# Calculation of Color Rate - NTSC

1. There is a lot of advice on this forum about recommended capture pixel format for color. Generally 4:4:4 is considered overkill and 4:2:2 is considered the best we can do from an NTSC signal (8mm in my case).

I tend to question everything, so I have attempted a calculation, but not sure if scan lines per frame should be 480 or 525 - used 480:

2. Consumer video tape has far less chroma resolution than theoretically possible by the NTSC spec. Even 4:1:1's 176 samples (across the 704 pixels of the active picture) is sufficient for the chroma. Take one of your 4:2:2 caps and try this:

Code:
`Interleave(last, MergeChroma(last, BilinearResize(width/4,height).Spline36Resize(width,height)))`
That reduces the chroma resolution from 352 samples per line to 88. Can you see mouch of a difference?
3. Originally Posted by jagabo
Consumer video tape has far less chroma resolution than theoretically possible by the NTSC spec. Even 4:1:1's 176 samples (across the 704 pixels of the active picture) is sufficient for the chroma. Take one of your 4:2:2 caps and try this:

Code:
`Interleave(last, MergeChroma(last, BilinearResize(width/4,height).Spline36Resize(width,height)))`
That reduces the chroma resolution from 352 samples per line to 88. Can you see mouch of a difference?
I will try that when I get back home. In the meantime, you have (as usual) clarified a few things for me; however, you have also caused me to question my assumptions. From https://en.wikipedia.org/wiki/Chroma_subsampling:

[Attachment 53386 - Click to enlarge]

Trying to figure out your statement:

Even 4:1:1's 176 samples (across the 704 pixels of the active picture) is sufficient for the chroma.
...I realize my math is wrong in the spreadsheet. Looking at a group of 8 (4 wide x 2 high) pixels, the denominator should be 8 and pixel width should be 704. The corrected calculation is:

[Attachment 53590 - Click to enlarge]

If my assumptions are correct on color content of the original signal (i.e., based on color carrier modulation frequency), color content lies a bit below 4:2:2. Reality is probably different, as I'm sure will be demonstrated by your code.

A question: Is my use of 480 scan lines correct?

The chart is updated below:
post 2584924
4. In a perfect theoretical NTSC analog signal, yes 4:2:2 is sufficient for capture. But you're dealing with a consumer analog tape. The chroma that's stored on the tape has far less resolution than the NTSC spec allows for.

Yes, 480 scan lines is correct. The actual active picture is 485 scan lines -- the topmost scanline containing actual picture on the second half of the line, the bottom most scanline only the first half of the line, and 484 full scan lines in between. When captured those half lines become full lines, for a total of 486 lines. But even those 486 lines usually don't all contain real picture information. Some lines are used for closed captions and other flags. From consumer tape there is head switching noise at the bottom of the frame. So typically only 480 scan lines are captured. 480 has the additional benefit that it's mod 32-- so mod 32 and mod 16 codecs can deal with it.

The remainder of the 525 scan lines that define the full NTSC signal are used for sync in analog TVs.

Someone posted a full 525 line cap from a VHS tape a while back:

5. Originally Posted by GrouseHiker
...I realize my math is wrong in the spreadsheet. Looking at a group of 8 (4 wide x 2 high) pixels, the denominator should be 8 and pixel width should be 704. The corrected calculation is:

[Attachment 53388 - Click to enlarge]

If my assumptions are correct on color content of the original signal (i.e., based on color carrier modulation frequency), color content lies a bit below 4:2:2. Reality is probably different, as I'm sure will be demonstrated by your code.
Don't forget that analog video tape based format use the color under format which is about 629 Khz vs 3.5Mhz or whatever for TV broadcast, It gets upsampled after leaving the tape but still too noisy to be compared to a broadcast TV.

https://forum.videohelp.com/attachment.php?attachmentid=53390&stc=1&d=1590094102
6. I'm getting way beyond my knowledge level, but comparing to the NTSC standard, the bandwidth contained on tape appears quite a bit less:

[Attachment 53391 - Click to enlarge]

If bandwidth is the proper comparison, the Video8 has (based on the Sencore sheet) 743 kHz chroma while NTSC standard shows 2 MHz chroma. Is that apples-to-apples?

I'm now wondering if my calculation is proper for NTSC... should I use bandwidth instead of subcarrier frequency? If yes, that would really bring the numbers down. Maybe bandwidth relates to color bit depth and subcarrier frequency relates to sampling interval?

