Raster Graphics
Raster graphics, or bitmap images, are digital images created using a matrix or grid of pixels, where each pixel holds a specific color. The collective arrangement of these colored pixels forms the complete picture. Each pixel in a bitmap image is stored as one or more bits in computer memory. File formats commonly associated with raster graphics include .jpg, .gif, .tiff, and .bmp.
Raster graphics are characterized by their grid-based structure, where the width and height are typically denoted by the number of rows and columns of pixels. Unlike vector graphics, which use mathematical relationships between points and paths, raster graphics are resolution-dependent. Changes in size can adversely affect the visual quality of the image. Vector graphics are often preferred for type work and line illustrations, while raster graphics excel in handling photographs and images with continuous tones and shading.
Raster Image
The size of a raster image is often described in terms of pixels, such as 640 x 480, indicating 640 pixels in a row and 480 pixels in a column. The resolution, denoted in pixels per inch (PPI) or dots per inch (DPI), determines the level of sharpness in the image. Higher-resolution raster graphics have smaller pixels, resulting in more detailed images. When displaying or printing raster graphics at larger sizes, higher resolution helps maintain image quality and prevents a grainy appearance.
In the context of color, black-and-white raster graphics use only black-and-white pixels, with each pixel requiring one bit of memory. Colored raster graphics, on the other hand, require additional bits to represent the red, green, and blue components of each pixel. The color depth, measured in bits per pixel, determines the range of available colors. An 8-bit color depth provides 256 colors, while a 12-bit color depth allows for 4,096 colors. Higher color depth enhances the graphic’s ability to display shading.
Raster graphics are well-suited for rich, detailed photos and web graphics. However, resizing can impact quality, making it essential to consider the trade-offs between resolution and size based on the intended use of the image.