2.4 Digital Graphics Terminology: Raster, Vector, Resolution, and Color

2.4 Digital Graphics Terminology: Raster, Vector, Resolution, and Color

Quick Summary: Objective 1.3 of the current exam guide asks you to define the vocabulary of digital graphics and to explain how color is represented on screens and in print. Expect selected-response items that check whether you can tell raster from vector, pixels per inch from printed size, trim from bleed and live area, and RGB, CMYK, HSB, grayscale, hex, spot, and rich black from one another.

Why This Vocabulary Matters

Nearly every later Illustrator task depends on these terms. Choosing a document profile, setting raster effects resolution, exporting a PNG at 2x, or deciding whether a logo needs a spot color all assume that you know what the words mean. The exam guide lists them as key terms because a designer who confuses image size with resolution, or trim with bleed, will make expensive production mistakes even when their drawing skills are strong.

Raster (Bitmap) vs. Vector Graphics

Illustrator is primarily a vector application, but its documents often contain raster content: placed photographs, embedded images, and raster effects. Knowing which parts of a file are which explains why a logo scales cleanly while the photograph behind it turns soft when enlarged.

Rasterizing and Rendering

Rasterizing converts vector artwork into pixels. You can rasterize permanently with Object > Rasterize, choosing the color model, resolution, background, and anti-aliasing, or temporarily through effects that generate pixels. Rendering is the broader term for calculating the final visible image, whether on screen, during export to a raster format such as PNG, or when a printer's raster image processor (RIP) images the file. Every export to PNG or JPEG renders the vector art at the resolution you choose.

Raster vs. Vector Effects

The Effect menu is divided into Illustrator Effects (such as Distort & Transform, Path, Warp, and Convert to Shape) and Photoshop Effects (such as Blur, Artistic, and Texture). Photoshop Effects always produce pixels. Some Illustrator Effects—Drop Shadow, Inner Glow, Outer Glow, and Feather—also rasterize their soft edges. The resolution of every rasterized effect comes from Effect > Document Raster Effects Settings, which is why a shadow created at Screen (72 ppi) looks soft in print even though the shape it belongs to is a crisp vector.

Resolution, Image Size, and Resizing

• Resolution of a raster image is measured in pixels per inch (ppi). Printers describe device output in dots per inch (dpi), and halftone screens in lines per inch (lpi). Offset print usually targets about 300 ppi at final size; screen graphics are specified in pixel dimensions.
• Image size measured in pixels is the real amount of data, for example 3000 × 2000 px. Document size measured in inches or centimeters is how large those pixels print: 3000 px at 300 ppi prints 10 inches wide.
• Effective resolution changes when you scale a placed image in Illustrator. A 300 ppi photo scaled to 200% has an effective resolution of 150 ppi; scaled to 50%, it becomes 600 ppi. The Links panel's link information reports the effective PPI of each placed image.
• Resizing is not adding detail. Scaling a raster image only changes how large its existing pixels print. Vector paths, by contrast, can be resized freely.

Worked example: A client supplies a 1200 × 900 px photo for a 6 × 4.5 in print ad. The effective resolution at that size is 1200 ÷ 6 = 200 ppi, which is below the usual 300 ppi target. Printed at 4 × 3 in, the same file reaches 1200 ÷ 4 = 300 ppi.

Print Geometry: Trim, Bleed, and Live Area

Units of Measurement for Print and Digital Output

Print work uses points (72 pt = 1 in), picas (6 picas = 1 in), inches, millimeters, and centimeters. Screen work uses pixels. You can set a document's units in File > Document Setup, from the ruler's context menu, or in the Units preferences. You can also type a value with a different unit, such as 3mm in an inch-based document, and Illustrator converts it.

How Color Is Represented

Reading a Hex Code

Each pair of hexadecimal digits is one RGB channel, from 00 (0) to FF (255). #FF6600 therefore means R 255, G 102, B 0, a saturated orange. #000000 is RGB black and #FFFFFF is white. Hex values describe RGB colors only, so a print vendor still needs CMYK or spot specifications.

Black on Screen vs. Black in Print

Illustrator's Appearance of Black preferences control whether pure 100% K displays as a dark gray (so you can tell it apart from rich black) or as a jet black. On press, 100% K alone prints as a dark but slightly translucent black. A rich black adds cyan, magenta, and yellow under the K for a denser solid on large areas. Small text and thin rules should stay 100% K so four plates do not have to register perfectly around fine strokes.

Process vs. Spot Color

Process (CMYK) colors are mixed on press from four inks using halftone dots. Spot colors are premixed inks that print solid on their own plate. Designers choose spot colors when a brand color must match exactly or falls outside the CMYK gamut, as metallic, fluorescent, and many bright orange and green inks do.