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<WEBPAGE chapter="hsc - " title="Get Size Of Images"
PREV="rplcent.html"
NEXT="spcattr.html">
<P>Several browsers support the attributes <CODE>WIDTH</CODE> and
<CODE>HEIGHT</CODE> for tags like <TG>IMG</TG>. If you know the
exact size of your image, you can tell it the browser. This might
speed up the layout-engine, because the browser doesn't have to
wait for the image to be transfered or needs to re-layout the page
after the transfer.</P>
<H2>Usage</H2>
<P>As you usually don't know the exact size of your images, let your
stupid computer handle this dull task by enabling the switch
<op_getsize> when invoking <hsc>. This will <hsc> tell to analyse the
image the attribute <CODE>SRC</CODE> refers to, and append the
attributes <CODE>WIDTH</CODE> and <CODE>HEIGHT</CODE> with the
dimensions obtained from the image data.</P>
<P>If you have already set those attributes yourself, <hsc> will
only validate the values, and warn about mismatches.</P>
<H2>Example</H2>
<P>Take a look at this nice picture of some nice guy:</P>
<P ALIGN="center"><IMG SRC=":image/niceguy.gif" ALT="Picture of some nice guy"></P>
This can usually be included in a document using something like
<$source PRE><IMG SRC="image/niceguy.gif" ALT="Picture of some nice guy"></$source>
but if a document called <FILE>niceguy.hsc</FILE> containing such a
tag is converted using
<PRE>hsc niceguy.hsc TO niceguy.html GETSIZE</PRE>
the <TG>IMG</TG>-tag seen above will be extended to
<$source PRE><IMG SRC="image/niceguy.gif" ALT="Picture of some nice guy" WIDTH="64" HEIGHT="64"></$source>
in the html-object. If you do not like the double quotes assigned to the
size values, use the CLI-option <op_quotestyle> to change this behavior.
<H2>Supported Image Formats</H2>
In the recent years several formats to store image data have been
established - mostly because none of these was really useful. Only a
few of them are supported by <hsc>. However these should be enough for
w3-authoring.
<H3>gif - Graphics Interchange Format</H3>
<P>In the early times of w3, this was the only format supported by
most browsers. It features only indexed-color (16 or 256 colors) and
an ugly looking progressive display option. It became very popular in
a negative sense because of it's compression algorithm and the
associated copyright.</P>
<P>Bye the way, did you know that "The Graphics Interchange Format(c) is
the Copyright property of CompuServe Incorporated. GIF(sm) is a
Service Mark property of CompuServe Incorporated."? So now you do; if
it makes them happy...</P>
<H3>jfif/jpeg</H3>
<P>Essentially this format does a good job as an idiot indicator. This
already starts with the name: jfif is short for JPEG File Interchange
Format (because it uses jpeg compression for image data). Nevertheless
jfif-pictures will have a file extension set to <qqc>.jpg</qqc> or
<qqc>.jpeg</qqc>.</P>
<P>The main feature about jpeg compression is that it is lossy, which
means that the output image is not identical to the input image.
Documents about software using jpeg compression usually claim that you
can obtain good compression levels with no visible change. As long as
you do not start to rotate or apply other complex image processing
operations on pictures, this might even be true. Otherwise an ugly grid
will appear soon.</P>
<P>Most important jfif is commonly used to encode images of more or
less undressed people. To store as many such pictures as possible on
as less space as possible, the compression rate is usually set to a
high value. This makes these people look if they are suffered by
leprosy or just a drawing by Egon Schiele.</P>
<P>Furthermore many people outside English speaking countries
pronounce jpeg (<qq>jay-peg</qq>) as GPEG (<qq>gee-peg</qq>), even if
they are normally capable of a proper English pronunciation.</P>
<H3>PNG - Portable Network Graphics</H3>
The <A HREF="http://www.w3.org/pub/WWW/TR/WD-png">PNG Specification</A> (<(HSC.Anchor)>)
claims this format to be
<BLOCKQUOTE>...an extensible file format for the lossless, portable,
well-compressed storage of raster images. PNG provides a patent-free
replacement for the GIF format and can also replace many common uses
of TIFF format. Indexed-color, grayscale, and truecolor images are
supported, plus an optional alpha channel. Sample depths range from 1
to 16 bits [and] it is fully streamable with a progressive display
option.</BLOCKQUOTE>
<P>Above all PNG supports most obvious things several other formats
failed to include. There is nothing really remarkable about it, but
today one has the be glad even about this. So it can be said that PNG
is one of the view positive things that happened in the last ten
years.</P>
<P>But even despite that their is free source code available to read
PNG-images, and the word <qq>Network</qq> is part of it's name (to
conform to the hype), it was only supported by very few applications
and w3-browsers for a long time. This slowly changes, so maybe you will
want to give it a try.</P>
<P>Bye the way, <hsc> supported it since ever - actually it was the first
working image format because it took some releases to end up with a
bugfree scanner for gif...</P>
</WEBPAGE>
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