AVR32 Stepper Motor

AT32UC3L0128 and L293D interfaced with bipolar (4-wire) stepper motors...

OpenCV Python: 2048 Game Solver

A sample application of Digit Recognition.
2048 solver algorithm based on term2048-AI

import cv2
import numpy as np
import win32api, win32gui, win32ui, win32con, win32com.client
from PIL import Image, ImageFont, ImageDraw, ImageOps

# create training model based on the given TTF font file
# http://projectproto.blogspot.com/2014/07/opencv-python-digit-recognition.html
def createDigitsModel(fontfile, digitheight):
    font = ImageFont.truetype(fontfile, digitheight)
    samples =  np.empty((0,digitheight*(digitheight/2)))
    responses = []
    for n in range(10):
        pil_im = Image.new("RGB", (digitheight, digitheight*2))
        ImageDraw.Draw(pil_im).text((0, 0), str(n), font=font)
        pil_im = pil_im.crop(pil_im.getbbox())
        pil_im = ImageOps.invert(pil_im)
        #pil_im.save(str(n) + ".png")

        # convert to cv image
        cv_image = cv2.cvtColor(np.array( pil_im ), cv2.COLOR_RGBA2BGRA)
        gray = cv2.cvtColor(cv_image, cv2.COLOR_BGR2GRAY)
        blur = cv2.GaussianBlur(gray,(5,5),0)
        thresh = cv2.adaptiveThreshold(blur,255,1,1,11,2)

        roi = cv2.resize(thresh,(digitheight,digitheight/2))
        responses.append( n )
        sample = roi.reshape((1,digitheight*(digitheight/2)))
        samples = np.append(samples,sample,0)

    samples = np.array(samples,np.float32)
    responses = np.array(responses,np.float32)
    
    model = cv2.KNearest()
    model.train(samples,responses)
    return model

class Board(object):
    UP, DOWN, LEFT, RIGHT = 1, 2, 3, 4
    FONT = "font/ClearSans-Bold.ttf"
    def __init__(self, clientwindowtitle):
        self.hwnd = self.getClientWindow(clientwindowtitle)
        if not self.hwnd:
            return
        self.hwndDC = win32gui.GetWindowDC(self.hwnd)
        self.mfcDC  = win32ui.CreateDCFromHandle(self.hwndDC)
        self.saveDC = self.mfcDC.CreateCompatibleDC()

        self.cl, self.ct, right, bot = win32gui.GetClientRect(self.hwnd)
        self.cw, self.ch = right-self.cl, bot-self.ct
        self.cl += win32api.GetSystemMetrics(win32con.SM_CXSIZEFRAME)
        self.ct += win32api.GetSystemMetrics(win32con.SM_CYSIZEFRAME)
        self.ct += win32api.GetSystemMetrics(win32con.SM_CYCAPTION)
        self.ch += win32api.GetSystemMetrics(win32con.SM_CYSIZEFRAME)*2

        self.saveBitMap = win32ui.CreateBitmap()
        self.saveBitMap.CreateCompatibleBitmap(self.mfcDC, self.cw, self.ch)
        self.saveDC.SelectObject(self.saveBitMap)

        self.tiles, self.tileheight, self.contour = self.findTiles(self.getClientFrame())
        if not len(self.tiles):
            return
        self.digitheight = self.tileheight / 2
        self.digitsmodel = createDigitsModel(self.FONT, self.digitheight)

        self.update()

    def getClientWindow(self, windowtitle):
        toplist, winlist = [], []
        def enum_cb(hwnd, results):
            winlist.append((hwnd, win32gui.GetWindowText(hwnd)))
        win32gui.EnumWindows(enum_cb, toplist)
        window = [(hwnd, title) for hwnd, title in winlist if windowtitle.lower() in title.lower()]
        if not len(window):
            return 0
        return window[0][0]

    def getClientFrame(self):
        self.saveDC.BitBlt((0, 0), (self.cw, self.ch),
                    self.mfcDC, (self.cl, self.ct), win32con.SRCCOPY)

        bmpinfo = self.saveBitMap.GetInfo()
        bmpstr = self.saveBitMap.GetBitmapBits(True)

        pil_img = Image.frombuffer( 'RGB',
            (bmpinfo['bmWidth'], bmpinfo['bmHeight']),
            bmpstr, 'raw', 'BGRX', 0, 1)

