LCD VGA timings and things... little help?

[London Geezer]

I have a little problem and i'm not sure what it is...

I'm definately getting 1:1 pixel mapping through VGA to my LE32R51, but for some reason i get some little flaws here and there in the form of very slight blurring and a sort of ghosting, noticeable with fonts.

The res used is 1360x768 and i'm definately getting 1:1 pixel mapping (3 pixels blank on each side). I played around with Powerstrip and i can get a slightly sharper image here and there...

I've tried to play around with the TV's PC Setup screen settings and the "Coarse" and "Fine" settings. I can get a very sharp image sometimes, but not for the whole screen.

To be precise, this happened also on my LCD monitor i used for my PC.

I just never really understood what these two settings do, on my LCD they were called something else but did the same thing... One basically fixes the left side of the screen and stretches the whole image towards the right when changed, and the other one... not sure what it does actually...

It's not a HUGE problem, the image is fine, but i can see i'm getting a much sharper image at times in parts of the screen (i think i kinda got it right now), but i just need to know what these settings are, and how the timing in Powerstrip changes things...

Any help here?

 

[Captain Chickenpants]

Because you are sampling an analog signal if you take a sample at the point where a pixel changes from one value to another then you can sometimes get the wrong value.
The settings you are talking about will probably be clock and phase.
Clock adjusts the frequency at which you take samples, phase adjusts where within each cycle you take samples.

Look here for some more info.
http://www.techmind.org/lcd/

Try creating a dithered pattern, that is generally very good for showing when the settings are incorrect, then tweak them manually to get the best image you can.

Note it is not always possible to get a perfect signal due to the way that devices generate a pixel clock (they use something called a Phase Locked Loop or PLL) it is not always possible to exactly match the pixel clock being used.

CC

 

[London Geezer]

Because you are sampling an analog signal if you take a sample at the point where a pixel changes from one value to another then you can sometimes get the wrong value.
The settings you are talking about will probably be clock and phase.
Clock adjusts the frequency at which you take samples, phase adjusts where within each cycle you take samples.

Look here for some more info.
http://www.techmind.org/lcd/

Try creating a dithered pattern, that is generally very good for showing when the settings are incorrect, then tweak them manually to get the best image you can.

Note it is not always possible to get a perfect signal due to the way that devices generate a pixel clock (they use something called a Phase Locked Loop or PLL) it is not always possible to exactly match the pixel clock being used.

CC

YES! Clock and Phase, that's what my other LCD called them.
Well i tried tweaking them and it's hard to get a perfectly sharp image all over the screen for some reason. I'd get a 100% sharp text on a big vertical part of the screen and a portion next to it with slightly blurred-or-ghosted-to-the-right text, and it's kinda cyclical.

Tried everything and i can't seem to get it right all over the screen.......

Though on my old LCD, eventually i got it right... somehow... Guess i'll just have to keep trying...

 

[Captain Chickenpants]

Try using the dither image on that site. It should help you a fair bit.
If they don't help then change the pixel clock slightly in powerstrip.

Basically tweak Phase and clock as best you can. Find best values you can and make a note of them.
Modify pixel clock a little and try again.

One thing that is worth a try is to download the EDID viewer app from here.
http://www.raylar.com/phoenix.php

Run it and see if you can read the EDID data for your display.
If it can see it then see if it has a listing in the detailed timings for the mode that you are trying to use. Then make sure that your settings are exactly the same. If the hActive and vActive are bigger than the mode you are trying to do then pad it out in the h and v borders.


CC

 

[London Geezer]

Try using the dither image on that site. It should help you a fair bit.
If they don't help then change the pixel clock slightly in powerstrip.

Basically tweak Phase and clock as best you can. Find best values you can and make a note of them.
Modify pixel clock a little and try again.

One thing that is worth a try is to download the EDID viewer app from here.
http://www.raylar.com/phoenix.php

Run it and see if you can read the EDID data for your display.
If it can see it then see if it has a listing in the detailed timings for the mode that you are trying to use. Then make sure that your settings are exactly the same. If the hActive and vActive are bigger than the mode you are trying to do then pad it out in the h and v borders.


CC

I'll definately try the dither image tonight, i was hopelessy looking for situations and images to test the settings (tried fine text) but that looks perfect.

Shame that my set doesn't do 1:1 pixel mapping through HDMI. Oh well.

I'll get it right. I always get it right in the end.

For some reason on my old LCD, setting the refresh to 60Hz got rid of all issues, so i'm not sure why it doesn't work on the new LCD. oh well.

