An Image is made up of coloured pixels similar to square tiles in a mosaic. If you enlarge the pixels (top right), they look like a random collection of coloured squares. However, reduce the pixels size, and they blend together to form an image that resembles a standard photograph (top left). GIMP tricks your eyes; counting on the distance that printing, or normal on-screen viewing, puts between your eye and the image’s pixels. Most of the time, this deception is successful. Naturally, there is a difference between mosaic tiles and pixels; pixels come in 16.7 million distinguishable colours, that can be resampled, cropped and separated. Mosaic tiles don’t.
Screen Resolution: This refers to the number of pixels displayed horizontally and vertically on your PC. Therefore, large screens have more pixels than small screens.
Your Screen’s dpi (Dots Per Inch) will be considerably lower than your printers potential dpi; if you intend to print your image, choose a higher ppi (pixels per inch), within the Image. Alternatively, if the image is for the screen only, for example, a website, select a resolution of (at least) 72 dpi. The file will be smaller, and therefore quicker to download. The screen resolution of your PC monitor is selected in the Screen Properties part of Windows XP, and in this context, Resolution refers to the dimensions of the screen in pixels; 620 X 480, 800 X 600 or, 1024 X 768. You can adjust the number of Dots Per Inch (dpi), of the screen.
Image Resolution is the number of pixels per linear inch, in the final printed image. Linear (as opposed to a square inch), because pixels are measured in a straight line. Image resolution is the fineness of detail you can see in an image. It is measured in Pixels Per Inch (ppi). The more pixels per inch, the greater the resolution. Generally, the higher the resolution of your image, the better the printed image quality will be.
Canvas Size describes the physical dimensions of an image, and you can find an image’s size by (from the top menu) choosing, Image then Canvas Size.
The size (or pixel dimensions) of an image is a measure of the number of pixels along an image’s width and height. For example, your digital camera may take a photo that is 1024 pixels wide and 768 pixels high. These two measurements have a direct correlation to the image’s file size, and both are an indication of the amount of image data in a photo.
Image Measurements Example: If the resolution of an image is 72 ppi (Pixels Per Inch), you get 5,184 pixels per square inch. This figure is derived from 72 pixels wide X 72 pixels high, which adds up to 5,184. Assuming the number of pixels in an image is fixed, increasing the size of an image, decreases its resolution; and vice versa. An image that looks good when printed on a postage stamp, will more than likely look blocky (pixelated) when printed as an 11” x 17” poster.
Pixels Per Inch (ppi)
Pixels are a measurement of resolution used within GIMP, and it represents how many pixels are in a (linear) inch.
Dots Per Inch (dpi)
This is a measurement for printers and scanners and a typical printer had 600 dpi. Dots are much finer than pixels, so one pixel (when printed) can be made up of many dots.
Setting The Correct Printing Resolution
In GIMP, you will be asked to select an image resolution when creating a New document, (Ctrl then N), as demonstrated below.
You can resample an image from the Set Image Canvas Size dialogue box.
Generally speaking, when creating work destined for Web Pages, (IE not for print), anything over a Resolution of 72 will be acceptable for Mac’s and Window PC’s. Some people, however, prefer a resolution of 96 (or above), for Windows PC’s. When creating work for Print, aim to set the resolution (in the Image Size dialogue box) of between 250 and 300 Pixels per Inch.
Finally, there is not a right - or wrong way - to setting image resolution. Experiment with different resolutions, and see what works best for you.
Wendi E. M. Scarth. Top of Page.