Resolving the Problem

Resolution: Concepts & Definitions

4 kinds of resolution

• Bit resolution (color depth)

• Image resolution (scanner resolution)

• Device resolution (printer or monitor)

• Halftone screen resolution (for print publication)

Image resolution

• Expressed as pixels per inch (ppi)

• Measures the amount of visual information stored in a digital image file

• Increasing the image resolution increases the amount of detail that can be seen in the image.

• Doubling resolution increases file size 4x

Bit Resolution

• Refers to the number of bits of stored information in each picture element (pixel)

• Determines the number of colors or shades of gray that can be displayed on a monitor

• Typically ranges from 1-bit (21 = black & white) to 24-bit (224 = 16.8 million colors)

• Increasing bit resolution increases file size proportionally

Device resolution

• Expressed in dots per inch (dpi)

• Refers to print output devices (such as laser printers and image setters) and monitors

• Laser printers range from 300 to 1,200 dpi

• High-end image setters more than 2,500 dpi

• Usually calculate 72-94 dpi for common monitor resolutions

Common screen image sizes for PC monitors

• 640 x 480 pixels

• 800 x 600

• 1,024 x 768

• 1,280 x 1,024

• Macintosh = 832 x 624 and 640 x 480

Image dimensions and screen resolution

Screen shot showing an image displayed with monitor resolution set at 640 x480 pixels

Actual image size on the screen varies with monitor size

and resolution.

Image dimensions and screen resolution

Same image file as previous slide, but displayed on a monitor with resolution set at 1024 x 768 pixels.

Halftone screen frequency

• Expressed in lines per inch (lpi)• Applies to print publication only• Essential step in reproducing continuous

tone images on a printer or printing press• Higher resolution halftone reproduces more

detail in final printed image• Affects digital file size indirectly: High res.

halftone requires high res. image file.

What’s a halftone?

An image in a magazine, newspaper or other printed product appears to the naked eye to have a full range of gray tones ranging from white to black.

What’s a halftone?

Magnification reveals a pattern of dots created by the halftone screen. Printing inks can print only solid colors. Shades of gray are optical illusions created by dots of varying sizes.

How ppi, lpi & dpi work together

If image resolution = 100 ppi, area above = .04 in. x .02 in.

How ppi, lpi & dpi work together

If image resolution = 100 ppi, area above = .04 in. x .02 in.

Halftone screen frequency = 50 lines per inch

How ppi, lpi & dpi work together

If image resolution = 100 ppi, area above = .04 in. x .02 in. Halftone screen frequency = 50 lines per inchOutput resolution = 500 dpi; tonal range = 101 shades of gray

Set in scanner

Set in print setup or in Photoshop

Built into printer. Some printers have

variable output.