Another thing that's got me stumped is the pixel color sampling is based on two, stacked, 4-pixel groups. If a scan line is one pixel high, where does the second, 4-pixel group come from?
7. 483 scan lines per frame + 42 lines vertical blanking = 525 scan lines.

or 262.5 lines per field * 2 fields = 525 scan lines.

Are you dealing with a 4:3 aspect ratio throughout?

I used to know this stuff by heart; now I have to sit down and figure it out.

Keep in mind that your analog 8mm NTSC tape has a phase-modulated color subcarrier (sine wave) so you have to be cautious when doing calculations for digital capture.

That line rate doesn't look right, either. Should be more like 15,734 Hz or 3.579545 × 2/455 MHz. You also have to factor in horizontal blanking (10.9 us).

I get 188 cycles of 3.579545 subcarrier per active H (52.65 us, excluding H blanking). Does that sound right?
8. Originally Posted by chris319
483 scan lines per frame + 42 lines vertical blanking = 525 scan lines.

or 262.5 lines per field * 2 fields = 525 scan lines.
I guess 525 should be used in the scan-rate calculation with respect to timing. Even though we're only capturing 480 vertical, the line-to-line timing is based on 525.

Originally Posted by chris319
Are you dealing with a 4:3 aspect ratio throughout?
Yes, 4:3 display .. 3:2 (720x480) Capture

Originally Posted by chris319
Keep in mind that your analog 8mm NTSC tape has a phase-modulated color subcarrier (sine wave) so you have to be cautious when doing calculations for digital capture.
I researched this a bit... Camcorderpedia states:

A video standard (or video system) describes the properties of a particular video signal used by a device (such as a camcorder). For example, the NTSC standard used for broadcasts and baseband video in the Americas, Japan, Korea, and Taiwan, defines a frame rate of 29.97 fps (frames per second), 525 horizontal lines, and a color subcarrier at 3.58MHz. Camcorders sold in these regions must be able to generate a signal that complies with this standard.

This is not to be confused with a format, which defines how the video is encoded or recorded to a medium (this typically has regional standards of its own); and in the case of tape formats, what kind of tape to use, and cassette dimensions. Physical properties of a format are usually universal.

Tape formats used in camcorders usually have their own unique variants of their native standard.
I believe this blows my whole premise of trying to calculate how much information can be produced off an 8mm tape and translate that to a minimum capture format.

Originally Posted by chris319
That line rate doesn't look right, either. Should be more like 15,734 Hz or 3.579545 × 2/455 MHz. You also have to factor in horizontal blanking (10.9 us).

I get 188 cycles of 3.579545 subcarrier per active H (52.65 us, excluding H blanking). Does that sound right?
Yes. That's what the spreadsheet outputs when 525 lines are used.

The various questions/comment have led me to a different way of looking at this:

The 8mm player is sending out a signal intended for TV with a resolution of ??? x 480-ish. Without knowing the best-possible horizontal resolution from 8mm, it seems the answer can't be calculated... back to trial and error and looking at pixels.
9. Originally Posted by jagabo
Consumer video tape has far less chroma resolution than theoretically possible by the NTSC spec. Even 4:1:1's 176 samples (across the 704 pixels of the active picture) is sufficient for the chroma. Take one of your 4:2:2 caps and try this:

Code:
`Interleave(last, MergeChroma(last, BilinearResize(width/4,height).Spline36Resize(width,height)))`
That reduces the chroma resolution from 352 samples per line to 88. Can you see mouch of a difference?
NO!!!!!!!!

Maybe it's worth trying to capture Video8 at 240 x 480 and resize to see of the software does it better than the player.
10. Another complication is that you haven't separated chroma and luma. You're sampling them together. Your 8mm analog original doesn't know about subsampling.

For H sampling the minimum is 4 x 188 = 752 samples (this is for the visible part of the scan line and does not include horizontal blanking).

You could also use 768 x 486 which is compliant with SMPTE 259M. It will capture a few pixels of H blanking and a few lines of V blanking, no big deal.

You also have to consider whether your digitized video will play with the correct aspect ration.

858 x 483 will capture all of your scan lines and make a 16:9 picture.

