Image Size and Resolution

Image size and resolution are stated in different and often confusing units. Here is a quick overview of the commonly used naming systems and labels:

@ File Size depends on the format and compression rate you use to save your image. File size is stated in KB or MB. The image in figure 4-5 is a compressed TIFF at about 41,4 MB. The same image requires about 15 MB of disk space as a compressed JPEG. File size can vary enormously!

® Image Size in Pixels is stated using the height and width of the image as it is captured by the camera. A Nikon D70 produces images measuring 3 008 x 2 000 pixels (i.e., 6.1 million pixels, or 6 megapixels). The rule of thumb here is: "more is better".

Width: 3Q0S Height: 12 000

Document Size: Width: 30.OS

U Scale Styles

Bicubic {best for smooth gradients)

Figure 4-5: Photoshop's Image Size dialog

Monitors have a resolution of between 72 and 100 pixels per inch (72-100 ppi).

> Halftones are simulated using collections of tiny printed dots and a process called "dithering".

We have produced acceptable results at resolutions of 180-360 ppi using our highend printers.

© Resolution is stated in pixels per inch (ppi). An uncropped photo print shot using a Nikon D70 and printed at 300 ppi results in a print size of:

3 008/300 x 2000/300 = 10.02" x 6.66" (24.46 cm x 16.93 cm)

If you print the same image on an inkjet printer at 180 ppi, the image size would be:

3 008/240 x 2000/240 = 12.53" x 8.33" (31.83 cm x 21.17 cm)

Printers (and other output devices) have resolution that is stated in (ink) dots per inch (dpi). Inkjet printer resolution is typically between 1400 and 5 760 dpi. However, inkjet printers simulate halftones using closely grouped collections of extremely small dots and thus print many fewer dots (180-300 ppi) than the image actually has. We therefore recommend that you print on inkjet printers at resolutions between 180 and 360 dpi. The correct input resolution (in ppi) depends on the type of output device you are using (see also section 11.2.1, page 413).

Pre-press applications still use the lines per inch (lpi) unit. This term is explained in section 11.2.1, page 413.

> Never resample an image if you don't have to!

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