While creating different types of composites and artworks using various softwares, you come across the basic digital image types — raster and vector.
Introduction: Raster images, sometimes called bitmap images, are composed of rectangular grid of picture elements called pixels. Each pixel is assigned a specific location and color value. When working with raster images, you edit pixels rather than objects or shapes.
Common use cases: Raster images are the most common electronic medium for continuous-tone images, such as photographs or digital paintings, because they efficiently represent subtle gradations of shades and color.
Popular software and file types: Most professionals use Photoshop for working with raster images. Commonly exported raster file types in Photoshop are JPEGs, GIFs, PNGs, and TIFFs.
Resolution and file size: Raster images are resolution-dependent—that is, they contain a fixed number of pixels. When you resize, your raster image loses or gains pixels, resulting in reduced image quality. Raster images usually have large file sizes due to the pixel information stored in them and often need to be compressed to keep file sizes down when used in certain Creative Cloud apps.
Introduction: Vector images, sometimes called vector graphics, vector shapes, or vector objects, are made up of geometric (points, lines, or curves), organic, or free-form shapes defined by mathematical equations according to their characteristics.
Common use cases: Vector images are the best choice for artworks such as technincal illustrations, letterheads, fonts, or logos — used in various sizes and in various output media. Vector graphics are also useful for specialty signage printing, CAD, and 3D graphics.
Popular file types and software: Preferably, Adobe Illustrator is used to create vector artworks. Some common vector graphic file formats are AI, EPS, SVG, CDR, and PDF.
Resolution and file size: You can freely move or modify vector graphics without losing detail or clarity, because they are resolution-independent—they maintain crisp edges when resized, printed to a PostScript printer, saved in a PDF file, or imported into a vector-based graphics application.
Photoshop supports creative projects ranging from photo editing and compositing to digital painting, animation, and graphic design. By default, most of the work created using Photoshop are raster files. However, you can also create vector files in Photoshop and convert raster files to vector.
To learn more about adding vector design elements to your Photoshop composite, see Working with Shape tools.
When combining vector graphics and raster images in a document, it’s important to remember how your artwork looks onscreen isn’t always how it would look in its final medium (whether commercially printed, printed on a desktop printer, or viewed on the web).
The following factors influence the quality of your final artwork:
- Transparency: Many effects add partially transparent pixels to your artwork. When your artwork contains transparency, Photoshop performs a process called flattening before printing or exporting. Usually, the default flattening process produces excellent results. However, if your artwork contains complex, overlapping areas and you require high-resolution output, you will probably want to preview the effects of flattening.
- Image Resolution: The number of pixels per inch (PPI) in a bitmap image. Using too low a resolution for a printed image results in pixelation—output with large, coarse-looking pixels. Using a very high resolution (pixels smaller than what the output device can produce) increases the file size without increasing the quality of the printed output, and slows printing of the artwork.
- Printer resolution and screen frequency: The number of ink dots produced per inch (DPI) and the number of lines per inch (LPI) in a halftone screen. The relationship between image resolution, printer resolution, and screen frequency determines the quality of detail in the printed image.