        array = np.array( pil_img )
        cvimage = cv2.cvtColor(array, cv2.COLOR_RGBA2BGRA)
        return cvimage

    def findTiles(self, cvframe):
        tiles, avgh = [], 0
        
        gray = cv2.cvtColor(cvframe,cv2.COLOR_BGRA2GRAY)
        thresh = cv2.adaptiveThreshold(gray,255,1,1,11,2)
        contours, hierarchy = cv2.findContours(thresh.copy(), cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

        def findBoard(contours): # get largest square
            ww, sqcnt = 10, None
            for cnt in contours:
                x,y,w,h = cv2.boundingRect(cnt)
                if w>ww and abs(w-h)<w/10:
                    ww = w
                    sqcnt = cnt
            return sqcnt

        board = findBoard(contours)
        if board==None:
            print 'board not found!'
            return tiles, avgh, board
        
        bx,by,bw,bh = cv2.boundingRect(board)
        #cv2.rectangle(cvframe,(bx,by),(bx+bw,by+bh),(0,255,0),2)
        #cv2.imshow('board',cvframe)
        #cv2.waitKey(0)
        #cv2.destroyWindow( 'board' )        
        maxh = bh/4
        minh = (maxh*4)/5
        count = 0
        for contour in contours:
            x,y,w,h = cv2.boundingRect(contour)
            if y>by and w>minh and w<maxh and h>minh and h<maxh:
                avgh += h
                count += 1
        if not count:
            print 'no tile found!'
            return tiles, avgh, board

        avgh = avgh / count
        margin = (bh-avgh*4)/5
        for row in range(4):
            for col in range(4):
                x0 = bx + avgh*col + margin*(col+1)
                x1 = x0 + avgh
                y0 = by + avgh*row + margin*(row+1)
                y1 = y0 + avgh
                tiles.append([x0, y0, x1, y1])
                #cv2.rectangle(cvframe,(x0,y0),(x1,y1),(0,255,0),2)
        #cv2.imshow('tiles',cvframe)
        #cv2.waitKey(0)
        #cv2.destroyWindow( 'tiles' )       
        return tiles, avgh, board
    
    def getTileThreshold(self, tileimage):
        gray = cv2.cvtColor(tileimage,cv2.COLOR_BGR2GRAY)
        row, col = gray.shape
        tmp = gray.copy().reshape(1, row*col)
        counts = np.bincount(tmp[0])
        sort = np.sort(counts)

        modes, freqs = [], []
        for i in range(len(sort)):
            freq = sort[-1-i]
            if freq < 4:
                break
            mode = np.where(counts==freq)[0][0]
            modes.append(mode)
            freqs.append(freq)

        bg, fg = modes[0], modes[0]
        for i in range(len(modes)):
            fg = modes[i]
            #if abs(bg-fg)>=48:
            if abs(bg-fg)>32 and abs(fg-150)>4: # 150?!
                break
        #print bg, fg
        if bg>fg: # needs dark background ?
            tmp = 255 - tmp
            bg, fg = 255-bg, 255-fg
        
        tmp = tmp.reshape(row, col)
        ret, thresh = cv2.threshold(tmp,(bg+fg)/2,255,cv2.THRESH_BINARY)        
        return thresh
    
    def getTileNumbers(self, cvframe):
        numbers = []
        outframe = np.zeros(cvframe.shape,np.uint8)
        def guessNumber(digits):
            for i in range(1,16):
                nn = 2**i
                ss = str(nn)
                dd = [int(c) for c in ss]
                if set(digits) == set(dd):
                    return nn
            return 0
        
        for tile in self.tiles:
            x0,y0,x1,y1 = tile
            tileimage = cvframe[y0:y1,x0:x1]
            cv2.rectangle(cvframe,(x0,y0),(x1,y1),(0,255,0),2)
            cv2.rectangle(outframe,(x0,y0),(x1,y1),(0,255,0),1)

            thresh = self.getTileThreshold(tileimage)
            contours,hierarchy = cv2.findContours(thresh.copy(),cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

