Really bad composite video out on Pi 3?

[amihart]

I have a CRT and I wanted to hook my Pi 3 up to it, but the composite video out quality is horrendous.

I configured it to be the same resolution/aspect ratio as my CRT but the image doesn't fit the screen and is stretched taller than it and curved at the top so it's not even exactly straight, there's a weird rainbow-ing effect with everything, and it flickers like crazy. Changing it from 480i to 240p gets rid of the flicker but then the resolution is so low I can't read the text, and all the other problems are still there.

I know it's not an issue with my Pi being damaged because I have two Pi 3s with the same issue. I know it's not the CRT because this is my main CRT for retro gaming and every console I have looks beautiful on it. I'm pretty sure it's not the composite cable because I bought a much higher quality cable to fix the issue but there was no change.

Anyone else having issues with the composite video quality? It's unusably bad.

[karrika]

This sounds like you have connected the pins wrong. Perhaps you have mixed ground with audio due to wrong cable pinout?

[rpiMike]

Are you aware there are different types of 3.5mm to phono cables :

https://www.element14.com/community/thr ... hread=true

[klricks]

Post a photo of your screen.
Flickering...... almost unreadable text is normal for composite especially on a CRT TV. Composite on a LCD TV are quit a bit better. The low resolution is fixed and can't be changed. Motion video is OK but static images and text are barely usable.
You can change the frame buffer size in config.txt to get the full image on the screen but the text will be unreadable.

[mahjongg]

Strange Raspberry PI's output a nearly perfect quality composite video signal, in either Pal or NTSC, as can be seen in this video, where composite video is used, and you can see the quality of the desktop picture:

https://www.youtube.com/watch?v=4KxZu3uaqGY

obviously PAL video will never reach the quality of a digital video signal (HDMI) but I must say that I was pleasantly surprised how good the quality was when I first tested it. Much better than say a Commodore 64.

[amihart]

This sounds like you have connected the pins wrong. Perhaps you have mixed ground with audio due to wrong cable pinout?

No clue, after my first cable didn't work I just looked up cables people specifically said worked well for the Pi and bought one of those. Of course, it didn't work well at all. I'd assume if ground was mixed with audio I'd have audio problems, but I don't at all. Audio comes through great.

Are you aware there are different types of 3.5mm to phono cables :

https://www.element14.com/community/thr ... hread=true

If you're claiming my cable is wrong, then please recommend me a specific cable. I already bought a cable that many many people said worked on the Pi. Also, I don't see how that thread is even talking about the same problem. If the rings were mixed up on the TRRS cable, then I wouldn't get a picture at all, yet I do get a picture. It's just bad, really bad.

Post a photo of your screen.
Flickering...... almost unreadable text is normal for composite especially on a CRT TV. Composite on a LCD TV are quit a bit better. The low resolution is fixed and can't be changed. Motion video is OK but static images and text are barely usable.
You can change the frame buffer size in config.txt to get the full image on the screen but the text will be unreadable.

This is by no means normal. As I pointed out, this is the CRT I play all my retro games on. It has very nice video out, text is never unreadable and has almost zero flicker normally. This is specific problem to the Pi.

I did change the frame buffer and it does not match what it states, if I set it to be the same pixel density as my screen I get an image that does not fit the screen and is distorted.

[amihart]

Here is what I mean by "rainbowing". That should just be white but instead it has multiple colors coming out of it. (Ignore the colors in the background, you only see those because my camera is zoomed in so close. I'm talking about the colored pixels floating around the white cursor, mainly on the top and bottom left of it.)


I don't get why only the Pi gives me these issues while I've never seen them on any other device. I have Debian on my Wii and the composite output looks completely fine.

[pcmanbob]

Hi.

If you want to check the cable for yourself you can using this diagram.
video should go to centre pin on your video plug and ground to the outer connection at the tv end of the cable.