In 2020, where are you going to find a 4:3 display? They're all 16:9 now.
11. On top of that the resolution of the camera or broadcast was even with less resolution....

Accordig to that Sencore tech tips paper... Hi8 was the best analog tape format, even better than U-matic.... shame about those crappy optical sensor chips used in those cameras. though Canon had some good models.. L-2, EX1, only for the semi pro user..
12. Originally Posted by chris319
Another complication is that you haven't separated chroma and luma. You're sampling them together. Your 8mm analog original doesn't know about subsampling.
I was thinking about this... I expect there is more luma information on the tape than chroma, so minimum sampling rate (i.e., horizontal pixels) should probably be based on luma resolution on the tape. However, the decision on pixel format is still open... i.e., does 4:1:1 produce the same quality as 4:2:2. Although there is probably no way to calculate, color depth with Video8 capture is probably less than 8 bit, so don't waste drive space with 10-bit capture.

Originally Posted by chris319
For H sampling the minimum is 4 x 188 = 752 samples (this is for the visible part of the scan line and does not include horizontal blanking).
Where does the "4 x 188" come from?

Originally Posted by chris319
You could also use 768 x 486 which is compliant with SMPTE 259M. It will capture a few pixels of H blanking and a few lines of V blanking, no big deal.
I was actually thinking along these lines in the beginning until I realized (correctly or incorrectly) the sample "window" is capturing actual scan lines vertically, not interpolating (expanding or compressing) the vertical scan lines to your vertical capture pixels. Is this correct?

Originally Posted by chris319
You also have to consider whether your digitized video will play with the correct aspect ration.

858 x 483 will capture all of your scan lines and make a 16:9 picture.

In 2020, where are you going to find a 4:3 display? They're all 16:9 now.
The way I understand it, capturing at 858 x 483 and displaying at 16:9 will simply make everything w i d e.
13. Originally Posted by Eric-jan
On top of that the resolution of the camera or broadcast was even with less resolution....

Accordig to that Sencore tech tips paper... Hi8 was the best analog tape format, even better than U-matic.... shame about those crappy optical sensor chips used in those cameras. though Canon had some good models.. L-2, EX1, only for the semi pro user..
That's what I am learning:

From lyberty.com/encyc/articles/tech/vid_horizontal_resolution"

Video Format.............................. Horizontal Resolution (resolution width)
Standard VHS............................. 210 Vertical "Lines"
Hi8............................................... 400 Lines
Laserdisc......................................425 Lines
DV...............................................5 00 Lines
DVD............................................540 Lines(?) [some actual DIGITAL sizes: 720(w)x480(h), 704(w)x480 or 352(w)x480 ]
From donsnotes.com/tech/video-resolution:

...VHS, 8mm, and 3/4-inch U-Matic VCRs can record about 240 lines of resolution. These, incidentally, are black-and-white lines or luminance resolution. Color sharpness is much lower but is not very noticeable to the eye. Since luminance resolution is responsible for most of what we preceive as a sharp picture, we will talk about luminance resolution. SVHS and Hi8 VCRs can record and play back 400 lines of luminance resolution. This higher resolution is only seen if you are using the Y/C connectors. If you use the composite outputs of these machines, the resolution is generally reduced to 330 lines. Broadcast television also uses 330 lines as its maximum picture resolution...
14. This statement from wikipedia.org/wiki/Chrominance, indicates Chroma Subsampling is related to bandwidth, not the carrier frequency:

Separating RGB color signals into luma and chrominance allows the bandwidth of each to be determined separately. Typically, the chrominance bandwidth is reduced in analog composite video by reducing the bandwidth of a modulated color subcarrier, and in digital systems by chroma subsampling.
If this is correct, my calculation approach in the spreadsheet is WRONG, and I have no idea how to convert the calculation to use bandwidth.
15. I don't know what are you trying to achieve here? The wheel has already been invented. What you can do is get a pro capture device that adhere to the SMPTE 259M standards, Capture at 720x486 4:2:2 8Bit, then crop to 704x480. the extra 6 lines will get rid of the head switch and V blanking pulses and the padded 16 pixels (8 on each side) that was added in the ITU-Rec 601 (CCIR-601 or D1) standards and adopted by every capture card out there will be removed. You will be left with about 95% of clean video as the picture shows bellow (no aspect ratio flag set yet).
From there if you want to reduce size encode to H.264 4:2:0 8Bit, give each pixel a SAR of 10/11 and keep a decent audio quality @ 192Kbps.

