Raster Graphics What does Raster mean Raster based

Raster Graphics

What does Raster mean?

Raster based software uses a Grid of Pixels (dots) to simulate a continuous tone image.

The quality of a Raster image is determined by two things: 1. Resolution (the total number of pixels). 2. Bit Depth (the amount of information each pixel is capable of displaying).

Resolution is simply how many Pixels (dots) make up an image. More dots mean higher quality. Less dots mean lower quality. We describe Resolution in terms of Pixels Per Inch (PPI).

2 x 3 inches @ 20 ppi (20 x 20) x (2 x 3) = 2400 pixels 2 x 3 inches @ 45 ppi (45 x 45) x (2 x 3) = 12150 pixels 2 x 3 inches @ 72 ppi (72 x 72) x (2 x 3) = 31104 pixels 2 x 3 inches @ 150 ppi (150 x 150) x (2 x 3) = 135000 pixels

Different mediums require different Resolutions. For example: • Most monitors display at 72 ppi. • Most inkjets will print well at 200 ppi. • Commercial printing applications require a minimum of 300 ppi.

Each pixel can contain only one solid color or value. Bit Depth (Color Depth) determines the range of colors and values that each pixel can be. Bit depth 1 -bit (21) 4 -bit (24) 8 -bit (28) 16 -bit (216) 32 -bit (232) No. of Colors 2 Colors (black or white) 16 Colors 256 Colors 65536 Colors 4294967296 Colors

2 -bit, 2 colors 4 -bit, 16 colors 8 -bit (standard), 256 colors 16 -bit, 65536 colors

A note about Resolution and Bit Depth: You cannot simply add more Resolution or increase Bit Depth. What you start with is what you get. You can always go down but you can’t go back up.

Color Modes.

Color Modes determined how the components of color are combined, based on the number of color channels in a color model.

There are three Color Modes that we will be concerned with in this class. 1. Grayscale - one channel 2. RGB (Red, Green, Blue) 3. - three channels CMYK (Cyan, Magenta, Yellow, Black) - four channels

The Grayscale Color Mode has one Color Channel.

The RGB Color Mode has three Color Channels.

The RGB Color Mode is based on the Additive Color Model of Light. Monitors, Televisions, Projectors and other light based systems use this color model

The CMYK Color Mode has four Color Channels.

The CMYK Color Mode is based on the Subtractive Color Model of Pigment. This is the Color Model used with Inks, Pigments, Paints, and 4 -color Printing.