Calculating resolution

To calculate a photo's resolution, divide the horizontal or vertical size of the photo (measured in pixels) by the horizontal or vertical size of the print you want to make (usually measured in inches). To find a photo's pixel dimensions in Windows, select the photo and choose File —+ Properties to open the window shown in Figure 16-1.

Photos printed on an inkjet printer look their best when printed at a resolution of 220 dpi or higher. Suppose, for example, a photo measures 1524 x 1016 pixels and you want to know if it's got the resolution for a good 4 x 6 print. 1524 pixels divided by 6 inches = 254 dpi. So, this photo exceeds the 220 dpi minimum. Your 4 x 6 print will have a resolution of 254 dpi and will look fantastic on paper.

Figure 16-1. You can find your photo's resolution using Windows Explorer. Find the photo file and then go to File —* Properties. (Or you can just right-click any image file and choose Properties from the shortcut menu.) Next, click the Summary tab to see details. At the top of the list, you find the width and height of the photo.

[>SC_0000 IPS PrffpefMI

General Summary

Property Image

Vaiue

Property Image

Vaiue

D Width

2000 pixels

D Height

3006 pixels

O Horizontal Resolution

240 dpi

_j Vertical Resolution

240 dpi

D Bit Depth

24

LS Frame Count

1

_j Equipment Make

NIKON CORPORATION

_j Camera Model

NIKON D100

LS Creation Software

Adobe Photoshop CS2 Wind.

O Color Representation

Uncalibrated

_j Shutter Speed

1/60 sec.

O Lens Aperture

F/3.5

D Flash Mode

Flash with strobe return

LS Focal Length

24 mm

O F-Nuriiber

F/3.5

LS exposure Time

1/60 sec.

D ISO Speed

ISO-200

[Metering Mode

Pattern

Cancel

Apply

Now then, say you try to print that same photo at 8 x 10. Essentially, you're stretching those pixels that made such a good 4 x 6 print across a larger print area. If you do the math, you can see right away the drop in image quality: 1524 pixels divided by 10 inches = 152 dpi.

Tip: While it's important to print photos at a resolution of 220 to 300 dpi on an inkjet printer, there's really no benefit to printing at higher resolutions600 dpi, or 800 dpi, or more. It doesn't hurt to print at a higher resolution, but you probably won't notice any difference in the final printed photos, at least not on inkjet printers. Some inkjets spray ink at finer resolutions720 dpi, 1440 dpi, and so onand using these highest settings produces very smooth, very fine printouts. But bumping the resolution on your photos higher than 300 dpi doesn't have any perceptible effect on their quality.

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