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Brightness / Black Levels

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Don Davies
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We are using a HD-223 to output a MP4 video to a pico projector HDMI.

The colors output from the HD-223 are significantly brighter than what we see when the same video is output via HDMI to the same projector from a laptop.  Also, the blacks produced by the Brightsign appear to be significantly more grey.

Any idea why the Brightsign's output is different?  Is there anything we can do on the hardware level to compensate?  Or, any suggestions for an alternative encoding format?

The video in question is 1280x800.  Encoding is H264, Main@L4.2, in a MP4 container.  The average bitrate is 17.5Mbps.

Thanks for your help.

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    ^UD\_$

    If you load a black image, does it look grey?

    https://i.ytimg.com/vi/vmnWJBRrVYo/maxresdefault.jpg

     

    Is it possible that the projector keeps different brightness/contrast settings for different signals?

    Can you simply correct the picture settings on the projector to get the desired result?

  • 0
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    Don Davies

    Thanks for the reply.

    We can live with the different brightness level -- still, it is strange.  The projector is definitely not remembering settings, but brightness appears higher from the Brightsign.  The blank JPG looked about the same as what we see with video.  Generally, turning the projector's brightness setting down by about 7% helps.

    There's another issue about the output from the Brightsign that is more problematic.  Output from the Brightsign has courser gradation -- our videos have images that "transition" from the black background smoothly.  So, there should be many levels of grey between the black background and the content.  This transition from black to white appears quite smooth when the H264 MP4 is output from a laptop.  From the Brightsign, the transitions are rougher, not showing as large of a range of color.  Does this make sense?

    Our designer found that if she increases the pixel noise on the image, the gradation produced by the Brightsign gets smoother.  Of course, this approach presents its own problems.

    Any idea what might be going on, or any suggestions on how to fix?  We've tried different encoding... CBR20/25/30, VBR (peak 25).. MP4/MOV containers... nothing seems to make much of a difference once it gets encoded into the Brightsign.

    Thanks so much for reading!

  • 0
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    ^UD\_$

    When you compare between laptop and player, are you using the same cable?

    Is your HDMI cable relatively long?

    You may have a color gamut issue in your workflow.

    I'm not sure if applicable, but h.265 may offer better image quality, when it come to banding.

    Can you include pictures that are showing the degraded image vs. the laptop generated image?

     

  • 0
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    Don Davies

    The HDMI cable was about 12'.  I substituted a 3' cable, no perceivable change.

    H265 does show better gradation -- great suggestion!  We used Handbrake, as Adobe Media Encoder was limited to 20Mbps.  Handbrake (OSX) seemed to videos that with imporoved video quality.  To get best results, we used the highest quality setting (3-4) we could go to without seeing lag during playback.

    Does anyone have an encoder recommendation?  Our designers typically use Adobe Media Encoder (CC 2015) on OSX, is it is pre-installed on their laptops.  As we are discovering as we explore Handbrake, AME may not be the best option.

    Will report back tomorrow with still photos comparing a projector displaying a video from Brightsign HDMI vs the same video from a MacBook (HDMI).

  • 0
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    Bright Scripters

    BrightSign themselves recommend using Handbreak, so look no further.

    We sometimes use the command line ffmpeg on OS X, which allows automation, detailed control, and an opportunity to pull one's hair out in the process.

    The MacBook may apply a display calibration profile to the output, based on how it recognizes the projector.

    What you are seeing coming out of the MacBook, may not be a reference point to compare the BrightSign to...

     

  • 0
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    Ben Conwy

    Echoing this issue. I've had it on all models of BrightSign. I believe it has to do with the player limiting the dynamic range on the HDMI output. I've run into this same issue with PC's and have had to change the graphics card to output the "full" range as opposed to "limited." Brightsign, are there any options to change the color space output? Or any other workarounds? It's very clear to see when using an LED wall . 

  • 0
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    Ben Conwy

    Update, if I run the signal through a Decimator MD-HX and come out SDI then my blacks are where they should be. Not an ideal workaround, but it will do. 

  • 0
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    Nathan

    I had the same issues and heard the following from Brightsign support:

    In TV resolutions (1280x720, 1920x1080, etc) the Brightsign players output TV/video signal in YCbCr format, rather than computer/graphics RGB. TV/video black is not true RGB black, as that's "Superblack" and is special in broadcast TV land, along with pure white, "Superwhite."

    So if you can feasibly drive the player at a computer resolution rather than a TV resolution, that might give you the blacker black that you need.

    and this:

    Technically you can change modes via roVideoMode, but changing modes usually requires a reboot, so you'd need to implement the change via a custom autorun which gets messy since you'd need to reapply your change every time you update BrightAuthor, unless you write your own script which is even more work and maintenance.
    http://docs.brightsign.biz/display/DOC/roVideoMode

    Also, DVI output uses RGB colourspace for all modes, so if your wall processor has a DVI input, that may be the way to go.  It might work to do a HDMI->DVI->HDMI conversion as well, since the HDMI connection knows whether it gets dropped to DVI or not. 
  • 0
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    Peter Behle

    Hello together,

    I had the same problems a few years later: The problem was the video material needed a tag for coulour space Rec.709. After I rendered it again everything was fine. I hope this helps everyone having the same problem... 

  • 0
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    Vijayan T

    I am seeing the same issue in the BrightSign XD4 model. Output from PC displays super-black in the monitor. But the same video's output from BrightSign XD4 is gray.

    I tried the video rendering with color space Rec.709. It doesn't work.
    I don't know how to change the mode via roVideoMode. Someone, please explain the solution to me.

    Thanks in advance.

     

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