Flat, Luma and Chroma filters for Waveform Monitor

[bavc]

Flat, Luma and Chroma filters for Waveform Monitor

[epiil]

I'm not sure if having a flat "filter" makes sense in the digital
environment of QCTools. IIRC, for analog video signals the flat filter
would be used in the context of viewing unmodulated RF, eg., the "RF
envelope". The lowpass filter would be used for viewing luminance as an
expression of IRE values.

On Sun, Feb 15, 2015 at 3:07 PM, clacinak [email protected] wrote:

It would be great to have a "flat" (no chrominance filter), "luma" and
"chroma" filter options for the waveform display.

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#66.

[clacinak]

I would not say that a flat filter is critical, but it can certainly be helpful and is a feature that every other software-based waveform monitor offers. Pics from Premiere attached as an example. You'll find the same thing in FCP, ScopeBox and more.

[epiil]

I see an advantage to having a flat filter (by definition an "unfiltered"
filter, btw) featuring both the luma and chroma characteristics on one
graph. In the context of QCTools this would allow a user to view both the
source picture in one window, and a graph containing luma and chroma
information in the other.

However, IMHO, monitoring chroma in this manner runs counterintuitive to a
vectorscope-measured approach (which is why, in my own workflow, I assign
the flat filter to measure things like RF). Given the limited graphical
output of the available QCTools graphs, it would be difficult to interpret
the data of both signal characteristics meaningfully.

Perhaps the better wish list request is to have dual waveform/vectoscopes
contained within one power window.

On Sun, Feb 15, 2015 at 3:35 PM, clacinak [email protected] wrote:

I would not say that a flat filter is critical, but it can certainly be
helpful and is a feature that every other software-based waveform monitor
offers. Pics from Premiere attached as an example. You'll find the same
thing in FCP, ScopeBox and more.

[image: flat_bars_premiere]
https://cloud.githubusercontent.com/assets/2552814/6204880/02c7d7fe-b528-11e4-87df-9f33384c8dc7.jpg
[image: luma_bars_premiere]
https://cloud.githubusercontent.com/assets/2552814/6204879/02c5cce8-b528-11e4-92a4-95f0ecfdddb2.jpg

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[clacinak]

"However, IMHO, monitoring chroma in this manner runs counterintuitive to a
vectorscope-measured approach"

I can see calling it redundant, but not counter-intuitive. They aren't in
opposition to each other in any way. It's all additive and helpful. As you
suggest, I think it probably comes down to personal preferences and how you
are use to working. I personally would like a flat filter. You mention an
additional wish list request, which I would be fine with as a separate
request but wouldn't replace my original request.

On Feb 15, 2015, at 3:53 PM, Erik Piil [email protected] wrote:

I see an advantage to having a flat filter (by definition an "unfiltered"
filter, btw) featuring both the luma and chroma characteristics on one
graph. In the context of QCTools this would allow a user to view both the
source picture in one window, and a graph containing luma and chroma
information in the other.

However, IMHO, monitoring chroma in this manner runs counterintuitive to a
vectorscope-measured approach (which is why, in my own workflow, I assign
the flat filter to measure things like RF). Given the limited graphical
output of the available QCTools graphs, it would be difficult to interpret
the data of both signal characteristics meaningfully.

Perhaps the better wish list request is to have dual waveform/vectoscopes
contained within one power window.

On Sun, Feb 15, 2015 at 3:35 PM, clacinak [email protected] wrote:

I would not say that a flat filter is critical, but it can certainly be
helpful and is a feature that every other software-based waveform monitor
offers. Pics from Premiere attached as an example. You'll find the same
thing in FCP, ScopeBox and more.

[image: flat_bars_premiere]
<
https://cloud.githubusercontent.com/assets/2552814/6204880/02c7d7fe-b528-11e4-87df-9f33384c8dc7.jpg

[image: luma_bars_premiere]
<
https://cloud.githubusercontent.com/assets/2552814/6204879/02c5cce8-b528-11e4-92a4-95f0ecfdddb2.jpg

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#66 (comment).

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#66 (comment).

[dericed]

Putting waveform and vectorscope in the same display is no problem. To make a 'flat' filter waveform, whether redundant or counter-intuitive, I'd need to better understand how to derive the information to plot from what is available. For instance in the waveform on the left edge it plots values at 9, 20, and 75. But then the flat filter plots every intermediate value between 0 and 40 at one level and also data from -20 to 45. I don't understand how we could plot a -20. Whether in 8 bit or 10 bit the lowest value is 0 which correlates to 0 IRE. The frequencies below 0 IRE were not represented in the digitized samples, only 0-100 IRE. Maybe there some math to get from here to there but I don't know it.

[dericed]

55deb05 addresses @epiil's idea for a "better wish list request"

[dericed]

Here are drafts: https://www.youtube.com/watch?v=EBqU31eZAUA or https://www.youtube.com/watch?v=rrrJETsmNHM.
The process is inferred by reverse engineering with the geq filter, bmdplay and an analog scope with a flat filter, but many parts of this need optimization and more RE.

[epiil]

This filter makes much more sense now that QCTools has capture capability...

On Tue, May 12, 2015 at 2:04 AM, Dave Rice [email protected] wrote:

Here are drafts: https://www.youtube.com/watch?v=EBqU31eZAUA or
https://www.youtube.com/watch?v=rrrJETsmNHM.
The process is inferred by reverse engineering with the geq filter,
bmdplay and an analog scope with a flat filter, but many parts of this need
optimization and more RE.

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[richardpl]

Could someone post more pictures of chroma and flat filter, it is not obvious to me how to implement them. Thanks.
I assume luma one is already available.

[dericed]

I gave the filterchains in the youtube links above which demo the flat filter.

[dericed]

I gave the filterchains in the youtube links above which demo the flat filter.

-vf "format=yuv444p,geq=lum=lum(X\,Y)+(­abs(cb(X\,Y)-128)+abs(cr(X\,Y)-128))*(0.­5-random(1))*0.86,histogram=mode=wavefor­m:waveform_mode=column:waveform_mirror=1­,crop=iw:256:0:0,scale=720:480,setdar=4/­3,histeq"

In this I'm converting y, u, and v to a new y plane in geq by adding the Y + ( abs(U-128) + abs(V-128) * ( 0.5 - random (1) * 0.86 ) and then plotting the result on a waveform.

The 0.5 - random(1) is because flat waveforms plot a range of values rather than points, so the random distributes samples in a range according to the combined offsets of u and v from the 128. That range is then centered off the Y values. The 0.86 is a rough way to convert 8 bit to IRE values to better line up with what's happening on an analog scope. Cc'ing @epiil who knows flat waveforms better than I.

[richardpl]

Hmm, than what about chroma filter?

[dericed]

Not sure what the OP meant. The histogram=mode=waveform already plots chroma. @clacinak, have an example?

[richardpl]

@rebschandler could you post picture of scopebox's chroma filter?

[rebschandler]

[dericed]

looks similar to flat (vertical fill according to saturation), but without the offset by the luma value

[richardpl]

@rebschandler thanks, but I'm looking for one with 0-255 scale.

[dericed]

@richardpl, I think it's using an analog IRE scale of 0-110, which ~ equals the digital 8 bit 0-255 scale. On the other hand, since the values reflect saturation levels I think the max value in a 0-255 scale would be sqrt(128_128+128_128). So a u=0 and v=0 values would fill a range on the 0-255 scale from 0-181.0193359837562.

[richardpl]

Unfortunately that doesnt seem to work so im looking for exact numbers.

[dericed]

@clacinak, please test in https://github.com/bavc/qctools/releases/tag/v0.7.2