Image Sequences vs. video file

Sorry about my ignorance toward this as I'm new to editing and such and I can't really find an answer to this as of yet.
I've seen a lot of posts about exporting and importing image sequences into and out of editors. I normally export and import in some form of video file. I've tried to scour the forums here to see what the advantages are in exporting/importing an image sequence and the most I've found is that if I export to a .png file, it keeps the resolution of the original file (I believe that's what I understood). Is there any other advantage of using an image sequence versus a video file? 
Also, when you guys add an effect to an image in a sequence, does it render to all the images in the sequence? Maybe I don't understand exactly how that works. I haven't used image sequencing, so I'm trying to understand how and why. 
Any information would be appreciated, even if it's a link to an old post that I may of missed. Thanks!


  • luxgud
    luxgud Posts: 127 Just Starting Out*
    edited April 2014

    Some applications work better if you provide them with an image sequence, for example 3D camera tracking software. This software analyses individual frames. If you supplied it with a video, whilst it might be smaller, interlacing or compression effects would make this hard and inaccurate.
    I too have software that only produces discrete images. These tend to be high quality renders that would be degraded if it when through the video compression process.
    The advantages of a single video file are obviously that it can be compressed and also effects can be applied throughout the video or selectively.

  • Triem23
    Triem23 Posts: 20,298 Power User
    edited April 2014
    Everything luxgud wrote is correct, but I want to add to it. Another reason to render image sequences is stability: if you are rendering a video file and you have a system crash or power failure then you re-render from the beginning. If you're rendering image sequences and have a failure, you re-render starting from the last frame.
    Also, if you render an image sequence: let's say you have one bad frame--something didn't comp right, or a glitch--with the image sequence, you fix the one frame. With a video, you either re-render the entire file, or patch the one frame over the rendered video and re-render--but that's double-compressing your video, which can lead to artifacts.
    Note: major studios/fx houses tend to render image sequences for the reason luxgud and I gave: some other software in the pipe wants uncompressed frames, having a highest-quality "supermaster," and render safety.
    Now, you ask if adding an effect to an image sequence effects all frames? This depends. If you import an image sequence into Hitfilm or any NLE, then it's treating the image sequence as a video file, so you can add effects just like to any other source. If you are taking images into a photo editor, then no--each frame is it's own file.
    Typically with an image sequence, you're rendering out either for import and further editing in other software, in which case you're into the point lux brought up, or you're maintaining a maximum quality "supermaster" and using your NLE to re-render a "delivery master."
    Hope this helps.
  • Budmas
    Budmas Posts: 4
    Thanks so much for the information. It makes sense now. I'll start doing that and see how my videos come out.
  • Triem23
    Triem23 Posts: 20,298 Power User
    edited April 2014
    No problem. Just bear in mind that a render to image sequence will take longer, and require far more disc space (a PNG of a 1080p will be a bit over a megabyte. Assuming you render a 30 second animation at 24 frames a second, you generate at least 750 megabytes of files, if not over a gig.) Make sure you have a lot of disc space if you go the image sequence route.