[drgeoff]

Here's what I mean by the picture seems distorted or bent almost. As you can see, that is the top of my CLI window. It should be straight, but on the right-hand side of the screen, it's about 1 pixel from the top of the screen, but on the left-hand side, it's like 5 pixels from the top of the screen. I put red boxes on both sides to point out the issue, they should be equal height if the screen was straight but instead they are not.

The geometrical distortion is caused by the CRT display. It is next to impossible for a RPi, even one with faulty components, to do that.

What make and model number is the display?

What OS are you running? I wasn't aware that Raspbian gives the option of 240p.

Your cable is wired correctly. You would not get anything near to a stable and coloured display if it had video and ground reversed.

[amihart]

Here's what I mean by the picture seems distorted or bent almost. As you can see, that is the top of my CLI window. It should be straight, but on the right-hand side of the screen, it's about 1 pixel from the top of the screen, but on the left-hand side, it's like 5 pixels from the top of the screen. I put red boxes on both sides to point out the issue, they should be equal height if the screen was straight but instead they are not.

The geometrical distortion is caused by the CRT display. It is next to impossible for a RPi, even one with faulty components, to do that.

But why does no other device give me this issue? That's what confuses me. I'm wondering if it's just a glitch with the display when the signal isn't right.

What make and model number is the display?

It's this display. Is it possible for my display to somehow be compatible with every other device but not the Pi for some reason? Does the Pi output composite slightly differently than a native composite out device?

What OS are you running? I wasn't aware that Raspbian gives the option of 240p.

Yeah, Raspbian has 240p. You just set sdtv_mode to 16 (for NTSC, I forget what PAL is).

Your cable is wired correctly. You would not get anything near to a stable and coloured display if it had video and ground reversed.

That's what I assumed, but that's why I'm so puzzled. I would assume it was just my display if my display didn't work perfectly for every other device. I can run an emulator on my Wii and emulate Mario 3 on NES and it looks great. I can emulate Mario 3 on NES on my Pi and I get rainbow-ing flickery colors. Even if I change it to 240p the rainbow-ing is still there. I also can't get it to display 1-to-1 with my display either and fit perfectly in it, while that's no issue on my Wii.

[fruitoftheloom]

Yeah, Raspbian has 240p. You just set sdtv_mode to 16 (for NTSC, I forget what PAL is).

This is for clarification....................

""Output 240p (instead of 480i) on composite RCA""

https://github.com/raspberrypi/firmware ... -283471444

[PiGraham]

Yeah, Raspbian has 240p. You just set sdtv_mode to 16 (for NTSC, I forget what PAL is).

Why do you mention 240p? Surely you need 480i for NTSC, typically 640 x 480 interlaced.

Any rotation or curvature of the edge of the image can really only be produced in the TV. Maybe it's there for other devices but they don't output a horizontal line so close to the top edge of the screen so you don't see it. IIRC a Wii overscans so you don't see an edge.

[klricks]

I did some experiments on my 27" CRT TV. RPi 2 V1.1 with Rasbian Desktop.

Using composite (NTSC) default settings:
Text on terminal screen is readable but jittery. Also horizontal lines are jittery. Very annoying. Gives me a headache...... Some distortion of image at top and side edges.

At default the screen area is larger than the display. This makes some programs useless. For example the Python Games - Tetris and other games are not playable as the playing field extends off the bottom of the visible screen. (The playing area windows of these games are programed at a fixed size with no provision to resize). Setting the frame buffer scaling will fix this. Note that setting frame buffer changes scaling. It does not change composite resolution which is fixed.
Setting the frame buffer to a minimum of about 800x600 allows the Tetris game to fit on screen and the game works OK, however text displayed in terminal is much worse.

240p setting: sdtv_mode = 16 (NTSC), default framebuffer.
The jitter on text and lines is almost completely eliminated. Much better in that respect.
Same distortion on edges.
Text on terminal console is still hard to read.
At framebuffer 800x600 text characters on terminal become unreadable multi color blobs.
Games are OK. Larger text in game such as "Press any key to start", is just readable.

