Open CV Error : Sizes of input arguments do not match

Question

I am novice in Open CV and Python, I was trying to run the following code, but it was showing an error! which I could not figure out.

import cv2
import numpy as np
import util as ut
import svm_train as st 
import re
model=st.trainSVM(17)
#create and train SVM model each time coz bug in opencv 3.1.0 svm.load() 
https://github.com/Itseez/opencv/issues/4969
cam=int(raw_input("Enter Camera number: "))
cap=cv2.VideoCapture(cam)
font = cv2.FONT_HERSHEY_SIMPLEX
def nothing(x) :
    pass
text= " "
temp=0
previouslabel=None
previousText=" "
label = None
while(cap.isOpened()):
    _,img=cap.read()
    cv2.rectangle(img,(900,100),(1300,500),(255,0,0),3) # bounding box which 
captures ASL sign to be detected by the system
    img1=img[100:500,900:1300]
    img_ycrcb = cv2.cvtColor(img1, cv2.COLOR_BGR2YCR_CB)
    blur = cv2.GaussianBlur(img_ycrcb,(11,11),0)
    skin_ycrcb_min = np.array((0, 138, 67))
    skin_ycrcb_max = np.array((255, 173, 133))
    mask = cv2.inRange(blur, skin_ycrcb_min, skin_ycrcb_max)  # detecting 
the hand in the bounding box using skin detection
    contours,hierarchy = cv2.findContours(mask.copy(),cv2.RETR_EXTERNAL, 2) 
    cnt=ut.getMaxContour(contours,4000)                       # using contours to capture the skin filtered image of the hand
    if cnt!=None:
        gesture,label=ut.getGestureImg(cnt,img1,mask,model)   # passing the trained model for prediction and fetching the result
        if(label!=None):
            if(temp==0):
                previouslabel=label
            if previouslabel==label :
                previouslabel=label
                temp+=1
            else :
                temp=0
            if(temp==40):
                if(label=='P'):
                    label=" "
                text= text + label
                if(label=='Q'):
                    words = re.split(" +",text)
                    words.pop()
                    text = " ".join(words)
                    #text=previousText
                print text      
        cv2.imshow('PredictedGesture',gesture)                # showing the 
best match or prediction
        cv2.putText(img,label,(50,150), font,8,(0,125,155),2)  # displaying the predicted letter on the main screen
        cv2.putText(img,text,(50,450), font,3,(0,0,255),2)
    cv2.imshow('Frame',img)
    cv2.imshow('Mask',mask)
    k = 0xFF & cv2.waitKey(10)
    if k == 27:
        break
cap.release()        
cv2.destroyAllWindows()

The error is as follows:

OpenCV Error: The sizes of input arguments do not match(The lower boundary is neither an array of the same size and same type as src,nor a scalar) in cv::inrange, file C : \build\2_4_winpack-bindings-win64-vc14-static\opencv\modules\core\src\arithm.cpp,line 2711
Traceback (most recent call last):
    File "C:\Users\satwik\Downloads\asl\asl\asl.py",line 29 in <module>
        mask = cv2.inRange(blur, skin_ycrcb_min, skin_ycrcb_max)  # detecting 
the hand in the bounding box using skin detection
cv2.error:C :\build\2_4_winpack-bindings-win64-vc14-static\opencv\modules\core\src\arithm.cpp,line 2711:error:(-209) The lower 
boundary is neither an array of the same size and same type as src,nor a 
scalar in function cv:inrange.

The screenshot of the error is here.

The project I was trying to run can be found here.

I would be thankful if you could help me fix the error.

Answer 1

this is due to transparency/alpha

print(img.shape[-1])
img = img[:,:,:-1]
print(img.shape[-1])

remove transparency/alpha

skin_ycrcb_min = (0, 138, 67)
skin_ycrcb_max = (255, 173, 133)
mask = cv2.inRange(blur[:,:,:-1], skin_ycrcb_min, skin_ycrcb_max)  # detecting

https://stackoverflow.com/a/54350676/22015116

or add transparency/alpha

skin_ycrcb_min = (0, 138, 67, 255)
skin_ycrcb_max = (255, 173, 133, 255)
mask = cv2.inRange(blur, skin_ycrcb_min, skin_ycrcb_max)  # detecting

Answer 2

These lines are wrong:

skin_ycrcb_min = np.array((0, 138, 67))
skin_ycrcb_max = np.array((255, 173, 133))

You have to use scalar (tuple), not array:

skin_ycrcb_min = (0, 138, 67)
skin_ycrcb_max = (255, 173, 133)