DPI refers to the dots of ink per inch that an image will be printed at. Making an image 300 DPI is recommended for professional print quality images. The resolution of the images taken on a digital camera are usually set at a certain value -- typically 72 DPI. To produce an image with a specific DPI value, you need to use an image-editing program on your computer.
Open Adobe Photoshop on your computer. You can access it from either a desktop icon, your “Start” menu or via “apps” or “Programs.” Alternatively, if Photoshop is your default image program and you've saved an image to your computer, double-clicking on the image will open it in Photoshop.
Click on the “Image” tab in the top toolbar. From the resultant drop-down menu, select “Image size.”
Uncheck the box beside the label “Resample image” at the bottom of the dialogue box if you want to keep the image at the same size. If the box remains checked, Photoshop will resize the image to account for the increase in DPI.
Navigate to the “Resolution” heading in the dialogue box. Enter “300” in the box directly to the left of the heading.
Click “OK.” The dialogue box will close.
Click on “File” in the top toolbar. Select “Save As.” Give the file a name so that you can identify it as the 300 DPI copy. Select the location to save it to and click “Save.”
Open the GIMP program. Go to “File” then “Open” and select the image you wish to alter.
Click on “Image” in the top toolbar. Select “Scale Image” from the top-down menu. This will bring up a dialogue box.
Enter 300 into the box to the right of the label “X resolution." Doing this will automatically resize the "Y resolution" as well. The values are measured in pixels per square inch, which is an equivalent to DPI.
Click on the chain image next to the "X" and "Y" resolution boxes if you wish to enter different values for the horizontal and vertical axes of your image. Avoid increments much higher than 300 DPI as the quality improvement will not be noticeable, but printing will use a lot more ink. Click “Scale” at the bottom of the dialogue box. Save your image with a file name to remind you it has the higher DPI.
Corel Paint Shop Pro
Open the Corel Paint Shop Pro program. Click on “File” then “Open” and select the image you wish to alter.
Click on “Image” in the top toolbar. Select “Resize” from the drop-down menu. This will bring up a dialogue box.
Enter 300 in the box to the right of the label “Width” under the heading “Pixel dimensions.” Doing this will automatically resize the “Height” value.
Click on the padlock image next to the width and height boxes if you wish to enter different values for the horizontal and vertical axes of your image.
Click “OK.” Save your image.
If printing at home, select the highest quality printing available on your printer to ensure the sharpness of the 300 DPI image is reproduced.
If taking the image to a professional printer, let it know that you have changed the DPI of your image.