Trying to do Definitive Colour Tests

[wiseant]

Hi all,

I don't know whether this post should be in "Avisynth Usage" or "Capturing Video" forum, but since I'll be using Avisynth tools I've opted for Avisynth Usage . . .

I'm planning on entering the uncertain waters of Video Color Testing

There seems to be a lot of confusion regarding YUY2, YV12, RGB along with the avisynth tools: ConvertoRGB, ...YUY2, ...YV12, Levels, Limiter, and ColorYUV

What I am looking for is a critque of my method(s)

So in order to make sense of this, my plan is as follows

1. Capture from VHS Tape to .avi using HuffYUV codec in YUY2 640x480 capture format
this will create an interlaced clip

Now will this clip have a maximum color range of 16-235 or 0-255?

I will do two captures in VirtualDub

a) with Extend luma black point and Extend luma white point enabled
range should be 16-235?

b) with Extend luma black point and Extend luma white point disabled
range should be 0-255?

I will use AvsP to preview clips a and b and use a ColorPicker tool to find the whitest whites and blackest blacks and see what values I find

I will keep the YUY2 color space and then evaluate the changes done by Avisynth tools: Levels, Limiter, and ColorYUV as follows:

Levels
re clip a
Levels(16, 1, 235, 0, 255, coring=false)
this should scale from [16,235] to [0,255]

re clip b
Levels(0, 1, 255, 16, 235, coring=false)
this should scale from [0,255] to [16,235]


Limiter
re clip b
Limiter(16, 235, 16, 240)
this should clip pixels under 16 to 16 and over 235 (or 240) to 235 (or 240).


ColorYUV
for clip a
ColorYUV(levels="TV->PC")
this should map the YUV values from (16,235) to PC values (0,255)

for clip b
ColorYUV(levels="PC->TV")
this should map the YUV values from (0,255) to TV values (16,235)


My goal here is to evaluate how consistent the results from each tool are but more importantly, that any values <16 and >235 do in fact get clipped/mapped to 16 and 235 respectively

In some quick tests done previously I noticed that <16 values did get "converted" to 16, but values >235, i.e. 255 did not become 235 but remained at 255


After testing these I plan to do VHS to MPEG-2 using MainConcept Capture program:
capture at 720x480 8000 kbps CBR

from MPEGEncoder_en.pdf October 28, 2005

"Input video is RGB 16-235

Ticking the checkbox Input Video is RGB 16-235, particular black and white values are preserved. During encoding and decoding the RGB color space with R=G=B=16 is used, which corresponds to the color black. Furthermore, the RGB color space with R=G=B=235 is used, which corresponds to the color white. Normally the values for white are R=G=B=0 [typo - should be 255], and for black R=G=B=255 [typo - should be 0]. The specification ITU601R now defines black (Y=16) and white (Y=235), i.e. the real video signal receives values which are "blacker than black" or "whiter than white" (so called super-black and super-white values). These super-black and super-white values get lost in the normal PC RGB 0..255 color space, but they are preserved with the Input video is RGB 16-235 option."

I don't really understand the explanation above - does it mean that MainConcept while capturing/encoding is capturing in RGB color space and encoding in YV12 colorspace, i.e. converting "on-the-fly" from RGB to YV12 - if so, and I want to make a DVD compliant clip for viewing on my TV, by demuxing and then using Muxman, should I enable or disable "Input Values are 16-235"?

clip c "Input Values are 16-235" enabled

clip d "Input Values are 16-235" disabled

Here, clip c should range from 0-255 and clip d from 16-235?

Here however my color space will be YV12 (default MPEG-2 Capture?) although I could capture in 4:2:2. Any comments re problems with YV12 versus YUY2 re capturing. Any comments on the advantages/disadvantages of demuxing 4:2:2 MPEG-2 with DGIndex or ProjectX?

Any suggestions, comments, criticism is appreciated.

TIA

[EncodeThis]

Wiseant,
Be careful on what capture card you use to capture your video. Some capture cards will pass through 16-235 color range and not clip any colors that go beyond that spectrum. Some capture cards will clip colors that go beyond the 16-235 color range and what will happen is that your encodes will look dark.

I know for a fact that the blackmagic design cards clip colors that go beyond the 16-235 color range and AJA cards will not. But if you are not sure on what your capture card will do just call the manufacturer tech support and they should be able to tell you.

Just a couple of things you should be aware of.

Hope this helps

[wiseant]

Hi EncodeThis

I never thought about that - looks like I need to look into this

BTW I have a MiroDC30 (Hardware MJPEG = RGB32 (I presume) and an ATI VE, and a Genius BDA713x . . .

I plan on using the ATI and the Genius cards for testing . . .

[Mug Funky]

I know for a fact that the blackmagic design cards clip colors that go beyond the 16-235 color range and AJA cards will not. But if you are not sure on what your capture card will do just call the manufacturer tech support and they should be able to tell you.

example? i've been able to capture out-of-range stuff before on a BMD card without issue (getting those values out of quicktime without changes is another story though).

true, we hardly ever do analog at work, and usually that's run into a digi deck first.

[EncodeThis]

I spoke to BMD's tech support and they told me this themselves.