[amihart]

Why do you mention 240p? Surely you need 480i for NTSC, typically 640 x 480 interlaced.

Because it's better for older games. NES for example only outputs 240p, so trying to force it to be 480i just worsens the images as it has to stretch it out and it ends up being flickery, while 240p is not flickery at all and is much clearer. 480i is only better for devices that actually output 480 lines of pixels, like the GameCube or Wii. But for NES or SNES it's pointless to try and display them in 480i, it just worsens the quality. My CRT be default doesn't even display 480i for a real NES or SNES, it will skip every other line in order to display a 240p image.

Any rotation or curvature of the edge of the image can really only be produced in the TV. Maybe it's there for other devices but they don't output a horizontal line so close to the top edge of the screen so you don't see it. IIRC a Wii overscans so you don't see an edge.

Okay let's just forget that, let's assume the image always being stretched too tall and the curving is purely just my display and not the Pi's fault. I can pad the edges a little bit to make it fit in the display, and the curvature is so slight I don't notice it much.

The biggest issue I have is the rainbowing and that's clearly not my display's fault. Let's just focus on that. The rainbowing is impossible not to notice and is a huge eyesore. It's by far the biggest issue and it's the one I care most about fixing. The colors simply aren't clean and the image quality is very bad because of it. I can't chalk this one up to "just being my TV" because then I should get that on other games, but I can run the same game on my Pi that I actually own on the original system and the rainbowing isn't there.

The rainbowing is impossible not to notice as well, especially when it's in 480i, because the rainbow colors flicker and it's really bad.

[drgeoff]

That TV has a comb filter in its NTSC decoder. If there is a menu option to turn it off, give it a try.

(A comb filter could give the colour fringeing effects if the horizontal frequency of the video signal is not quite bang on the NTSC spec.)

And ensure the Digital Noise Reduction is also turned off. (That can also introduce artifacts on signals which don't quite have the same number of TV lines as the NTSC spec.)

[amihart]

That TV has a comb filter in its NTSC decoder. If there is a menu option to turn it off, give it a try.

(A comb filter could give the colour fringeing effects if the horizontal frequency of the video signal is not quite bang on the NTSC spec.)

And ensure the Digital Noise Reduction is also turned off. (That can also introduce artifacts on signals which don't quite have the same number of TV lines as the NTSC spec.)

I cannot find an option for comb filtering. I already disabled DNR because it makes games noticeably blurrier, and turning it back on again didn't help either.

[PiGraham]

Why do you mention 240p? Surely you need 480i for NTSC, typically 640 x 480 interlaced.

Because it's better for older games. NES for example only outputs 240p, so trying to force it to be 480i just worsens the images as it has to stretch it out and it ends up being flickery, while 240p is not flickery at all and is much clearer. 480i is only better for devices that actually output 480 lines of pixels, like the GameCube or Wii. But for NES or SNES it's pointless to try and display them in 480i, it just worsens the quality. My CRT be default doesn't even display 480i for a real NES or SNES, it will skip every other line in order to display a 240p image.

If that's true I have learned something today, although I don't understand it. Could you link me to an explanation of why outputting 240p into an interlaced NTSC TV improves the picture?
AFAIK any NTSC TV is a 480i device and will display two interlaced fields no matter what you feed it. For 240p and I'm pretty certain it will display two consecutive fields of the 240p as if it were interlaced. Since both fields will be identical for static images you may see less flicker, but may see a comb effect on moving vertical edges because two consecutives 240p fields will be different for fast moving graphics, but you get the same thing on 480i, just with a finer pitch comb.

Granted if you have a display that support 240p and a console that outputs 240p a matched setup will be the best option.

I see nothing in the specs of your TV to suggest it can display progressive scan. It will display 240p by interlacing it, showing each successive field between the lines of the previous field.

Have you tried with 480i out of the Pi? That should match the TV best, but maybe not the game itself.

