Resizing an image

Sometimes you want to make an image smaller or larger, or create a thumbnail of an image. Keep in mind that making an image larger will usually result in a more grainy looking image.  Choose the Image: Image Size... menu command. Then enter the new width or height in the lower portion of the resulting dialog box. Finally, click OK.  Note: If the Constrain: Proportions check box is checked, then the aspect ratio of the image is locked. Changing the Width will automatically change the Height, and vice versa, to keep the image proportion constant.

Sharpening an image

The human eye has a natural tendency to view a scanned image as "soft" or out-of-focus. You'd think that a higher resolution scan would help, but that's not the case. All scanned images need some sharpening, even those scanned on high-end drum scanners. Master printers and color separators will attest to this fact--they've been dealing with this problem for years.

"Unsharp masking" is the trade term for a standard technique that printers and color separators use to sharpen images by accentuating the differences between adjoining areas of significantly different hue or tone. The traditional technique uses a mask that's a slightly out-of-focus duplicate of the original image. When the original is rescanned with this mask, there is an increase in the degree of contrast at the boundaries of tone shifts, however, subtle gradations in tone and hue remain untouched. The result is increased sharpness where you would normally want it--in the most highly detailed areas of the image.
 
 

To apply an unsharp mask to in image using Photoshop, select the Filter: Sharpen: Unsharp Mask... menu command. There are three settings you can choose. Toggling the Preview check box on and off while watching your image will give you feel for the results of changing each setting.        Radius refers to the dimension, in width, of every sample that will be affected by the Unsharp Mask algorithm. You should choose a setting between 0.3 and 1.5, depending on the resolution of the file and what you've designated for the Amount (below). The higher the resolution of the image, the greater the numerical setting for Radius. A good rule of thumb is to use the output resolution divided by 200. For example, designate a Radius of 1 for a 200 dpi image. Designate a radius of 1.5 for a 300 dpi image. The more Amount you use, the less Radius is necessary.
Amount refers to the intensity of the Unsharp Mask effect. A setting between 50% and 150% will do, depending on the Radius. The bigger the Radius, the less Amount needed. A "good" setting for 72 dpi images is 60%; however, some images need more than this, and others less.
Threshold specifies how many numbers of samples in an image will be sharpened. A setting of 0 will affect every sample, whereas a setting of 50 will affect almost none of the samples. Highly detailed images such as line art, require a setting of 3, whereas portraits look best with a setting between 5 to 9. (We want to keep minor wrinkles down to a minimum, don't we?)
It can take a while to come up with the right combination of settings for an image. That's why many manufacturers of scanning software now offer sharpening as an option during image capture.

Amount=25  Radius=1  Threshold=5

Amount=120  Radius=1  Threshold=5

Amount=200  Radius=2  Threshold=20