Python - resize image

Question

I'm using the code below (which is a googling result) to detect faces:

import io
import picamera
import cv2
import numpy
import PIL
from PIL import Image
from resizeimage import resizeimage

#Load a cascade file for detecting faces
face_cascade = cv2.CascadeClassifier('/usr/share/opencv/haarcascades/haarcascade_frontalface_alt.xml')

#Create a memory stream so photos doesn't need to be saved in a file
stream = io.BytesIO()

#Get the picture (low resolution, so it should be quite fast)
#Here you can also specify other parameters (e.g.:rotate the image)
with picamera.PiCamera() as camera:
    camera.resolution = (640, 480)
    camera.vflip = False
    camera.hflip = False
    camera.brightness = 60
    camera.capture(stream, format='jpeg')

#Convert the picture into a numpy array
buff = numpy.fromstring(stream.getvalue(), dtype=numpy.uint8)

#Now creates an OpenCV image
image = cv2.imdecode(buff, 1)

#Load a cascade file for detecting faces
#face_cascade = cv2.CascadeClassifier('/usr/share/opencv/haarcascades/haarcascade_frontalface_alt.xml')

#Convert to grayscale
gray = cv2.cvtColor(image,cv2.COLOR_BGR2GRAY)

#Look for faces in the image using the loaded cascade file
faces = face_cascade.detectMultiScale(gray, 1.1, 5)

print "Found "+str(len(faces))+" face(s)"

#Draw a rectangle around every found face
#Crop faces and save to separate files
id = 1
for (x,y,w,h) in faces:
    cv2.rectangle(image,(x,y),(x+w,y+h),(255,0,0),2)
    cropped = image[ y : y+h, x : x+w ]
    #RESIZE IMAGE to 92x112
    cropped = cv2.resize(cropped,None,92,112)
    cv2.imwrite("../reco/test_faces/cropped_face" + str(id) + ".png", cropped)
    id = id + 1

At the end I want to crop the faces into image files and resize them to 92x112. This is what I try with:

cropped = cv2.resize(cropped,None,92,112)

When I run this I get:

OpenCV Error: Assertion failed (dsize.area() || (inv_scale_x > 0 && inv_scale_y > 0)) in resize, file /build/opencv-ISmtkH/opencv-2.4.9.1+dfsg/modules/imgproc/src/imgwarp.cpp, line 1835
Traceback (most recent call last):
  File "1track.py", line 48, in <module>
    cropped = cv2.resize(cropped,None,92,112)
cv2.error: /build/opencv-ISmtkH/opencv-2.4.9.1+dfsg/modules/imgproc/src/imgwarp.cpp:1835: error: (-215) dsize.area() || (inv_scale_x > 0 && inv_scale_y > 0) in function resize

Saransh Kejriwal · Accepted Answer · 2016-05-01 03:10:46Z

1

To resize the image to new dimensions, you need to know the ratio between the new dimensions and the current ones. So if you want to set (for example) a 640x480 image into a 92x112 image:

92/640=0.143 112/480=0.233

You use these ratios in the cv2.resize function:

cropped = cv2.resize(cropped, (0,0), fx=0.143, fy=0.233)

answered May 1, 2016 at 3:10

Saransh Kejriwal

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