YUV PC/TV question

[tiffytaffy]

I know there are a lot of discussion about this topic and I read many of them. Can someone explain why I get a luma Y minimum of 7 instead of 16 with following scrip:

ColorBars(pixel_type="YV12")
ColorYUV(analyze =true)

Thanks

[Gavino]

The lower part of the color bars (the 'pluge') contains a section (-4 IRE) that is 'blacker than black', with Y=7, used in adjusting for correct brightness of your monitor/TV.

See http://avisynth.org/mediawiki/ColorBars.

[tiffytaffy]

@Gavino
Ok, thank you.

Here my next problem that belongs to this topic. I have an AVI source file with full range in RGB24
(sorry but I can't upload any image. Get an error: not valid)
I used following script to convert it to YV12 16-235

AviSource("test.avi",audio=false,pixel_type="RGB24").AssumeTFF()
ConvertToYV12(matrix="PC.709",interlaced=false)
SmoothLevels(preset="pc2tv",gamma=0.90, Lmode=2,darkSTR=100, smooth=100,dither=50)
ColorYUV(analyze =true)

This works fine for me. ColorYUV reports a range between 16 and 235. I used the same script(without ColorYUV(analyze =true)) to encode wit MeGui :

program --crf 20 --colormatrix bt709 --output

After that I double checked the target file(using DGAVC Index)

AVCSource("test.dga")
ColorYUV(analyze =true)

Now ColorYUV reported a range between 0 and 255. Why not 16 and 235?
What's happened?

[Keiyakusha]

why you went through such a weird way to convert your source from PC to TV scale is beyond me, but what you sse after encoding... If picture looks right and ColorYUV reports out of range pixels - these may be just artifacts added during encoding.

[tiffytaffy]

Is there a way to encode without out of color range artifacts? I looked at a commercial blue-ray and noticed that the video is completely in range(16-235). How do they do this?
I use a little Sony Cyber-shot for my videos and ColorYUV(analyze=true) reports me a range from 16 to 255. Maybe it should be 16-235 and the internal h264 encoder add artifacts too. Is it true that consumer camcorder normally use TV-Range? I can't find any information about this for my product.

When I watch a clip on my TV I would assume that 16 is black and 235 is white. So write this script and create a blue-ray disc:

left = BlankClip(length=30000, width=960, height=480, fps=24, color=$FFFFFF,pixel_type="YV12",audio_rate=48000)
left = AddBorders(left, 0, 300, 0, 0, $000000)
left = AddBorders(left, 0, 0, 0, 300, $191970 )
left=ColorYUV(left,analyze =true)

right = BlankClip(length=30000, width=960, height=480, fps=24, color=$FFFFFF,pixel_type="RGB32",audio_rate=48000).killaudio()
right = AddBorders(right, 0, 300, 0, 0, $000000)
right = AddBorders(right, 0, 0, 0, 300, $191970 )

right=ConvertToYV12(right,matrix="PC.709",interlaced=false)
right=ColorYUV(right,analyze =true)
comb = StackHorizontal(left, right)

return comb

But on my TV the left part has no black and white. It looks washed out. I guess I misunderstand something, but what?

[Keiyakusha]

I believe there is someone who have better ideas of what is going on with your workflow but since noone is answering, maybe they don't really understand where is the problem?
Personally I don't understand what your goals is.
You have RGB source. I assume this source has PC range levels as normal RGB usually would be, you using Converttoyv12() (with the right matrix= depending on resolution) before encoding and that's all you need to do. If there will be some out of range pixels after encoding - this is not something you should worry about. Its how encoder works, it doesn't means your blacks is no longer black or something like that.
converttoyv12(matrix="Rec601") is for SD resolution, converttoyv12(matrix="Rec709") is for HD. You shouldn't use PC.709.

If resulting file looks wrong after that then you have playback problems which are pretty common.

[Ghitulescu]

Is it true that consumer camcorder normally use TV-Range? I can't find any information about this for my product.

It depends on the camcorder, some do clip at 235, while others do record whiter-than-white signals (so up to 255) to avoid the clipping. This is generally not noticed since there's no white limitation on TVs (there is however a PAL/NTSC limitation in terms of signals).

[tiffytaffy]

Thank you for answering.
My RGB-AVI source was only a test case. My workflow is:

Source:
Camcorder source: MTS container with h264 stream, 50fps progressive 1920x1080, YV12, color range=unknown. Now I assume it is 16-255 or the internal camcorder encoder creates artifacts and it is 16-235.

Target:
Samsung LCD TV. The TV has the color options AUTO and NATIVE. After reading in some forums, I think native means 0-255. AUTO is not clear. It could be 16-235 or the TV try to analyze and detect the color range. That is why I wrote the test script above(with blank clip and borders). With this script AUTO and NATIVE shows no difference on TV. Left side looks gray and right side looks black and white. This let me assume that the AUTO modus analyze the video. and detect the correct range from 0 to 255. In this case my problem is following: When encoding with x264 creates out of range artifacts, then the TV have to detect a wrong color range.
However, your answers were helpfully for me. I guess you are right and it is not a real problem. I only try to understand the correlations. I think in my case it is a good solution, when I don't convert the color range and let the thing as they are.

[Didée]

When checking the difference between "Auto" and "Native" on a Samsung LCD TV, don't use greyscale clips. Instead, use something with strong red colored objects. Then you'll see a difference. It seems to me this setting is rather related to BT.601 / BT.709 color schemes.

However you are correct - there are several things "not quite clear" about what-does-this-setting-do in Samsung TVs.