Imageio usage examples¶
Some of these examples use Visvis to visualize the image data, but one can also use Matplotlib to show the images.
Imageio provides a range of example images,
which can be used by using a URI like
'imageio:chelsea.png'. The images
are automatically downloaded if not already present on your system.
Therefore most examples below should just work.
Read an image of a cat¶
Probably the most important thing you ever need.
import imageio im = imageio.imread('imageio:chelsea.png') print(im.shape)
Read from fancy sources¶
Imageio can read from filenames, file objects, http, zipfiles and bytes.
import imageio import visvis as vv im = imageio.imread('http://upload.wikimedia.org/wikipedia/commons/d/de/Wikipedia_Logo_1.0.png') vv.imshow(im)
Note: reading from HTTP and zipfiles works for many formats including png and jpeg, but may not work
for all formats (some plugins “seek” the file object, which HTTP/zip streams do not support).
In such a case one can download/extract the file first. For HTTP one can use something like
Iterate over frames in a movie¶
import imageio reader = imageio.get_reader('imageio:cockatoo.mp4') for i, im in enumerate(reader): print('Mean of frame %i is %1.1f' % (i, im.mean()))
Grab screenshot or image from the clipboard¶
(Screenshots are supported on Windows and OS X, clipboard on Windows only.)
import imageio im_screen = imageio.imread('<screen>') im_clipboard = imageio.imread('<clipboard>')
Grab frames from your webcam¶
Use the special
<video0> uri to read frames from your webcam (via
the ffmpeg plugin). You can replace the zero with another index in case
you have multiple cameras attached.
import imageio import visvis as vv reader = imageio.get_reader('<video0>') t = vv.imshow(reader.get_next_data(), clim=(0, 255)) for im in reader: vv.processEvents() t.SetData(im)
Convert a movie¶
Here we take a movie and convert it to gray colors. Of course, you can apply any kind of (image) processing to the image here …
import imageio reader = imageio.get_reader('imageio:cockatoo.mp4') fps = reader.get_meta_data()['fps'] writer = imageio.get_writer('~/cockatoo_gray.mp4', fps=fps) for im in reader: writer.append_data(im[:, :, 1]) writer.close()
Read medical data (DICOM)¶
import imageio dirname = 'path/to/dicom/files' # Read as loose images ims = imageio.mimread(dirname, 'DICOM') # Read as volume vol = imageio.volread(dirname, 'DICOM') # Read multiple volumes (multiple DICOM series) vols = imageio.mvolread(dirname, 'DICOM')
import imageio import visvis as vv vol = imageio.volread('imageio:stent.npz') vv.volshow(vol)
Writing videos with FFMPEG and vaapi¶
Using vaapi (on Linux only) (intel only?) can help free up resources on your laptop while you are encoding videos. One notable difference between vaapi and x264 is that vaapi doesn’t support the color format yuv420p.
Note, you will need ffmpeg compiled with vaapi for this to work.
A little bit of explanation:
vaapi_devicespeficifies the encoding device that will be used. *
formattell ffmpeg that it must upload to the dedicated
hardware. Since vaapi only supports a subset of color formats, we ensure that the video is in either gray or nv12 before uploading it. The
oroperation is acheived with
pixelformat: set to
'vaapi_vld'to avoid a warning in ffmpeg.
codec: the code you wish to use to encode the video. Make sure your hardware supports the chosen codec. If your hardware supports h265, you may be able to encode using