OpenCV notes

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

While unrelated, You may also be looking for

Compute: OpenCL

Graphics: OpenGL · OpenVG

Sound: OpenAL · OpenSL

Python

Interfaces

tl;dr: you probably want to use cv2

• cv

official

thin wrapper, with cvMat types as in C++, and cvSeq for things like contours

generally somewhat cumbersome, and sometimes less efficient

• cv2

official, replaced cv (you can still get this interface via cv2.cv)

uses numpy and native python types only

• pyopencv

seems abandoned

• SimpleCV

a wrapper (around cv2?(verify) that makes it easier to set up quick and dirty experiments

maybe nice for an intro but you may end up using cv2

Also not exposing as much, so sometimes slower depending on the task (verify)

uses PyGame as an interface to the Simple Directmedia Layer (SDL).

SimpleCV example:

# use first camera, detect face, draw rectangle
import SimpleCV
cam = SimpleCV.Camera()
while True:
    img = cam.getImage()
    faces = img.findHaarFeatures('haarcascade_frontalface_alt.xml')
    if faces:
        for face in faces:
            face.draw()
    img.show()

See also:

• http://simplecv.sourceforge.net/doc/cookbook.html

Errors

nvcc fatal  : Unsupported gpu architecture 'compute_11'

When compiling OpenCV with CUDA support, you probably want to specify CUDA_GENERATION, e.g. to Kepler (3)

Cannot move to target thread

Something like:

QObject::moveToThread: Current thread (0x1ac0000) is not the object's thread (0x1b35290).
Cannot move to target thread (0x1ac0000)

This is typically a mix of versions of opencv finding each other.

Isolate them properly, or uninstall older versions.