SCART image quality

[exxos]

So after some scart experiments, I found something a little confusing.

Take this image for example.

2.jpg

Notice the trashcan handle "V", just to the right is a "bent" vertical line which you would assume is simply wrong.
But also notice the TRASH text, in particular the "S".

So with a modified cable we now get this.

1.jpg

The vertical line next to the trash handle is now actually straight. There is still some grey vertical issues but its not as bad as before.
But now the "S" looks wrong. It looks like its got pixels missing on its bends... BUT..

When I look at steem, thats actually how its supposed to look.

3.png

It seems a bit of a dilemma. As the first image which seems to be wrong, has bolder black text, which IMO looks better, but its simply not looking how its supposed to look.

Another now new problem, is the "H" now seems to have a chunk missing out its side. So I wonder if the H-sync timing is slightly erratic causing a very small pixel shift. Or it could just simply be erratic ghosting. Or just bad scaling on my monitor. I think whichever, its not really fixable.

Brightness could may well be a factor in the second image, so black could be darker with less brightness. But still...

I also wonder how both scart images have a jagged line on the sides of the trash icon.

I need to look at the gem desktop background more as it looks like on the image, its "lost" the detail of the background pattern. But that could have been a camera issue.

It seems to look better in low resolution. But larger pixels, so less effect. Though I wonder if there is any sort of "test card" images for medium res ?

Can anyone else upload images of the trash icon with scart cable only , on a LCD TV ? on a STE would probably be better as that is what I cam currently using. I will try my H5 tomorrow and see if the video DAC has any effect on any of these problems.

[chronicthehedgehog]

IMG_20240407_104640.jpg

I get this using SCART via my OSSC, but notice the trash can lid is not completely filled (perhaps the OSSC needs a bit more fine tuning but it's good enough generally)

EDIT:
Sorry - missed the bit about LCD TV. FWIW, this is an STe, OSSC, IPS panel combo

[exxos]

I get this using SCART via my OSSC, but notice the trash can lid is not completely filled (perhaps the OSSC needs a bit more fine tuning but it's good enough generally)

The OSSC is to HDMI I presume ? I assume it has some active noise filtering as well. Looks pretty good to me anyway.

Looking on steem, the green pixels on the lid seem normal..

Your not getting the rough sided vertical lines either. Its difficult to know if that is normal for scart, or bad TVs, or its something the STE is doing, or all of the above!

[chronicthehedgehog]

The OSSC is to HDMI I presume ? I assume it has some active noise filtering as well. Looks pretty good to me anyway.

Yes to HDMI.

[stephen_usher]

Your not getting the rough sided vertical lines either. Its difficult to know if that is normal for scart, or bad TVs, or its something the STE is doing, or all of the above!

It's usually the TV. They generally seem to have, in effect, a low pass filter which smears the signal out and then they try to compensate with sharpening after it's digitised, which makes things worse as it merely adds artefacts.

The OSSC samples at double the pixel rate so doesn't n effect smear the data and it doesn't sharpen afterwards but sends (usually) the double resolution data over HDMI. The TV doesn't usually filter HDMI signals so you see a good image. I say usually because the Samsung I have does filter and smear the HDMI, even if it's supposedly pixel perfect resolution for the display. It's pants. (It does this on the VGA input as well, which is inexcusable as this was marketed as a TV/Monitor and Samsung's monitors don't do this with the same signal.)

[exxos]

I didn't realise how bad scart was on a LCD tv until I started looking at it more closely :roll:

I get interference across the whole image. I can filter it, and text still looks reasonable. But the checkered background green ends up a solid colour. Can't seem to solve one problem without creating another :roll:

Even LC filters fail badly. They seem to introduce ringing in the image. Caps alone help but then you still loose the checkered background. I think the problem is the interfence is at the frequency of the RGB signals, so you can't simply filter it out. There may be active filters but I don't know of any. But at that point it would probably just be simpler to go with a ossc.

I think what I need to do is try a screened RGB cable to see if the interference is coming from the TV itself and / or the cable. Though it's not simple to individually screen all, as such cable doesn't exist anymore. I have some single core screened , so I'll have to try and hack that up.. That be fun.

[stephen_usher]

Without something with a known good high sample rate and good A-to-D you’re not going to get anywhere. Most LCD TVs have rubbish analogue to digital conversion with poor signal noise filtering. They’d designed with crummy VHS resolution in mind and barely work. The aliasing of the luminance levels are terrrible so you’ll get banding too, though this is less of a problem with the ST’s output.

Remember that most TVs are built down to a cost and not up to a specification.

The SCART cable is probably fine if used on an OSSC, or even one of those cheap SCART->HDMI boxes!

[exxos]

I had the thought of putting a ferrite core around the cable and that reduced the "dot crawl" type problems.

WITH the core, the pattern is "fixed"

IMG_2152.JPG

WITHOUT the core, the pattern is "scrolling".

IMG_2153.JPG

As I thought a few days ago, it is just common mode noise it seems. I can reduce it with caps but then but inherently starts causing other problems as previously mentioned. I think there are clip-on ferrites for cables, so I will see if I can find something to fit that way.. I have a feeling only a looped core is only going to be effective.

[exxos]

Ultimately this is as good as it's going to get. Getting rid of the interference also means it loses the green desktop background checkered look. But realistically, that would not even be noticeable on a CRT anyway. So while it is *just* noticeable on a unmodified cable, is not a massive side-effect in using the pattern if it means not having weird wavey interference all over the place.

IMG_2166.JPG

IMG_2167.JPG

IMG_2168.JPG

I have got some slight ghosting on the black lettering. I will see if I can reduce that any more. But pretty much any change I do just ends up bringing back the interference again.

I am not sure if I will build this circuit into the scart cable itself. I may just do some sort of passthrough scart adapter initially, so any interested people can try that out.

Technically it could be used on any scart cable, so may help anyone else with odd scart problems. But overall, scart is just 50 years old now and bad TV's and upscaling all isn't helping. So there isn't much can be done.