cvFindContours : comportement étrange

4 pièce(s) jointe(s)

Bonjour,

Je poste ce message pour faire part de ma récente expérience avec cvFindContours. Peut être que quelqu'un qui connait mieux que moi opencv pourra donner une explication au problème que j'ai rencontré !

J'utilise opencv pour faire un logiciel de reconnaissance de caractère que je souhaite baser sur la comparaison des contours stockés sous la forme de chain code. Pour les obtenir, j'utilise la fonction cvFindContours avec la méthode CV_CHAIN_CODE sur des images 32*32 contenant les lettres de l'alphabet avec un cadre blanc autour (lignes blanches ((0,0)(0,31) ; (0,0)(31,0) ; (31,31)(0,31) ; (0,31)(31,31)) (voir l'image C.png attachée).

L'appel

Code:

cvFindContours(<c.bmp>, storage, &contour, sizeof(CvChain), CV_RETR_LIST, CV_CHAIN_CODE);

suivi de

Code:

cvDrawContours(<c_border.bmp>, contour, CV_RGB(128,128,128)/*gris*/,CV_RGB(0,0,0)/*noir*/,1,1,8);

donne l'image C_border.png. Comme vous pouvez le voir, cela ne correspond pas vraiment aux contours extérieurs de la lettre C puisque les lignes extérieures restent blanches.

J'ai trouvé une méthode pour éviter le problème, mettre 3 lignes blanches en haut, en bas, à gauche et à droite au lieu d'une (comme pour B => B_border en pj). Le résultat est correct mais bon...

Si quelqu'un pouvait m'expliquer le pourquoi du comment, j'apprécierais :-) !
Merci !

PS : pour mieux voir les images, faire clic droit > enregistrer sous puis ouvrir et zoomer pour voir les pixels.

Salut

Il me semble que le cvfind contour travail sur un histogramme de petit morceau de ton image, pour trouver les disparités le souci c'est que les bords de ton C sont collés au bords de ton image, est ce qu'en réalisant un C plus petit tu obtiens le même problème ?

Effectivement, lorsque je met la lettre plus au centre de l'image ça fonctionne, c'est d'ailleurs ce que j'ai fais pour la lettre B qui est en PJ du premier post.

J'obtiens le contours extérieur du B ainsi que les contours intérieurs. Par contre cvFindContours détecte également comme contour le plus extérieur la bordure grise que l'on peut voir autour du B dans l'image B_border. Et je ne comprend pas pourquoi ! (ce contour est également présent si la lettre est très petite par rapport à la taille de l'image)

Merci pour ta réponse,
Teriblus

Tu dis que si tu color le contour en blanc, celui ci n'est plus détecté ?
Si oui es tu sur que ton contour d'origine est vraiment blanc, à savoir la valeur des pixels en héxa et non le rendu visuel ?

Voici le code hexa de ma lettre B (type bmp)

Code:

42 4d 36 14 00 00 00 00 00 00 36 04 00 00 28 00 00 00 40 00 00 00 40 00 00 00 01 00 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 01 01 00 02 02 02 00 03 03 03 00 04 04 04 00 05 05 05 00 06 06 06 00 07 07 07 00 08 08 08 00 09 09 09 00 0a 0a 0a 00 0b 0b 0b 00 0c 0c 0c 00 0d 0d 0d 00 0e 0e 0e 00 0f 0f 0f 00 10 10 10 00 11 11 11 00 12 12 12 00 13 13 13 00 14 14 14 00 15 15 15 00 16 16 16 00 17 17 17 00 18 18 18 00 19 19 19 00 1a 1a 1a 00 1b 1b 1b 00 1c 1c 1c 00 1d 1d 1d 00 1e 1e 1e 00 1f 1f 1f 00 20 20 20 00 21 21 21 00 22 22 22 00 23 23 23 00 24 24 24 00 25 25 25 00 26 26 26 00 27 27 27 00 28 28 28 00 29 29 29 00 2a 2a 2a 00 2b 2b 2b 00 2c 2c 2c 00 2d 2d 2d 00 2e 2e 2e 00 2f 2f 2f 00 30 30 30 00 31 31 31 00 32 32 32 00 33 33 33 00 34 34 34 00 35 35 35 00 36 36 36 00 37 37 37 00 38 38 38 00 39 39 39 00 3a 3a 3a 00 3b 3b 3b 00 3c 3c 3c 00 3d 3d 3d 00 3e 3e 3e 00 3f 3f 3f 00 40 40 40 00 41 41 41 00 42 42 42 00 43 43 43 00 44 44 44 00 45 45 45 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ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

A part au départ (je suppose que c'est le header), on a bien une image en noir et blanc, profondeur 8bits et 1 seule couleur...

A moins que cvLoadImage modifie l'image... Je pense pas mais j’essaierais quand j'aurai un peu de temps.

Pour info le bout de code qui génère les images en pj du premier post :
Code:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 void fonction (){ char lettre = 'A'; int i; IplImage* src; CvMemStorage* storage; CvSeq* contour = 0; char *filename = (char*) malloc(32*sizeof(char)); for (i=1; i<=26; i++) { storage = cvCreateMemStorage(0); contour = 0; sprintf(filename, "/sdcard/OCR/ref/%c.bmp",lettre); if(!(src=cvLoadImage(filename, CV_LOAD_IMAGE_GRAYSCALE))) LOGE("ARG ! erreur load image"); IplImage *negative = cvCreateImage( cvGetSize(src), IPL_DEPTH_8U, 1); cvFindContours(src, storage, &contour, sizeof(CvChain), CV_RETR_LIST, CV_CHAIN_CODE); // EXTERNAL => mieux mais marche pas... contour = null // draw the contours on a white image and save it IplImage* dst = cvCreateImage(cvGetSize(src), src->depth, src->nChannels); cvSet(dst , CV_RGB(255,255,255)); //ext:gray //holes:black cvDrawContours(dst, contour, cvScalar(128),cvScalar(0),1,1,8); LOGE("Lettre %c", lettre); sprintf(filename, "/sdcard/OCR/%c.bmp",lettre); cvSaveImage(filename,dst); lettre++; } fclose(fcode); free(filename); }

J'ai réglé le problème, en fait cvFindContour détecte les contours des éléments blancs sur un fond noir et je lui donnais des images noires sur fond blanc...

Ca fonctionne parfaitement à présent !

Merci pour vos réponses,
Teriblus