<br><tt><font size=2>Toni Asensi Esteve <asmond@orange.es> wrote
on 19/05/2010 14:31:06:<br>
<br>
Hi Toni</font></tt>
<br>
<br><tt><font size=2>> Chris wrote:<br>
> <br>
> Before adding the new information to the FAQ I would like that we
discuss one <br>
> thing:<br>
</font></tt>
<br><tt><font size=2>OK </font></tt>
<br>
<br><tt><font size=2>> > RGB is lossless encoding, ie mostly don't
compress </font></tt>
<br><tt><font size=2>> <br>
> > Personally, I find it slower than a steamroller, unless on a
LAN link. <br>
> > jpeg is everywhere for a reason !! <br>
> Mmm... I beg to differ, jpeg is not everywhere :-(. You'll see a lot
of .png <br>
> files.</font></tt>
<br>
<br><tt><font size=2>Yes. Thank you, Toni . I didn't mean exculsively everywhere.</font></tt>
<br>
<br><tt><font size=2>> Apart of being a lossless compression, the reason
of using a RGB <br>
> compression is that if you are going to save an image that has not
<br>
> photographs <br>
> nor gradients, for example a screenshot of a simple window of a program...
if </font></tt>
<br>
<br><tt><font size=2>yup . . .</font></tt>
<br><tt><font size=2><br>
> you use a jpeg compresion you'll have a big file and inside the <br>
> resulting image <br>
> you'll have "blurry text" and "blurry lines".
This is because jpeg compresion <br>
> was designed for photographs and similars, not for images that have
<br>
> only text, <br>
</font></tt>
<br><tt><font size=2>yup</font></tt>
<br>
<br><tt><font size=2>> lines, squares and so. For those cases, a png
compresion produces smaller <br>
> files.<br>
> </font></tt>
<br>
<br><tt><font size=2>right . . .</font></tt>
<br><tt><font size=2><br>
> The JPEG FAQ explains it in </font></tt><a href="http://www.faqs.org/faqs/jpeg-faq/part1"><tt><font size=2>http://www.faqs.org/faqs/jpeg-faq/part1</font></tt></a><tt><font size=2>
(search <br>
> inside the text "When should I use JPEG, and when should I stick
with GIF", <br>
> knowing that the PNG format can represent all the necessary colors,
<br>
> unlike the <br>
> GIF one).</font></tt>
<br>
<br><tt><font size=2>Right . . . for hard lines and areas of the same colour.</font></tt>
<br><tt><font size=2>gif compresses to smaller</font></tt>
<br><tt><font size=2>png is mostly better than gif for the above</font></tt>
<br><tt><font size=2>jpeg for the above is larger and may won't be lossless
even if the image</font></tt>
<br><tt><font size=2> is just an area of all the same colour.</font></tt>
<br>
<br>
<br><tt><font size=2>But . . .</font></tt>
<br>
<br><tt><font size=2>I didn't bother with that, I just compared response
times over NX</font></tt>
<br><tt><font size=2>sessions, which takes everything into account.</font></tt>
<br>
<br><tt><font size=2>All of the other forms of compression involved - X
session traffic</font></tt>
<br><tt><font size=2>compression, the disk/memory cache sizes, the cache
access time,</font></tt>
<br><tt><font size=2>cpu, number of users, link speeds etc</font></tt>
<br>
<br><tt><font size=2>ie. all the things nomachine included, (except the
localized X round</font></tt>
<br><tt><font size=2>trip reduction, which applies to all sessions equally).</font></tt>
<br>
<br>
<br>
<br><tt><font size=2>I'm not sure what NX uses when you select RGB compression,</font></tt>
<br><tt><font size=2>because they don't say, though as it differs from
X bitmaps there</font></tt>
<br><tt><font size=2>must be some compression, so I guess it's just zipped
in one form</font></tt>
<br><tt><font size=2>or another, which would be lossless.</font></tt>
<br>
<br><tt><font size=2>It may involve gif or png . . .</font></tt>
<br>
<br><tt><font size=2>or </font></tt>
<br>
<br><tt><font size=2>it may just be a compressed bitmap.</font></tt>
<br>
<br><tt><font size=2>This would fit in with what nomachine say in their
instructions :-</font></tt>
<br>
<br><tt><font size=2>QUOTE ( from client-guide )</font></tt>
<br>
<br><tt><font size=2>Only use RGB compression</font></tt>
<br><tt><font size=2>------------------------------</font></tt>
<br><tt><font size=2>Use only the lossless encoding. </font></tt>
<br><tt><font size=2>This compression is advisable on fast links, since
the high image</font></tt>
<br><tt><font size=2> quality increases the data to be sent.</font></tt>
<br>
<br><tt><font size=2>UNQUOTE</font></tt>
<br>
<br><tt><font size=2>Which I take to mean : -</font></tt>
<br>
<br><tt><font size=2>"advisable ONLY on fast links, since . . . increases
the data . . .sent"</font></tt>
<br>
<br>
<br><tt><font size=2>So</font></tt>
<br>
<br>
<br><tt><font size=2>Viewing the NX session overall, rather than just compression
algorithms . .</font></tt>
<br>
<br>
<br><tt><font size=2>The other algorithms used in an NX session, may in
fact prove more</font></tt>
<br><tt><font size=2>significant than straight compression, for example
differential</font></tt>
<br><tt><font size=2>updates of screens and cache hits particularly . .
