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Documented PNG plug-in

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Nick Lamb /GIMP 2000-06-30 03:46:36 +00:00
parent 29017c2bd5
commit c2ff0cc442
2 changed files with 70 additions and 9 deletions
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75
help/C/filters/png.html
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 TRANSITIONAL//EN">
<html>
<head>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<title>Help Page for png</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Help Page for PNG files</title>
</head>
<body text="#000000" bgcolor="#FFFFFF" link="#0000FF"
@ -11,18 +11,75 @@
<table width="100%" cellspacing="1" cellpadding="1">
<tr bgcolor="black">
<td width="100%" align="center">
<font size="+2" color="white">png help page</font>
<font size="+2" color="white">PNG help page</font>
</td>
</tr>
<tr bgcolor="white" >
<td width="100%" align="left">
<p>
<a href="index.html">Index</a><p>
(/filters/png.html)<p>
Sorry but the help file for png is not yet done.
<p>
/Karin & Olof
<p>
<h1>Saving PNG files</h1>
<p>Gimp will automatically choose a type of PNG file appropriate to the
image you are saving. All applications which can handle PNG files should
be able to read <em>any</em> PNG saved from Gimp.</p>
<h2>Parameter Settings</h3>
<h3>Interlacing (Adam7)</h3>
<p>The Adam7 interlacing option stores image data in an order
which allows browsers or viewers to show progressively more detail as
they load the file, at the cost of increased file size.</p>
<h3>Save background color</h3>
<p>This adds a bKGD chunk to your PNG file which advises viewer software
to choose a background color like your currently selected Gimp background
color. Adding this chunk increases file size slightly.</p>
<h3>Save gamma</h3>
<p>This adds a gAMA chunk to your PNG file which reflects the current
Gamma factor for your display (set globally for Gimp). Viewers with a
different display can compensate to ensure the image doesn't look too
dark or too bright. Adding this chunk increases file size slightly.</p>
<h3>Save layer offset</h3>
<p>If you are saving a single layer which has been shifted (offset)
from the top-left of the image, this will add a oFFs chunk to your
PNG file to preserve this offset factor in other viewers. Adding
this chunk if it's needed increases file size slightly.</p>
<h3>Save resolution</h3>
<p>This adds a pHYs chunk to your PNG which records the physical
resolution of the image. This is needed by Gimp and other viewers
for printing or <q>actual size</q> previews. Adding this chunk increases
file size slightly.</p>
<h3>Save creation time</h3>
<p>This adds a tIME chunk to your PNG which records the exact date
and time when the image was last saved. This will be preserved
and can be viewed in other applications. Adding this chunk increases
file size slightly.</p>
<h3>Compression</h3>
<p>This controls the amount of compression used to reduce the
file size. Larger numbers will usually reduce file size but will
make saving slower. The default (6) is often an acceptable
compromise, but see below.
<h2>PNG for the web</h2>
<p>On the web, size isn't everything but it is important. I suggest
that finished web graphics should be saved with level 9 compression
and without bKGD, oFFs, pHYs and tIME chunks.</p>
<p>For large web graphics, like maps and diagrams, you should consider
using Adam7 interlacing. For simple icons or logos, try converting
with Image/Mode/Indexed... before saving.</p>
<hr>
<h1>Loading PNG files</h1>
<p>This plug-in loads all known PNG files with following restrictions:
</p>
<ul>
<li>16 bit <b>per channel</b> data is reduced to 8 bit precision
<li>Transparency in paletted images is preserved but may not be
properly displayed. Image/Mode/RGB will display the full transparency.
</ul>
<p>These restrictions will be addressed in a future version of Gimp.
</p>
</td>
</tr>
</table>

4
help/ChangeLog
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2000-06-30 Nick Lamb <njl195@zepler.org.uk>
* C/filters/png.html: PNG documented to my satisfaction
2000-06-30 Nick Lamb <njl195@zepler.org.uk>
* makedummyhelpfile.sh