Vectorization (graphics)
In the field of computer graphics processing, the term vectorization , sometimes also (image) tracing , refers to the automated process of converting raster graphics into vector graphics .
concept
The vectorization attempts to identify simple geometric objects in a raster image. The usual variant uses edge detection to search for areas of the same or similar brightness or color , also known as posterization , which are then expressed as graphic primitives or Bézier curves . It is then exported to various vector graphic file formats such as SVG , AI , CDR , EPS , TTF , PDF or various CAD formats.
Classic edge detection methods that are used in vectorization are z. B. Roberts operator , Canny algorithm and the Sobel operator .
Manual vectorization
A graphic designer can manually vectorize an image by hand drawing paths with digital illustration tools. The paths are traced by shapes in a source image. The digital tracing is usually done directly over the source image. Graphics such as logos and symbols are often created using manual vectorization.
Software vectorization can sometimes be very imprecise. Images vectorized with software or online tools tend to be deformed and imperfect after vectorization. Graphic designers can often vectorize their images with greater accuracy.
With manual vectorization, your image is often cleaner and more prominent than the original bitmap image. Illustrations, photos, and complex logos tend to be of higher quality when vectorized. The imperfections and inaccuracies of automatically generated images often render the images unusable.
The quality of a manual vectorization largely depends on the graphic designer's drawing and tracing skills. Manual vectorization is generally more flexible because a source image can be vectorized regardless of its resolution.
The quality of an automatic vectorization depends on the quality of the source image. A high-resolution source image is often required so that an image can be automatically drawn cleanly.
As with many things that are done automatically, automatic vectorization can save a lot of time - especially with a very detailed source image. Despite the setting options, auto tracing can often leave too much detail or create strange shapes that don't match the source image.
For a cleaner, cleaner look, manual vectorization with a good graphic designer is probably the better method. In most cases, your image will be cleaner than an auto-tracked image, which can contain incomplete lines and tiny, unwanted artifacts.
The image can be vectorized manually. A person could look at the picture, take some measurements, and then handwrite the output file. This was the case with the vectorization of a technical illustration using neutrinos. The illustration contains some geometric shapes and a lot of text. It was relatively easy to convert the shapes, and the SVG vector format makes it easy to enter the text.
The original image had no curves, so conversion is straightforward. Curves make the conversion difficult. Manual vectorization of complicated shapes can be made easier with the tracking functionality built into some vector graphics editing programs.
Once a machine readable bitmap is available, the image can be converted to a graphics editing program, e.g. B. Adobe Illustrator , CorelDraw Graphics Suite or Inkscape can be imported. A person can then manually track the elements of the image using the program's editing features. Curves in the original image can be approximated with lines, arcs and Bézier curves . An illustration program can be used to adjust spline nodes for a snug fit. Manual vectorization is possible, but it can be tedious.
Michael Ploch recreated a design from a digital photograph . The JPEG was imported and some basic shapes were drawn by hand and colored in the graphics drawing program. More complex forms were treated differently. Ploch used a bitmap editor to remove the background and crop the more complex image components. He then printed out the picture and drew it by hand on tracing paper to get a clean black and white line drawing. This drawing was scanned and then vectorized with a program.
Strengths and Limits of the Methodology
In contrast to the reverse process, rasterization , automatic (or semi-automatic) vectorization is not clearly defined or a unique process; there are many different methods and degrees of freedom. Each of these different methods offers a different abstracting approximation of the raster image with its vectorization approach. Different methods and parameterizations are also differently suitable for different image contents, formats and resolutions, which means that it is often necessary to manually try out different combinations.
Furthermore, images of natural objects are difficult to representatively vectorize in contrast to images of artificial objects, such as. B. Computer graphics, as these typically have fewer color or brightness gradients and less irregular structures.
File size
Vectorizations of high-resolution images with few colors and gradients (crack drawings, writing, computer graphics) can be significantly smaller than the original image if they are highly representative.
In the case of images of natural objects, a significant increase in the amount of data is often necessary in order to achieve an only acceptable vectorization result. This is particularly true for the vectorization of images of natural objects in JPEG format, a graphic format which is particularly suitable for smooth transitions and which codes them effectively.
Rendering effort
The strength of vector graphics in general, and thus also of vectorized images, is the independence of the resolution, i. That is, they are suitable for reproduction (screen, printing) in any resolution. However, this always requires a complex “rendering” ( rasterization ) of the vector format in a raster format. A disadvantage of vector graphics compared to raster graphics is an unknown, content-dependent rendering effort (in terms of computing time and working memory). Raster graphics generally have the advantage that the rendering effort is constant and independent of the content. To minimize this disadvantage of vector graphics, Wikipedia, for example, provides server-side pre-rendered raster graphics preview images of SVG vector graphics in several resolutions.
variants
Since the fully automatic vectorization of images of objects with gradients only leads to unsatisfactory results, manual work often has to be done. This can range from the removal of vectorization artifacts , the introduction of new shadows or color gradients to the complete manual creation with a vector graphic program , see example Tux below.
Known fields of application
- With CAD , drawings ( crack drawings etc.) are scanned, vectorized and exported as CAD files; this process is also called paper-to-CAD conversion or drawing conversion .
- When geographic information system (GIS) satellite - or aerial images vectorized order cards to create.
- In graphic design and photography , images are sometimes vectorized to make them easier to use and scalable .
- With font design, drawn designs are converted into a font vector format via vectorization.
- Handwritten notes and signatures are easy to vectorize because they are typically only two-colored (white + ink color) and have a great contrast . This is also the first step in text recognition .
Influence of various vectorization programs and parameters
Natural object
Since photographs of natural objects often contain many smooth transitions and small details and the result also depends heavily on the raster resolution of the input image, acceptable automatic vectorization is difficult. It is often necessary to experiment manually with the parameters number of colors, noise reduction / quality for a long time until an acceptable compromise between the image fidelity and file size is achieved.
Original image : Silversmith photography in JPEG raster graphic format (610 × 818 pixels), 25 KB
Vectorized with 12 colors in VectorMagic with the parameter High Quality , 369 KB
Vectorized with AutoTrace in the Delineate GUI, 677 KB
Vectorized with VectorMagic with the parameters High Quality and unlimited colors , 744 KB (column artifacts occurred)
Vectorized with RaveGrid , 1.64 MB
Vectorized with BMP2SVG , with an excessive spline parameter of 25000, 4.4 MB (file size overwhelms the Wikimedia SVG renderer)
Lettering
Lettering of Jeanne d'Arc as JPG raster format (627 × 480 pixels), 24 KB
Vectorized, two-color variant, 10 kB
Lettering of Christoph Columbus as a JPEG raster graphic (1.308 × 481 pixels), 63 kB
Vectorized, two-tone variant, 19 kB
Computer graphics
Vectorized with sketch, also manually post-processed, 219 kB
Manual creation as a vector graphic using gradients and transparency, 21 kB
See also
Web links
- autotracer.org Online vectorization based on the AutoTrace library (English)
Individual evidence
- ↑ UMBRELLA consulting, as: Manual vectorization vs Auto-Tracing software
- ↑ Michael Ploch: CorelDRAW Handbook: Insights from the Experts . In: Corel Corporation (Ed.): CorelDRAW X3 Graphics Suite . 2005.