How do I take the best photos for fragmentation analysis?

The better the images, the better the results. Develop a sampling strategy. Taking images is like taking samples for sieving or other tests. The results must statistically represent the product as a whole.

 

To adequately compensate for rockpile segregation and heterogeneity, each image must contain a sufficient number of fragments, and the results from dozens of images per blast must be merged and averaged. Accurate estimation of larger blocks in particular requires merged data because of the scarcity of such blocks. High-fidelity, high-speed automatic edge detection is essential.

  • Fill the field of view with fragmented rock, preferably at least 200 particles
  • Video and still images greatly improve when a tripod is used. Hand-held shots are seldom sharp particularly telephoto shots where the slightest movement causes image blur.
  • Include all sizes. No single block should occupy more than 20% of the width of image. For improved resolution of fines, use WipFrag's zoom-merge capability to combine images at different scales of magnification.

  • Take several shots, preferably of at least five at random locations on a large rockpile, or of several truckloads or drawpoints. For improved estimates of oversize, increase the number of full-scale shots to at least ten.

  • Beware of rockpile segregation. Large blocks tend to roll to the outer edges and fines may cover the surface or become hidden as a result of gravity or rainfall. The effects can be minimized by increasing the number of images per sample but only with careful selection of image locations.

  • 1024x768 is recommended for digital pictures to find an edge detection parameter (EDP) easily. Good clarity and contrast is better than size. (Although, any size picture can be used.)

  • Wide angle lens have edge distortion. Try to avoid them.

  • Digital Zooming results in interpolated pixels and should not be used.

  • You should try to use a suitable size scale for each picture. Avoid using balls as they are dimensionally unstable (i.e. Air filled balls expand/contract, softballs are two small, etc. Range rods, yard/meter sticks work well.)

  • Don’t waste an image. Get images of the particles in question, not the sky and area around it.

  • WipFrag measures what it can see. If your pictures are far away, fines will not be resolved. If the image is taken too close, oversize may be missed. Get a good mix of images of the sample in question.