            dh = self.digitheight
            digits = []
            for cnt in contours:
                x,y,w,h = cv2.boundingRect(cnt)
                if  h>w and h>(dh*1)/5 and h<(dh*6)/5:
                    cv2.rectangle(cvframe,(x0+x,y0+y),(x0+x+w,y0+y+h),(0,0,255),1)
                    roi = thresh[y:y+h,x:x+w]
                    roi = cv2.resize(roi,(dh,dh/2))
                    roi = roi.reshape((1,dh*(dh/2)))
                    roi = np.float32(roi)
                    retval, results, neigh_resp, dists = self.digitsmodel.find_nearest(roi, k=1)
                    digit = int((results[0][0]))
                    string = str(digit)
                    digits.append(digit)
                    cv2.putText(outframe,string,(x0+x,y0+y+h),0,float(h)/24,(0,255,0))

            numbers.append(guessNumber(digits))
        return numbers, outframe

    def getWindowHandle(self):
        return self.hwnd

    def getBoardContour(self):
        return self.contour
    
    def update(self):
        frame = self.getClientFrame()
        self.tilenumbers, outframe = self.getTileNumbers(frame)
        return self.tilenumbers, frame, outframe

    def copyTileNumbers(self):
        return self.tilenumbers[:]

    def getCell(self, tiles, x, y):
        return tiles[(y*4)+x]

    def setCell(self, tiles, x, y, v):
        tiles[(y*4)+x] = v
        return tiles

    def getCol(self, tiles, x):
        return [self.getCell(tiles, x, i) for i in range(4)]

    def setCol(self, tiles, x, col):
        for i in range(4):
            self.setCell(tiles, x, i, col[i])
        return tiles

    def getLine(self, tiles, y):
        return [self.getCell(tiles, i, y) for i in range(4)]

    def setLine(self, tiles, y, line):
        for i in range(4):
            self.setCell(tiles, i, y, line[i])
        return tiles

    def validMove(self, tilenumbers, direction):
        if direction == self.UP or direction == self.DOWN:
            for x in range(4):
                col = self.getCol(tilenumbers, x)
                for y in range(4):
                    if(y < 4-1 and col[y] == col[y+1] and col[y]!=0):
                        return True
                    if(direction == self.DOWN and y > 0 and col[y] == 0 and col[y-1]!=0):
                        return True
                    if(direction == self.UP and y < 4-1 and col[y] == 0 and col[y+1]!=0):
                        return True
        if direction == self.LEFT or direction == self.RIGHT:
            for y in range(4):
                line = self.getLine(tilenumbers, y)
                for x in range(4):
                    if(x < 4-1 and line[x] == line[x+1] and line[x]!=0):
                        return True
                    if(direction == self.RIGHT and x > 0 and line[x] == 0 and line[x-1]!=0):
                        return True
                    if(direction == self.LEFT and x < 4-1 and line[x] == 0 and line[x+1]!=0):
                        return True
        return False

    def moveTileNumbers(self, tilenumbers, direction):
        def collapseline(line, direction):
            if (direction==self.LEFT or direction==self.UP):
                inc = 1
                rg = xrange(0, 4-1, inc)
            else:
                inc = -1
                rg = xrange(4-1, 0, inc)
            pts = 0
            for i in rg:
                if line[i] == 0:
                    continue
                if line[i] == line[i+inc]:
                    v = line[i]*2
                    line[i] = v
                    line[i+inc] = 0
                    pts += v
            return line, pts
        def moveline(line, directsion):
            nl = [c for c in line if c != 0]
            if directsion==self.UP or directsion==self.LEFT:
                return nl + [0] * (4 - len(nl))
            return [0] * (4 - len(nl)) + nl
            
        score = 0
        if direction==self.LEFT or direction==self.RIGHT:
            for i in range(4):
                origin = self.getLine(tilenumbers, i)
                line = moveline(origin, direction)
                collapsed, pts = collapseline(line, direction)
                new = moveline(collapsed, direction)
                tilenumbers = self.setLine(tilenumbers, i, new)
                score += pts
        elif direction==self.UP or direction==self.DOWN:
            for i in range(4):
                origin = self.getCol(tilenumbers, i)
                line = moveline(origin, direction)
                collapsed, pts = collapseline(line, direction)
                new = moveline(collapsed, direction)
                tilenumbers = self.setCol(tilenumbers, i, new)
                score += pts
                
        return score, tilenumbers      

# AI based on "term2048-AI"
# https://github.com/Nicola17/term2048-AI
class AI(object):
    def __init__(self, board):
        self.board = board
        