As for your main issue of "rainbowing" I wonder if it could be poor impedance matching on the wiring. What you show looks a bit like ringing which would be typical of poorly matched impedance. I've never seen a TV with option on termination, but some CCTV monitors allow 75 ohm termination to be switched on of off (so that several monitors can be connected to the same line without loading the signal, which would lead to a dark image. If there is an option of a switch turn it to 75 ohm.
It could also be high capacitance smearing out high contrast edges. Looking at the photo the bright character shows tails as the bright level fades out rather than switching to black in a nice sharp edge. How long is the cable? Long cables could be a problem. Is it coaxial screen cable? I assume it is since that's typical for cables using RCA plugs or 3.5mm jacks. Is it just wires or is there any audio circuitry in it? That would cause problems.

You know that CRTs have red, green and blue dots or stripes to make a colour picture, don't you? I assume so, but mention it to be thorough. What looks like a white character is bright red, bright green, bright blue. If the edge fades out the signal level can drop from the red strip to the green to the blue and you see a little rainbow on the edge. If you can reduce the exposure setting on your camera so that the middle of the character isn't blown out to white you sill see RGBRGBRGB there as well, but each triple should be similar to the ones next to it

[drgeoff]

AFAIK any NTSC TV is a 480i device and will display two interlaced fields no matter what you feed it.

Not true.

I won't say that the following applies to all NTSC TVs but it certainly applies to many if not the vast majority. It definitely applies to the purely analogue, CRT based ones with no digital processing.

The horizontal and vertical sweeps are determined by the sync information. When fed with 480i (technically 525 line video) the vertical sync info occurs every 262.5 line periods. That is what gives the interlace. Alternate field lines trace a path between the lines of the other fields. This is what makes the refresh rate of a point on the screen be 29.97Hz. Feed the system with an even number of lines (eg 524 or 526, colloquially "240p") and the interval between vertical sync infos is an integer number of lines. The 240-ish visible picture lines of all fields fall in the same place. The refresh rate of any point is 59.94 Hz.

[dudealert2018]

Sorry if this needs special formatting to be posted here:

# For more options and information see
# http://rpf.io/configtxtreadme
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
disable_overscan=0

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
overscan_left=16
overscan_right=16
overscan_top=16
overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=2
#hdmi_mode=87
#hdmi_cvt 480 800 60 6 0 0 0
#dtoverlay=ads7846,cs=1,penirq=25,penirq_pull=2,speed=50000,keep_vref_on=0,swapxy=0,pmax=255,xohms=150,xmin=200,xmax=3900,ymin=200,ymax=3900
#display_rotate=3

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
sdtv_mode=0 #This is NTSC

sdtv_aspect=1 #This is 4:3 aspect ratio


#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable the lirc-rpi module
#dtoverlay=lirc-rpi

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

program_usb_boot_mode=1

gpu_mem=512
#gpu_mem_256=128
#gpu_mem_512=256
#gpu_mem_1024=256

overscan_scale=1


#arm_freq=1000
#sdram_freq=500
#core_freq=500
#over_voltage=2
#temp_limit=80 #Will throttle to default clock speed if hit.

[drgeoff]

@dudealert2018
What was your point that your post has failed to make?

[PiGraham]

AFAIK any NTSC TV is a 480i device and will display two interlaced fields no matter what you feed it.

Not true.

I won't say that the following applies to all NTSC TVs but it certainly applies to many if not the vast majority. It definitely applies to the purely analogue, CRT based ones with no digital processing.

The horizontal and vertical sweeps are determined by the sync information. When fed with 480i (technically 525 line video) the vertical sync info occurs every 262.5 line periods. That is what gives the interlace. Alternate field lines trace a path between the lines of the other fields. This is what makes the refresh rate of a point on the screen be 29.97Hz. Feed the system with an even number of lines (eg 524 or 526, colloquially "240p") and the interval between vertical sync infos is an integer number of lines. The 240-ish visible picture lines of all fields fall in the same place. The refresh rate of any point is 59.94 Hz.

