Blurring Number Plate

Python
,
1

Hi everyone.

Hello everyone,

I’m trying to blur license plate on video for a project. I managed to create a rectangle which identifies the plate but I can’t blur the interior of this rectangle. I saw that we could use cv2.GaussianBlur() but I can’t set it up (I’m a newbie i know ahah)

Below the code :

import cv2

plate_cascade=cv2.CascadeClassifier("./haarcascade_russian_plate_number.xml")
cap=cv2.VideoCapture(0 + cv2.CAP_DSHOW)

while True:
    ret, frame=cap.read()
    tickmark=cv2.getTickCount()
    gray=cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    plate=plate_cascade.detectMultiScale(gray, scaleFactor=1.2, minNeighbors=3)
    for x, y, w, h in plate:
        cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 255, 0), 10)
        blur_image = cv2.GaussianBlur(frame,(23, 23), 30)
        blur_image[y:y+plate.shape[0], x:x+plate.shape[1]] = plate

    if cv2.waitKey(1)&0xFF==ord('q'):
        break
    fps=cv2.getTickFrequency()/(cv2.getTickCount()-tickmark)
    cv2.putText(frame, "FPS: {:05.2f}".format(fps), (10, 30), cv2.FONT_HERSHEY_PLAIN, 2, 
    (255, 0, 0), 2)
    cv2.imshow('video', frame)
cap.release()
cv2.destroyAllWindows()

The following error :

ValueError: could not broadcast input array from shape (1,4) into shape (1,4,3)

Thanks in advance.

2

as a sidenote, you got it backwards. you want to blur the number plate region, not the frame, exluding the number plate

(but what you do is: blur the whole frame, then re-assign the unblurred numberplate)

3

Oh yes sure… So you mean that i need to replace the frame by the plate ?

I tried this but i have a assertion failed. Whe he mean that the gauss is empty ?

*for x, y, w, h in plate:
        cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 255, 0), 2)
        blur_image = plate[y:y+h, x:x+w]
        blur_image = cv2.GaussianBlur(blur_image,(23, 23), 30)
        plate[y:y+blur_image.shape[0], x:x+blur_image.shape[1]] = blur_image*
4

what is that supposed to do ? you don’t need that line at all.

(numpy ‘slices’ should work on a refeerence of the image, like cv::Mat does)

5

as suggested, you could blur the whole picture, and then copy the subregion into the unblurred image. the blur done that way will behave differently around the border of your subregion.

blur_image = cv2.GaussianBlur(frame, (23, 23), 30) # blur everything
for x, y, w, h in plate: # coordinates
    frame[y:y+h, x:x+w] = blur_image[y:y+h, x:x+w] # copy subregion from blurred version
    cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 255, 0), 2) # draw box on top

this tells me that you’re a little confused with your variables:

plate is all the rectangles resulting from the multi-scale detection that uses the cascade classifier. it’s a list of coordinates (x,y,w,h).

you have no use for plate.shape at all.

6

You’ve right i’m really lost…
I’m just a little System Administrator and i’m trying to learn Python and Opencv at the same time for someone and i have a dead line.
I’m trying to find what i want on the net but i don’t understand everything. That’s why i have no response for @berak and i’m sorry for that.

@crackwitz
I made the changes you indicated previously but i have the same issue. The first error was
NameError: name ‘blur_image’ is not defined

Pretty logic because i’m in a whyle loop so i declared the variable at the beginning. After that it seams to work. But when the camera find the plate i have the same error that before. I don’t understand ( I know it’s just a matter of logic but I can’t figure it out…)

7

this all you need:

        frame[y:y+h, x:x+w] = cv2.GaussianBlur(frame[y:y+h, x:x+w],(23, 23), 30)

note the slice invocation on the left side, python does not have references (as in c++)