 

[Nappe1]

I'll definately try the dither image tonight, i was hopelessy looking for situations and images to test the settings (tried fine text) but that looks perfect.

Shame that my set doesn't do 1:1 pixel mapping through HDMI. Oh well.

I'll get it right. I always get it right in the end.

For some reason on my old LCD, setting the refresh to 60Hz got rid of all issues, so i'm not sure why it doesn't work on the new LCD. oh well.

it's all about how good ADC side is in LCD. my 15" Philips 150f3 is sharp as DVI on my philips 26pf5520D. (26" dvb-t) again, using VGA (D-SUB) on TV, image get's blurred quite lot.

at least it used to be a good rule that if LCD monitor don't have DVI and so it's only connector is D-Sub, you propably have pretty good AD Converter on it. Again, if it has DVI, then the D-Sub has just ok AD Conveter. (because if user wants better image, he can use DVI. on the other monitor, he does not have other choice than buy competitive product, which again manufacturer's don't want.)

 

[London Geezer]

Captain,

i've done all that stuff in the first link, but i still get a slight sort of ghosting on the right, mostly seen on text or on vertical lines (like the ones on this forum for example). I really don't know what to do. I think i got it slightly better by tweaking the Fine setting, but still not perfect. Strange cause at times it's perfectly sharp in some places.

I've used the dithered pattern thing and i got it to show no shimmering and stuff, but i still get that very slight ghosting and general not-100%-sharp look if you know what i mean.

Do you think it could be the VGA cable i'm using? It's the same old VGA cable i got with my GF5900...

It's not a huge problem, in fact from even from a close distance it's hard to see, but it does bug me a lot cause i could see how sharp it looks when it's as sharp as it should be...

 

[Captain Chickenpants]

Doesn't sound like the cable, as it would cause ghosting all over.
It is worth trying the app in the other link I sent (http://www.raylar.com/phoenix.php), just to verify that the timings you are using are the same as the ones that it is expecting.




CC

 

[London Geezer]

Doesn't sound like the cable, as it would cause ghosting all over.
It is worth trying the app in the other link I sent (http://www.raylar.com/phoenix.php), just to verify that the timings you are using are the same as the ones that it is expecting.




CC

Uhm well i tried that, installed it and all, but i .. uhm... didn't really know what to do with it...?

 

[Captain Chickenpants]

No probs.

Run it and Select Tools->Extract Registry EDID.

It should list 1 or more device's which represent the monitors connected to your system. These are the monitors for which windows has read and stored EDID information, this information is transmitted by the monitor at bootup and contains details such as mode limits, color settings etc.

Select the device that looks like it is refering to your TV. (May be hard to tell as the ID's used are not necesarily very useful). And click Extract Edid

You should now have a dialog box with a number of tabs.
The first Tab is just general information. E.g. Serial Number, device ID, date of manufacture and edid structure version.
The other tabs contain other bits of information, that you can look at.
The one that you want to look for is the Detailed Timings tab.
This lists modes for which the monitor expresses a particulat preference, hopfully one of these will be mode you are interested in displaying. Try the different descriptor blocks to see if the mode you are after is listed (look at the values for hActive Pxl and V Active Lines). If you find it then make a note of the other values as they are what need to be used to plug into powerstrip.

If you like you can save the edid data and send it to me to have a look at, to see if the mode you need is listed and what values to try in powerstrip.
If you send me the values that you are using in powerstrip I can check them over and see if they add up.

CC

 

[London Geezer]

No probs.

Run it and Select Tools->Extract Registry EDID.

It should list 1 or more device's which represent the monitors connected to your system. These are the monitors for which windows has read and stored EDID information, this information is transmitted by the monitor at bootup and contains details such as mode limits, color settings etc.

Select the device that looks like it is refering to your TV. (May be hard to tell as the ID's used are not necesarily very useful). And click Extract Edid

You should now have a dialog box with a number of tabs.
The first Tab is just general information. E.g. Serial Number, device ID, date of manufacture and edid structure version.
The other tabs contain other bits of information, that you can look at.
The one that you want to look for is the Detailed Timings tab.
This lists modes for which the monitor expresses a particulat preference, hopfully one of these will be mode you are interested in displaying. Try the different descriptor blocks to see if the mode you are after is listed (look at the values for hActive Pxl and V Active Lines). If you find it then make a note of the other values as they are what need to be used to plug into powerstrip.

If you like you can save the edid data and send it to me to have a look at, to see if the mode you need is listed and what values to try in powerstrip.
If you send me the values that you are using in powerstrip I can check them over and see if they add up.

