DIG: Graphic Arts Technology | Digital Imaging

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Computer graphics are graphics created using computers. The term computer graphics includes technologies used to create and manipulate pictorial data.

Computer Graphics Objective: Students will describe the difference between print and web documents. Checking for Understanding: 1. In your own words describe what computer graphics is.

Products of Computer Graphics

Fine Art Illustrations Newspapers Magazines Logos Brochures Movies Animations Billboards Posters Video Games Postcards Websites Banner Ads Books Displays Merchandising materials Products And much more! What are some other products you can think of that are created on computers?

Types of Images

There are two main types of images in computer graphics: Raster graphics are composed of pixels.

A pixel is the smallest unit of a video display.

Vector graphics are composed of paths. These paths are created by mathematical relationships that describe the points and the paths that make up the image.

Raster Graphics

The main program you will work with that creates raster graphics is Adobe Photoshop.  Raster graphics are composed of pixels.

A bitmap image (another word for raster graphics) is a grid that is made up of individual pixels. The image is created by how many squares in the grid are filled in and what color they are.

Bitmap images are best for photographs and images with subtle shading.

The biggest problem with raster graphics is that you cannot enlarge them any larger than the size they were created at.

Because the artwork is made of pixels, when you enlarge it the program guesses where to fill in the pixels in the grid. That is why when you enlarge a raster graphic it looks jagged.

Vector Graphics

The main program you will use that creates Vector Graphics is Adobe Illustrator.

 Vector graphics are composed of paths. These paths are created by mathematical relationships that describe the points and the paths that make up the image.

 Vector graphics are best suited for page layout, type, line art, and illustrations. The main benefit of vector graphics is that they can be enlarged to any size and still display exactly as they were drawn.

The Main File Types

There are several different file types that you can save your work in. Native File Formats These formats are meant to save them in the program’s native format for work in the program only.

When you want to publish the file you will want to save it as another file type.

 Adobe Illustrator (.ai): This is the standard format to save work files in Adobe Illustrator.

 Photoshop (.psd): This is the standard format to save work files in Adobe Photoshop.

Vector-Based Formats

 Encapsulated PostScript (.eps): This is the next best choice for saving vector graphics. The EPS format will maintain the mathematical descriptions of your file. EPS files are supported by most graphics applications.

It is best to use EPS files for illustrations because they can be reproduced at any size or resolution and display exactly as they were drawn.

Raster Based Formats

 JPEG (.jpg): Joint Photographic Experts Groups. This format is used for photographic (continuous tone) images. The JPEG format also uses compression for smaller files and faster downloads.

 Graphics Interchange Format (.gif): This format is used mainly for compressing images to smaller size so they can be downloaded faster. This format is mainly used for images on the internet. The GIF format uses a fixed color palette limited to 256 colors or less.

 Tagged-Image File Format (.tiff): This file format is used for bitmap images only. It is supported by almost all graphics programs. Multipurpose Formats

 Portable Document Format (.pdf): The Adobe Portable Document Format is used for publishing electronic documents.

Once a document is saved in this format anyone can open it with the Adobe Acrobat Reader (which can be downloaded for free) without having the program the art was created in and the artwork looks exactly as you created it. This makes it a great format for transferring files.

Graphics for Print When you have something professionally printed you’ll probably be asked for an “EPS” or a “PDF” of the file. Ever wonder why you can’t just use a JPG, like on your website? What is the difference between an EPS (Encapsulated PostScript) and a JPEG (Joint Photographic Experts Group).

In brief, an EPS is the standard file format used for printing (e.g., business cards, brochures, signage, etc.), while JPG and GIF files are the most common file formats used on the Internet.

Here’s why an EPS is better for print: An EPS file contains vector information, which means its resolution is not determined by pixels.

As a result, an EPS can be made as large or small as necessary without compromising print quality or losing design detail.

There’s a good chance an EPS file will display poorly on your computer screen, but this does not mean it will print badly.

Regardless of how it looks on your screen, it is the file you need to produce professional-grade printed materials.

Graphics for Web

 A jpeg is a compressed image file suitable for use on the Internet (e.g., your website). It contains raster information, which means that its resolution is determined by the size of its pixels.

A jpeg can display images consisting of millions of colors. As a result of its powerful compression capabilities, jpegs are good for displaying photos and images with complex color schemes.

 Computer monitors only display about 72 dpi (dots per inch or pixels per inch). A high-resolution image displayed on a web page will contain all of the original pixels, but will only display slightly under half of them.

For this reason, graphics for the web are generally created at a resolution of 72 dpi to reduce the amount of time and bandwidth wasted to download extraneous information. 300 dpi 150 dpi 72 dpi10 dpi

Things to Consider When Printing

 Graphics for print generally need to be at least 300 dpi or created in a vector-based program so they maintain their integrity of the images even if they are reduced are enlarged.

 Encapsulated Postscript (eps) is the format of choice for most printers. Although, many printers or publishers now accept Adobe Portable Document Format (pdf).

 The most important thing to bear in mind is that your artwork is at the correct resolution for the image size you are printing. If you artwork is vector-based (Adobe Illustrator) you don’t need to worry about resolution.

If your image is raster-based then your artwork needs to be at least 300 dpi at the size you are commercially printing it.

 If you are printing on a digital printer you can get away with a lower resolution.

Understanding Color in Graphics RGB Color Model

RGB mode is an additive color model. Additive color models use light to display color. This mode is used for computer displays. The light colors result from transmitted light. Red+Green+Blue=White. CMYK Color Model: CMYK is a subtractive model.

Subtractive models use printing inks. Colors perceived in subtractive models are the result of reflected light. This model is used for designs that will be printed. Cyan+Magenta+Yellow=Black. When these designs are printed they use four colors: cyan, magenta, yellow and key(black) ink. RGB (Red, Green, Blue) CMYK (Cyan, Magenta, Yellow, Key)

Wrap Up The two main uses of computer graphics are; Print Graphics for images that will be printed. Digital Graphics for images that will be seen on the internet, video games, or on a screen.

Vector Graphics Mathematically based CMYK Color Format Print Graphics Raster Graphics Pixel Based RGB Color Format 72 dpi Digital Graphics.

NOTE:

DIGITAL IMAGES are electronic snapshots taken of a scene or scanned from documents, such as photographs, manuscripts, printed texts, and artwork.

The digital image is sampled and mapped as a grid of dots or picture elements (pixels). Each pixel is assigned a tonal value (black, white, shades of gray or color), which is represented in binary code (zeros and ones).

The binary digits (“bits”) for each pixel are stored in a sequence by a computer and often reduced to a mathematical representation (compressed). The bits are then interpreted and read by the computer to produce an analog version for display or printing.

Pixel Values: As shown in this bitonal image, each pixel is assigned a tonal value, in this example 0 for black and 1 for white.