Video microscopy trials with the USB Live View output of a DLSR camera.

by David Walker

 

 

 

'Live View' from the main sensor is an increasingly popular feature on the digital SLRs offered by most makers. The live image can be viewed in a number of ways: on the camera's LCD, on a TV via the video output(s) and also on a computer screen via a USB cable with the maker's remote control software (if available).

The author has been using a Nikon D300 with its live view feature for critical focussing in photomicroscopy (see January 208 Micscape article) and wondered if the PC screen video stream could be captured, so that the DSLR effectively became both a still image camera and a video camera.

I was unfamiliar with what software could capture the video stream on screen but an online search showed that live view video capture from DSLRs was already being explored e.g. by photographers interested in video macroscopy. One useful forum discussion 'How to capture video from 40D?' in a DPreview forum discussed software that users had been trying. The software that most appealed to me, both in effectiveness and price, was ZDSoft's 'Video Recorder'. A 30 day free trial is available and good value to buy at $29.

The videos below were all captured using this software and the Nikon D300, but any DSLR that has control software that presents live video on the PC screen should be fine. The software was very robust and gave no problems at all with Nikon's software.

Video recording alternative routes: The video output from a DSLR with live view can of course also be captured via the composite video output (and/or high definition if offered) to a suitable video recorder. This should give the best quality but the potential benefit of capturing the USB video stream is for computer and web page use without the need to play back the video recorder and use a video capture board.

ZDSoft's Video Recorder screen shown right is very intuitive. The software detects the video codecs on the PC and offers them in a drop down box. The parameters available for each codec can be altered via the 'Config' button, e.g. compression rates etc.

When the Start button is pressed the arrowed film reel icon in the status bar rotates to indicate recording is in progress. The button to stop and start video can be configured to suit.

By default video files are saved with sequential file names so no danger of overwriting them.

If the PC has a built in microphone or one is connected to the PC's audio card, an audio commentary could be added.

 

 

Videos - to play a video of interest below, click on an image and it will play in an external window using the default avi player on the local PC. Note that the Xvid compression codec is used. Readers may need to download the codecs from www.xvid.org if not on local PC.

Clips edited with free Virtual Dub. Apart from cutting out frames and compression, the videos are as seen on the PC screen from the Nikon D300's Live View window. The video quality on Live View screen was higher than shown here because of compression and frame rate reduction to save file size. (fps in captions = frames per second).

 

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Comments to date

Various types of camera can capture both stills and video e.g. webcams and dedicated microscope cameras; the quality being dependent on cost and specs. From the tests above with a Nikon D300, a DSLR with Live View of main sensor also seems to offer reasonable quality video typically up to VGA size in addition to hi-res stills. A dedicated high performance microscope camera can probably exceed the DSLR video quality captured via the screen but the author does not own one for comparison as can be very expensive.

The results above are from the D300 where the Live View is taken from the main sensor. Some maker's offer DSLRs where the Live View is taken from a separate sensor. If the computer control software presents this video on screen, the same video capture method should be possible. I'd be interested to hear from users of other DSLRs with Live View either from the main or subsidiary sensor as to the quality of such video clips.

DSLR prices are steadily dropping and Live View is becoming a standard feature on the 'budget' models in a maker's range, e.g. the Canon 1000D (Rebel XS) just announced and current Canon 450D. So the ability to additionally capture video off screen and/or save to a dedicated video recorder may be a useful option. Some consumer digicams with remote control software and Live View should also be able to do this.

Ideally saving the master video to the hard drive uncompressed would minimise compression artifacts if the clip is to be edited and further compressed, but no compression can generate huge files. The author used a modest compression on the master videos and heavier compression for the edited clips for a reasonable web file size, but careful choice of video codec / compression needs to be made to keep artifacts to a minimum.

Comments to the author David Walker are welcomed.

 

 

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