3 Common Problems When Converting Image Files to DXF

Updated Apr 14, 2017
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DXF, PDF and layers Raster to vector file conversion software can save precious hours of your time: instead of creating a vector image from scratch, click a few buttons and let the software convert the image to DXF – in a matter of seconds!

However, the quality of your output DXF file depends heavily on the input file. If you convert a poor image, you may end up spending hours afterwards tidying it up. Here are three common problems to avoid and how to troubleshoot them.

1. Poor image quality

This is a common problem with raster images. They are often of poor quality or low resolution, which can cause issues when converting a PDF or a GIF to DXF. The first thing you can do to check is to zoom into the image.

Here are few common tell-tales of poor image quality:

  • Heavy pixelation
  • Low resolution. The rule of thumb is that lines need to be about 5 pixels thick in order to obtain a good quality vector output.
  • Hairy lines, or lines that have fuzzy/ragged edges
  • Dithered lines, or lines that are made up of black speckles. This is often a case if you scanned a pencil-drawn image
  • Lines with holes. This may happen when you scan an image at too high a resolution.
  • Broken lines, where parts of the line is very faint.
  • Shadows. This is common when scanning physical objects
  • Merged lines or overlapping elements of your drawing. For example, you could have written some text over a line or overlaid a wiring plan on top of a floor plan. No vectorization software can distinguish one from another.
  • Text characters that are touching each other or other drawing elements
  • Illegible text. It may sometimes be quicker to retype the text manually than to fix individual text vectors!

Poor image quality for raster to vector conversion

You can solve this by:

  • Straightening or deskewing the image. Click Raster Effects > Rotate > Autodeskew.
  • Cleaning up the image before converting. Click Raster Effects > Clean > Remove Speckles. You can also manually remove dirty spots using the area erase or freehand erase tool. Be careful not to remove inch signs (“) or full stops!
  • Crop the image. This one is a no-brainer. If there are unnecessary borders around the edge of your image (common with scans), delete this by cropping the image.
  • Smooth the image to remove hairy lines. Click Raster Effects > Smooth
  • Thicken lines or pixels.Click Raster Effects > Thicken > Lines / Pixels
  • Increase threshold of the image.
  • Fill in holes using Raster Effects > Clean > Remove Holes.
  • Connect broken lines to produce a continuous vector. Click Type > Settings > Gap Jump Distance

2. Not tidying the image up after conversion

Conversion software like Scan2CAD can save you a lot of time, but it really only does about 80% of the work. You’ll still have to check the image after conversion to make sure that the elements are correctly recognized. For example, a dashed line can be easily mistaken as many short lines. A sharp corner may also be converted into a smooth arc.

Scanned PDF to DXF to uploaded for editing with CAD software: PDF to DXF File Conversion

Scan2CAD comes with a complete suite of raster and vector editing tools

Here’s one of our favourite tips to facilitate the tidy-up process: use grids (the keyboard shortcut is Shift+I). You’ll have to be zoomed in really close to view the grid, as each grid square is one pixel. This allows you to check whether your lines are clean, straight and so on.

Use of Grid in Image Tidy-up Process

Here are few clever uses of the grid when tidying up images: to align shapes and ensure clean lines

3. Not understanding the output required before conversion

If you’re converting files into DXF for CNC software, learn about the limitations of the CNC cutting system (such as cut width)

Selecting the right vectorization settings also goes a long way in getting a good quality conversion. If the image contains a lot of straight, orthogonal lines, choose Mechanical. If the image contains straight but non-orthogonal lines, choose Site Plan. Drawings with curvy lines suit Contour Map well, as this setting converts shapes into Bezier curves and splines. Select Outline if you want to trace the outline of a solid shape.

While Scan2CAD has default settings to make the most of your image, you can help it recognize some forms better. If your drawing contains elements like dashed lines, arrows, polylines, hatches or circles, make sure these are selected in your settings. Go to Type > Settings > Object Identification to configure these.


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