Tv images.

Discussion in 'UK Photography' started by Bertie Doe, Oct 26, 2009.

  1. Bertie Doe

    Bertie Doe Guest

    Hallo. I have an EOS 350 and a Sky box, I've been
    trying to get some images from the tv. Trying to get
    rid of those vertical lines you get on the photo. Using
    google, the suggestions I got were :
    ~ don't use flash
    ~ try and get speed below 1/25th
    ~ use a tripod.

    Sadly it didn't work. Anyone help on this please? TIA.
     
    Bertie Doe, Oct 26, 2009
    #1
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  2. In what way didn't it work?
    The suggestions are correct, so you need to tell us what happened.
     
    Willy Eckerslyke, Oct 26, 2009
    #2
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  3. Bertie Doe

    Simes Guest

    I would have thought that you would be more likely to get horizontal
    lines from a TV pic. As you say above - a shutter speed of slower than
    1/25 - ideally longer if the scene on the screen is not fast moving -
    maybe a 10th of a second so that several scans are completed to avoid the
    darker/brighter lines.
     
    Simes, Oct 26, 2009
    #3
  4. Bertie Doe

    Bertie Doe Guest

    The picture is spoilt by numerous thin lines, similar
    to a finger print or lines on an OS map, but mostly in
    a North/South direction.
     
    Bertie Doe, Oct 26, 2009
    #4
  5. That sounds like moire patterns, a clash between the pixels of the tv
    screen and the pixels of the camera sensor. Were you using a low
    resolution such as 1024x768? If so I would try using a high resolution and
    then downsize the image to TV resolution afterwards.

    It may be worth blurring the image before resizing to help suppress
    artefacts. Eg. a digital tv picture has a resolution of 1024 x 576 (if we
    assume square pixels), if you shot at a resolution that was say 3072 pixels
    wide and applied a radius-1 blur (either precisely in photoshop or by eye
    in a program like Irfanview) then you still have 1536 pixels of detail (in
    other words more than enough) but when you downsize to the final 1024
    pixels wide (or whatever size you choose) you will be less likely to get
    moire patterns. This strategy is basically the same as the one that the
    anti-aliasing filter in a camera uses.
     
    Gordon Freeman, Oct 26, 2009
    #5
  6. Bertie Doe

    Bertie Doe Guest

    "Gordon Freeman" wrote in message
    Higher resolution Gordon, but blurring did help a
    little.


    "Garry Douglas" < wrote in message
    Thanks Garry, I should have used the freeze-frame on
    the Sky digi-box, I'd forgotten it had a couple of hard
    drives. It did the trick. Strangely, the optimum speed
    was 1/50th.
    Thanks all.

    ..
     
    Bertie Doe, Oct 26, 2009
    #6
  7. Bertie Doe

    Simes Guest

    <Chucks in lighted fuse>

    At 1/50th you are just capturing one field - on a standard UK TV picture
    it's an interlaced display - so half the lines are doen in a 50th of a
    second, then the other half - so you've captured only about 300
    horizontal lines of detail.

    It's probably fine though :)
     
    Simes, Oct 26, 2009
    #7
  8. Bertie Doe

    Bertie Doe Guest

    "Simes" wrote in message
    This sequence was at 1/50th
    http://www.flickr.com/photos/[email protected]/tags/adverts/

    Thin lines at 1/20th and dark horizontal bar at 1/125th
    sec.
    http://www.flickr.com/photos/[email protected]/sets/72157622552680591/
     
    Bertie Doe, Oct 27, 2009
    #8
  9. Your point?

    You've captured one-half raster at 1/50, and it's fine. 1/25 would have
    given you better clarity, but there may be differences between the two
    half rasters (if there's movement on screen etc.)

    The 1/125th image merely show the lack of persistence of the screen - so
    you've got about 40% bright, another 30% fading and 30%dark.

    Mike
    --
    Michael J Davis

    Now with added pictures on http://www.flickr.com/photos/watchman

    <><
    I have a photographic memory;
    but then I forget to load the film
    <><
     
    Michael J Davis, Oct 28, 2009
    #9
  10. Bertie Doe

    Simes Guest

    Simes, Oct 28, 2009
    #10
  11. Bertie Doe

    Bertie Doe Guest

    Interestingly, when I download from the camera to my
    PC, I look in My Documents etc, the moiré patterns/wavy
    lines on the picture, are quite obvious. Yet when it's
    stored on Flickr or photopic, there's little evidence
    of these lines. I tried some at 1/25th today - not much
    evidence of lines but 1/50th seems a little sharper?
    http://paul962.photos.gb.net/c1773799.html
    I tried another sequence at 1/25th, but this time I
    tweaked the manual focus and you can see it creeping in
    on 'screen_focus_004'
    http://paul962.photos.gb.net/c1773818.html
    With my original post I was snapping moving images, so
    "using Sky HDR to freeze frame" thanks Garry and
    "blurring the image" thanks Gordon, has all helped to
    solve the problem. This w/end I'll download Irfanview
    and have a play.

    ..
     
    Bertie Doe, Oct 28, 2009
    #11
  12. Bertie Doe

    Simes Guest

    I'd say on that page that they are equally sharp - just the 1/25th second
    shot is rather overexposed, so the contrast loss is making it look less
    sharp.

    The 1/50th second shot has a dark line across it.

    I'd try it at 1/25 and reduce the apperture a bit - and buy a newer TV!
    I don't know but I reckon an LCD TV would solve some of your problems -
    as would a TV tuner card in your PC and just save screenshots as you go
    along - avoiding the need for the camera altogether. Less fun maybe, but
    I bet you'd get a better jpeg.
     
    Simes, Oct 28, 2009
    #12
  13. Bertie Doe

    Bertie Doe Guest

    Yes the set is a 15yr old Ferguson; the wife hopes it
    dies, so she can substitute with HD. At the moment she
    saves any classic films onto a VHS tape. Perhaps a tv
    tuner card for her laptop for stills and save some of
    the spectacular shots you see on travel and discovery
    channels.
     
    Bertie Doe, Oct 28, 2009
    #13
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