INTRODUCTION TO PHOTOSHOP 4.0

SCANNING & FINE-TUNING IMAGES

by Mark Engfer, Santa Monica College
April 28, 1998

IMAGE BASICS

VECTOR VS RASTER IMAGES

Vector Image - Created by Adobe Illustrator. Composed of mathematically defined lines and curves called vectors. Each object in and image can be moved, resized or rotated and still retain shape and clarity.

Raster Image - Created by Adobe Photoshop. Composed of a grid, or raster of small squares, called pixels. To edit an image, you edit the pixels. Resizing an image can change clarity of the image.

DIGITAL VS PRINTED IMAGES

Photographs - called continuous-tone images, since the development method creates the illusion of perfect continuous tone throughout the image.

Digital (pixel-based) Images - create the illusion of continuous tone, since each pixel (on a computer screen) can be colored independently.

Printing Presses / Printers - are not capable of reproducing continuous tones; They create the illusion of continuous tone using halftone dots (rows of small, variously sized dots that create the appearance of different shades of color when printed).

RESOLUTION TYPES

Resolution - refers to the unit of measurement used to determine the size of an image, the way it is displayed on the monitor, and the device on which an image is output.

Image Resolution - refers to the size fo the file in pixels, called pixels per inch (ppi). The more pixels per inch, the higher the resolution (and the larger the resulting image file - roughly the ppi squared)

Monitor Resolution - determines how your image is displayed on your monitor, called dots per inch (dpi). Monitors have a fixed resolution, (usually 72 dpi for Macintoshes, and 96 dpi for IBM-compatibles). Because an image may have a higher resolution than the monitor, an image with a higher resolution will appear larger on-screen than in print.

Output Device Resolution - determines the quality of the final printed image, measured in both dots per inch (dpi) and lines per inch (lpi). It refers to the number of dots per inch that the output device produces. (i.e., laser printer resolution ranges from 300 - 600 dpi; high-quality imagesetters range from 1200 - 2400 dpi. Output devices also have a screen frequency, which determines the number of halftone cells printed per inch, measured in lines per inch. (i.e., newspapers range from 75 - 85 lpi; high-quality art books range up to 200 lpi.)

COLOR MODELS & GAMUTS

Color Model - a method for displaying and measuring color. The visible spectrum of wavelengths for light range from white (the full spectrum present) to black (the total absence of light), as perceived by the human eye. This is the full gamut of color found in nature.

Gamut - the range of colors that can be displayed or printed. Nature contains the largest viewable color gamut. Monitors and printers use different subsets of this gamut.

RGB Color Model - named after Red, Green and Blue, the primary colors of light. A color TV or monitor has 3 guns; Red, Green and Blue. This color model is known as Additive Color (equal amounts of red, green and blue produce white).

CMYK (Cyan, Magenta, Yellow and Black) Color Model - - The 4 process inks used to print images. Called Subtractive Color, since combining cyan, magenta and yellow subtracts color and becomes black (or rather a muddy brown, hence the need to add black ink).

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Image Basics

Image File Types

Scanning Basics

Photoshop Work Area

Basic Image Correction

How to Scan, Adjust and Save an Image

VECTOR VS RASTER IMAGES
	Vector Image - Created by Adobe Illustrator. Composed of mathematically defined lines and curves called vectors. Each object in and image can be moved, resized or rotated and still retain shape and clarity.
	Raster Image - Created by Adobe Photoshop. Composed of a grid, or raster of small squares, called pixels. To edit an image, you edit the pixels. Resizing an image can change clarity of the image.

DIGITAL VS PRINTED IMAGES
	Photographs - called continuous-tone images, since the development method creates the illusion of perfect continuous tone throughout the image.
	Digital (pixel-based) Images - create the illusion of continuous tone, since each pixel (on a computer screen) can be colored independently.
	Printing Presses / Printers - are not capable of reproducing continuous tones; They create the illusion of continuous tone using halftone dots (rows of small, variously sized dots that create the appearance of different shades of color when printed).

RESOLUTION TYPES
Resolution - refers to the unit of measurement used to determine the size of an image, the way it is displayed on the monitor, and the device on which an image is output.
	Image Resolution - refers to the size fo the file in pixels, called pixels per inch (ppi). The more pixels per inch, the higher the resolution (and the larger the resulting image file - roughly the ppi squared)
	Monitor Resolution - determines how your image is displayed on your monitor, called dots per inch (dpi). Monitors have a fixed resolution, (usually 72 dpi for Macintoshes, and 96 dpi for IBM-compatibles). Because an image may have a higher resolution than the monitor, an image with a higher resolution will appear larger on-screen than in print.
	Output Device Resolution - determines the quality of the final printed image, measured in both dots per inch (dpi) and lines per inch (lpi). It refers to the number of dots per inch that the output device produces. (i.e., laser printer resolution ranges from 300 - 600 dpi; high-quality imagesetters range from 1200 - 2400 dpi. Output devices also have a screen frequency, which determines the number of halftone cells printed per inch, measured in lines per inch. (i.e., newspapers range from 75 - 85 lpi; high-quality art books range up to 200 lpi.)

COLOR MODELS & GAMUTS
Color Model - a method for displaying and measuring color. The visible spectrum of wavelengths for light range from white (the full spectrum present) to black (the total absence of light), as perceived by the human eye. This is the full gamut of color found in nature.
Gamut - the range of colors that can be displayed or printed. Nature contains the largest viewable color gamut. Monitors and printers use different subsets of this gamut.
	RGB Color Model - named after Red, Green and Blue, the primary colors of light. A color TV or monitor has 3 guns; Red, Green and Blue. This color model is known as Additive Color (equal amounts of red, green and blue produce white).
	CMYK (Cyan, Magenta, Yellow and Black) Color Model - - The 4 process inks used to print images. Called Subtractive Color, since combining cyan, magenta and yellow subtracts color and becomes black (or rather a muddy brown, hence the need to add black ink).