16. Originally Posted by dellsam34
I don't know what are you trying to achieve here? The wheel has already been invented. What you can do is get a pro capture device that adhere to the SMPTE 259M standards, Capture at 720x486 4:2:2 8Bit, then crop to 704x480. the extra 6 lines will get rid of the head switch and V blanking pulses and the padded 16 pixels (8 on each side) that was added in the ITU-Rec 601 (CCIR-601 or D1) standards and adopted by every capture card out there, You will get about 95% of clean video as the picture shows bellow (no aspect ratio flag).
From there if you want to reduce size encode to H.264 4:2:0 8Bit give each pixel a SAR of 10/11 and keep a decent audio quality @ 192Kbps.
Unfortunately, my captures haven't matched the quality of the one you posted.

While I waited for a replacement player to come in, I was trying to prove to myself 4:2:2 8-bit is the best we can do (or maybe overkill). I have no problem capturing 4:4:4 10-bit, but I'm thoroughly convinced this would be WAY overkill for Video8 capture. I have the Magewell Pro Capture HDMI card, and the eBay non-digital camera came in late yesterday. Guess I'll be riding that wheel that was already invented. I'll include a comparison with this new camera back in my thread comparing Composite, S-Video, and DV... hopefully it will be better.
17. I will have to research the answer to your 4 x 188 question.

The way I understand it, capturing at 858 x 483 and displaying at 16:9 will simply make everything w i d e.
What aspect ratio is your display hardware expecting? As I said, where are you going to find a 4:3 display in the year 2020? If this is for distribution to a mass audience, I think it's safe to assume it will be viewed on a 16:9 display, 4:3 displays having gone the way of the dinosaur.

I tried making a video of a test pattern with a circle on it and had to use 858 x 483 so the circle would come out looking round on my 16:9 monitor.

You can simulate some of this. Do you know how to program graphics or write an ffmpeg script?
18. You would not gain anything from 4:4:4 at least visual, 10bit comes in handy if you do a lot restoration with filters otherwise 8 bit should be fine, shame that most script type application work in 8 bit only. S-Video is the best output and closest to the tape. it has been compared already. What you need is a good camcorder with line TBC.
19. Originally Posted by chris319
As I said, where are you going to find a 4:3 display in the year 2020? If this is for distribution to a mass audience, I think it's safe to assume it will be viewed on a 16:9 display, 4:3 displays having gone the way of the dinosaur.
You don't have to have a 4:3 TV even in 2030, that's what the aspect ratio flag used for, If you keep the video at 720 you will see two grey bands on the sides. The active horizontal video resolution for all analog video formats was set to 704 by standard, but it is not always in the center some videos have more black area on one side than others, that's the whole purpose of adding the 16 padded pixels. But with software like Vdub you have the option to crop as many pixels as you want on each side as long as the total removed pixels is 16. Once you have only active video then you have to correct the aspect ratio by setting the SAR to 10/11 because capture cards used more resolution horizontally than what the 4:3 aspect ratio calls for, which is good for better details.
20. As I said, I made a test at 720 or 768 (I forget which) using a test pattern with a perfect circle, and the circle was distorted, i.e. not perfectly round on my monitor which is set for 16:9.

Maybe there was a flaw in the way I generated the file (ffmpeg) but that's what I got. I was trying to emulate the O.P.'s 4:3 original image.

I'm sure the O.P. doesn't have a test pattern on hi 8 tape.
21. Originally Posted by GrouseHiker
Originally Posted by dellsam34
I don't know what are you trying to achieve here? The wheel has already been invented. What you can do is get a pro capture device that adhere to the SMPTE 259M standards, Capture at 720x486 4:2:2 8Bit, then crop to 704x480. the extra 6 lines will get rid of the head switch and V blanking pulses and the padded 16 pixels (8 on each side) that was added in the ITU-Rec 601 (CCIR-601 or D1) standards and adopted by every capture card out there, You will get about 95% of clean video as the picture shows bellow (no aspect ratio flag).
From there if you want to reduce size encode to H.264 4:2:0 8Bit give each pixel a SAR of 10/11 and keep a decent audio quality @ 192Kbps.
Unfortunately, my captures haven't matched the quality of the one you posted.
Even with his image you can see that the chroma channels have much less horizontal resolution than the luma:

