Home · Feedback · Estimates · Contact us · Site map
Image resolution
Choosing the right image resolution
Do you know that the pictures you see on your computer screen often aren't suitable for high-quality printing? Many people don't understand that the resolution of an image on a computer screen is much coarser than the resolution of a laser printer or a printing press. When printed, many images that look perfectly fine on your computer screen can become fuzzy or less distinct. Here are seven points to consider when you're working with images on your computer.
1. How are you planning to use the image? Generally speaking, the resolution of an image should match the resolution of the printer or printing press that will be used to print the final image. A 72 dpi image is fine for viewing over the internet but will print very poorly. Although many of today's laser printers have resolutions of 600 dpi or more, 300 dpi will still provide good image quality on most digital laser printers and for most offset printing.
2. How big is the image — and how big do you want the final image to be? Compare the dimensions of your original image to the size at which it will be printed. Enlarging an image reduces the image resolution, since the total number of dots or pixels in the image is spread over a larger area. Reducing an image increases the image resolution, since the total number of dots or pixels is compressed into a smaller area. For example, a digital camera may create an image 8"x10" at 72 dpi. If that image is reduced to fit into your document as a 2"x2.5" image, the resolution of the reduced image will be 288 dpi — reasonable quality on most digital laser printers.
3. Most images copied from web pages don't print well. Never assume that an image from your web site will be adequate for digital or offset printing — especially if you want to enlarge the image. If you request an image from your web designer, tell the designer how you intend to use the image. When in doubt, some clients ask RE:Print to discuss image resolution with their designer; other clients use RE:Print's in-house design services.
4. Pay attention to bitmap images. The issue of image resolution usually only applies to bitmap images such as .jpgs, .tifs and .gifs. Paint programs and software intended to manipulate photography (such as Photoshop) produce bitmap images. Other graphics programs can create vector graphic files, which usually print well at any size.
5. Good-quality images can be very large computer files. Image file size increases with image resolution, so it's important to plan ahead. If you want to use an 8"x10" color image for the front page of a newsletter, you'll probably have to supply the image file on a CD since it will be too large to fit onto a floppy disk and may be too large for e-mail. The same can be true if you intend to make a high-resolution scan of an image.
6. Don't confuse ppi and dpi. Pixels per inch, or ppi, is a measurement applied to digital photos and scanned images. Dots per inch, or dpi, is a term describing printed pages. For instance, your digital camera may take an 8"x10" photo at 72 ppi, but your laser printer may print at 300 dpi. Some software describes images in ppi and other software uses dpi, but the terms are not interchangeable (with one exception: some image-scanning software may use the term dpi when actually describing ppi). Generally speaking, 150 to 240 ppi or 300 to 600 dpi should be adequate for most printing applications.
7. Print photography from higher-resolution files. Generally speaking, when offset printing photography, you should use higher-resolution files. Here are a few examples comparing printed size to image file dimensions in pixels:
for a 2"x3" printed image, file dimensions should be 400 x 600 pixels minimum
for a 4"x6" printed image, file dimensions should be 800 x 1200 pixels minimum
for a 5"x7" printed image, file dimensions should be 1000 x 1400 pixels minimum
for an 8"x10" printed image, file dimensions should be 1600 x 2000 pixels minimum
Tech Tip: Many graphics programs, such as Adobe Illustrator and CorelDRAW!, can be used to create both bitmap and vector graphic images. When designing an image that will be used at several different sizes, such as a company logo, a vector graphic is much better than a bitmap image, since vector graphics can be enlarged and reduced with no change in image quality.
Click here to download a PDF brochure about image resolution.