bVNC: Allow user to control JPEG compression level for Tight encoding

[bwDraco]

While it may make sense on a slow connection, the JPEG compression level used for the Tight encoding is a bit excessive for my taste, resulting in strong compression artifacts at times. I'd like to be able to control the JPEG compression level so that I can get the right trade-off between quality and bandwidth requirements, without falling back on the less efficient Hextile encoding.

Ideally, this should be possible while the session is running, just as the desktop TigerVNC client allows, so that I don't need to disconnect and reconnect to make the change.

[bwDraco]

I'd like to expand upon this to state that the zlib compression level should be adjusted as well. The desktop TigerVNC client states that compression levels above 3 have little benefit; however, it is set to 6 within the app's code. Given the limited CPU resources on mobile devices, changing this value (line 263 of eclipse_projects/bVNC/src/com/iiordanov/bVNC/RfbProto.java) to 3 would noticeably improve performance without significantly increasing data use.

Again, though, there should be a user setting for JPEG compression.

[bubnikv]

I would be interested in a fine control of JPEG compression level as in the TurboVNC client. This would allow one to pick the right compression for low bandwidth conditions to still support smooth enough interaction (coding in an editor / IDE, browser / PDF scrolling). On desktop systems, the fine control provided by the TurboVNC client makes a difference: With a bit of JPEG artifacts, one can get a bit better interactivity with TurboVNC/TurboVNC server than with RDP/XRDP server on Linux.

[Dirk-LG]

Could it be that this type of image processing affects the contents of the image (brightness, gamma)? Effectively, bVNC has a much brighter image than other VNC viewers.

[iiordanov]

I can't quite see how that could be the case!

Give me an example client that uses TightVNC encoding (jpeg) that is dimmer than bVNC please.

On Wed, Dec 16, 2020, 3:47 PM Dirk [email protected] wrote:

Could it be that this type of image processing affects the contents of the image (brightness, gamma)? Effectively, bVNC has a much brighter image than other VNC viewers.

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[Dirk-LG]

I'm not familiar with the technologies behind but I can tell you my observations. I'm running UserLand X11, and then I connect one of the following VNC viewers:

• bVNC, RealVNC or MultiVNC viewer on Android 10 (shared screen or desktop mode)
• RealVNC viewer on PC (Windows 10, or Linux)

And bVNC shows a much brighter output.