Python OpenCV access webcam maximum resolution

Question

I am trying to acquire images from my webcam using a python code that imports OpenCV. The code is the following:

import sys sys.path.append("C:\\opencv\\build\\python\\2.7") import cv2 import cv2.cv as cv import time  # Set resolution cap = cv2.VideoCapture(0) print "Frame default resolution: (" + str(cap.get(cv.CV_CAP_PROP_FRAME_WIDTH)) + "; " + str(cap.get(cv.CV_CAP_PROP_FRAME_HEIGHT)) + ")" cap.set(cv.CV_CAP_PROP_FRAME_WIDTH, 800) cap.set(cv.CV_CAP_PROP_FRAME_HEIGHT, 600) print "Frame resolution set to: (" + str(cap.get(cv.CV_CAP_PROP_FRAME_WIDTH)) + "; " + str(cap.get(cv.CV_CAP_PROP_FRAME_HEIGHT)) + ")"  # Acquire frame capture = cv.CreateCameraCapture(0) img = cv.QueryFrame(capture) 

The code works fine, except that the Camera default resolution is 640x480, and my code seems to be able to set only resolution values lower than that. For example, I can set the image size to 320x240, but I can't change it to 800x600. I have no error appearing: simply the resolution is set to the default one (640x480) as I try to set it to higher values.

The camera I am using (no other webcam is connected to the computer) is the QuickCam V-UBK45: with the software provided by Logitech, I am able to take pictures at full resolution (1280x960) and at all intermediate ones (e.g. 800x600).

Therefore, those frame sizes are supported from the hardware, but my code can't access them.

Does anyone know what I can do?

Answer 1

The problem as mentioned above is caused by the camera driver. I was able to fix it using Direct Show as a backend. I read (sorry, but I do not remember where) that almost all cameras provide a driver that allows their use from DirectShow. Therefore, I used DirectShow in Windows to interact with the cameras and I was able to configure the resolution as I wanted and also get the native aspect ratio of my camera (16: 9). You can try this code to see if this works for you.

import cv2  cam = cv2.VideoCapture(0,cv2.CAP_DSHOW)  cap.set(cv2.CAP_PROP_FRAME_WIDTH, 1280) cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 720)  r, frame = cam.read() ... print('Resolution: ' + str(frame.shape[0]) + ' x ' + str(frame.shape[1])) 

In the OpenCV documentation, I found the following information for those who want to know more about OpenCV backends (OpenCV docs)

I hope this can help you!

Answer 2

I used the different resolutions to set image resolution from List of common resolutions by looping over

def set_res(cap, x,y):     cap.set(cv.CV_CAP_PROP_FRAME_WIDTH, int(x))     cap.set(cv.CV_CAP_PROP_FRAME_HEIGHT, int(y))     return str(cap.get(cv.CV_CAP_PROP_FRAME_WIDTH)),str(cap.get(cv.CV_CAP_PROP_FRAME_HEIGHT)) 

It seems that OpenCV or my camera allows only certain resolutions.

• 160.0 x 120.0

• 176.0 x 144.0

• 320.0 x 240.0

• 352.0 x 288.0

• 640.0 x 480.0

• 1024.0 x 768.0

• 1280.0 x 1024.0