MATLAB: Is getsnapshot on videoinput object much slower than vid.snapshot on webcam object

Image Acquisition Toolbox

When I call "getsnapshot" on a "videoinput" object, why is it much slower than calling "vid.snapshot" on a "webcam" object?

Best Answer

"webcam" and "videoinput" have different design and implementation. When using "webcam" the camera starts streaming video as soon as the object is created. The "snapshot" function only grabs the latest frame from the stream. The camera will continue streaming until "webcam clear" is called.

When using "videoinput" the camera does not start streaming when the "videoinput" object is created. If the camera is not already streaming video "getsnapshot" will start it and then grab the latest frame. The timing overhead is due to the camera start taking additional time.

If you are looking for a low latency version of the "getsnapshot" function, can configure the "videoinput" in manual trigger mode and then start (or preview) the camera.

Please see this example for more information on how to accomplish this workflow:

https://www.mathworks.com/help/imaq/examples/acquiring-a-single-image-in-a-loop.html

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MATLAB: Logitech Brio 4K webcam delivers only 1920×1080 still image (4k not available)

The likely reason for higher resolutions not being listed as available is because Logitech Brio 4k supports only compressed video formats at resolutions higher than 1920x1080.

Support for compressed video formats when using MATLAB WEBCAM is currently not available, but is under consideration for a future MATLAB release.

Note that Image Acquisition Toolbox with the winvideo adaptor (on Windows) does support compressed video formats such as MJPEG, so this might be used a workaround if Image Acquisition Toolbox is available. However, note that Image Acquisition Toolbox does not currently (as of MATLAB R2018b) does not support H.264 format (which some camera models might use for high resolution video formats). To detect which resolution and video formats a camera supports you can use the detectDevices utility in MATLABROOT\toolbox\imaq\imaqextern\utilities\detectDevices\win64

More information about winvideo adaptor you can find here in the documentation:

https://www.mathworks.com/help/imaq/image-acquisition-support-packages-for-hardware-adaptors.html

MATLAB: Am I unable to preview 16-bit image data from the camera

If using MATLAB R2008b or later, a possible workaround is to use the following command before creating the videoinput object:

imaqmex('feature', '-previewFullBitDepth', true);

You can also configure the preview axes CDataMapping and CLim properties.

vid = videoinput('winvideo') 
h = preview(vid); 
a = ancestor(h, 'axes');
set(h, 'CDataMapping', 'scaled');
% Modify the following numbers to reflect the actual limits of the data
returned by the camera.
% For example the limit a 16-bit camera would be [0 65535].
set(a, 'CLim', [0 65535]);

Please ensure that the preview window remains open while setting the image properties.

Best Answer

Related Solutions

MATLAB: Logitech Brio 4K webcam delivers only 1920×1080 still image (4k not available)

MATLAB: Am I unable to preview 16-bit image data from the camera

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