Category Archives: Compression

Powerpoint file sizes

Was dealing with a big Powerpoint presentation (PPT) file.

In the older PPT format, 6063 Kb.

When zipped, 4826 Kb. Not a bad saving given the number of pictures in it.

Here’s the interesting thing: in PPTX format: 3293 Kb.

Remembering that PPTX and other Office Open XML formats (DOCX, XLSX etc) do their compression on the file as a whole, not the individual componenets, so this is an interesting result.

Perhaps the old binary format is inherently less efficient/compressible than the new XML format.

Mind you, another big PPT I tried it with didn’t compress down as much; the PPTX was about the same size as the ZIPped PPT, so it obviously depends on the exact content

Easy ways to save bandwidth

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After reading Jeff Atwood’s terrific post about saving bandwidth on web sites I’ve moved the Geekrant RSS feeds over to Feedburner, using Steve Smith’s mavellous WordPress Feedburner plugin, which works in WP 2.0x and 1.5x.

I also turned on HTTP compression, which in WordPress is as easy as clicking a checkbox. It not only saves you bandwidth, but users get your pages served quicker, since the bottleneck is bound to be their bandwidth, not their browser’s ability to decompress.

We’ll see how it goes. Bandwidth has been growing recently: January 2.8Gb; February 2.7Gb; March 3.4Gb. It’s not at ludicrous levels, but if it keeps climbing, I’ll end up paying more for the hosting. Hopefully this will help bring it back down.

Update 8:40pm. First thing I notice is that when reading the feed from within the Feedburner site, it doesn’t treat relative paths to images properly. I guess I’ll have to put absolute paths, ‘cos at the moment in the previous post it’s trying to load http://feeds.feedburner.com/files/2007/mediagate-mg35.jpg instead of http://www.geekrant.org/files/2007/mediagate-mg35.jpg. I wonder how it treats relative links?

File listings from zips

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Need to get a file list out of a zip file? Winzip is a fine product, but don’t muck about with their recommended method, setting up a text file printer driver to print a list to, then having to chop out the paper-style headings and linefeeds.

No… Instead go to Info-Zip and grab their command-line zip package.

unzip -l filespec.zip [Optional filespec if you don't want them all] > filelist.txt

Easy.

PNG! PNG!

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JPEG artefacts I’ve been discovering just how great PNG is for screendumps. It’s not lossy, yet it compresses particularly well for screendumps off Windows… even when there’s those gradient title bars that have become fashionable over the last couple of years.

For instance, the Path Not Found dump out of Windows explorer the other day:

PNG 22,140 bytes
JPG (saved out of Photopaint at compression 100 out of 255, noticeable loss of quality in the letters – See right) 76,824 bytes
GIF (converted to 256 colours, so some colour lost) 22,345 bytes
GIF (converted to 16 colours, so LOTS of colour lost) 17,285 bytes

Okay, so the 256 colour GIF is only marginally bigger, but to produce it you have to fiddle the colours, and of course it uses the proprietary LZW algorithm for which Unisys once would have wanted all our souls. PNG is just a save, no having to even think about it. Coolness.