Programming_Tips/opencv.md

OpenCV

Memos and Tips about the OpenCV library.

In C/C++:

Placing a pointer to the beginning of pixel in an image:

Can be used to naviguate through pixels easily (and more efficiently than some openCV functions).

char *pImage = iplImage->ImageData

Short review of the IplImage structure:

What’s really needed to work with an Image

* IplImage struct {
    depth # Number of channels (gray level, color, . . .)
    sizeX
    sizeY
    * ImageData } #Pixels of the image
    ...}

Simple tips for Image Processing optimization in C:

An image is stored in a memory a a long line (n*m size)

Always go trough the buffer way, and not the opposite!

for (i in nb_lines):
    for (j in nb_cols):
        //do stuff
    }
}

and

for (j in nb_cols):
    for (i in nb_lines):
        //do stuff
    }
}

are different ! The second one is 10% faster than the other !

##In Python :

Error on compiling OpenCV with Python bindings:

If you get this error when trying to compile OpenCV in Linux

Could NOT find PythonLibs (missing: PYTHON_INCLUDE_DIRS) in cmake

Simply try installing python-dev packages.

$ sudo apt-get install python-dev

It should solve the problem.