smaller and more densely packed pixels than lower- resolution images. Upsampling increases the resolution of an image by adding more pixels per unit of measure. Image quality may be reduced because the new pixels are interpolated based on the colors of neighboring pixels; the original pixel information is simply spread out. You cannot use upsampling to create detail and subtle color gradations where none existed in the original image. When you increase image resolution, the image size increases on your screen; by default the image maintains its original size when printed.
Downsampling decreases the resolution of an image by removing a specific number of pixels per unit of measure. This produces better results than upsampling. Best results are usually achieved when downsampling is done after correcting an image’s color and tone but before sharpening. For more information about correcting and sharpening images, see “Adjusting color and tone” on page 287 and “Retouching” on page 315.
You can change theresolution and size of an image at the same time. The center image is the original, the first image is downsampled, and the third image is upsampled.