|Printing Digital Photos
How big should you print your photos? What media should you use? These questions are important to photographers at all levels. We’ve looked at the relationship between a camera’s megapixel count, the size of the image sensor and the size of the light-collecting photosites in the Chapter 2 on megapixels. In this chapter, we’ll consider the relationship between a camera’s megapixel count and the maximum size at which shots taken with the camera should be printed.
How Large Should You Print?
There’s a direct relationship between the resolution of your digital camera’s sensor and how large you should make prints. When you shoot with the highest resolution and quality settings it’s relatively easy to calculate just how much you can enlarge your image files; it’s a matter of matching the image resolution from your camera to the output size.
You must then decide the appropriate output resolution for the print size. Essentially, two output resolutions are in common use: 300 pixels per inch (ppi) for prints up to A4 size and 200 ppi for larger prints. (A lower ppi count is acceptable for larger prints because they are normally viewed from a greater distance so individual pixels in the print are less visible.) For poster-sized prints, output resolution can be dropped to 180 ppi or even 150 ppi.
The table below gives the maximum 200 and 300 pixel print sizes for a range of camera, camcorder and camera-phone resolutions.
Note how a 2-megapixel camera doesn’t even have enough resolution to make a standard snapshot print at 300 ppi and that you require at least an 8-megapixel camera to produce prints larger than A4 size.
You can tell when images have been over-enlarged for printing because they start to lose sharpness before individual pixels become visible. It is usually easier to detect over-enlargement on the computer screen than when the image is actually printed. However, the print will not look anything like as vibrant as it would if printed at the correct size for its resolution. The illustrations below simulate the effect of over-enlarging an image for printing.
||File Size at High Resolution
||Maximum Print Size at 300 ppi:
||Maximum Print Size at 200 ppi:
||1600 x 1200
||135 x 101 mm
||2048 x 1536
||173 x 130 mm
||2464 x 1632
||208 x 138 mm
||3008 x 2000
||255 x 169 mm
|| 3264 x 2448
||276 x 207 mm
||414 x 310 mm
||3888 x 2592
||329 x 219 mm
||492 x 329 mm
||4000 x 2800
||338 x 237 mm
||508 x 355 mm
|| 4920 x 3264
||416 x 276 mm
||625 x 414 mm
||5616 x 3744
||475 x 317 mm
||713 x 475 mm
The enlarged section on the right shows the deterioration in sharpness that occurs when digital photos are printed too large.
The resolutions in the table above do not distinguish between cameras that record images in 4:3 aspect ratio (most digicams and all Olympus and Panasonic DSLR models) and cameras that record in the standard 3:2 used for 35mm cameras (some digicams and all DSLRs). Some cameras offer both 4:3 and 3:2 aspect ratios and an increasing number also provide an elongated 16:9 (or ‘widescreen’) ratio. The Nikon D3 DSLR also offers a 5:4 aspect ratio setting for producing images that will be printed on standard photographic paper (8×10-inch, 11×14-inch, 16×20-inch).
The 3:2 aspect ratio, shown above, is mainly used by DSLR cameras, although many digicams have a selectable 3:2 shooting mode that produces pictures that can be printed without cropping on snapshot-sized paper.
Because they can affect the way the image will appear when printed – and how it will fit onto the printing paper – camera users should be able to recognise the most popular aspect ratios and match them to the way they will display their pictures. The three most popular aspect ratios are illustrated below.
The 4:3 aspect ratio, shown above, is used by all digicams and camera-phones and by Olympus and Panasonic DSLR cameras.
The 16:9 aspect ratio is a selectable setting that enables photographers to take pictures with the correct dimensions for viewing on widescreen TV sets and computer monitors.
Paper Size Issues
When the aspect ratio of the image files from your camera doesn’t match the aspect ratio of the paper you print on, you are forced to decide between cropping the image or allowing white borders to appear either at the top and bottom or at opposite sides of the printed image. The first option is the only choice if you wish to make borderless prints. Otherwise, attractive prints can be made by allowing between 5mm and about 35mm (depending on the paper size) borders around the picture.
When printing from editing software it is easy to set the size of the image on the paper, ensure it is centrally positioned and determine the size of the margins around the picture. Some editing applications also allow you to ‘enlarge’ image files by interpolation, which increases the number of pixels. However, be careful when using this function, especially on shots from digicams, because any defects in the image (particularly unsharpness and compression or sharpening artefacts) will be magnified and the result could be a fuzzy-looking print.
When you print a picture taken with a 4:3 aspect ratio on paper that has a 3:2 aspect ratio (‘postcard’ size), white bars are left at each end of the picture – unless the shot is cropped at top and/or bottom.
You can print the same image on an A4 sheet of paper with white borders and produce a more attractive result.
Different image editors provide varying levels of control over output size. With the simplest applications, many functions are automated and, therefore, hidden from the user, although you can usually set the position of the image on the paper and determine its width and height. Most applications have a ‘Fit to Page’ button that lets you make the image as large as the paper allows – but may involve some cropping. Some examples of user interfaces are shown below.
Users of Google’s freeware image editor, Picasa2, have more options. As well as being able to match the image size to the paper size, they can also crop shots, access the printer driver and produce multiple copies.
Photoshop CS3 provides the greatest range of user adjustments, including check boxes for centering images and scaling them to fit the paper. You can see the effect of these changes on the screen.
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