Re: permanent page cacheing by WWW browsers
daeron@geom.umn.edu
Wed, 7 Dec 94 22:30:12 CST
> Date: Wed, 7 Dec 1994 19:58:22 -0800
> From: hitchner@netcom.com (Lew Hitchner)
> Subject: Re: permanent page cacheing by WWW browsers
>
> This morning I posted a reply to the VRML list and included in it some
> wonderings about whether there exist any current WWW browsers that save
> cached pages between sessions. This afternoon while at my part-time
> job I got the answer to my question.
>
> Yes -- Netscape's netscape browser (i.e., the formerly named Mosaic,
> Inc. of Jim Clark and Mark Andreason). It allows the user to set
> preferences that specify how long cached pages are kept around in days,
> ranging from 0 to forever. It also creates a directory where it stores
> your cached pages which by default is a hidden directory in your $HOME
> dir. Of course, you can set a preference that overrides the dir. name
> and location. The browser has a lot of other better-than-Mosaic
> features including the ability to load inline images via progressive
> refinement, i.e., low res blocky image replaced by gradually higher
> res. images. We counted 4 resolutions on some .gif images, but
> couldn't figure out how it works. I know .gif supports a 'postage
> stamp' minature embedded within the file, but I'm not aware that .gif
> also supports multiple resolution versions. Maybe there's a new GIF94
> std. that supports this??? Another better-than-Mosaic feature is the
> option to have it open more than one channel, so e.g., it can actually
> be fetching two or more inline images simultaneously (if you've got the
> bandwidth, that is).
>
Yes, netscape is a very cool application, though it is a bit hungry for
colors under X windows (i.e. it takes the whole colormap). The phenomena
you experienced with loading gifs in low res, than progressively higher
res is accomplished by the GIF "interlace" feature. This allows an image
to be loaded by every other line, or every second line or fourth line,
etc...
Since netscape displays gifs while it is loading them, it simply takes each
interlaced line of a gif and expands it to fill all the way down to the
where the next interlaced line will be. So on one pass down the image, you
will have a very blocky looking image, and with each new pass it gets
progessively finer. This is because all the bogus fill lines are eventually
being replaced with real lines from the image.
Hope this makes sense, :-)
Daeron