gif vs png

[Hugo Pfoertner]

Neil, 

If high quality and scalable resolution is important, then
vector graphics is the only choice. I guess that photographs
and continuos tone pictures are not the main focus for the
visualization of sequences. There may be exceptions, e.g.
the sequence in http://www.enginemonitoring.org/sphere/ 
where color definitely helps ;-)
I prefer to have a Postscript or EPS file that can be edited,
e.g. with Adobe Illustrator. For the final presentation
a PDF file keeps all the graphical details at minimum file size.
For a web page the difference between .png and .gif both in quality
and size isn't dramatically different, unless you need animation,
which is only available in .gif. The PNG format includes the
ability to handle continuous tone pictures/photographs thus avoiding
the need for two different formats gif/jpeg. 
PNG is now also well supported in MS office applications, making a
MS word document with embedded PNGs astonishingly small.
Including EPS files in MS office documents had some problems (previewing
etc.) that may have disappeared with later MSOffice versions.
(The latest I now is "2000")

In Netscape Communicator 4.73 PNG and some other graphic and multimedia
formats are handled in my installation by the QuickTime Plug-In,
which makes the display of PNG's much slower than the embedded display of
GIFs or JPEGs. Here are some examples, together with the reference pdf,
where you can zoom into all details without any loss of quality.

The GIFs and PNGs in the following examples were all created
from Postscript files with Adobe Illustrator 9 with the function
"Save for use in the Web" (German: Fuer Web Speichern...).
This function tries to avoid aliasing effects caused by the
rasterizing by adding gray tones to the original B&W picture.
The resulting GIFs or PNGs only look good in the selected
resolution, but may look awful if zoomed or reduced in size.

The reference (2 pictures)
http://www.enginemonitoring.org/random/stwalk4d/stw4d25s.pdf  (14k for 2 pics)
Legibility strongly dependent on background color:
http://www.enginemonitoring.org/random/stwalk4d/st25lin.gif (15k)
My Plug-In displays this one with white background:
http://www.enginemonitoring.org/random/stwalk4d/st25lin.png (10k)

Look at the right part of the diagram where lines get closer and closer:
http://www.enginemonitoring.org/random/stwalk4d/st25log.gif (29k)
http://www.enginemonitoring.org/random/stwalk4d/st25log.png (12k)

Thanks to NJAS for:
http://www.enginemonitoring.org/sphere/icoscov.pdf
(156k for 4 pict, page 4 corresponds with the following pictures)
http://www.enginemonitoring.org/sphere/5072.gif (77k)
http://www.enginemonitoring.org/sphere/5072.png (78k)

Hugo Pfoertner

Contact Info: http://www.pfoertner.org/

---- Original message ----
>Date: Wed, 5 Jun 2002 09:03:32 -0400 (EDT)
>From: "N. J. A. Sloane" <njas at research.att.com>  
>Subject: gif vs png  
>To: seqfan at ext.jussieu.fr
>Cc: somos at grail.cba.csuohio.edu, njas at research.att.com
>
>Michael Somos, who has made many valuable updates to the OEIS
>over a period of many years, has written to recommend
>switching to png instead of gif format for illustrations.
>How do seqfans feel about this? In particular, do people
>generally have access to png readers on their computers?
>Here is what Michael says:
>
>I quote:
>I was just looking at "a1523.gif" (about which more later) and
>wondered why you have not switched over to PNG format. There is a
>nice GPL program 'gif2png' which will do it automatically and easily.
>Do a 'google.com' search for that name to find out why it is a good
>idea to switch to PNG. There are many advantages. For example :
>
>feynman:/tmp/local> gif2png a1523.gif
>gif2png: 248 unused colors; convert with -O to remove
>feynman:/tmp/local> ls -l a1523*
>-rw-r--r--    1 somos    somos        9011 Jun  4 23:31 a1523.gif
>-rw-r--r--    1 somos    somos        2019 Jun  4 23:45 a1523.png
>
>The converted file is much smaller in this case. Usually the size is
>more comparable but dramatic gains can be achieved. All major browsers
>now support PNG. It is great for the kind of illustrations that you
>want for EIS.
>(end of quote)
>
>What do people think?  Please reply directly to me
>
>Neil