Dawid Anioł Blog

1. Initial requirements. I mean tools which we will use while compilation. XCode application contains compilers C and C++, standard library and necessary header files. All mentioned above is a base for C/C++ environment on OS X platform. Cmake is a tool for building C/C++ projects.

• Xcode – might be installed from apple store
• Cmake – https://cmake.org/download/

This is a good idea to make a special catalog in which you can keep all source files, additional files, library files and all stuff necessary for compilation.

• Mkdir blender-build

2. Sources. In this section we download sources of the Blender itself with submodules. Blender sources contain a lot of scripts and configuration files. It contain also files helping with buildup and making packages under various platforms but we are not interested in that yet. We will download the sources first.

• git clone git://git.blender.org/blender.git

Having Blender sources we need yet submodules. Submodules are sources which for some reason are not included in the main repository, but they have influence for addition functions. As for us to be able to download submodules we should enter to the folder of cloned repository

• cd blender

And now we can download submodules

• git submodule update –init –recursive

• git submodule foreach git checkout master

• git submodule foreach git pull –rebase origin master

We got submodules now. Next step is to download dependency libraries. Those are complicated static and dynamic files with the headers. These libraries we can compile oureself or download from SVN repository.

• svn checkout https://svn.blender.org/svnroot/bf-blender/trunk/lib/darwin lib
  • I encountered a problem with braking connection, when downloading some files. You can go back re-download those files but before that you have to cleanup repository
  • cd lib
  • svn cleanup
  • cd ..
  • svn checkout https://svn.blender.org/svnroot/bf-blender/trunk/lib/darwin lib

Downloading might take some time 

3. Compilation. Compilation take place with the command ‚make’, but we can have a few types of this command. 

• make full – it makes version with all possible options and dependencies
• Make like – it makes version with minimal number of dependencies 
• Make headless – it makes version without interface
• Make deps –  it makes libraries of decency

And this is all, after compilation we have working version of Blender.

Background removing is one from the problems in image processing which seem to be pretty easy but gives headache instead. OpenCV library has section dedicated to background removal in videos. BackgroundSubtractorMOG , BackgroundSubtractorMOG2, BackgroundSubtractorGMG are the functions that appears in the library. They remove background from each frame, the mask is made which allow to separate object of interest. Form one side these functions are not perfect. From the other side we oftenly have only two frames, on one of them is only background, and the other frame is the same background but with the object of interests. We can use functions mentioned above or we can go with something lower level which maight be more precise in some cases. 

If given frames are prepared by precision computer image functions meaning that background any shifts and each pixel of the background on one image is equivalent to the other image pixel, also value of these pixels has to be identical. In this case we can use compare function and this is how we can do it:

To make a mask, firstly process image in cvtColor by making it one layer image, and than use compare node with code setting set on CMP_NE. In that step the output image is a small trail with some noise around, which is byproduct of the image compression. Small differences of value of the pixels may depend from the type of compression and its settings. These noise artifacts are removed by erode function. Mask which we achieved has to be process by bitwise function and as effect we can get image without background. These approach is autonomous because it doesn’t require change in settings for other images. 

For background removing we can use another different method which is based on the function watershed. Method is very precise but it required a key regions of the object which we want to separate from the background. But it will be covered in the next article.