Digital Prints

Table 2.1 The Magic Numbers of Inkjet File Resolution
Brand Manufacturer’s PPI Recommendation at Final Size
Canon 200–300 ppi
Epson 300–360 ppi
HP 150–200–300 ppi
Lambdas, which are, respectively, 300 dpi and 400 dpi at their maximum settings; an
image resolution of 300 ppi should work well for them, too.
Chances are that if you are anywhere between 240 to 360 ppi in terms of image resolution
at final print size, you’re going to be fine with most digital print devices, although the
best answer is to either test several resolutions with the intended output device and evaluate
the resulting prints, or ask a printmaker for recommendations if you’re using an outside
printing service.
Measuring Image Resolution
Here are the most common measurement methods:
Chapter 2 ■ Understanding Digital Printing 43
■ By pixel array or dimension: Some people just say, “Here’s a 1600×1200 image” (pixels is understood). Once you’re familiar with certain
files sizes, you’ll automatically know what a 1600 × 1200-pixel image (or any other size) will do.
■ By total number of pixels: Multiply the number of horizontal pixels by the vertical ones, and you’ve got the total number of pixels or the
pixel dimensions. A 1600×1200 image totals out at 1,920,000 pixels or about 2 megapixels.
■ By pixels per inch and image
size: As long as you know both
the intended output size and the
ppi, you’re set. For example, an
uncompressed, 24-bit, RGB,
color 300-ppi image set to an output
size of 4 × 5 inches is just over
a 5-megabyte (MB) file.
Pixel dimensions are one method of
measuring image resolution. (See
more about sizing and scaling
images in Chapter 3.)
■ By file size: Take the total number
of pixels (pixel dimensions),
multiply that by 3 (total RGB
color bit depth—24 divided by
8), and you’ve got the file size in
bytes (one byte is eight bits).
Divide that by one million, and
you have the approximate final file size in megabytes. Example: 1600×1200 pixels = 1,920,000 pixels. 1,920,000×3 = 5,760,000 bytes or
5.76 MB. Pretty close.
■ By single-side measure: Film-recorder users typically refer to the width of the image in pixels. A standard “4K file” is one that measures
4,096 pixels horizontally (as already stated, the reason it’s not 4,000 pixels is because of the way the binary system works). Because most
film-recorder output ends up as standard 35mm transparency film, the other dimension (2,730 pixels) is understood to be in the correct
proportion to the first and isn’t mentioned.