neurophant / enimda-cpp

Entropy-based image border detection

ENIMDA

Entropy-based image border detection algorithm: detect border or whitespace offset for every side of image, supports animated GIFs.

Prerequisites

GraphicsMagick (http://www.graphicsmagick.org/)

Algorithm (simplified)

For each side of the image starting from top, rotating image counterclockwise to keep side of interest on top:

• Get upper block 25% of image height
• Get lower block with the same height as the upper one
• Calculate entropy for both blocks and their difference
• Make upper block 1px less
• Repeat from p.2 until we hit image edge
• Border is between blocks with entropy difference maximum

Example

Find image borders:

#include "ENIMDA.hpp"
#include <iostream>

using namespace std;
using namespace Magick;
using namespace ENIMDA;

int main(int argc, char **argv) {
  InitializeMagick(*argv);

  Loader em("example.jpeg", 0, 0, 0.25, 0);
  vector<unsigned int> borders = em.scan(true, true, 0.5);

  for (auto &border : borders) {
    cout << border << " ";
  }
  cout << endl;

  return 0;
}

Demo

For demo please refer to ENIMDA Demo

Also it lives at Picture Instruments as 'Remove borders' instrument