You may be right there. If every 240p 'field' is shown with no vertical shift it would reduce flicker especially on contrasty horizontal lines.

Some TVs may be better at this resync every VSYNC pulse than others. Some PLLs may lock faster than others. I suspect a set prone to rolling picture will not do well with 240p because it takes a few VDYNCs to lock-on.

The vertical offset can be set by VSYNC to HSYNC timing or just from the number of lines and a constant sweep rate.

[drgeoff]

Some TVs may be better at this resync every VSYNC pulse than others. Some PLLs may lock faster than others. I suspect a set prone to rolling picture will not do well with 240p because it takes a few VDYNCs to lock-on.

The vertical offset can be set by VSYNC to HSYNC timing or just from the number of lines and a constant sweep rate.

You are merely giving further proof that you don't really understand video and TV technology. While PLL type circuitry has been in common use in the horizontal scan section for years (eg valve TVs with "flywheel sync") the same is not true in the vertical section.

Line sync pulses are separated from mixed sync by a differentiator whereas field sync pulses are obtained by integrating. The former is much more susceptible to noise. That is the motivation for the horizontal 'PLL'. Incidentally when domestic VCRs appeared, TVs often had a designated VCR channel button which shortened the time constant of the horizontal loop to better track the timing variations caused by the mechanics of the replay process.

[PiGraham]

TVs often had a designated VCR channel button which shortened the time constant of the horizontal loop to better track the timing variations caused by the mechanics of the replay process.

That's a fair point since this is from the end of the VCR era, a CRT (reviews from 2007?) with digital circuitry designed to cope with unstable field to field timing. What was a benefit for noisy UHF signals became a liability with sloppy timing form tape mechanisms.
I know about the history of old CRTs and not so old digital frame grabbers. This is a bit of a mix of the two.

So is that the benefit of 240p - that it avoids flicker at the cost of resolution?

[bensimmo]

That TV has a comb filter in its NTSC decoder. If there is a menu option to turn it off, give it a try.

(A comb filter could give the colour fringeing effects if the horizontal frequency of the video signal is not quite bang on the NTSC spec.)

And ensure the Digital Noise Reduction is also turned off. (That can also introduce artifacts on signals which don't quite have the same number of TV lines as the NTSC spec.)

I cannot find an option for comb filtering. I already disabled DNR because it makes games noticeably blurrier, and turning it back on again didn't help either.

/Just as an aside
Have you looked in the service menu (if you haven't already) ?


Also pop you config.txt or tvservice setting you use up.


I was just reading through a link given above and came across this, same thing possibly ?
https://github.com/raspberrypi/firmware ... -287445721

[Burngate]

That TV has a comb filter in its NTSC decoder. If there is a menu option to turn it off, give it a try.
(A comb filter could give the colour fringeing effects if the horizontal frequency of the video signal is not quite bang on the NTSC spec.)
And ensure the Digital Noise Reduction is also turned off. (That can also introduce artifacts on signals which don't quite have the same number of TV lines as the NTSC spec.)

I cannot find an option for comb filtering. I already disabled DNR because it makes games noticeably blurrier, and turning it back on again didn't help either.

I wasn't much involved in NTSC, but in PAL televisions or monitors as far as I know, there was never an option for removing the comb-filtering.

The colour information was split off the rest of the video information by a simple band-pass filter (the luminance was often also low-pass-filtered, due to the penchant of presenters for wearing check jackets), then sent both directly and via a one-line delay to a sum-and-difference circuit.
Because of the phase inversion between lines, R-Y and B-Y were automatically separated and could easily be decoded.
(Actually, there were some TVs, early Sony Trinitons, that didn't use that method. The rumour was that Sony didn't want to pay Telefunken for the privilege. Instead they treated it as a simple NTSC signal, using the phase of the colour burst to effect the separation and decoding. I never saw a problem caused by that)

NTSC = Never Twice the Same Color
SECAM = Something Essentially Contrary to the American System
PAL = Perfection At Last