[libreoffice-users] Png vs Jpg

Hi :)

Yes, true.  Png is 'lossless compression' whereas Jpg is lossy but Png is still 
compressed and Gimp can set the compression rate.  


Jpg often introduces strange artifacts (like ripples or the wake from a boat) 
which can inflate file-size!  You see this a lot on badly done logos or images 
that have been manipulated while being jpgs (eg heavily cropped and re-sized),  
I have seen Pngs suffer a little at extreme rates of compression but Jpg 
compression is far worse  even at low levels of compression.  


There are some clever ways of reducing Png sizes so that they can compete 
favourably with Gifs for things like logos and simple stylised images.  I've 
seen very light Pngs that have very low colour range. say only 2 or 3 colours 
and no shading or blending.  The corresponding jpgs have been very much heavier 
and looked messy whereas the png stayed clean.

Regards from
Tom :)




________________________________
From: Isaac Hummel <isaac@daedaleus.com>
To: users@libreoffice.org
Sent: Sat, 30 April, 2011 21:04:55
Subject: Re: [libreoffice-users] exported PDF file size

On 04/30/2011 03:33 PM, Tom Davies wrote:
> PS. Png is also set to take over from Jpg as it also handles larger images
> better and again Jpg is a proprietary format (i think).

PNG will only take over from JPG when bandwidth and storage become irrelevant 
for images. PNG is lossless and so cannot compress as well as JPEG (which is 
lossy). Even high quality JPGs are smaller than PNGs.

-- Isaac Hummel
isaac@daedaleus.com
http://daedaleus.isaachummel.com


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