CC

Oooh right, thanks!! I'll try that tonight if i'm at home.
(just thinking about this... should things be much easier than this?!)

 

[Captain Chickenpants]

In an ideal world yes!

Ok, a quick look at powerstrip reveals that it specifies the video signal in slightly different way to the edid tool. (Information on how to convert below)

A standard video signal consists of active data, border, and blanking.
The blanking consists of the front porch, the sync pulse and the back porch. This is how powerstip is looking at the data. Unfortunatly it doesn't seem to allow modification of the border , as this would allow you to display 720 content fullscreen (as far as your computer is concerned) with no scaling whatsoever.

What you need to do is convert between the EDID tools, description of a mode to Powerstrips.

Active = Active
Front Porch = Sync Offset.
Sync Width = Sync Width
Back Porch = Blank - (syncwidth + front porch)
Total = Active + Blank

CC

 

[London Geezer]

See, usually i'd just get a different video card.

 

[darkblu]

not really wanting to sound negative or disheartening but my personal experience with pursuing good output from a scaled analog source on an inherently digital monitor has been quite unsatisfactory to this day - you really need a bunch of conditions met which appear hard to meet even on expensive digital equipment, and that's in order to achieve the quality you can otherwise get on an ordinary CRT VGA by default. so don't change your videocard - just get a spare 19-22" CRT monitor - anyway they're not more expensive than a high end videocard these days.

 

[Guden Oden]

L-B, don't your TV have DVI input, or are you already using the DVI-out on your vidcard?

You could try to see if your TV's manufacturer supplies a windows .inf file for your TV. Sony does for my TV. Maybe installing that would help, as windows would then know what video modes the TV supports, and maybe the .inf can supply more precise timings than just using general PnP monitor allows...

 

[Silkworm]

Assuming that "Coarse" is Clock, then with each adjustment to this setting, you may want to tweak the horizontal position settings as well. H-positioning on LCDs is usually done by changing the horizontal back-porch which, as captain chickenpants has shown, makes up a part of the total horizontal signal.

Play around with the vertical frequency as well; different vertical refreshes = different horizontal "Total", which means you may have more chances of "locking" your PLL to the source. Normally lower is better, because the ADC has less to keep up with, but you never know.

 

[London Geezer]

L-B, don't your TV have DVI input, or are you already using the DVI-out on your vidcard?

You could try to see if your TV's manufacturer supplies a windows .inf file for your TV. Sony does for my TV. Maybe installing that would help, as windows would then know what video modes the TV supports, and maybe the .inf can supply more precise timings than just using general PnP monitor allows...

Nope. The TV has VGA and HDMI and HDMI only supports "video" resolutions like 720p and 1080i, not PC resolutions.

Still have the problem even after all the things you guys (and other people) told me...

 

[Nappe1]

Nope. The TV has VGA and HDMI and HDMI only supports "video" resolutions like 720p and 1080i, not PC resolutions.

Still have the problem even after all the things you guys (and other people) told me...

this is worst flaw for ages in TVs. I can confirm that most of Samsung models and Sony Bravias do not support anything else than 720p and 1080i via DVI/HDMI. Those displays just select one of the standards and puts the image middle of that resolution before scaling it for panel. as a result, you'll get picture with strong black bars on all sides, while you should be getting native resolution. Also, when using 720p or 1080i, you get the standard overscan, just because these old formats had it during CRT time. (video signals are still mastered with some amount of overscan, so usually black borders are left on the edges, which CRT overscan eliminates from viewable area. on LCD/Plasma, picture could be shown with zero overscan, but because video signals expect some overscan to be present, LCDs overscan standard signals as well.)

I have recently started to understand how lucky I am with my Philips 26pf5520D and it's way of implementing DVI (with HDCP) input. In Screen menus, you have two options for DVI input. PC and HD.
On PC mode, you'll get all standard resolutions with zero overscan plus the TV supports wide variety of non standard modes. TV does not list them in EDID, but with powerstrip and a bit of knowledge, you can get them work. (as an example, I am using native 1366x768 with DVI.)
Again, on HD mode, the DVI accepts EICTA standarlized HD signals with standard amount of overscan.

Why only philips seems to be thinking when designing digital interfaces? Why all the others make their HDMI / DVI as "video signal only" and don't support PC properly? As to me this is just absurd!

 

[London Geezer]

Beats me... At the moment i've put my PC back in my room so it's not a problem anymore, still it's kinda frustrating to think we spend a lot of money on those things and the simples most logical features are not there... Go figure...