OpenCV error (-215) raspberry pi doesn't make sense

Question

So this is my first time working with opencv. I have it installed on my raspberry pi. I am using a project that I found on instructables to test it out and I am getting error (-215)

OpenCV Error: Assertion failed ((scn == 3 || scn == 4) && (depth == CV_8U || depth == CV_32F)) in cvtColor, file /build/opencv-ISmtkH/opencv-2.4.9.1+dfsg/modules/imgproc/src/color.cpp, line 3959 Traceback (most recent call last): File "balltracking.py", line 50, in hsv = cv2.cvtColor(frame,cv2.COLOR_BGR2HSV) cv2.error: /build/opencv-ISmtkH/opencv-2.4.9.1+dfsg/modules/imgproc/src/color.cpp:3959: error: (-215) (scn == 3 || scn == 4) && (depth == CV_8U || depth == CV_32F) in function cvtColor

The code that I am testing is the following:

    import cv2
import cv2.cv as cv
import numpy as np

kernel = np.ones((5,5),np.uint8)

# Take input from webcam
cap = cv2.VideoCapture(-1)

# Reduce the size of video to 320x240 so rpi can process faster
cap.set(3,320)
cap.set(4,240)

def nothing(x):
    pass
# Creating a windows for later use
cv2.namedWindow('HueComp')
cv2.namedWindow('SatComp')
cv2.namedWindow('ValComp')
cv2.namedWindow('closing')
cv2.namedWindow('tracking')


# Creating track bar for min and max for hue, saturation and value
# You can adjust the defaults as you like
cv2.createTrackbar('hmin', 'HueComp',12,179,nothing)
cv2.createTrackbar('hmax', 'HueComp',37,179,nothing)

cv2.createTrackbar('smin', 'SatComp',96,255,nothing)
cv2.createTrackbar('smax', 'SatComp',255,255,nothing)

cv2.createTrackbar('vmin', 'ValComp',186,255,nothing)
cv2.createTrackbar('vmax', 'ValComp',255,255,nothing)

# My experimental values
# hmn = 12
# hmx = 37
# smn = 145
# smx = 255
# vmn = 186
# vmx = 255


while(1):

    buzz = 0
    _, frame = cap.read()

    #converting to HSV
    hsv = cv2.cvtColor(frame,cv2.COLOR_BGR2HSV)
    hue,sat,val = cv2.split(hsv)

    # get info from track bar and appy to result
    hmn = cv2.getTrackbarPos('hmin','HueComp')
    hmx = cv2.getTrackbarPos('hmax','HueComp')


    smn = cv2.getTrackbarPos('smin','SatComp')
    smx = cv2.getTrackbarPos('smax','SatComp')


    vmn = cv2.getTrackbarPos('vmin','ValComp')
    vmx = cv2.getTrackbarPos('vmax','ValComp')

    # Apply thresholding
    hthresh = cv2.inRange(np.array(hue),np.array(hmn),np.array(hmx))
    sthresh = cv2.inRange(np.array(sat),np.array(smn),np.array(smx))
    vthresh = cv2.inRange(np.array(val),np.array(vmn),np.array(vmx))

    # AND h s and v
    tracking = cv2.bitwise_and(hthresh,cv2.bitwise_and(sthresh,vthresh))

    # Some morpholigical filtering
    dilation = cv2.dilate(tracking,kernel,iterations = 1)
    closing = cv2.morphologyEx(dilation, cv2.MORPH_CLOSE, kernel)
    closing = cv2.GaussianBlur(closing,(5,5),0)

    # Detect circles using HoughCircles
    circles = cv2.HoughCircles(closing,cv.CV_HOUGH_GRADIENT,2,120,param1=120,param2=50,minRadius=10,maxRadius=0)
    # circles = np.uint16(np.around(circles))

    #Draw Circles
    if circles is not None:
            for i in circles[0,:]:
                # If the ball is far, draw it in green
                if int(round(i[2])) < 30:
                    cv2.circle(frame,(int(round(i[0])),int(round(i[1]))),int(round(i[2])),(0,255,0),5)
                    cv2.circle(frame,(int(round(i[0])),int(round(i[1]))),2,(0,255,0),10)
                # else draw it in red
                elif int(round(i[2])) > 35:
                    cv2.circle(frame,(int(round(i[0])),int(round(i[1]))),int(round(i[2])),(0,0,255),5)
                    cv2.circle(frame,(int(round(i[0])),int(round(i[1]))),2,(0,0,255),10)
                    buzz = 1

    #you can use the 'buzz' variable as a trigger to switch some GPIO lines on Rpi :)
    # print buzz                    
    # if buzz:
        # put your GPIO line here


    #Show the result in frames
    cv2.imshow('HueComp',hthresh)
    cv2.imshow('SatComp',sthresh)
    cv2.imshow('ValComp',vthresh)
    cv2.imshow('closing',closing)
    cv2.imshow('tracking',frame)

    k = cv2.waitKey(5) & 0xFF
    if k == 27:
        break

cap.release()

cv2.destroyAllWindows()

Whatever is in your frame doesn't have the right bit depth or number of channels to be convertible from BGR to HSV, check that you have proper data of the proper BGR format. — paisanco
Can you explain more please? This is my first time and I don't really follow. — MrPianoman2010

mkrinblk mkrinblk · Accepted Answer · 2017-04-04T23:22:05

You can check the datatype of a numpy array using hsv.dtype this should be one of the types listed in the error message CV_8U or CV_32F. What opencv is telling you is that it wants a dtype of uint8 or float32. To convert your array you can use hsv.astype(np.uint8) which will convert your array to uint8.

While I am checking the datatype I also like to check the shape of the array use: hsv.shape this should output something like (rows,cols, 3) if you have a color image.

OpenCV error (-215) raspberry pi doesn't make sense

1 Answers