    def nextMove(self):
        tilenumbers = self.board.copyTileNumbers()
        m, s = self.nextMoveRecur(tilenumbers[:],3,3)
        return m

    def nextMoveRecur(self, tilenumbers, depth, maxDepth, base=0.9):
        bestMove, bestScore = 0, -1
        for m in range(1,5):
            if(self.board.validMove(tilenumbers, m)):
                score, newtiles = self.board.moveTileNumbers(tilenumbers[:], m)
                score, critical = self.evaluate(newtiles)
                newtiles = self.board.setCell(newtiles,critical[0],critical[1],2)
                if depth != 0:
                    my_m,my_s = self.nextMoveRecur(newtiles[:],depth-1,maxDepth)
                    score += my_s*pow(base,maxDepth-depth+1)
                if(score > bestScore):
                    bestMove = m
                    bestScore = score
                
        return bestMove, bestScore

    def evaluate(self, tilenumbers, commonRatio=0.25):

        maxVal = 0.
        criticalTile = (-1, -1)
        
        for i in range(8):
            linearWeightedVal = 0
            invert = False if i<4 else True
            weight = 1.
            ctile = (-1,-1)

            cond = i%4
            for y in range(4):
                for x in range(4):
                    if cond==0:
                        b_x = 4-1-x if invert else x
                        b_y = y
                    elif cond==1:
                        b_x = x
                        b_y = 4-1-y if invert else y
                    elif cond==2:
                        b_x = 4-1-x if invert else x
                        b_y = 4-1-y
                    elif cond==3:
                        b_x = 4-1-x
                        b_y = 4-1-y if invert else y
                        
                    currVal=self.board.getCell(tilenumbers,b_x,b_y)
                    if(currVal == 0 and ctile == (-1,-1)):
                        ctile = (b_x,b_y)
                    linearWeightedVal += currVal*weight
                    weight *= commonRatio
                invert = not invert
            
            if linearWeightedVal > maxVal:
                maxVal = linearWeightedVal
                criticalTile = ctile

        return maxVal, criticalTile

    def solveBoard(self, moveinterval=500):
        boardHWND = self.board.getWindowHandle()
        if not boardHWND:
            return False
        bx, by, bw, bh = cv2.boundingRect(self.board.getBoardContour())
        x0, x1, y0, y1 = bx, bx+bw, by, by+bh

        win32gui.SetForegroundWindow(boardHWND)
        shell = win32com.client.Dispatch('WScript.Shell')
        print 'Set the focus to the Game Window, and the press this arrow key:'
        keymove = ['UP', 'DOWN', 'LEFT', 'RIGHT']

        delay = moveinterval / 3 # milliseconds delay to cancel board animation effect
        prev_numbers = []
        while True:
            numbers, inframe, outframe = self.board.update()
            if numbers != prev_numbers:
                cv2.waitKey(delay)
                numbers, inframe, outframe = self.board.update()
                if numbers == prev_numbers: # recheck if has changed
                    continue
                prev_numbers = numbers
                move = ai.nextMove()
                if move:
                    key = keymove[move-1]
                    shell.SendKeys('{%s}'%key)
                    print key
                    cv2.waitKey(delay)
                    cv2.imshow('CV copy',inframe[y0:y1,x0:x1])
                    cv2.imshow('CV out', outframe[y0:y1,x0:x1])
            cv2.waitKey(delay)
        cv2.destroyWindow( 'CV copy' )
        cv2.destroyWindow( 'CV out' )
        

# http://gabrielecirulli.github.io/2048/
# http://ov3y.github.io/2048-AI/
board = Board("2048 - Google Chrome")
#board = Board("2048 - Mozilla Firefox")

ai = AI(board)
ai.solveBoard(360)

print 'stopped.'

download: 2048opencv.py

# open this site with Chrome: http://gabrielecirulli.github.io/2048/
board = Board("2048 - Google Chrome")
ai = AI(board)
ai.solveBoard()

demo video:


==================================
update:
Solving the Android version of 2048..
Android phone is running a VNC server (vnc server & viewer are both slow!).

python script: 2048opencv_adb.py

tip: send [touchscreen]swipe event through adb:

adb shell input swipe x1 y1 x2 y2

sources:
gabrielecirulli.github
diaryofatinker.blogspot
stackoverflow.com

OpenCV Python: Digit Recognition

Here's an example of OpenCV digit recognition with a given TrueType font (*.ttf) and digit height. It uses python PIL module to load digit glyphs. These glyphs (converted to CV images) are then used to train a K-Nearest model.

