Python to detect the rank and value of a playing card

card_id.py

# Author: Lokno Ketchup
# Description : Script to detect the rank and value of a playing card 
#               using OpenCV 2.4.12 template matching. User must provide
#               a local directory "templates" with cropped PNG files
#               of each rank and suit, labeled using the keys in 
#               dictionaries 'ranks' and 'suits' below. For example,
#               the image for the ace rank template will be A.png
#
#               Rotation, distance, and perspective are not accounted for,
#               so the templates must match roughly what the camera will 
#               capture.

import sys
import cv2
import numpy as np

# script expects a folder 'templates' with PNGs labeled with the keys of these dictionaries
ranks = { 'A' : None, '2' : None, '3' : None, '4' : None, '5' : None, '6' : None, 
          '7' : None, '8' : None, '9' : None, '10' : None, 'J' : None, 'Q' : None, 'K' : None }
suits = { 'D' : None, 'S' : None, 'C' : None, 'H' : None }

# translates shorthand for labels to display
suitsFull =  { 'D' : 'Diamonds', 'S' : 'Spades', 'C' : 'Clubs', 'H' : 'Hearts' }
valuesFull = { 'A' : 'Ace', '2' : '2', '3' : '3', '4' : '4', '5' : '5', '6' : '6', 
               '7' : '7', '8' : '8', '9' : '9', '10' : '10', 
               'J' : 'Jack', 'Q' : 'Queen', 'K' : 'King' }

# checks an image against a template and check for best match
def checkTemplate(img, template, method, idx, bestIdx, bestVal):
	res = cv2.matchTemplate(img,template,method)
	min_val, max_val, min_loc, max_loc = cv2.minMaxLoc(res)

	if bestVal < max_val:
		bestVal = max_val
		bestIdx = idx

	return bestVal,bestIdx

# determine the suit and rank of a playing card in img, using method 
# and requiring a minimum value of at least threshold
def determine( img, method, threshold = 0.8 ):
	bestRank  = 0
	bestSuit  = 0
	rankValue = 0
	suitValue = 0

    # determine rank
	c = 0
	for t in ranks.keys():
	    rankValue,bestRank = checkTemplate(img, ranks[t], method, c, bestRank, rankValue)
	    c += 1

    #  determine suit
	c = 0    
	for t in suits.keys():
	    suitValue,bestSuit = checkTemplate(img, suits[t], method, c, bestSuit, suitValue)
	    c += 1

	ret = ''
	if suitValue > threshold and rankValue > threshold:
		ret = '%s of %s' % (valuesFull[ranks.keys()[bestRank]], suitsFull[suits.keys()[bestSuit]])
	else:
		ret = 'Cannot Read Card'

	return ret

# load template images
for t in ranks.keys():
	ranks[t] = cv2.imread('templates/' + t + '.png',0)
	if ranks[t] == None:
		print 'ERROR : Could not load template images'
		sys.exit(-1)

for t in suits.keys():
	suits[t] = cv2.imread('templates/' + t + '.png',0)
	if suits[t] == None:
		print 'ERROR'

# The method I used because it worked best in my case
method = cv2.TM_CCOEFF_NORMED
font   = cv2.FONT_HERSHEY_SIMPLEX

# Main Loop
cap = cv2.VideoCapture(0)
while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    # get grayscale image
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # resize to half size (640x400 on test camera)
    img = cv2.resize(gray,None,fx=0.5, fy=0.5, interpolation = cv2.INTER_AREA)

    # process card
    cardID = determine( img, method )

    # add result to image for display
    cv2.putText(img,cardID,
    	        (200,30),  # postion of text in image
    	        font, 1, (255,255,255),2)

    # Display the resulting frame
    cv2.imshow('Template Matching',img)

    # quits on escape (in window focus)
    if cv2.waitKey(1) & 0xFF == 27:
        break

cv2.destroyAllWindows()