#1  
07-23-2019, 07:48 PM
VideoTechMan VideoTechMan is offline
Free Member
 
Join Date: Feb 2012
Location: Texas
Posts: 186
Thanked 26 Times in 23 Posts
Have a quick question in regarding waveform monitors, I know they are used to examine brightness and black levels on the output signal from whatever deck I am using as well as catching Macrovision signals on certain tapes.

I was thinking of the possibility of obtaining a waveform monitor in order to do that once I start some transfers, as I could make the adjustments with the proc amp prior the signal going to the capture device.

I know there are scopes that can be done in software too, but not certain of the accuracy of the software ones compared to the hardware based monitors.

Any ideas or thoughts on a waveform monitor? The few broadcast VTRs I have got the proc amp controls built in for adjustments and TBC with built in proc controls as well. I will be testing the AJA FS1 for this operation since it has S-Video in and output jacks.
Reply With Quote
Someday, 12:01 PM
admin's Avatar
Ads / Sponsors
 
Join Date: ∞
Posts: 42
Thanks: ∞
Thanked 42 Times in 42 Posts
  #2  
07-24-2019, 12:22 AM
jwillis84 jwillis84 is offline
Free Member
 
Join Date: Aug 2017
Location: College Station, TX
Posts: 800
Thanked 217 Times in 174 Posts
Its really only good for setting the IRE levels, approximately. The waveform varies all over while the tape is being played.

A vectorscope was usually paired with a waveform scope to adjust color and saturation, but again it varied all over the place from minute to minute.. so its mostly an exercise in imprecise approximation.

The IRE is important since if its too low or too high, or does not span the dynamic range of the broadcast standard then you can loose information that cannot be recovered after the digital capture. But its not a precise art.. as I said it varies during the playback. A VTR is generally not a precise instrument for reproducing signal, its a servo motor with a feedback loop that stretches and relaxes tape and introduces all sort of variability into the field lines and frame.

The color and saturation on the other hand can be rotated back and forth after capture as long as the color sample is complete, or as near as you can afford with an uncompressed stream. If you compress it however before you correct it then you loose that ability.

Waveform and Vector scopes were mostly used for broadcast transmissions to stay within the FCC guidelines. They are interesting from the standpoint that you can see whats going on, and sort of match that up to what you might know about photography.. but in practice for a VHS playback capture they don't really add much. And they were based on the use of a Broadcast Composite signal with a lot more stability and resolution than what you could fake with the composite coming out of an old VCR.

I've seen people suggest they would use the Composite out at the same time as the S-Video out and with a Tape that had something like a Test pattern on it. But there are a lot of holes in that logic. The test tape is not a real tape, and its an artificial setup that is nothing like the real conditions that went into producing the tape your trying to capture. Its even likely the capture tape will not have even been created on the machine you'll be playing it back on.

I think people think they can calibrate a VCR like a flatbed scanner or a monitor.. but you can't.. its vastly different. Every playback is unique, tape conditions at the time of recording are different, condition of the tape, age, tracking ability of the VCR for that particular tape. Even if you could calibrate your VCR to null out problems in the video amps, it would only be good for that one test tape.. and you really can't even for a test tape. A photo is more or less a static field uniform across the frame taken in a tenth of a second. A Video frame is a series of variable lines drawn in two fields to make one frame. Each line is going to vary, each field is going to vary, each frame is going to vary and compound the variables. If your trying not to get a "ticket" from the FCC for broadcasting signal that leaks into other radio bands.. scopes make sense.. but if your trying to calibrate from the studio camera lens to the television in your living room.. that's a misunderstanding of what the scopes were for..

Digital is a whole other ball of wax.. if you bypass the VCR and the analog reproduction scenario.. you can always playback a digital file twice and get the same signal. Laser disc is digital. Over the Air HDTV is digital. You playback a VHS tape twice and you will get two different signals.. they will be different in brightness, contrast and color.. and vary from minute to minute. Even film like from a projector is closer to digital, same picture, same color if you play them back twice.. but not an analog tape through a "slinky machine".

On the other hand.

Once you've captured your analog video and made it digital. Any corrections you apply to that digital copy will "stay" and will be reproducible the same way twice, thrice or a quadrillion times. So it makes more sense to not worry about the color or saturation during capture as long as you capture as much of the color sample space as possible.

The color component is actually layered on top of the luminance signal. IRE more or less determines whether you capture the luminance signal or loose parts of it. The color is wrapped around it in a kind of Fourier space.. sort of like FM radio.. its all there if you got the luminance.. and you can rotate it back and forth like spinning a color wheel.. the colors maintain their radial separation like the primary and secondary colors on a color wheel.. that's baked in at the original studio cameras.. so for us.. for good or bad.. we get one control "Hue" or used to be called "Tint" to rotate it around. Color correction specialist can dabble in rearranging the relationships between colors.. but mostly its a futile gesture since they can't predict what the true relationships were in the studio.. if that information wasn't captured and transmitted in the original signal.. they are "guessing" and trying to add something back in that they have no real way of knowing.. sort of like Turner Classics making a B&W film color.. you can do it.. but its like Nickleback doing the Beetles.

I'm not saying you can't "ride" the proc-amp wheels and try to correct as you go along, for the entire playback.. you can sort of do that.. but imagine trying to correct for that variable after the fact on the digital copy? You've just added another variable.

