OpenCV (via python) on Linux: Set frame width/height?

Question

I\'m using openCV via python on linux (ubuntu 12.04), and I have a logitech c920 from which I\'d like to grab images. Cheese is able to grab frames up to really high resolut

Answer 1

I had the same problem as you. Ended up going into the OpenCV source and changing the default parameters in modules/highgui/src/cap_v4l.cpp, lines 245-246 and rebuilding the project.

#define DEFAULT_V4L_WIDTH  1920
#define DEFAULT_V4L_HEIGHT 1080

This is for OpenCV 2.4.8

Answer 2

## Sets up the camera to capture video
cap = cv2.VideoCapture(device)

width = 1280
height = 720

#set the width and height
cap.set(3,width)
cap.set(4,height)

Answer 3

It seems to be variable by cammera.

AFIK, Logitech cameras have particularly bad linux support (though It;s gotten better) Most of their issues are with advanced features like focus control. i would advise sticking with basic cameras (IE manual focus Logitech cameras) just to play it safe.

My built in laptop camera has no issue and displays at normal resolution.
My external logitech pro has issues initalizing.

However, I can overcome the resolution issue with these two lines.

Yes, they are the same as you used.

cv.SetCaptureProperty(self.capture,cv.CV_CAP_PROP_FRAME_WIDTH, 1280)
cv.SetCaptureProperty(self.capture,cv.CV_CAP_PROP_FRAME_HEIGHT, 720)

My Logitech still throws errors but the resolution is fine.

Please make sure the resolution you set is a supported by your camera or v4l will yell at you. If I set an unsupported native resolution, I have zero success.

Answer 4

From the docs,

The function cvSetCaptureProperty sets the specified property of video capturing. Currently the function supports only video files: CV_CAP_PROP_POS_MSEC, CV_CAP_PROP_POS_FRAMES, CV_CAP_PROP_POS_AVI_RATIO .

NB This function currently does nothing when using the latest CVS download on linux with FFMPEG (the function contents are hidden if 0 is used and returned).

Answer 5

Not sure if it works, but you can try to force the parameters to your values after you instantiate camera object:

import cv
cam = cv.CaptureFromCAM(-1)

os.system("v4l2-ctl --set-fmt-video=width=1920,height=1080,pixelformat=1") 
os.system("v4l2-ctl --set-parm=30")

image = cv.QueryFrame(cam)

That's a bit hacky, so expect a crash.