Vector and Bitmap Graphics Info
- What is the difference between vector graphics and raster graphics?
- Where do vector graphics come from?
- Where do raster graphics come from?
- Can raster graphics be converted to vector graphics, and vice versa?
- What are the different types of raster graphics?
- What guidelines do you have for raster graphics resolution?
- Can I resize raster graphics in a page layout application?
- Can I resize raster graphics in Photoshop?
- I've heard Encapsulated PostScript (EPS) and Portable Network Graphics (PNG) mentioned in the context of both vector and raster graphics. How can it be both?
- Can I copy a graphic and paste it into my document?
Q.
What is the difference between vector graphics and raster graphics?
A.
A vector graphic is defined in a mathematical nature, which makes it resolution-independent. This means it can be printed clearly at any size. A raster image is formed by a rectangular grid of small squares, known as pixels. Each pixel contains data that describes whether it should be rendered as black, white, or a level of color. Raster graphics are resolution-dependent and can appear jagged or in loose detail if they are created at a low resolution and then enlarged or printed at a higher resolution (commonly referred to as "pixelated").
Q.
Where do vector graphics come from?
A.
Vector graphics are typically created by illustration software such as Adobe Illustrator or CorelDraw.
Q.
Where do raster graphics come from?
A.
Raster graphics are typically created by pixel-based image editing software such as Adobe Photoshop. Additionally, raster graphics are generated from digital cameras and scanners.
Q.
Can raster graphics be converted to vector graphics, and vice versa?
A.
Yes. Software such as Adobe Illustrator may be able to convert raster images to vector images; although, slight variation from the original can sometimes occur in the process. Vector images can be converted to raster images by opening and saving them with Adobe Photoshop or a similar image editing program. Please note that converting a vector image to a raster image is rarely necessary, removes the resolution-independence of vector graphics, and should only be done if you have a very specific reason to convert the graphic.
Q.
What are the different types of raster graphics?
A.
A one-bit image refers to an image that is a solid color, with no shades of that color. A continuous tone image refers to photographic images, whether they are full color, black-and-white images with shades of gray (grayscale), or single-color images with shades of that color.
Q.
What guidelines do you have for raster graphics resolution?
A.
One-bit images require 600 pixels per inch (1200 preferred). Full-color continuous tone images, grayscale images, and single-color continuous tone images require 300 pixels per inch.
Q.
Can I resize raster graphics in a page layout application?
A.
These guidelines are for raster images that are used at their actual size. If the image is enlarged in a page layout application, the requirements enlarge by the same amount. For example, enlarging a full-color, continuous tone image 225% in InDesign would require a resolution of 675 pixels per inch (the original requirement of 300 pixels per inch multiplied by the enlargement of 225%). It is best to avoid performing scaling in a page layout application, as these programs have no ability to change the actual pixels in an image.
Q.
Can I resize raster graphics in Photoshop?
A.
Photoshop can increase the resolution of a low-resolution image. However, increasing the resolution of an image scanned or created at a lower resolution only spreads the original pixel information across a greater number of pixels and rarely improves image quality as it cannot add in the missing detail.
Q.
I've heard Encapsulated PostScript (EPS) and Portable Network Graphics (PNG) mentioned in the context of both vector and raster graphics. How can it be both?
A.
EPS and PNG files act as a container for transferring graphic information. When illustration software such as Adobe Illustrator creates an EPS or PNG file, it is a vector file. When pixel-based image editing software such as Adobe Photoshop creates an EPS or PNG file, it is a raster file.
Q.
Can I copy a graphic and paste it into my document?
A.
While copy-and-paste is supported by most software, you will have much more predictable results by creating a link to your graphic. The graphic then remains outside of your document and is referenced as needed. Please refer to your software's documentation for full details about creating links to your graphics.