import cv2
import numpy as np
from PIL import Image, ImageFont, ImageDraw, ImageOps

# create training model based on the given TTF font file
def createDigitsModel(fontfile, digitheight):
    ttfont = ImageFont.truetype(fontfile, digitheight)
    samples =  np.empty((0,digitheight*(digitheight/2)))
    responses = []
    for n in range(10):
        pil_im = Image.new("RGB", (digitheight, digitheight*2))
        ImageDraw.Draw(pil_im).text((0, 0), str(n), font=ttfont)
        pil_im = pil_im.crop(pil_im.getbbox())
        pil_im = ImageOps.invert(pil_im)
        #pil_im.save(str(n) + ".png")

        # convert to cv image
        cv_image = cv2.cvtColor(np.array( pil_im ), cv2.COLOR_RGBA2BGRA)
        gray = cv2.cvtColor(cv_image, cv2.COLOR_BGR2GRAY)
        blur = cv2.GaussianBlur(gray,(5,5),0)
        thresh = cv2.adaptiveThreshold(blur,255,1,1,11,2)

        roi = cv2.resize(thresh,(digitheight,digitheight/2))
        responses.append( n )
        sample = roi.reshape((1,digitheight*(digitheight/2)))
        samples = np.append(samples,sample,0)

    samples = np.array(samples,np.float32)
    responses = np.array(responses,np.float32)
    
    model = cv2.KNearest()
    model.train(samples,responses)
    return model

# digit recognition part
def findDigits(imagefile, digitheight, fontfile="C:\\Windows\\Fonts\\Arial.ttf"):
    im = cv2.imread(imagefile)
    out = np.zeros(im.shape,np.uint8)
    gray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
    thresh = cv2.adaptiveThreshold(gray,255,1,1,11,2)

    contours,hierarchy = cv2.findContours(thresh.copy(),cv2.RETR_EXTERNAL ,cv2.CHAIN_APPROX_SIMPLE)

    model = createDigitsModel(fontfile, digitheight)
    for cnt in contours:
        x,y,w,h = cv2.boundingRect(cnt)
        if  h>w and h>(digitheight*4)/5 and h<(digitheight*6)/5: #+/-20%
            cv2.rectangle(im,(x,y),(x+w,y+h),(0,255,0),1)
            roi = thresh[y:y+h,x:x+w] # crop
            roi = cv2.resize(roi,(digitheight,digitheight/2))
            roi = roi.reshape((1,digitheight*(digitheight/2)))
            roi = np.float32(roi)
            retval, results, neigh_resp, dists = model.find_nearest(roi, k=1)
            string = str(int((results[0][0])))
            #cv2.drawContours(out,[cnt],-1,(0,255,255),1)
            cv2.putText(out,string,(x,y+h),0,1,(0,255,0))

    cv2.imshow('in',im)
    cv2.imshow('out',out)
    cv2.waitKey(0)
    cv2.destroyWindow( 'in' )
    cv2.destroyWindow( 'out' )

findDigits('pi.png', 32)
print 'done.'

download: digitrecognition.py

sources:
opencvpython.blogspot.com
stackoverflow.com

AVR32 GCC IDE

AVR32 IDE (C/C++)
- uses AVR32 GNU toolchain
- requires FLIP 3 for uart bootloading
- tested only on eGizmo AVR32 mcu board (AT32UC3L0128)

download:  avr32-gcc-ide-svn191.7z 25MB
svn repo source: 
svn co http://yus-repo.googlecode.com/svn/trunk/AVR32/avr32-ide

forum link:  AVR32 GCC IDE


.

OpenCV ARM - Face Detect

Here's another application that uses opencv libraries in the Debian disto. It performs face detection using Haar cascade.

