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Date: Thu, 29 Jan 2009 09:47:57 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Re: [PATCH 7/7] Add tight encoding (jpeg) to vnc.c
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To: qemu-devel@nongnu.org
Cc: Alexander Graf <agraf@suse.de>

Stefano Stabellini wrote:
> Anthony Liguori wrote:
>
>   
>> If we implement Tight and then use jpeg by default, for most clients,
>> the default is going to be lossy encoding.  While lossy isn't so bad for
>> high detailed images (like pictures), it's pretty terrible for simple,
>> high contrast images (like windows in a desktop).
>>
>> TightVNC has some sophisticated heuristics for determining whether to
>> use jpeg or not (when it's enabled).  I think that sort of heuristic is
>> a prerequisite for enabling tight's jpeg support.
>>
>> FWIW, Tight essentially does hextile encoding but adds zlib
>> compression.  That's probably a better place to start as it should
>> outperform hextile while remaining lossless.
>>
>>     
>
> Another thing to consider is that using jpeg compression is going to
> worsen qemu performances, so I think it should be used only when
> necessary, e.g. the network connection between client and server is  bad.
>   

Most clients I know do not enable JPEG by default.  It requires a user 
to explicitly do so.

Regards,

Anthony Liguori