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I'm still going back and forth with some programmer friends on just how reckless I should be in
my approach to "simplifying" FLVs in iWeb, so I'm afraid I'll have to string you on for a bit longer on that article.  But rest assured -- I've not forgotten, and the Frame Controls article is coming up relatively soon as well.

In the meantime, here's a piece that's hopefully more useful than most "filler" -- the technical story behind Portable Network Graphics, or PNGs.  Read on for what they are, where they came from, and (most importantly) when they're a good idea in the video production workflow.
Background
PNG arose from Internet needs back in the day when GIFs were all the rage (remember those horrible blinking things?).  Back then, your images were basically GIFs -- which were pixel-accurate, but only accommodated 256 colors -- or JPEGs, which were lossy.  Unfortunately, Unisys owned the patent on one of the algorithms behind GIF technology, and it had the annoying habit of asking for royalties.  Internet politics being what they are, the whole thing got blown out of proportion, and people started whining.

Fortunately, some of those people were incredibly smart computer scientists.  They took the pixel-accurate (read: lossless) feature of the GIF format, and they added some bonuses: the option of a true alpha channel for effective transparency, the option of full "Millions of Colors" of depth, and a spiffy new compression algorithm.

Flavors
PNGs come in all kinds of bit depths and sizes, but if you're dealing with Photoshop, you'll probably want to select the LZW compressor and 24 bits of color depth.  As we've discussed before (Part 1, 2, 3), an alpha channel simply refers to whether the image has transparency.

Uses

  • PNGs are lossless and support alpha channels, which basically puts them on a par with TIFFs and Targa (TGA) sequences.  If you're not doing funny things outside of RGB color space (if you were, you'd know), PNG sequences can be a good choice of intermediate format for computer-generated animation and graphics: they're better-standardized than TIFFs (so they surprise you less often), and they're more widely supported (and smaller) than TGAs.
  • If you're looking to publish stills of video on the Internet or email them, JPEGs are a better choice for most purposes.  Although their compression is lossy, it's designed for "real" photos so it tends to be minimally noticeable.
  • By contrast, if you're looking to publish screenshots or computer-generated imagery on the Internet or by email, lower bit-depth PNGs might make sense.  You may not need the full range of color, and JPEG doesn't handle "unrealistic" elements like sharp lines, text, and empty spaces very well.
  • If you're publishing to the Internet and want to use a true alpha channel, PNG's pretty much your only choice.  Do note, though, that versions of Internet Explorer up to and including version 6.0 will NOT support PNG transparency (without some hacking).
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Quicktime for the Internet was the previous entry in this blog.

What's In a GOP? is the next entry in this blog.

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