The code below continuously captures frames with a USB web-camera. (In this demo, I displayed a sample picture on a separate laptop but this will also work for actual faces). Using the input frames and a loaded Haar classifier cascade, vector of rectangles containing the detected faces is returned to the user. A bounding box is drawn to each face to show successful detection.

face_detect.py

import cv2.cv as cv

HAAR_CASCADE = "/usr/local/share/OpenCV/haarcascades/haarcascade_frontalface_default.xml"

cv.NamedWindow( "mycamera" )
capture = cv.CreateCameraCapture(0)
storage = cv.CreateMemStorage()
cascade = cv.Load(HAAR_CASCADE)

while True:
    image = cv.QueryFrame(capture)
    faces = cv.HaarDetectObjects(image, cascade, storage, 1.1, 3, cv.CV_HAAR_DO_CANNY_PRUNING, (100,100))
    for((x,y,w,h),i) in faces:
        cv.Rectangle(image, (x,y), (x+w, y+h), (0,255,0), 3)
    cv.ShowImage( "mycamera", image )
    if cv.WaitKey(5) > 0:
        break

cv.DestroyWindow( "mycamera" )

Below is the C/C++ equivalent of the above python script. (The code appears lengthy due to the comments and cleanup routines.)

face_detect.cpp

#include <opencv2/highgui/highgui.hpp>
#include <opencv2/objdetect/objdetect.hpp>
using namespace cv;

#define HAAR_CASCADE "/usr/local/share/OpenCV/haarcascades/haarcascade_frontalface_default.xml"

int main(int argc, const char ** argv)
{
    cvNamedWindow( "mycamera" /*, CV_WINDOW_AUTOSIZE*/); // create camera window, 1=CV_WINDOW_AUTOSIZE(default,the user cannot resize the window)
    CvCapture *capture = cvCreateCameraCapture(0); // start capturing frames from camera (i.e. /dev/video0 device)
    CvMemStorage *storage = cvCreateMemStorage(); // create new memory storage
    CvHaarClassifierCascade *cascade = (CvHaarClassifierCascade *)cvLoad(HAAR_CASCADE); // load frontal face detector

    while (1){
        IplImage *image = cvQueryFrame(capture); // grab and retrieve frame
        CvSeq *faces = cvHaarDetectObjects(image, cascade, storage, 1.1, 3, CV_HAAR_DO_CANNY_PRUNING, cvSize(100,100)); // find rectangular regions that contain faces
        for(int i=0; i < faces->total; i++){
            CvRect *r = (CvRect *)cvGetSeqElem(faces, i); // get bounding rectangle of the detected face
            cvRectangle(image, cvPoint(r->x, r->y), cvPoint(r->x + r->width, r->y + r->height), cvScalar(0,255,0), 3); // draw a green rectangle
        }
        cvShowImage( "mycamera", image ); // display image within window
        if (cvWaitKey(5) > 0) // press any key to exit
            break;
    }
    // cleanups
    cvReleaseHaarClassifierCascade( &cascade ); // release cascade
    cvReleaseMemStorage( &storage ); // release memory storage
    cvReleaseCapture( &capture ); // stop capturing/reading
    cvDestroyWindow( "mycamera" ); // end camera window
    return 0;
}

OpenCV ARM - Hello World

Here is a sample application that utilizes OpenCV in my customized Debian disto. Sample codes are posted below. The demo simply displays images captured by the camera. This can be extended to utilize other opencv functions.

hello_camera.py

import cv2.cv as cv

cv.NamedWindow( "mycamera", 1 )
capture = cv.CreateCameraCapture( 0 )

while True:
    img = cv.QueryFrame( capture )
    cv.ShowImage( "mycamera", img )
    if cv.WaitKey(20) > 0:
        break

cv.DestroyWindow( "mycamera" )

Below is the C/C++ equivalent of the above Python script.

hello_camera.cpp

#include <opencv2/highgui/highgui.hpp>
using namespace cv;

int main( int argc, const char** argv )
{
    cvNamedWindow( "mycamera", 1 ); // create camera window
    CvCapture *capture = cvCreateCameraCapture( 0 ); // start capturing frames from camera (i.e. /dev/video0 device)

    while(1){
        IplImage* img = cvQueryFrame( capture ); // grab and retrieve frame
        cvShowImage( "mycamera", img ); // display image within window
        if( waitKey(20) > 0 ) // press any key to exit (interval=20ms)
            break;
    }
    // cleanups
    cvReleaseCapture( &capture ); // stop capturing/reading // not needed in python (?)
    cvDestroyWindow( "mycamera" ); // end camera window
    return 0;
}

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- thanks to hilite.me for formating the codes. (best viewed with Firefox browser)
- webcam can also be tested with guvcview (Applications Menu->Multimedia->guvcview)