OpenCV: can't set resolution of video capture

问题:

I am using OpenCV 2.4.5 on Ubuntu 12.04 64-bit. I would like to be able to set the resolution of the input from my Logitech C310 webcam. The camera supports up to 1280x960 at 30fps, and I am able to view the video at this resolution in guvcview. But OpenCV always gets the video at only 640x480.

Trying to change the resolution with cap.set(CV_CAP_PROP_FRAME_WIDTH, 1280) and cap.set(CV_CAP_PROP_FRAME_HEIGHT, 960) immediately after the VideoCapture cap is created has no effect; trying to set them immediately before getting every frame causes the program to crash immediately. I cannot reduce the resolution with this method either. I am also getting the error "HIGHGUI ERROR: V4L/V4L2: VIDIOC_S_CROP". I think this may be related, because it appears once when the VideoCapture is created, and once when I try to set the width and height (but, oddly, not if I try to set only one of them).

I know I'm not the first to have this problem, but I have yet to find a solution after much Googling and scouring of SO and elsewhere on the internet (among the many things I've already tried to no avail is the answer to this StackOverflow question: Increasing camera capture resolution in OpenCV). Is this a bug in OpenCV? If so, it's a rather glaring one.

Here's an example of code that exhibits the problem (just a modified version of OpenCV's video display code):

#include <cv.h>
#include <highgui.h>
using namespace cv;

int main(int argc, char** argv)
{
    VideoCapture cap(0); // open the default camera
    if(!cap.isOpened())  // check if we succeeded
            return -1;

    cap.set(CV_CAP_PROP_FRAME_WIDTH, 160);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT, 120);

    Mat image;
    namedWindow("Video", CV_WINDOW_AUTOSIZE);

    while(1)
    {
            // cap.set(CV_CAP_PROP_FRAME_WIDTH, 160);
            // cap.set(CV_CAP_PROP_FRAME_HEIGHT, 120);
            cap >> image;

            imshow("Video", image);

            if(waitKey(10) == 99 ) break;
    }
    return 
}

As it is, that gets me two "HIGHGUI ERROR"s as described above and I get a 640x480 output. I know that 160x120 is a resolution that my camera supports from running v4l2-ctl --list-formats-ext. If I uncomment the two commented-out lines in the while loop, the program crashes immediately.

These might be related or have possible solutions: http://answers.opencv.org/question/11427/decreasing-capture-resolution-of-webcam/, http://answers.opencv.org/question/30062/error-setting-resolution-of-video-capture-device/

回答1:

This is a bug in the v4l "version" (build) of OpenCV 2.4 (including 2.4.12), but the bug is not in the libv4l version. For OpenCV 3.1.0, neither the v4l nor the libv4l version has the bug.

(Your error error message HIGHGUI ERROR: V4L/V4L2: VIDIOC_S_CROP indicates that you have the v4l version; the message is in cap_v4l.cpp, see code, but not in cap_libv4l.cpp.)

A workaround to get the v4l version of OpenCV 2.4 to work at a fixed resolution other than 640x480 is changing the values for DEFAULT_V4L_WIDTH and DEFAULT_V4L_HEIGHT in modules/highgui/src/cap_v4l.cpp and re-building OpenCV, kudos to this answer.

If you want to build the libv4l version instead, all you likely need to do is install libv4l-dev and rebuild OpenCV; WITH_LIBV4L was enabled by default for me. If it is not, your cmake command should contain

-D WITH_LIBV4L=ON

The cmake output (or version_string.tmp) for a libv4l build contains something like

  Video I/O:
    ...
    V4L/V4L2:   Using libv4l1 (ver 0.8.6) / libv4l2 (ver 0.8.6)

(For a v4l build, it is just V4L/V4L2: NO/YES.)

回答2:

You can use v4l2-ctl to set frame size of captured video like below.

v4l2-ctl --set-fmt-video=width=1920,height=1080,pixelformat=1

You can find more information at this link

回答3:

Just wanted to add my CMAKE options to build with Java on the Raspberry Pi 3 based on Ulrich's comprehensive answer for OpenCV 3.2.0. Make a /build folder a in the same folder as OpenCV CMakeList.txt and execute this script for the new /build folder:

sudo cmake -D CMAKE_BUILD_TYPE=RELEASE -D WITH_OPENCL=OFF -D BUILD_PERF_TESTS=OFF -D BUILD_SHARED_LIBS=OFF -D JAVA_INCLUDE_PATH=$JAVA_HOME/include -D JAVA_AWT_LIBRARY=$JAVA_HOME/jre/lib/arm/libawt.so -D JAVA_JVM_LIBRARY=$JAVA_HOME/jre/lib/arm/server/libjvm.so -D CMAKE_INSTALL_PREFIX=/usr/local -D BUILD_TESTS=OFF -D WITH_MATLAB=OFF -D WITH_CUFFT=OFF -D WITH_CUDA=OFF -D WITH_CUBLAS=OFF -D WITH_GTK=OFF -D WITH_WEBP=OFF -D BUILD_opencv_apps=OFF -D BUILD_PACKAGE=OFF -D WITH_LIBV4L=ON ..

回答4:

Maybe you can try this, but I am not sure if this is what you want:

#include <X11/Xlib.h>

Display* disp = XOpenDisplay(NULL);
Screen*  scrn = DefaultScreenOfDisplay(disp);
int height = scrn->height;
int width  = scrn->width;

//Create window for the ip cam video
cv::namedWindow("Front", CV_WINDOW_NORMAL);

cvSetWindowProperty( "Front", CV_WND_PROP_FULLSCREEN, CV_WINDOW_FULLSCREEN );

//Position of the screen where the video is shows
cvMoveWindow("Front", 0, 0);
cvResizeWindow( "Front", width, height );

Like this you get the full screen for any screen.