The way the color shifts back and forth is sort of like the train whistle that rises in pitch and then falls as the train passes you.. its like red shifting and blue shifting if you've seen Cosmos. The color information on the luminance carrier is itself another waveform, higher pitch.. and when the "slinky machine" that is your VCR pull or pushes the wheel in your tape cassette it pushes and pulls the tape and that see saws the wavelength of that color signal "skewing" it in one direction and another. Overall its not bad.. but its very hard to predict and depending on the conditions in that tape housing it might be one way at the beginning of the tape and entirely different at the far end. For a one hour tape the color variations might not be bad.. for multiple recordings made at different times, across days or weeks on an eight hour tape.. well you can't just set it and forget it.. if you really want real time color correction.. your going to have to make micro adjustments all the way and try nulling those out in your digital copy.. eek!

Last edited by jwillis84; 07-24-2019 at 12:54 AM.
Reply With Quote
The following users thank jwillis84 for this useful post: lordsmurf (07-24-2019)
  #3  
07-24-2019, 01:53 AM
lordsmurf's Avatar
lordsmurf lordsmurf is offline
Site Staff | Video
 
Join Date: Dec 2002
Posts: 13,610
Thanked 2,458 Times in 2,090 Posts
Quote:
Originally Posted by jwillis84 View Post
A VTR is generally not a precise instrument for reproducing signal
Every playback is unique, tape conditions at the time of recording are different, condition of the tape, age, tracking ability of the VCR for that particular tape.
The color is wrapped around it in a kind of Fourier space.. sort of like FM radio.. its all there if you got the luminance.. and you can rotate it back and forth like spinning a color wheel..
The way the color shifts back and forth is sort of like the train whistle that rises in pitch and then falls as the train passes you.. its like red shifting and blue shifting if you've seen Cosmos. The color information on the luminance carrier is itself another waveform, higher pitch.. a
FYI, this is related to why "VHS colors fade" is a really stupid myth.
Again, it's not a printed/negative photograph.

(Trivia: slides/slidefilm really doesn't fade unless mis-stored. WWII slides can look like you shot it yesterday.)

- Did my advice help you? Then become a Premium Member and support this site.
- For sale in the marketplace: TBCs, workflows, capture cards, VCRs
Reply With Quote
  #4  
07-24-2019, 01:54 AM
sanlyn sanlyn is offline
Premium Member
 
Join Date: Aug 2009
Location: N. Carolina and NY, USA
Posts: 3,648
Thanked 1,307 Times in 982 Posts
Quote:
Originally Posted by jwillis84 View Post
Laser disc is digital.
Nope. Laser disc is analog.
Reply With Quote
  #5  
07-24-2019, 01:59 AM
lordsmurf's Avatar
lordsmurf lordsmurf is offline
Site Staff | Video
 
Join Date: Dec 2002
Posts: 13,610
Thanked 2,458 Times in 2,090 Posts
Quote:
Originally Posted by sanlyn View Post
Nope. Laser disc is analog.
Analog signal on digital medium.
And video is analog, but audio can be digital.

Such a screwy format. Not quite VHS, not quite DVD. The missing link!

- Did my advice help you? Then become a Premium Member and support this site.
- For sale in the marketplace: TBCs, workflows, capture cards, VCRs
Reply With Quote
  #6  
07-24-2019, 09:10 AM
jwillis84 jwillis84 is offline
Free Member
 
Join Date: Aug 2017
Location: College Station, TX
Posts: 800
Thanked 217 Times in 174 Posts
Looking at the output of a vectorscope, and knowing its called "Hue" literally "discernable difference in color relative to another color" or "Tint".. I've often wondered why its not just called (knob). Twisting the control knob or the sliders in a pro-amp or proc-amp program doesn't really do anything to the colors except shift them back and forth "relative" to their transmitted relationship.

Its not like you have three independent color controls for R,G,B like you have in a colorist tool for Photoshop or something.. its kind of a clue that proc-amps aren't really for correcting color.. only skewing their "fixed" relationship on the color wheel like basting a turkey on a rotisserie. If you want to white balance a scene that has to be done in the studio under the lights that actually illuminate the camera sensor.. beyond that point its artificially guessing.

Last edited by jwillis84; 07-24-2019 at 09:45 AM.
Reply With Quote
  #7  
04-02-2024, 07:35 AM
lordsmurf's Avatar
lordsmurf lordsmurf is offline
Site Staff | Video
 
Join Date: Dec 2002
Posts: 13,610
Thanked 2,458 Times in 2,090 Posts
Quote:
Originally Posted by jwillis84 View Post
Its not like you have three independent color controls for R,G,B like you have in a colorist tool for Photoshop or something..
This is an ancient thread, but was linked to today.

FYI, Sima has RGB proc amps. Those are rare, and interesting. Real-world use case is generally achieved by stacking the Sima RGB with a quality SignVideo YUV. This can get interesting when you stack TBCs. At that point, it's either a wild restoration, or some sort of video/glitch art scenario.

- Did my advice help you? Then become a Premium Member and support this site.
- For sale in the marketplace: TBCs, workflows, capture cards, VCRs
Reply With Quote
Reply




Similar Threads
Thread Thread Starter Forum Replies Last Post
Adding a Waveform / Vectorscope to workflow Sergei316 Project Planning, Workflows 0 03-28-2019 07:56 PM
Usefulness of a vectorscope/waveform monitor? ehbowen Restore, Filter, Improve Quality 0 03-15-2018 11:07 AM
Proc amp filter adjustments, ATI capture card? metaleonid Restore, Filter, Improve Quality 37 04-16-2017 04:07 PM
Advanced VCR adjustments for VHS capture? JasonCA Capture, Record, Transfer 7 01-01-2013 09:56 PM
Will I have to make adjustments daMaddColombian Videography: Cameras, TVs and Players 1 08-08-2005 04:28 AM

Thread Tools



 
All times are GMT -5. The time now is 08:40 AM