Digital Video Forum

Digital Video Forum Discuss camcorders, HD video, HD DSLRs, video editing, DV software, and video techniques. Your DV forum moderator is Skyman.
Read and Write Camcorder Reviews >>
Results 1 to 8 of 8
  1. #1
    Junior Member
    Join Date
    Dec 2007
    Location
    UK
    Posts
    4

    Live preview and software

    Hi Guys.

    As a college student in the UK, we've been asked to find a solution for a project over the holidays. I'm studying Photography, but this involves a small change which I don't know anything about.

    We need to video a model moving in our studio and be able to capture a selected still frame and import it into another background already being displayed on a monitor, to make her appear in another scene. Our tutor wants us to develop this into a greenscreen idea in the future which we've done with our SLR's, but importing live video is something we've never done.

    Can someone explain how we capture a still frame while watching a live feed and let us know if there is any software available to merge this still with a previous image already on screen. Our technical department are happy to spend some money to buy the correct equipment and software if necessary.

    Thanks

    Roger Smith

  2. #2
    Moderator Skyman's Avatar
    Join Date
    Feb 2004
    Location
    Sydney, New South Wales, Australia
    Posts
    1,507

    Re: Live preview and software

    I am assuming this all needs to happen in real time? if so I can't recommend any brands etc, but my gut feeling is that a broadcast live vision mixer should be able to handle it. preferably a digital one but you should still be able to do it with an analogue one.

  3. #3
    Panarus biarmicus Moderator (Sports) SmartWombat's Avatar
    Join Date
    Mar 2004
    Location
    UK
    Posts
    11,750

    Re: Live preview and software

    I assume the model is already against a green screen in the studio.

    Since it's capturing a still frame from a video feed, that's simple.
    There's off the shelf hardware that can do that.

    Then if it's just putting a still frame into an image, you've already done that with DSLR?
    Or go to Digital Anarchy for Primatte Chromakey for stills http://www.photoshopsupport.com/tool...-primatte.html.

    This is what's used in the photo applications you see in most little stalls in the shopping centres, and in department stores. They rarely use still camera, but a video camera and frame grabber in a PC. Usually they don't use green screen, but a white background, and insert only the face not the whole person.


    If you want video chromakey, it's available off the shelf - green or blue background.

    In theory it's simple.
    Two video inputs, one of the background image, one of the model.
    Very high speed video switcher.
    Control switcher from the colour of the model image, if it's green use the background input, if not use the model image.

    Of course the devil is in the details.
    Like what if your model is wearing green? She's see through !
    What about the sync on both sources, do you have genlock?
    How about the signal levels, do you have good black level clamping, and no DC offset?
    How do you set the colour parameter for the background/model detection?
    What do you do about background colour highlights in the hair?
    How do you avoing colour bleeding round the edges of your model?


    Using peak white is simple, because you can sample that off the composite video feed without digitisation or analysing the colour. You'd have to be very careful with the lighting though, or you get a hole in the head of you get forehead glint off a bearded slaphead like me !


    There are plenty of post-production tools that can do this to video.
    But you need to have captured both images, I assume this is not what you want.

    Even for free http://www.instructables.com/id/How-...effects-to-a-/ though I am not sure I'd trust downloads like this on a computer connected to the web, or one with data I valued ... just in case there's a back door in the software.
    PAul

    Scroll down to the Sports Forum and post your sports pictures !

  4. #4
    Junior Member
    Join Date
    Dec 2007
    Location
    UK
    Posts
    4

    Re: Live preview and software

    Hi SmartWombat

    Thanks for a great reply. I think what the tutor's after us trying to achieve is something like the shopping mall, but more instant. Typical that the model we wanted to get to do this would be in college colours - green and blue. Never thought of the see-through bit! Would it work initially with a white or black background for the model?

    This is actually for part of a college production in January and we need to get the model's feet and legs only, but to be in exactly the right place for it to work, and it needs to be, like, instant results, so that the audience can see it being done as it happens. The 3backgrounds are going to be pre-made, something like a jpeg and then swapped, almost like changing layers in photoshop. The same part of the backgrounds is dropped out on each one, which is why the legs need to be in exactly the right position. Screen grab or similar of the exact frame seems to sound like what we need to do.

    There's off the shelf hardware that can do that.> Can you advise of something to start us off? Which program can blend or mix the 2 images to give quick results?

    Thanks

    Roger

  5. #5
    Panarus biarmicus Moderator (Sports) SmartWombat's Avatar
    Join Date
    Mar 2004
    Location
    UK
    Posts
    11,750

    Re: Live preview and software

    Would it work initially with a white or black background for the model?
    Yes, but with the same problem. A bit too much light and your model is see through. Or the shadow areas are see through. Colour gives better results.

    which program can blend or mix the 2 images to give quick results?
    Ah it's the quick that's a problem.


    Is this to be a still display, or video ?


    If it's live video there are lots of products - I've not tried any, just googled.
    Prices vary widelyFrom $499 to over $10000, as will quality I suspect.
    Not just quality of the video but also the dealers.

    http://www.videoguys.com/sfxm.htm
    http://www.libraprobroadcast.co.uk/p...Edirol-LVS-400
    http://www.creativevideo.co.uk/publi...r=ultimatte_dv
    http://www.crmav.com/dj/51/korg_kf4_...eo_mixer.shtml
    http://www.videoguys.com/MX4.html
    http://www.creativevideo.co.uk/publi..._synergy100-sd
    http://www.videotexsystems.com/detail.aspx?ID=55909
    http://www.holdan.co.uk/datavideo/dvk100.htm
    http://www.venturaes.com/electronics...ent/index.html

    Hardware will always be quicker than software.
    PAul

    Scroll down to the Sports Forum and post your sports pictures !

  6. #6
    Junior Member
    Join Date
    Dec 2007
    Location
    UK
    Posts
    4

    Re: Live preview and software

    SmartWombat

    At the end, it will need to be a still image, and he wants to print something for some of the audience who are VIP's from the local Council. Printing's not a big problem as we've got a small printer which will do the job.

    Thanks for the links.


    Roger

  7. #7
    Panarus biarmicus Moderator (Sports) SmartWombat's Avatar
    Join Date
    Mar 2004
    Location
    UK
    Posts
    11,750

    Re: Live preview and software

    Are you displaying the overlaid image ?
    If not, if it's only for printing, then I'd take the video off to a recorder, probably DVD (I have one spare).
    Then do the sampling and overlay offline.
    You get more than one go at capturing the legs in the perfect position for overlay.
    PAul

    Scroll down to the Sports Forum and post your sports pictures !

  8. #8
    Junior Member
    Join Date
    Dec 2007
    Location
    UK
    Posts
    4

    Re: Live preview and software

    Smartwombat.

    We think that we'd like to project the image and then go to print. It's actually planned to be the very last scene in the production, which has a technology theme throughout. The plan to print is therefore needed before the VIP's leave the auditorium, or as soon as possible after. The head is keen to push this production through as it develops, without realising the complexity! The VIP's are the first line of an application, so impressing them is high on his agenda. So, we should try to push it in this direction if we possibly can.

    Thanks


    Roger

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •