Digital Images

There are two main types of digital images:
• Object Graphics
• Pixel Graphics
Object Graphics consist of mathematically calculated curves and lines that create surfaces and shapes.
Pixel Graphics are images consisting of pixels of different colors, squared to picture elements.

Object Graphics

Object graphics can include simple curves, straight lines, circles, squares, typefaces and other graphic objects.

Object vs. Vector Graphics
• Vector images are based on straight lines
• Object images are based on “bezier” curves
Bezier curves were named after a mathematician at the French car manufacturer, Renault.

Object Graphics are based on a number of basic components:
• Outlines and Lines
• Fill
• Patterns
• Gradients
• Knockouts
• Superimpositions & Transparency
Advantages and Disadvantages
+ contain an unlimited number of colors
+ Can be rescaled without compromising image quality
+ Easy to edit without compromising qualtiy
+ Don’t take up a lot of memory
– Cannot be used for photographic images

Applications for Object Graphics
Object graphics are created in illustration software:
• Illustrator
• Macromedia Freehand
• Flash
Pixel graphics can be converted to object graphics using:
• Adobe Streamline
• Freesoft Silhouette

File Formats for Object Graphics

Below are descriptions of the most common file formats used when saving Object graphics along with some advantages and disadvantages for consideration:
PDF
+ Can be opened by everyone
+ Is the same for Mac and Windows
+ Files use little memory
+ Can include fonts
+ Is managed like ordinary PDF files
+ Can be protected with a password
+ Can include ICC profile
– Cannot be managed by older layout programs
EPS
+ Commonly used
+ Can be mounted with most layout applicaitons
– Takes up somewhat more memory than illustration application files
– Does not retain all the editorial features of the illustration application
– Different file formats for Mac and Windows
– Requires and illustration or layout program to be viewed
– Only newer file versions can include fonts
Illustrator AI
+ Uses little memory
+ Can use all editing features
+ Can include fonts
+ Can include ICC profiles
– Cannot be managed by all layout programs
WMF and EMF
• Windows Metafile and Enhanced Metafile
• used for simpler object graphics in windows setting
• supported by most office applications
SVG
• Scalable Vector Graphics
• format for object-based images for the web
• not intended for printed documents
DWG and DXF
• short for drawing
• standard format to store drawing files produced with a CAD application
• files can be imported into illustrator
• make up the foundation of packaging design
SWF
• Shockwave File
• object-based animations and interactive images
• created by Flash
• format is web based and not intended for print

Pixel Graphics

An image divided into tiny squares of color (pixels), almost like a mosaic.
Creation of Pixel Images
• scanned
• digitally photographed
• created directly on the computer

Applications for Pixel Graphics
• Adobe Photoshop
• Adobe Photoshop Elements
• Intellihance
• Photo Perfect
• Paintshop Pro
• Painter

Color Modes of Pixel Images

Pixel-based images can be black and white or color and contain different numbers of color.
line art
• composed of completely black and white
• no mid range tones
• the higher the resolution the better the print quality
examples: one-color logotype, graphic illustrations, screen fonts
grayscale
• composed of pixels in black, white and shades of gray
examples: black and white photos, marker drawings that contain mid-range tones but composed of a single color
duotone
• tinted grayscale images
• made up of two printing inks

Exercise: Creating Duotone Images

four color
• made up of C M Y K
• used to produce full color images in print
• takes up 33% more memory than the same image in RGB

Resolution

Image resolution is determined by two factors:
1. The screen frequency you wish to print in
2. Whether or not you need to change the size of the image
The Right Resolution for Images
• images should be 2 x’s in resolution the value of the linescreen they will be printed at.
The Right Resolution for Line Art
• requires much higher resolution
so that image does not appear jagged
• Printing process determines resolution needed
laser and newsprint = 600 – 800 ppi
fine uncoated paper = 800-1200 ppi
fine coated paper = over 1200 ppi

File Formats for Pixel-Based images

Pixel based images can be saved in a number of formats. Some of them have become more or less industry standards. Listed below are some of these popular formats with their pros and cons:
PSD
• primary function is image editing stage
• cannot be compressed
TIFF
• tagged image file format
• bitmaps, grayscale, RGB or CMYK images
• can use LZW compression (lossless)
EPS
• encapsulated postscript file
• both object and pixel graphics
• like a font has two parts: low res preview and high res print file
DCS and DCS2
• desktop color separation file
• contains 1 low res preview and 4 additional parts (CMYK)
• DCS2 evolved from DCS
• allows us to save an image in as many parts as colors are used
PDF
• can be read by anyone
• handles most color modes and funcitons
• can be compressed to be quite small
JPG
• joint photographic experts group
• compression and quality loss
JPG 2000
• evolved form JPG format
• works for both web and print
• better / higher quality of compressed image

Image Compression

Because pixel based images often take up storage space in the computer, which is for the most part not a big deal, it can become an issue when time to transport images or files via the net.
LZW
ZIP
JPG

LZW Compression

Named after the scientists Lemple,
Ziv and Welch is a lossless form of compression. Which means:
• when compressed the image will not be ruined
• when used with GS, RGB or CMYK images the file size will be about half
NOTEthis type of compression may cause problems for the printer.

ZIP

• Also lossless
• mainly used for images in or included in PDF format /file.

JPG / JPEG

The most common type of compression method.
• not a lossless form of compression
• actually removes information from the image

Capturing & Scanning Images

The way in which an image is acquired will in large part determine it’s level of quality or “usability”.

Digital Photography

• Comparison to traditional photography
– good digital cameras are more expensive
– have a poorer dynamic range, more difficulty producing tones
– less sensitive to color temperatures of light
• Marketed based on number of Megapixels camera can capture
• The better the optics the better the image quality

Scanning

A means for transferring original images to the computer for viewing and editing.
There are 3 types:
• Drum
• Film
• Flatbed

Drum Scanners
• original art mounted on a glass drum
• large and expensive
• very high quality
• only for flexible media
• good for large volume
Film Scanners
• used for slides or film negatives
• scans only one picture at a time
• similar to drum scanner
Flatbed Scanners
• original art placed on flat glass plate

Good (and Bad) Image Formats

As far as off set printing is concerned, there are only two image formats that you want to “end up with”:
1. Tiff or TIF
2. EPS
The “Bad Image Formats” are identified as such because they should not be included in files sent out for offset printing. Identified as:
• RGB images
• GIF images
• JPG images
• below 300 dpi at 100% size (150 is acceptable)

Using TIF Images: GOOD

• multi-layered vs. flat
• managing files and file naming
• only use layered tif files to preserve type in vector format

Using EPS Images: GOOD

• best for vector art or object art
• also used with basic clipping paths

Exercise: Creating A Clipping Path

Image Editing