
Learning OpenCV 3 Computer Vision with Python (Update)
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Running a few sample scripts is a good way to test whether OpenCV is correctly set up. The samples are included in OpenCV's source code archive.
On Windows, we should have already downloaded and unzipped OpenCV's self-extracting ZIP. Find the samples in <unzip_destination>/opencv/samples
.
On Unix-like systems, including Mac, download the source code archive from https://github.com/Itseez/opencv/archive/3.0.0.zip and unzip it to any location (if we have not already done so). Find the samples in <unzip_destination>/OpenCV-3.0.0/samples
.
Some of the sample scripts require command-line arguments. However, the following scripts (among others) should work without any arguments:
python/camera.py
: This script displays a webcam feed (assuming that a webcam is plugged in).python/drawing.py
: This script draws a series of shapes, such as a screensaver.python2/hist.py
: This script displays a photo. Press A, B, C, D, or E to see the variations of the photo along with a corresponding histogram of color or grayscale values.python2/opt_flow.py
(missing from the Ubuntu package): This script displays a webcam feed with a superimposed visualization of an optical flow (such as the direction of motion). For example, slowly wave your hand at the webcam to see the effect. Press 1 or 2 for alternative visualizations.To exit a script, press Esc (not the window's close button).
If we encounter the ImportError: No module
named cv2.cv
message, then this means that we are running the script from a Python installation that does not know anything about OpenCV. There are two possible explanations for this:
$ python python/camera.py
You can also use the following command:
$ python2.7 python/camera.py
As another possible means of selecting a different Python installation, try editing the sample script to remove the #!
lines. These lines might explicitly associate the script with the wrong Python installation (for our particular setup).
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