[aprssig] Re: Symbol set revisions

Heikki Hannikainen hessu at hes.iki.fi
Thu Apr 24 02:23:36 EDT 2008

   Hi Gerhard,

On Fri, 18 Apr 2008, Gerhard wrote:
> On Fri, Apr 18, 2008 at 7:16 AM, Heikki Hannikainen <hessu at hes.iki.fi> wrote:
>>   I also have to serve both GIF files (for browser compatibility, IE6
>> doesn't do transparency in PNG images), and PNG files (for Google Earth, it
>> doesn't do transparency in GIF images). So that doubles the disk+cache
> My Web server generates the symbol PNGs on the fly from Stephen's
> tiles with GD and then caches them. The file size on the disk is only
> about 170 bytes. The transparent PNGs render without problem in IE6.

   Yeah, I was educated at work about this last week, too. IE6 renders 
transparent PNGs if they're in indexed-color mode (like in GIF). If it's 
an RGB PNG with an alpha channel (controlling the level of opacity), IE6 
doesn't render it. I apparently tried with RGB PNGs and went for GIFs 
when it didn't work. :)

   Most filesystems allocate space in fixed-size blocks. A really small 
file, smaller than a single block, will still take a single block. On a 
typical Linux system with ext2/ext3 it's 4096 bytes. It will still show up 
as 170 bytes in the directory listing, but 'du -k' will show the true disk 
usage for the directory in kilobytes, it'll probably be 4096 multiplied by 
the number of files. Plus one or more blocks for the directory itself. The 
same happens on Windows systems.

   There are exceptions - some filesystems can stick a very tiny file next 
to the file's entry in the directory tree (next to the file's name, 
attributes, ownership and modification time info) and avoid allocating 
storage blocks for the file.

   - Hessu

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