.</font></tt>
<br>
<br><tt><font size=2>Lots of small chunks of screen won't compress much.</font></tt>
<br>
<br><tt><font size=2>Hitting them in the cache however, will be much quicker
than any</font></tt>
<br><tt><font size=2>compression over a slow link, particularly with differential</font></tt>
<br><tt><font size=2>screen updates.</font></tt>
<br>
<br>
<br>
<br><tt><font size=2>In my view, each site needs to choose the setting
which are best for that</font></tt>
<br><tt><font size=2>site's OVERALL performance, which when other things
are taken into account</font></tt>
<br><tt><font size=2>cache, partial updates etc, may well not be the smallest
form of compression</font></tt>
<br><tt><font size=2>at all.</font></tt>
<br>
<br>
<br>
<br><tt><font size=2>What I did when I was looking at this, was to try
the same tasks using both</font></tt>
<br><tt><font size=2>high quality jpeg and RGB and compare how it seemed
to be on the screen.</font></tt>
<br>
<br><tt><font size=2>I found that I couldn't distinguish between the quality
of image ( on a </font></tt>
<br><tt><font size=2>spreadsheet, which is one of our core apps,</font></tt>
<br><tt><font size=2>lots of thin straight black lines</font></tt>
<br><tt><font size=2>on a white background,</font></tt>
<br><tt><font size=2>just what the jpeg people say they aren't good at
)</font></tt>
<br>
<br><tt><font size=2>but</font></tt>
<br>
<br><tt><font size=2>that the RGB response time was noticably slower, even
for typing.</font></tt>
<br>
<br>
<br><tt><font size=2>I've just tried it again now, seeing that you've mentioned
it.</font></tt>
<br>
<br>
<br><tt><font size=2>When I try swinging a window around in RGB only, it
goes round a</font></tt>
<br><tt><font size=2>couple of times than stops with a jerk for a few second.</font></tt>
<br>
<br><tt><font size=2>I type a line of high speed gobbledegook (as you can
see I'm good</font></tt>
<br><tt><font size=2>at that) and even that doesn't keep up with me.</font></tt>
<br>
<br><tt><font size=2>It reminded me of driving behind a slow moving vehicle.</font></tt>
<br>
<br>
<br>
<br><tt><font size=2>Under jpeg compression, even at high quality, the
window just</font></tt>
<br><tt><font size=2>keeps on moving around under the mouse pointer.</font></tt>
<br>
<br><tt><font size=2>OK it's not real world (for a user doing some work
anyway), but</font></tt>
<br><tt><font size=2>it certainly generates some traffic and hits the end
stops.</font></tt>
<br>
<br>
<br><tt><font size=2>I'm running this over two adsl links from the same
provider, one</font></tt>
<br><tt><font size=2>6M the other 12M , so it's deferring updating the
screens a little </font></tt>
<br><tt><font size=2>but it fits in with what nomachine say as quoted above
about RGB</font></tt>
<br><tt><font size=2>and fast links.</font></tt>
<br>
<br>
<br>
<br><tt><font size=2>All this prompted me to leave the default settings
at just jpeg,</font></tt>
<br><tt><font size=2>not even going to both.</font></tt>
<br>
<br><tt><font size=2>The setting :-</font></tt>
<br>
<br><tt><font size=2>QUOTE</font></tt>
<br>
<br><tt><font size=2>Use both JPEG and RGB compression</font></tt>
<br><tt><font size=2>------------------------------------------</font></tt>
<br><tt><font size=2>The adaptive compression dynamically selects a lossy
or a lossless </font></tt>
<br><tt><font size=2>encoding depending on how compressible the image data
is. </font></tt>
<br>
<br><tt><font size=2>UNQUOTE</font></tt>
<br>
<br><tt><font size=2>Adaptive compression, as they call it may give smaller
compression,</font></tt>
<br><tt><font size=2>but I think you have to compress both ways to prove
which is the best.</font></tt>
<br>
<br>
<br>
<br>
<br><tt><font size=2>Its the overall performance which counts and that's
the only way</font></tt>
<br><tt><font size=2>to approach it.</font></tt>
<br>
<br><tt><font size=2>All the algorithms are tied together to work best
overall </font></tt>
<br><tt><font size=2>ie the compression must work with differential screen
updates</font></tt>
<br><tt><font size=2>and caching, not just on its own.</font></tt>
<br>
<br><tt><font size=2>It's a case of try each in turn and choose the best
for your</font></tt>
<br><tt><font size=2>circumstances.</font></tt>
<br>
<br><tt><font size=2>Obviously other's experiences help and we could do
with</font></tt>
<br><tt><font size=2>more feedback . . . . .</font></tt>
<br>
<br><tt><font size=2>> <br>
> Greetings:<br>
> Toni<br>
> ________________________________________________________________<br>
> Were you helped on this list with your FreeNX
problem?<br>
> Then please write up the solution in the FreeNX Wiki/FAQ:<br>
> <br>
> </font></tt><a href="http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ"><tt><font size=2>http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ</font></tt></a><tt><font size=2><br>
> <br>
> Don't forget to check the NX Knowledge
Base:<br>
> </font></tt><a href=http://www.nomachine.com/kb/><tt><font size=2>http://www.nomachine.com/kb/</font></tt></a><tt><font size=2>
<br>
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