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TOPIC: Reading Waveform

Reading Waveform 2 years, 8 months ago #17374

  • royfphoto
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The waveform in LW is scaled from 0-100, is this based on RGB (0-255) or R709 (16-235)?
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Re: Reading Waveform 2 years, 8 months ago #17791

you can choose which one you need
right click on the top of the window as far as I remember
Cyril_Kazis

Re: Reading Waveform 2 years, 8 months ago #17794

  • royfphoto
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adjustment is for vector scope not waveform, anyone else?
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Re: Reading Waveform 2 years, 8 months ago #17800

I generated a gradient

16 to 235 shows 0 to 85% on the waveform
0 to 255 shows 0 to 100% on the waveform

from RGB 0 0 0 to RGB 32 32 32 you always get 0% on the waveform

2 possibilities:

the waveform is wrong or the gradient generator is wrong...or both....
Cyril_Kazis

Re: Reading Waveform 2 years, 8 months ago #17806

Hi royfphoto

As far as I can tell Lightworks operates/processes video in a YUV colour space environment not RGB.

It conforms to ITU-R-BT-601 standard for SD
ITU-R-BT-709 standard for HD

The Standard colour space environment in YUV is 16-235 = RGB 0-255
The Expanded colour space environment in YUV is 0-255 = RGB 0-255

I haven't found any switching available in Lightworks for Expanded colour space, so I assume it is set to Standard. I would therefore assume the waveform display scaling would also assume O IRE units to be black and 100 IRE units to be peak white.

FWIW. I notice that there are also no Gammut Limiters or RGB Limiters which can be applied to the O/P within Lightworks but usually these are supplied with any attached I/P O/P hardware devices anyway for example the Black Magic drivers and or Matrox Hardware.

Hope that helps.

Cheers
RO
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Re: Reading Waveform 2 years, 8 months ago #17810

  • khaver
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I created a png graphic in an external photo editing app with a 0 to 255 gradient and imported it into Lightworks. Added it to an edit. The waveform monitor shows a straight diagonal line from 0% to 100%. I created another from 32 to 0 and the waveform monitor shows a straight diagonal line from 13% to 0%.

I don't know for sure but it seems Lightworks works in RGB 0 to 255 (actually it converts to floating point 0 to 1. So what you put in is what you get. As to color space, I don't know. Though in the LwFxResource.dll file there are some references to color space conversion effects. These might get applied automatically at import time or they might be used to convert RGB to YUV for use in the Waveform Monitor.
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Last Edit: 2 years, 8 months ago by khaver.

Re: Reading Waveform 2 years, 8 months ago #17811

  • royfphoto
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Thanks everyone, I need time to think about this.In my previous editor Vegas I could select either 16-235 or 0-255 for the waveform parameters. By selecting 16-235 and outputting to DNxHD the contrast range/gamma was well suited for television viewing, and seemed to conform to what most internet providers wanted.
I know that LW is for the movie industry, just need to know what the waveform and display is really showing.
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Re: Reading Waveform 2 years, 8 months ago #17812

Hi khaver

Thinking and reading a little further into this subject, it appears the term YUV is a bit ambiguous in that it really is a term that is probably relavent more to analogue signals as opposed to digital which uses the YCbCr convention. I would, as you state, assume there would be certain processes where (YUV) YCbCr conversion to RGB would be relevant, say in Colour Correction where colour accuracy is important. Possibly Chroma Keying would be another and so maybe thats where the conversions in an NLE come into play. It appears (YUV) YCbCR processing hides some compression artifacts for example of captured digital video.
Then there are the pure graphics programs that give you the option of selecting how you want to process images. CMYK, RGB, HSL etc but I guess thats a discussion for another time. My Head hurts....lol
I would imagine processing digital video in a purely RGB environment, from what I have read, would require perhaps some fairly hefty processing (Bandwidths etc).

Cheers

Ronnie
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17" Full 1920x1080 LED Display
2 x USB 3, 1 x ESata, 1 Gig Ethernet, HDMI 1.4 O/P 2 x USB 2.0 Ports.
Display Port, Blu-Ray / DVD Recorder
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Re: Reading Waveform 2 years, 8 months ago #17813

  • khaver
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A dev stated a while back that all clips in Lightworks go through a DirectX pass of the GPU. This means that everything gets converted to floating point 0.0 to 1.0 RGB on import and re-enters integer 0-255 on export. YCbCr -> RGB -> YCbCr conversions aren't loss-less so it makes sense for Lightworks to do this only once.

It would be nice if Editshare could release an explanation of exactly what conversions (if any) Lightworks does internally when importing video of different color spaces and standards. Can Lightworks import a 10bit source clip directly into a 10bit project without a 10bit -> 8bit -> 10bit conversion? Can Lightworks export back directly to a 10bit codec?

These are things I would like to know.
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Re: Reading Waveform 2 years, 8 months ago #17814

It would be nice if Editshare could release an explanation of exactly what conversions (if any) Lightworks does internally when importing video of different color spaces and standards. Can Lightworks import a 10bit source clip directly into a 10bit project without a 10bit -> 8bit -> 10bit conversion? Can Lightworks export back directly to a 10bit codec?

Assuming that you don't select 'transcode' when importing, no conversions are done at import time, so 10-bit sources remain as 10-bit once imported. As I recall, when a frame needs to be displayed :

  • It is copied to the GPU then converted to either 8-bit RGB (if your project precision is 8-bit) or 16-bit RGB if your precision is set to 10-bit
  • Aspect-ratio conversion is applied (to match the format selected on the project card)
  • Any/all effects are processed
  • Any letterboxing is applied
  • The image is displayed
  • When exporting, the GPU-based RGB images are converted to the format that is required for the target codec, and then transferred back from the GPU
  • When showing vectorscope/waveform, the GPU images are converted to YUV then transferred back to CPU memory where they are analysed


Hope that helps!
Lightworks development

Re: Reading Waveform 2 years, 8 months ago #17815

  • khaver
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Thanks HH. That's exactly what I wanted to know.
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Re: Reading Waveform (and workflow) 2 years, 8 months ago #17817

Yes, me too! I have a new Sony HD camera with a big, single CMOS sensor and an HDMI output so I plan to record in the field with Blackmagic's new Hyperdeck Shuttle. The Shuttle uses a removable 2.5" SSD which will record native, uncompressed HD video direct from the camera's sensor, thus by-passing any 'on-board' compression algorithm to tape, disk or card.

For post production, I could place the SSD into a docking station, then (without transcoding??) import 'uncompressed' clips directly into LW for editing, colour correction etc. Under this workflow scenario, waveform monitors and vectorscopes are very important tools BUT it is important too that LW itself performs a minimum amount of transcoding or picture manipulation within so final output will remain at optimum quality. Any clues?
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