Pictures of screen displaying example of RPi composite output?


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by gsw » Fri Jan 06, 2012 4:00 am
After reading the other threads on resolution, etc. of RPi via composite output, I'm really curious if I could see some real world example photos of terminal output, like displaying some command-line stuff or some code that students might be editing in vim/emacs, via composite output on what is assumed to be most common size television in the target market, which I think is students in households with low income. From what I understand, in the beginning, these are the displays that students will be using, as a good number of them won't have HDMI. My past experience with composite is that it was too low res and too fuzzy (in NTSC at least, maybe PAL is better!) even on larger (34") televisions to be usable unless the text size was huge, but that might have been due to the VGA to composite converter I used to have.
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by Jason Ozolins » Fri Jan 06, 2012 7:42 am
Unfortunately, your past experience is a good guide to future experience. :^/   The composite video signal only has so much bandwidth to offer, so composite video from the RPi will look quite a lot like any other old machine's composite video output.  The old C64 format of 320*200 is about as good as you will get without going to interlaced output (which is really not very easy on the eyes - long ago, I spent a couple of years using an Amiga 2000 with a long-persistence monochrome phosphor monitor in interlaced mode, and even with the reduced flicker it was... okay-ish, but not great.)

With small LCD televisions getting very cheap these days, the odds are not bad that the family TV could already be capable of accepting an HDMI input.  There were certainly plenty of houses when I was a kid where the home computer could only be used when there was nothing to watch on the TV.   :-)

It seems to me that the composite output is more for applications like gaming or driving tiny LCD screens like the ones that come on portable DVD players, than as a way to use it for programming.  Of course, for people with impaired vision, it could be that large text from an RPi connected to a TV is just fine, and that would be a very worthwhile use of the composite video output.  I'm just saying, it will not look that much better than composite displays of yesteryear.
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by meltwater » Fri Jan 06, 2012 8:59 am
Jason Ozolins said:


There were certainly plenty of houses when I was a kid where the home computer could only be used when there was nothing to watch on the TV.   :-)


Should be in luck if you live in the UK, there is nothing decent to watch on TV at anytime!

I can remember using WinAmp through composite and making extensive use of the windows magnifier, a pain but was enough to use it.  I would imagine unless you are doing terminal stuff (which for some is fine) you will struggle to program through an IDE etc (will probably be fine with a suitable GUI as media player though).  Also fine for playing games etc.

Hopefully, we can make use of other higher resolution screens we do have available (mobile phones, tablets, laptops) through remote software like VNC via network or even USB.

Will have to see if the refresh rates are sufficient though, hopefully that'll be clear once the unit is available.  It's certainly a mode of use I would like to have available if possible.
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by doug » Fri Jan 06, 2012 2:42 pm
I've worked in the STB industry so I have a bit of experience putting readable text out on a composite display so here is a little insight. It's a shame the output isn't RGB or YC as that would be a bit better but I suspect that is not an option on a mobile SoC.

There are two main considerations I found in CVBS (composite) output. The size of the text and the colour. Generally you'll need a chunky font because small, thin fonts tend to show up poorly due to fuzziness and the side effects of interlacing.

In the UK there is a specific font used for clarity on TV screens in applications like the interactive services (MHEG) called Tiresias. So if you use the red button to catch up with the news, consider what you see there as some indication of what readability is achievable.

The other consideration using composite, particularly on CRT displays is colour. Pure black and pure white can cause distortion of the image, so the colour range needs to be compressed ideally, something between the range of RGB 16, 16, 16 and 232, 232, 232. Also red tends to look really fuzzy on composite which can be a right pain ;-)
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by Davespice » Fri Jan 06, 2012 3:40 pm
I would imagine the team have considered this.  Off the top of my head I would guess that when you boot the Pi up with the Composite connector in use the display would adjust accordingly.  As far as I know NTSC is 720×480 (interlaced at 2 x 243 lines) and PAL is 720×576 (interlaced at 2 x 288 lines).

I would have thought that would be good enough to do some level of programming on.  I agree though that it would look a bit like workbench on the old Amiga.  Some pictures of this would be really nice though, so I would like to second that request.
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by hippy » Fri Jan 06, 2012 3:58 pm
Davespice said:


Off the top of my head I would guess that when you boot the Pi up with the Composite connector in use the display would adjust accordingly.


