Further analysis reveals that TigerVNC's Compression Level 5 and 6
(which are basically identical when JPEG is enabled) can already produce
roughly the same compression ratio (within +/- 5%) as the maximum useful
mode in TightVNC 1.3.x, so actually, I think the only thing that might
need addressing here is the fact that the higher Zlib levels are not
needed for Compression Levels 7-9. I can find no dataset for which
moving from CL 6 to CL 9 in TigerVNC produces more than a 5% increase in
compression ratio, and generally this move increases CPU time by a
factor of 4-5. Thus, I would suggest the following modification, which
extends the Zlib levels from CL 6 through CL 7-9 as well:
--- a/common/rfb/TightEncoder.cxx
+++ b/common/rfb/TightEncoder.cxx
@@ -70,9 +70,9 @@ const TIGHT_CONF TightEncoder::conf[10] = {
{ 65536, 2048, 12, 6, 7, 3, 32, 96, 62, SUBSAMP_422 }, // 4
{ 65536, 2048, 12, 7, 8, 4, 32, 96, 77, SUBSAMP_422 }, // 5
{ 65536, 2048, 16, 7, 8, 5, 32, 96, 79, SUBSAMP_NONE }, // 6
- { 65536, 2048, 16, 8, 9, 6, 64, 96, 86, SUBSAMP_NONE }, // 7
- { 65536, 2048, 24, 9, 9, 7, 64, 96, 92, SUBSAMP_NONE }, // 8
- { 65536, 2048, 32, 9, 9, 9, 96, 96,100, SUBSAMP_NONE } // 9
+ { 65536, 2048, 16, 7, 8, 5, 64, 96, 86, SUBSAMP_NONE }, // 7
+ { 65536, 2048, 24, 7, 8, 5, 64, 96, 92, SUBSAMP_NONE }, // 8
+ { 65536, 2048, 32, 7, 8, 5, 96, 96,100, SUBSAMP_NONE } // 9
};
On 1/23/14 4:01 AM, Pierre Ossman wrote:
> On Wed, 22 Jan 2014 17:30:25 -0600,
> DRC wrote:
>
>>
>> My proposal is for TigerVNC to adopt four compression modes: CL 0, CL
>> 1, CL 2, and CL 5. CL 3 and 4 would map to 2, and CL 6-9 would map to
>> 5, and the GUI could be restructured so that it sets the compression
>> level to "low, high, and very high", with a warning that "very high" is
>> only better than "high" in some rare cases.
>>
>> Just a suggestion. I can provide a server-side patch for this if requested.
>>
>
> Interesting stuff. I'd definitely like to know more about the
> discussion and the testing that was done.
>
> I'm shuffling around all of that code at the moment though, so please
> hold off on that patch for a while. :)
>
> Rgds
>
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