Raster to Vector Conversion
Raster to Vector "Need to Know" Facts
Raster to vector (R2V) conversion is not a standardized process. There is no a single correct method, no "one size fits all" that enables you to convert everything from blueprints to photographs. Even within the same category, blueprints for instance, there are many different R2V algorithms that can be used and each gives different results. It's important to recognize that vector representations of graphics can be more abstract than raster representations.
While there are software packages that do provide automatic raster to vector conversion, we've found that even the best automatic conversion software, requires some human intervention in order to ensure an accurate CAD drawing.
This is because automatic raster to vector software programs can have difficulties with some parts of a raster image where parallel or concentric entities touch. Where the lines touch, the automatic program can make mistakes because it can't clearly see where one line ends and another begins. This is an area where someone who is inexperienced with raster to vector conversion may not understand how to correct the problem, while a raster to vector CAD expert can quickly look at the drawing and make a hand-drawn adjustment to preserve the integrity of the design.
Other areas that may be problems for automatic raster to vector include hatch patterns. Hatch patterns generally will not auto-vectorize well. In addition, dot-type hatch patterns will likely need to be removed completely using the raster to vector software despeckle command. In this case, once the drawing is converted from raster to vector, an experience CAD operator will need to replace the hatches in the CAD program.
For every 100 drawings that we convert from raster to vector, we find that for 30%, we use one method of conversion; 40% require a completely different method; and the remaining 30% need to be completely redrawn. That's what people don't realize when they buy R2V software - it's going to take more than that one software package to do the job. And that's where we really save our customers time and money.Scott Shuppert, President
Here at CAD CAM Services, we realize that regardless of what we're converting, or what method we're using, starting with a clean raster image that has been scanned at the correct resolution will improve the final outcome. Cleaning means de-speckling, getting rid of unwanted artifacts, smoothing and fixing lines and removing any holes. This can be a time consuming process.
One of the advantages of using us to perform your conversions from start to finish is that we will ensure that the drawing is scanned at the correct resolution and that it is clean and ready for R2V. In this respect, we can save you considerable time.
Another reason for using CAD CAM Services is because over the years, we've learned lots of "tricks of the trade" that speed the process when converting to AutoCAD; Revit; Navisworks; MicroStation; VectorWorks; SolidWorks; Catia; ArcInfo and other common CAD programs.
We've even compiled a list of Raster to Vector information to help you make a decision about the best way for you to go about converting your raster images to vector drawings.
Raster to Vector Information List
1. Files such as JPEGs, BMP, TIFF, IMG, GEM, CIT, GIF and PNG are considered to be raster images.
2. Raster images use many colored pixels to form a complete image. Generally, this dot matrix data structure is represented in a rectangular grid.
3. Because raster images are constructed using a fixed number of colored pixels, they can't be dramatically resized without compromising their resolution. When stretched to fit a space they weren't designed to fill, their pixels become visibly grainy and the image distorts.
4. Raster files can be imported into CAD programs, but they cannot be edited. CAD programs require vector files in order to edit a drawing.
5. Vector files consist of lines and are constructed using mathematical formulas rather than individual colored pixels like raster images.
6. Vector image file types include DXF, DWG, DGN, HPGL, SVG, EMF, WMF and PDF* (which can contain raster images, vector images or both).
7. Vector files are excellent for creating drawings that need to be resized, edited and measured - drawings such as CAD or AEC drawings.
8. *Depending how a PDF is originally created, it can be either a vector or a raster file. Whether you opt to flatten the layers of your file or choose to retain each one will determine the image type.
9. Logos and brand graphics are also often created as vector files so that they can be sized extra-large for signage and extra-small for business cards.
10. Vector files include geometrical primitives such as points, lines, curves, and shapes or polygon(s). These are all based on mathematical expressions that represent images in computer graphics.
11. Vector files are based on vectors (also called paths, or strokes) which lead through locations called control points. Each of these points has a definite position on the x and y axes of the work plan. Each vector point is formed from a variety of data including the location (on the X, Y axis) and the direction of the vector 'track'.
12. Each vector track can be assigned a color, shape, thickness and fill. This does not affect the size of the files in a substantial way because all information resides in the structure; it describes how to draw the vector.
13. Vector primitives, paths, shapes, thickness and fill are vital parts of CAD design drawings for mechanical and architectural cad, and help to specify how the final object will be built.
14. Raster images vary in quality depending upon how they were created.
15. Scanning at low resolution can negatively affect the raster to vector conversion process and accuracy.
16. If shapes in your raster image are defined by only a few pixels and look jagged, your image is too low resolution. The drawing needs to be rescanned at a considerably higher resolution - aim for lines that are about 5 pixels thick.
17. Scanning can introduce skewing and other errors into the raster image which must be corrected prior to conversion.
18. Raster images must be cleaned, deskewed, despeckeled, rubbersheeted and QC'd for scanning errors prior to beginning the R2V process.
19. A "dirty raster image" or "noisy raster image" is one that has not been cleaned to get rid of unwanted artifacts, lines or holes.