Composite out is purely "output only" so the R-Pi would have no means to determine what is connected. It won't likely be a problem for a TV which can auto adjust to any signal but some are PAL or NTSC only.

In those cases it's probably best to use a boot image which configures the composite as required; displaying an option and having the user select which to use won't work well if the default is not displayable and they don't know that option is there.

I also agree with doug; composite isn't that bad with the right choice of font, size and colour, but it can look terrible if not right.
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by Luny » Fri Jan 06, 2012 4:58 pm
doug said:


I've worked in the STB industry so I have a bit of experience putting readable text out on a composite display so here is a little insight...

Would that be a certain Welsh company?

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by Davespice » Fri Jan 06, 2012 5:05 pm
hippy said:


Davespice said:


Off the top of my head I would guess that when you boot the Pi up with the Composite connector in use the display would adjust accordingly.


Composite out is purely "output only" so the R-Pi would have no means to determine what is connected. It won't likely be a problem for a TV which can auto adjust to any signal but some are PAL or NTSC only.


I wonder if it would be able to do it from the absense of the HDMI connection?
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by mc349 » Fri Jan 06, 2012 5:08 pm
Do you remember  Ceefax / Teletext?  That level of quality should be possible?

http://en.wikipedia.org/wiki/Ceefax
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by doug » Fri Jan 06, 2012 5:16 pm
Luny said:


doug said:


I've worked in the STB industry so I have a bit of experience putting readable text out on a composite display so here is a little insight...

Would that be a certain Welsh company?



Probably, but there is more than one Wales based company that operates in that industry that I've been involved in ;-)
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by waveform » Fri Jan 06, 2012 5:26 pm
mc349 said:


Do you remember  Ceefax / Teletext?  That level of quality should be possible?

http://en.wikipedia.org/wiki/Ceefax



I would hope that the quality would be far superior to that of Teletext, at least twice the resolution, I have no idea what resolution teletext actually uses,

one can't assume its the resolution of PAL as it's more than likely upscaled.
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by Emanuele » Fri Jan 06, 2012 5:28 pm
I believe that the most authoritative info is still an old post from Gert:

Gert said:


Yes, it can go down in resolution. We are still working in how the user can define these parameters. Probably a (text) configuration file on the SD-card. The same holds for the composite video output. It can do PAL-BGHID, PAL-M, PAL-N, NTSC, NTSC_J. It just a matter of programming the TV-out hardware. We might not support all standards from the beginning though.


http://www.raspberrypi.org/for.....ideo-modes

My gut feeling is that how to get an usable programmable environment in 480i/576i is something that will be worked out by the community in the coming months.

In my opinion, the most pressing question right now is if out of the box the console output in NTSC/PAL mode will take care of the overscan. IIRC, on the standard linux console you can select the font and limit the number of columns/rows to be displayed, but you cannot set an offset for the topmost/leftmost character. Maybe GNU screen could be an option, but my experience with it is very limited.
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by doug » Fri Jan 06, 2012 5:37 pm
Davespice said:


I wonder if it would be able to do it from the absense of the HDMI connection?


Given that the only output options are composite and HDMI then you can logically assume that if the HDMI 5V line is not active then either composite or no display device is connected.
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by Luny » Fri Jan 06, 2012 7:56 pm
Emanuele said:


I believe that the most authoritative info is still an old post from Gert:

Gert said:


Yes, it can go down in resolution. We are still working in how the user can define these parameters. Probably a (text) configuration file on the SD-card. The same holds for the composite video output. It can do PAL-BGHID, PAL-M, PAL-N, NTSC, NTSC_J. It just a matter of programming the TV-out hardware. We might not support all standards from the beginning though.


http://www.raspberrypi.org/for.....ideo-modes

My gut feeling is that how to get an usable programmable environment in 480i/576i is something that will be worked out by the community in the coming months.

In my opinion, the most pressing question right now is if out of the box the console output in NTSC/PAL mode will take care of the overscan. IIRC, on the standard linux console you can select the font and limit the number of columns/rows to be displayed, but you cannot set an offset for the topmost/leftmost character. Maybe GNU screen could be an option, but my experience with it is very limited.



