Raster Image Formats in CAD
There are many 3D CAD file formats for storing and transmitting data. CAD file formats can be classified in terms of two distinct formats: the bitmap or raster (pixel-based) format, and the vector format. The distinction between the two formats is clarified by pointing out the main difference between them.
- The raster format represents images in terms of pixels. On a display monitor, the pixels are dots which carry colour attributes and levels of intensity in RGB (Red, Green, and Blue) colours. Raster graphics are suitable for photographic images and they are resolution-dependent. They do not scale up to higher resolutions without loss of quality, because the image becomes grainier and image details become lost.
- The vector format represents images as points, lines, curves and polygons (called primitives) on an algebraic grid. The primitives are utilized to create vector-based images. Vector images can scale up to any resolution without loss in quality.
The most important difference between raster and vector-based images is that raster images are poor when they are scaled higher than the resolution at which they were created. On the other hand, vector images can be scaled up or down without any loss in image quality:
- Popular raster (bitmap) based formats are JPEG, PNG, BMP, TIFF formats.
- Popular vector-based formats are EPS, PDF or AI (Adobe), SVG (Scalable Vector Graphics), DXF (Drawing eXchange Format), WMF (Windows Metafile Format), DRW, and DWG formats.
- Compound formats such as EPS, PDF, SWF, and PICT contain both pixel and vector-based data.
In order to determine whether the raster image format could disappear from CAD file systems, this article tries to answer these specific questions:
- How popular is the vector format among leading CAD vendors?
- Which CAD file formats are most popular with 3D printing technology?
- Is any particular CAD file format best suited for CAD data exchange?
- Why would the raster format remain an important part of CAD file systems?
How Popular Is the Vector Format among Leading CAD Vendors?
It appears that modern CAD software packages store design and drawing information in the vector format. To confirm this observation, it is worthwhile to look at CAD formats that leading CAD vendors use:
- AutoDesk has its own native file format, but it supports DWG, DXF and many other file formats.
- AutoCAD uses the DXF and DWG vector formats.
- SolidWorks uses a structured format in which different file formats are embedded. The design information is stored in the DXF vector-based format. Other formats such as AI, CGR, and STL (for 3D printing) are stored within the structured format. The structured format also stores raster formatted images.
It is interesting to note that many software applications are available to convert images between the raster and vector formats. Some of the significant image converters include CorelDRAW, Easy Trace, Freehand, VP Software, WiseImage, and many others. Many leading CAD vendors also provide convertors between raster and vector file formats.
Which CAD File Formats are Most Popular With 3D Printing Technology?
The format used for 3D printing is the STL (STereoLithography) format. It is not clear whether any type of CAD file format is most suitable for 3D printing, because leading 3D companies such as Stratasys and 3D Systems automatically convert recognizable CAD files into STL language. Furthermore, many CAD vendors who are capable of exporting their files into STL include Autodesk Inventor, Catia, SolidWorks, ProEngineer and SolidEdge.
Is any Particular CAD File Format Best Suited For CAD Data Exchange?
There is no simple answer to this question. The preferable CAD file exchange software will have the ability to convert between raster and vector formats. The reason for this requirement is that modern CAD file systems are moving toward the use of a structured file format in which both raster and vector file formats are embedded. Because modern CAD files contain much more than drawings and design information, it makes sense to have different file formats stored within a structure, so that minimal information is lost during file transmissions and conversions.
A good example of integrating different types of information into a CAD file is provided by BIM (Building Information Modeling). BIM integrates activities of all parties and disciplines involved in a building project into a synergistic body which exchanges different types of information. When different teams work together on a project, it is necessary to use different file formats for information exchange. Raster formats are required for pictorial displays, animation and virtualization, while vector formats are required for design drawings which should be scalable. Strictly speaking, BIM provides a useful extension on the CAD file format, but it is not recognized as a CAD file format.
As complexities involved in creating integrated CAD file formats continue, it may become necessary to coin a different acronym for a unified file format which does not primarily contain CAD information.
To answer the question “Is any particular CAD file format best suited for CAD data exchange?”, the answer is no, with qualifications.
- If the CAD data to be exchanged is strictly in the form of design drawings, then the vector format is best suited for the data exchange. It provides scalability without loss of information.
- If the CAD data to be exchanged is strictly in the form of pictorial views or animations (such as for marketing or advertising purposes), then the raster format, created at a high enough resolution, is best suited for the data exchange.
Why Would The Raster Format Remain An Important Part Of CAD File Systems?
Although raster images do not scale up without losing information, they are indispensable for conveying pictorial information and for producing animations. The current trend for storing CAD data is leaning towards the use of a structured file format in which different file formats are embedded. Because each of the two primary CAD formats (raster and vector formats) are useful in their own right, the raster format will undoubtedly remain an important part of CAD file systems.