Our job is to reproduce those photographs in websites, printed brochures, email blasts, marketing material, newsletters, signs, banners, and business cards. We want the photographs to reproduce in the best possible quality. So, we offer you some technical tips on digital photos for printing and web applications. These are tips on what to do once the images are captured and you’re ready to send the photos to us.
What is a pixel?A pixel is a contraction of the words picture element. A pixel is a square that contains a series of numbers that describe its color (for color photographs) or intensity (for black and white photographs).
The greater the number of pixels in an area, the smaller each one is, the more tightly they are packed, and the better our eyes can blend the edges together to create a complete image. As the number of pixels decreases, the larger each one must be to fill the area, the more space there is between them, and the more evident the square shape becomes. If there are too few pixels in too large an area, we will see the individual squares just as we see the individual tiles in a mosaic. One telltale sign of a low resolution photo print is pixelation, known informally as the jaggies – a curved or diagonal line made up of stair-stepped squares.
Pixels and resolutionResolution is the term for the amount of detail in an image file. You can think of resolution as pixel density. One specification of a digital camera is the resolution it is capable of, expressed in megapixels (one million pixels). A smart phone’s 1.5 megapixel camera can capture roughly one-and-a-half million pixels of information per inch, while an 8 megapixel digital camera can capture eight million pixels per inch. The amount of detail is directly related to photo quality. The higher the mega-pixels, the better the quality.
Likewise, the resolution of a photo file or print, whether offset, digital or inkjet, is the amount of detail it contains. Photo file resolution is expressed as pixels per inch (ppi), while print resolution is expressed as dots per inch (dpi). In general, the higher the value, the more detail in the file and the higher the image quality.
For printing, the recommended resolution is 300 dpi when the photograph is at the desired size on the page. By multiplying the size in inches that you want the printed photograph to measure by 300, you’ll be able to determine the resolution in pixels you’ll need for the photo file. For example, if you want to print an 8x10 photograph, multiply 8 x 300 and 10 x 300, yielding 2400 x 3000 pixels in the photo file.
To determine whether your camera has sufficient resolution for this size of file, multiply the two pixel dimensions (2400 x 3000 = 7,200,000). To translate into megapixels, divide by 1 million, which in this case yields 7.2 megapixels.
Resolution for web-based photographs
Using web-based photos for printIf your business uses product shots in its advertising and marketing materials, you may be tempted to download product photos from the manufacturer’s or distributor’s website. Considering the resolution requirements for web (72 ppi) and print (300 ppi), it becomes clear that using a web-based photo will not result in a high quality photo in the printed piece when the two photos are of identical size. In fact, you’re likely to see the individual pixels and the jaggies on curves and diagonal lines.
What may be possible, however, is to reduce the size of the web-based photo until the resolution nears 300 ppi. In general, web-based images print with acceptable quality (for most purposes) at about half the size they appear on screen. So a photograph that measures 2x2 inches on screen can be printed as 1x1 inches with acceptable quality (for most purposes).
File formats for photographsFile formats for photographs are a means of organizing and storing an image. The data may be stored in compressed or uncompressed format, then rasterized into a grid of pixels whose bits define color and depth. Images can be cropped, colorized, converted to grayscale or monochrome by using an image editing program such as Adobe Photoshop.
File compression is a way to reduce file size. There are two types of image file compression. One, called lossless, keeps all the pixels of the original image but finds more efficient ways to represent recurring patterns of pixels in the file. Another, called lossy, eliminates pixels that aren’t needed to maintain quality. Lossy compression results in smaller file sizes than lossless, but trades that for lower image quality.
For photographs, the preferred file format is Tagged Image File Format (TIFF). TIFFs can be either lossy or lossless, and some digital cameras can save in TIFF format using Lempel-Ziv-Welch (LZW) compression.
Another format for photographs is Joint Photographic Experts Group (JPEG). JPEG compression is lossy and produces a significant reduction in file size. Repeated opening and saving of JPEG files results in continual loss of pixels which degrades file resolution over time.