I think your right. The agreed resolution was 40 x 24 as matched with the Acorn mode 7.
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by arm2 » Fri Jan 06, 2012 8:41 pm
waveform said:


mc349 said:


Do you remember  Ceefax / Teletext?  That level of quality should be possible?

http://en.wikipedia.org/wiki/Ceefax


I would hope that the quality would be far superior to that of Teletext, at least twice the resolution, I have no idea what resolution teletext actually uses,

one can't assume its the resolution of PAL as it's more than likely upscaled.



I think you will be dissapointed, Mode7 (Teletext mode) and MODE 1 on a BBC B were both 40 characters horizontaly but Text in MODE 7 used the SAA5050 which almost doubles the pixel resolution of each character, see:http://en.wikipedia.org/wiki/M.....rd_SAA5050

With a PAL output I don't think you can ever get better than 35+ year old Teletext chips, they output as a higher resolution as PAL can cope with.
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by foo » Sun Jan 08, 2012 1:30 am
Will the composite output do that horrible crawling checkerboarding for solid reds like every other modern composite-out device seems to do?
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by Luny » Sun Jan 08, 2012 8:59 am
Will the composite output do that horrible crawling checkerboarding for solid reds like every other modern composite-out device seems to do?

It would certainly make a realistic Spectrum emulator :)
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by Emanuele » Sun Jan 08, 2012 10:27 am
foo said:


Will the composite output do that horrible crawling checkerboarding for solid reds like every other modern composite-out device seems to do?


I don't know about that, but I think you cannot expect pixels to be sharp and perfect anyway; AFAIK, it's a limitation of the PAL/NTSC signals.

http://blargg.parodius.com/ntsc-presets/
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by Prometheus » Sun Jan 08, 2012 10:57 am
foo said:


Will the composite output do that horrible crawling checkerboarding for solid reds like every other modern composite-out device seems to do?


If your TV has a comb-filter (some sets have one built-in - I was quite surprised when I found that my own, which is a CRT that I got from Argos a few years ago, has one), it won't. If it doesn't, then it probably will.
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by Piw32 » Sun Jan 08, 2012 12:05 pm
Do you remember the MediaGX processor ? It was and early days almost Soc (x86) and has some technology to improve screan readability on TV sets.
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by Davespice » Sun Jan 08, 2012 6:38 pm
When I get my Pi I plan to test it out on a number of old CRT TV sets.  I’ll post my findings in a youtube video I expect.  One thing that did occur to me was that LXDE could be configured to use larger UI elements and maybe different colours in order to make it look okay.

Anyway, let’s not digress too much.  After all this thread was about a request for some pictures of what the output looks like.
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by gsw » Tue Jan 10, 2012 6:34 pm
Thanks to everyone for the comments, but I agree with Davespice about getting back to trying to find a good pic. Could someone who has a Pi hook it up to a T.V. and show us what a terminal window (showing command-line with some code) looks like via composite at the highest usable resolution and post a pic here?
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by larsth » Mon Mar 19, 2012 5:39 am

Davespice said:


Off the top of my head I would guess that when you boot the Pi up with the Composite connector in use the display would adjust accordingly.


Composite out is purely "output only" so the R-Pi would have no means to determine what is connected.

It is true that composite video is output only, but that doesn't mean that it is impossible to detect whether something had been connected or not.

How to detect a signal:

A resistor in series with the signal. A current through the resistor creates a voltage across the resistor (ohm's law). The voltage across the resistor is amplified, then get a DC voltage out of the now amplified signal: use a diode, a resistor, and a capacitor. The DC voltage is then wired to a schmitt trigger. The digital output of the schmitt trigger could then be wired directly back to the GPU. "1" is then s-video connected, and "0" is s-video not connected.

The above circuit is very likely to be inside the BCM2835 SoC, if it exists.

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by oztrailrider » Mon Mar 19, 2012 7:21 am
@andytuk took this photo of composite output during his time with Raspberry Pi beta board #7 (the one that was donated to the computing history museum).

Raspberry Pi - Composite video + ls -la
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by tufty » Mon Mar 19, 2012 7:35 am
oztrailrider said:


@andytuk took this photo of composite output during his time with Raspberry Pi beta board #7


Looks usable, would be interesting to see what it does on a CRT rather than a flat panel.  We'll probably have to wait for that, though.
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