Manual Vs Automated Raster to Vector Conversion

Raster and Vectors are two formats of data structures used for storing engineering data. All major CAD software are developed primarily using these data structures. Based on the usage of the data the engineering drawings are stored either as raster images or vector data. Engineering drawings which are to be frequently updated or any changes to be made then it is stored in vector format. If no changes are required and the engineering data is just to be stored then the data is stored in raster format. A raster image is majorly used for viewing purpose.

Raster images are made up of a grid of dots known as pixels. Raster images are digital images captured using a raster imaging device. The resolution of raster image captured depends on the resolution of an imaging device and original data source. Since a raster image is made up of pixels it’s quality changes when the image is scaled up or down.

Vector data is made up of points, lines, and curves which are associated mathematically. Because of this mathematical association, the vector image can be scaled up or down without changing the quality of the image. Points are stored using coordinates (x,y) and lines using coordinates (x1,y1) and (x2,y2) indicating a line between them.

Raster to Vector Conversion:

Raster to Vector Conversion is a process which involves the transformation of image data (which is in form of pixels) captured from an image capturing devices such as Scanners and Cameras into which are un-editable to an editable Vector image (made of points, lines, and curves). All CAD software requires these vector images for further changes in the image.

There are basically three approaches to convert a raster image to vector format.

  1. Manual Digitizing: It is a process which involves a device known as the digitizer to digitize raster image to vector. In this process an operator uses a pointer or a Mouse to trace the lines on a hard copy and an image is created on his computer. The operator traces the line on hard copy by collecting a series of points on the line which is digitized.
  2. Automated Raster to Vector Conversion: An Automated Raster to Vector Conversion software is used in this process. The software is installed on a computer which is to be used for the conversion process. The software traces lines automatically from raster image which is scanned using image processing and pattern recognition technique. The primary idea behind developing an automated technique for raster to vector conversion is to remake the computer trace raster image lines. The involvement of a computer reduces the time take to complete the conversion process.
  3. Manual Conversion Using CAD Software: This process is basically known as drafting. The process includes insertion of a raster image in the CAD Application and a Drafter assigned to the process draws vector lines over the raster image inserted in CAD Software.

This article discusses which conversion process (Automated R2V or Manual Conversion Using CAD Software) is better.

Below is Vector converted using Automated Software.


Below image shows Vector Manually converted using CAD Application:


One will always think why to use a manual conversion process when there is an automated software which makes the job easy and saves a lot of time. Firstly, though the automated software vectorizes raster image it is not 100% accurate and some amount of human involvement is required to clean up the vector generated. The quality of vector also depends on the quality of raster scan. Unwanted lines crop up if the Raster Scan image quality is worse.

An automated process usually vectorizes what appears on the scanned raster image. If during the scan an unwanted line crops up because of an error in the scanner even that line is scanned as the automated software doesn’t identify it as an unwanted line. Additionally, automated software packages do not work well when hard copy drawings that are 30 years or older have been scanned, due to the deterioration of the originals.

Another major concern when using an automated process is they usually don’t identify the critical joints. They just replicate whatever is there in the raster image without using any knowledge regarding exactly what those lines represent.

Usually, the Automated software uses OCR to convert text. The text is converted as a character and it never identifies a text which is used for NC tooling should be the vector. Conversion of logos is also not Cad perfect. Parameters such as scaling, image skewing are not considered in Automated Conversion.

Whatever might be the quality of scanned image a manual conversion using CAD application will produce a CAD Perfect vector output. The manual conversion starts with the scaling of the raster image and then calibrating if necessary. Then an image is deskewed to start the conversion process. All the instructions from the customer are considered during the conversion process. A CAD Drafter uses appropriate layers and formats for conversion. Even text is converted to Characters or Vectors based on their utility. The manual conversion will produce a vector image which is 100% accurate and which can be used in future for further applications.


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