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Thread: NDI video color band

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    NDI video color band

    I'm using Scan Converter on one computer as NDI source, and Studio Monitor to check the video quality. I happened to run a monitor gray scale test on the source computer, which basically is a grayscale gradient image. (http://www.lagom.nl/lcd-test/gradient.php). It looks smooth on the source computer, but in the Studio Monitor, I can see some color bands in the image. Is it normal? Is this something to do with the color depth?

    I attached a screenshot. Hopefully it is visible here.

    Click image for larger version. 

Name:	grayscale_banding.png 
Views:	31 
Size:	30.5 KB 
ID:	148404

  2. #2
    I took that image, ran it out of NDI Test Patterns into NDI Studio Monitor and then did a screen capture. The grabbed image in a paint program shows the same values for R, G and B in every location that I tried which tells me there is no color in the image, only grey.
    Kane Peterson
    Solutions Architect
    NewTek, Inc.

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    Quote Originally Posted by kanep View Post
    I took that image, ran it out of NDI Test Patterns into NDI Studio Monitor and then did a screen capture. The grabbed image in a paint program shows the same values for R, G and B in every location that I tried which tells me there is no color in the image, only grey.
    Sorry I don't quite follow what you were doing. Which picture did you took? Both the gradient picture from the website in my first post and the attachment picture show colors changing from black to white. How do they have same RGB values?

    But I did try your way, which I took a screenshot of the original gradient picture and fed it to the Test Pattern then into the Studio Monitor, and now the color bands don't show up. Perhaps it is a issue of Scan Converter?

    Maybe I didn't make myself clear about the "color" band. The variation of colors in the original gradient picture from the website looks really smooth, but in my attachment, you can find some not too obvious but still noticeable rectangle bands.

    Thank you.

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    Sorry my bad. Now that it is "grayscale" gradient image, it should be gray. But the bands do exist.

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    Quote Originally Posted by slcf2003 View Post
    I'm using Scan Converter on one computer as NDI source, and Studio Monitor to check the video quality. I happened to run a monitor gray scale test on the source computer, which basically is a grayscale gradient image. (http://www.lagom.nl/lcd-test/gradient.php). It looks smooth on the source computer, but in the Studio Monitor, I can see some color bands in the image. Is it normal? Is this something to do with the color depth?

    I attached a screenshot. Hopefully it is visible here.

    Click image for larger version. 

Name:	grayscale_banding.png 
Views:	31 
Size:	30.5 KB 
ID:	148404
    Converting a Ramp pattern to RGB then to 8-bit YUV can lead to the sort of banding you are seeing.
    If you generate a ramp natively in 8 bit YUV in NDI, it can be smooth.

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    Sorry for the late reply. I don't know much about the pixel format. How can I generate a ramp in YUV in NDI?

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    Quote Originally Posted by livepad View Post
    Converting a Ramp pattern to RGB then to 8-bit YUV can lead to the sort of banding you are seeing.
    If you generate a ramp natively in 8 bit YUV in NDI, it can be smooth.
    Sorry for the late reply. I don't know much about the pixel format. How can I generate a ramp in YUV in NDI?

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    Quote Originally Posted by kanep View Post
    I took that image, ran it out of NDI Test Patterns into NDI Studio Monitor and then did a screen capture. The grabbed image in a paint program shows the same values for R, G and B in every location that I tried which tells me there is no color in the image, only grey.
    I'm also having the same issue in UE4, can you take a look if possible? Thank you.

    https://forums.newtek.com/showthread...th-NDI-for-UE4

  9. #9
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    As Kane says, there's no "color" banding here. What I do see is luma banding - caused by the luminance of the pixels not smoothly changing across the ramp image.

    I think this is just an artefact of NDI's lossy compression. You can see a similar thing by selecting the "Ramp" test pattern with NDI Test Pattern Generator, then viewing that in Studio Monitor. It's quite noticeable with the "Color Ramp" test pattern in the darker areas, too.

    The effect is probably worse if you're using scan converter to grab an image displayed by another application, as there's probably extra rounds of gamma and/or colourspace conversion happening. When you're working in 8-bit colourspaces it doesn't take much to introduced these kinds of artefacts.

    The second images from Unreal Engine are a lot worse, with a serious lack of dynamic range in the shadows. That's definitely not just NDI artefacts.

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