[Attachment 53450 - Click to enlarge]

Code:
```ImageSource("frame.jpg")
ConvertToYV24()
StackVertical(StackHorizontal(last, GreyScale().SubTitle("Y")), StackHorizontal(Tweak(sat=3.0).UtoY().Subtitle("U"), Tweak(sat=3.0).VtoY().Subtitle("V")))```
Note that saturation was increased for the U and V plots in order to have more contrast in the images.

A simlar plot from one of your YUY2 video:

[Attachment 53453 - Click to enlarge]

And a true YV24 video (downscaled from 4K to SD)

[Attachment 53455 - Click to enlarge]
22. Originally Posted by chris319
As I said, I made a test at 720 or 768 (I forget which) using a test pattern with a perfect circle, and the circle was distorted, i.e. not perfectly round on my monitor which is set for 16:9.

Maybe there was a flaw in the way I generated the file (ffmpeg) but that's what I got. I was trying to emulate the O.P.'s 4:3 original image.

I'm sure the O.P. doesn't have a test pattern on hi 8 tape.
You may have the wrong aspect ratio to begin with, I've tested this process already, But I will do an analog camcorder test to confirm it.
23. Do you have a test pattern or something with a perfect circle that you can shoot with your camcorder?
24. Originally Posted by chris319
Do you have a test pattern or something with a perfect circle that you can shoot with your camcorder?
I'll figure out something doesn't have to be a pattern, a CD on the wall or a clock should be fine.
25. Originally Posted by chris319
Do you have a test pattern or something with a perfect circle that you can shoot with your camcorder?
I can draw something in CAD, but I know how it's going to turn out. To produce the original, real-life proportions, the videos have to be resized to square pixels (PAR of 1:1). I could crop my 4:3 top and bottom to produce 16:9, but I'm not interested in doing that. For these home videos, the edge bands are fine when someone displays on a wide monitor or TV:
26. Originally Posted by jagabo
Even with his image you can see that the chroma channels have much less horizontal resolution than the luma:
Those are VERY dramatic examples that demonstrate the "shallow" (if that's the word) color off the 8mm tape.

LOVE that code - keep it coming!
27. I think dellsam has a camcorder he can use to shoot some 4:3 footage of a round object for a test.

To do it right you need to measure the on-screen dimensions of a round object rather than eyeball it, so his test is potentially very useful.
28. Originally Posted by chris319
I think dellsam has a camcorder he can use to shoot some 4:3 footage of a round object for a test.

To do it right you need to measure the on-screen dimensions of a round object rather than eyeball it, so his test is potentially very useful.
You should check to make sure your monitor is displaying its "native resolution" when viewing these tests. As far as I know, native resolution doesn't distort the image to fill the screen.
29. For both captured 720x480 and cropped 704x480 the PAR is the same which is 10/11. With 704 the DAR is exactly 4:3 but for 720 it is slightly wider (exactly 16 pixels wider), but the active 704 of the 720 is exactly 4:3. Also 486 is not a legal resolution in the SDTV standard, it is a transitional step after capturing and it should be cropped to 480 immediately, The same thing should apply to 720 and should be cropped to 704 right after capturing but because a lot of people are confused between 720 DVD anamorphic widescreen which it contains all 720 active pixels with DAR of 16:9 and the 720 capture (704 active + 16 padded pixels) with a DAR of 4:3, they tend to keep it that way, but they are completely two different things.

Wikipedia

If you want to make 16:9 with 1:1 PAR (square pixel) you will have to crop to 704 and convert the 704 to 640 and add approx 213 dummy pixels horizontally, If you want 16:9 with the same 10:11 PAR you will have to add approx 235 dummy pixels to 704 or 219 to 720.
30. Originally Posted by dellsam34
For both captured 720x480 and cropped 704x480 the PAR is the same which is 10/11. With 704 the DAR is exactly 4:3 but for 720 it is slightly wider (exactly 16 pixels wider), but the active 704 of the 720 is exactly 4:3. Also 486 is not a legal resolution in the SDTV standard, it is a transitional step after capturing and it should be cropped to 480 immediately, The same thing should apply to 720 and should be cropped to 704 right after capturing ....
Thanks for clarifying the SDTV standards. Would these numbers apply if the video is produced for a computer screen instead of a TV?

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