Graphic Image File Types - What Do They Mean?
Graphic Image Files
It's sometimes confusing working with graphic files, there many different file extensions (.tif,.wmf,,cdr,.ai, etc). Some graphic file types are proprietary, you can only open / edit them with the program that created them. However, most graphic design software will allow you to Export or Save As specific file type such as.jpg or.pdf. Although there seems to be and endless number of file types, they all can be divided into two basic ways of storing a graphic, vector or raster. Each of these types has its own characteristics.
RASTER or pixel based images are composed of square pixels (dots). Each pixel is assigned a position and color in the image file. The pixels are aligned end to end across and vertically in the file. The resolution of the image tells you how may pixels or Dots per Inch (DPI) the image has. The more dots, the higher quality the image will be. But higher resolution comes at a cost, storing all those pixel locations and colors take up quite a bit of memory, that's why raster images sometimes have very large file sizes. 10, 15 or more Mega Bytes (1MB = 1 million bytes). You also have seen images where curved lines have a saw tooth appearance, square pixels lined up make great looking vertical and horizontal lines but not very good curved lines. The lower the resolution (DPI) the more obvious the saw tooth pattern this becomes.
VECTOR or line based images are composed of lines that specified by coordinates on a grid. There is a beginning point, straight or curved line and an end point. There are no pixels or resolution. You can make the image any size from 2 inches to 20 ft, it will look the same, just a perfectly smooth line. That's why Computer Aided Design (CAD) software stores images in a vector based file, it provides infinite resolution (accuracy). Another advantage is that the file size is typically small, it has to only store a few coordinates for a specific shape within the image file.
Converting from Raster to Vector / Vector to Raster images.
Vector based image files can sometimes contain raster images. However raster image file types don't store any vector image data. That's important to note if you want to Export or Save As to a different file type. It's easy in most vector software to convert a vector (line based) image to a raster (pixel based) image, you just save as a .tif, .jpg or other raster image only format. But going from a raster image to a vector based image isn't that easy. Yes, there are programs that do a raster to vector conversion, but they all work by tracing the pixel image. Some raster to vector programs work better than others, but you always lose some detail on the image, or you get a saw tooth line.
Common File Types
If your image file type is .jpg, .tif, .gif, .bmp or .png file extension, it is a raster (pixel) image. Common programs for editing raster images are PhotoShop, Paintbrush, Corel Photo-Paint
If your image file type is .ai, .wmf, .cgm, .cdr, .eps, .ai, .pdf it may contain vector images, raster images or a combination of both. You would need to open and with vector design software and do a View Outlines or Wireframe to see if vector based lines are present. Common programs for editing vector images are Adobe Illustrator, Corel Draw, Canvas, Quark.
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