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The new DSLR camera released by Canon, 760D, has capability of recording HDR movie. My question is how does this work? In still photography, when setting the camera to HDR, the camera will take 3 shots (the mirror will flip 3 times), with different shutter speed to adjust the exposure and then process it to combine into 1 picture.

For movie, definitely the mirror will need to be flipped all the time while simultaneously need to record at different exposure level. So how does the camera manage to handle this?

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    For DSLRs, when shooting video the mirror does not cycle between each frame, it stays up the entire time. In fact, the shutter does not cycle between each frame either: it stays open. The sensor is read out electronically at specified intervals. – Michael C Jun 5 '15 at 0:18
  • @MichaelClark Sounds great. Why not converting this into an answer? – p2or Jun 5 '15 at 12:48
  • Because it doesn't really answer the crux of your question: it merely addresses one of your mistaken assumptions. – Michael C Jun 6 '15 at 1:29
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At a guess, it will be a similar technology to HDRx from RED or Magic Lantern - 2 frames instead of one recorded for every single video frame.

In Magic Lantern every frame is recorded at 2 ISO values, in the case of the RED camera, two frames are captured instead of one with different shutter speeds with the second frame "2-6 stops faster". The selection of ISO/"stops faster" is carried out by the user in both case prior to recording.

All that has to be done then, is to blend the resulting "dual frames" into a single video frame for an HDR video. Also, keep in mind that you do not need 3 frames for an HDR - you just want to cover a greater range than a single exposure can cover, this can be 2 frames or 200 frames. For video it is 2.

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    You could also do it with a single frame from a camera that converts the raw data from that single frame into two disparately processed frames, one darker and one lighter. There is as much information in a single 14-bit raw file as there is in a -3, 0, +3 series of JPEGs. – Michael C Jun 6 '15 at 1:34
  • @Michael Clark You can, however normally one uses HDR to capture a dynamic range beyond what the sensor covers. I would not refer to compressing a single RAW file as HDR - plus, very few cameras record RAW video (outside of very expensive professional models). – DetlevCM Jun 6 '15 at 13:01
  • High Dynamic Range Imaging (HDR imaging) is much broader than combining multiple images into a 32-bit floating point file. It is any photographic method that allows a scene with a higher dynamic range than the display medium to be rendered by squeezing that range into the display medium. In the 1850s it was what Gustave LeGray was doing by combining an image of a sky and another image of the beach to create seascapes. In the mid 20th century it was what Ansel Adams was doing with the zone system and dodging and burning – Michael C Jun 7 '15 at 8:34
  • Since the predominant display medium today is an 8-bit JPEG displayed on an 8-bit monitor, squeezing all of the information of a 14-bit file with 10-12 stops of dynamic range into a JPEG file with about 7 stops of DR is a form of High Dynamic Range imaging. – Michael C Jun 7 '15 at 8:35

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