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Chapter Nine. Sizing > Resolution & Sizing

Resolution & Sizing

Q1:Is it possible to increase the resolution of a file? Someone sent me a 72-ppi file. Is it possible to keep the physical dimensions the same but increase the resolution for printing?

A1: While it is possible, it is not advisable. Increasing the resolution without changing the physical dimensions is called “interpolation,” a process where new pixels are “invented” to make the image appear higher in resolution. Usually this operation creates a file that technically has higher resolution, but the quality suffers. One possible solution is to gradually increase the size 10% at a time. You do that by going to Image>Image Size and changing the Width and Height measurements to Percent and entering 110 in each field. Repeat this operation a number of times, which will increase the physical size. Then with Resample Image still checked, increase the Resolution amount. Another setting that can help when you increase the resolution is to change the Resample Image option to Bicubic Sharper.

Note: Depending on the image, it may not be a total loss to use interpolation, particularly if the image doesn't contain fine detail or is going to be incorporated in a design where it might be blurred or faded.

Q2:How do I lower the resolution of a file? I scanned an image at a higher resolution than I really needed and now I need it to be at a lower resolution. Where do I do that?

A2: Use the Image Size command found under the Image menu. Make sure that Resample Image is checked. Now type the resolution you want in the Resolution field—you should not see the document's width or height change, only the resolution. Click OK. Note: Although technically possible, do not use this method to increase the resolution of a file, since it is an “artificial” improvement.
Q3:How do I calculate resolution for images sent to a commercial printer?
A3: Your best bet is to talk to the printing company to get their requirements. Most printers will either tell you what resolution to use in Photo-shop, or will tell you the line screen they're using on their printing press. As a general rule of thumb, take the line screen they use and double it. For example, newsprint is often printed at a line screen of 70–85 lpi, whichmeans you would need a resolution of 140–170 ppi. Although some people always use a figure of 300 ppi, you can see how in certain cases (such as newsprint), 300 ppi is much more than needed, meaning your file size would be much larger than necessary.
Q4:Why is it that when I paste one image into another, the pasted image is too large/small?
A4: This happens when the two documents are not in the same resolution. For example, if you copy some pixels from an image at 72 ppi and paste into a document that's 150 ppi, the pasted area will appear much smaller. Pasting from a higher resolution to a lower resolution file will result in larger pasted pixels. Since there's no way to avoid this, just make sure you are prepared by looking at the resolutions of both files before you start (by going to Image>Image Size and checking the Resolution field).



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