Encoding issue on bright colors on Mac

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  • #24717

    Hi there

    Recently I notice an issue on color shift & pixelation. It only becomes very noticeable when the screen on server side has bright colors e.g. visiting Reddit. Anything with bright red on a dark background is a good test like the one below. Screenshots to demonstrate the issue I saw:

    • NX with H264 at max quality: nx_h264_max.png
    • Apple Screen Sharing at max quality: apple_vnc_max.png
    • The test image (a screenshot of the live website): “Screenshot 2019-12-09 at 12.58.23 PM.png”
    • URL of the live webpage tested

    Note the pixelation of small features in red such as words and the dullness in bright colors.

    Server is Catalina 10.15.1 (I saw the same on Mojave before upgrade). It runs AMD GPU with Metal support at 2560×1440 resolution. H264 software encoder. NX display quality at maximum. I’ve also tried VP8 and MJPEG encoding. See the same problem.

    Client is Mojave. Also played with different combinations available on NX display settings to no avail.

    Cheers & thanks


    Hi kvic,

    it seems the ‘lossless refinement’ feature is not being used. Can you send send server (https://www.nomachine.com/AR10K00697) and client (https://www.nomachine.com/DT10O00163#2.2) logs so we can take a further look? You can send them to forum[at]nomachine[dot]com.


    Thanks for the logs. Please check if any of the these helps:

    1) turn off UDP (Edit connection -> Advanced -> uncheck ‘Use UDP communication for multimedia data’);

    2) uncomment and set the EncoderMode key (in /Applications/NoMachine.app/Contents/Frameworks/etc/node.cfg) to the following:

    EncoderMode bitrate

    (then restart the server)


    Hi fra81

    Thanks for the prompt help. I tried your suggestion but no difference unfortunately. Based on in-line comments in the file, I also tried ‘EncoderMode quality’ but no difference either.




    I wasn’t able to reproduce your problem. Could you send a screenshot of the scaling options from the display settings of both your client and server Macs?


    Hi there,

    Server side has four items listed under “Scaled” resolutions:

    • 2560×1440
    • 1600×900
    • 1080p
    • 720p

    Client side has exactly the same items.

    I tried to set server to different scaled resolutions in macOS. I also realized that NX client can request custom resolution as well as setting to match client. Played with them individually or in combination. Make no difference.

    I believe the issue may be before the encoder (as it happens in h264, VP8 and MJPEG). Perhaps a common setting applicable to all of them in the encoding pipeline.

    I’m no expert in video encoding. Google pointed me to discussions about color space. In particular, some people mentioned YUV 4:4:4 vs YUV 4:2:2. The latter hurts bright colors in non-video materials (such as graphics and text). Don’t know if it’s relevant but worth checking.



    Thanks for info!

    Finally we reproduced something similar between two Macs in our labs. I’ll let you know the results of investigations.

    About color spaces you are right, but NoMachine dealt already with this problem (see https://www.nomachine.com/FR03M02907).

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