How to improve Digitization Accuracy

Errors usually creep in from the following sources.

We now elaborate on how to minimize these errors and improve the accuracy.

Remove the errors from Camera Distortion

What is camera distortion?

Even the best cameras suffer from some errors due to imperfect lenses. A perfect lens would render straight lines as straight, no matter where they occur. Most practical lenses aren’t that good, though, and instead bend lines outwards (barrel distortion) or inwards (pincushion distortion). This is called lens distortion. Wide-angle lenses often suffer particularly badly from this.

Correcting this distortion in the image geometry is of critical importance in our digitizing application.

The two typical lens distortions that occur are called barrel and pin-cushion distortion. They are named by the effect that they have upon an image, as shown in Figure.

Distortion free image Barrel Distortion Pincushion Distortion

Barrel distortion is found in wide-angle views and it is the result of the squeeze that is applied in order to fit the image in a smaller space.

Pin-cushion is found in telephoto because of the stretching applied in the image.

The squeezing and the stretching of images vary radially due to the design of the lenses, making these distortions visually most prominent at the image corners and sides. Barrel and pincushion distortion typically appear at the shorter and longer ends of a zoom lens respectively, with continuous variation in between.

How can it be corrected by Camera Calibration?

In order to avoid this distortion, we have to calibrate the camera. Camera calibration is the estimation of a set of parameters that describes the camera's imaging process. By calculating those parameters and using them while digitizing we will get the perfect image with minimum distortion error.

How to calibrate the camera?

For calibrating the camera we need some photographs of a regular ChessBoard pattern.

  1. Take a printout of the “chessboard.pdf” file.
  2. Take atleast 25 clear (sharp) photographs from different angles keeping in mind the following
  1. Input the photographs into PLUS Replicam – and let it do the rest.

Getting a better photograph for digitization

Following are few guidelines that can help you get a better picture for digitization.

Picture Background

Reference Plane




A lot of pixels are wasted in the left picture. In the RIGHT picture the maximum amount of pixels are utilized are devoted to the template, which is better.

The photo should be clear so that edges of template are clearly visible. Focus the camera properly before snapping the picture.

See Also