False contouring in iMovie?

Discussion in 'Digital Video' started by Eauboy, Mar 2, 2011.

  1. Eauboy macrumors regular

    Eauboy

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    Washington, DC
    #1
    Hey everyone,

    I've just started using iMovie. I've been experimenting with time lapse photography and star trails. This calls for bringing in a large number of still photos into iMovie then playing them in rapid succession (without the Ken Burns effect).

    iMovie seems to work quite well for this, but I am encountering false contouring that isn't present in the still images. In fact, the effect is quite bad both when exported using .m4v and .mov formats.

    Please keep in mind that the images have consistently black backgrounds (the problem occurs when using night shots), which I know is a condition likely to bring out false contouring. But the effect is so pronounced that the movies are practically worthless.

    Does anyone have any suggestions?


    Thanks...
     
  2. xStep macrumors 68000

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    #2
    I'm wondering what you mean by contour?

    iMovie is limited to a minimum length of time each image can be displayed. Something like 5 frames. This can make your movie a little jerky.

    Another possible tool is QuickTime Player 7. Under the File menu it has "Open Image Sequence...". You choose the first image in a sequence of images in a folder and it creates a movie for you. You get to choose the frame rate. You require the Pro license though, for $29.

    There may be some other tools others might mention. Check this forum for the word timelapse, or time lapse.
     
  3. martinX macrumors 6502a

    martinX

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    #3
    This could be as a result of the compression applied to the images using an 8 bit codec (e.g. DV and AIC). A 10 bit codec (like ProRes) may yield a better result. Do you have access to FCP?
     
  4. Eauboy thread starter macrumors regular

    Eauboy

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    #4
    xStep - False contouring is when transitions between similar lightness ranges show up as obvious bands. In other words, instead of seeing a very gradual lightening across an image, you see two or three bands of very different lightness. Very obvious and very ugly.

    martinX - Yeah, that's a pretty good guess. I don't happen to have access to FCP. This is a tiny portion of my hobby and I'm reluctant to invest much $$$ into it. I don't suppose there is a way to apply a better codec using iMovie or another freeware/inexpensive product? I see the contouring as soon as I open the still in iMovie, even going frame by frame. The same still images in preview or any other application look normal.


    Thanks...
     
  5. xStep macrumors 68000

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    #5
    Eauboy, thanks for that explanation of contouring. I think I recall seeing that in the past.


    Are you importing full size images, or preprocessed images to the size you expect the video to be? I ask because I wonder if preprocessing might be helpful here. Specifically because that processing would not be occurring in a video editor. I know there are tricks to help remove the noise in astronomy photography too. Are you doing that? I'm just thinking out loud here.

    For output, there are several high-end options, at least to test how good the output can be. Using the QuickTime export option, you can pick the codec to use. Some of the higher end ones are; Animation, Apple Pixlet Video, and the Uncompressed 8-bit & 10-bit 4:2:2 ones. The files would be very large and not intended for internet playback. I have web page titled iMovie Export Guide that explains how to use the QuickTime Export option of iMovie.

    For some reason I have this list of software used for time-lapse, or combining images into a video. Perhaps one of them has an import option that could help. I thinks is my list of free apps. There are other retail apps that might be helpful.

    Gawker
    Smoovie
    FrameByFrame
    GifFun can combine gifs
    I Can Animate
    SingleFramer (last update 2007)​

    P.S. I'm interesting in this topic as currently I am experimenting writing an time-lapse app for my iPod touch. I have many ideas for it, including importing images from a collection such as yours.
     
  6. gameface macrumors 6502

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    #6
    Open quicktime. File > Open image Sequence. Navigate to the first still in the sequence and select it. Select what framerate you want it to play as. Export to quicktime if you want it framed for normal video (like 1920x1080) or click save as to create a full size quicktime.

    If you do it full size in quicktime, you should then be able to take that file movie file into iMovie and do a pan and scan to add some motion to it since the image will be bigger than your HD timeline.

    I do all this in After Effect but there is no reason this shouldn't work for you.
     
  7. Eauboy thread starter macrumors regular

    Eauboy

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    #7
    I'm importing full res still images, no preprocessing, so I suppose iMovie does have to convert the image to get resolutions at the size it will produce. Maybe I'll try shooting in lower res and see if that makes a difference, or possibly try batch-editing the images beforehand.

    My originals aren't great. I'm in D.C. so the sky has a lot of light pollution. Mostly I'm practicing for a trip to the desert I'm taking shortly. There isn't much noise, since they are short exposures (four seconds each, in my last batch). But regardless, there is no contouring in the original images, but it is immediately obvious in iMovie. And this does happen with .m4v and .mov files.

    Thanks for the tips. I'll keep playing around.
     
  8. LethalWolfe macrumors G3

    LethalWolfe

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    #8
    In the video world this is called, wait for it, 'banding' and, like martinX suggested, it is the result of compression and getting access to a higher quality, 10-bit codec will reduce the banding.


    Lethal
     
  9. Eauboy thread starter macrumors regular

    Eauboy

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    #9
    Thanks Lethal
     
  10. martinX macrumors 6502a

    martinX

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    #10
    iMovie is limited by the compressor (codec) it uses. That is the limitation of all video, but some are less limited than others.

    How about you zip a bunch of images and drop them here so a few of us can have a go with FCP using ProRes, a 10-bit codec.
     

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