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First post, by feipoa

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If such an adapter exists, could someone recommend an adapter which would convert an interlaced output signal from a graphics card to a standard non-interlaced mode for use on LCD monitors? Thanks!

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Reply 1 of 37, by darry

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feipoa wrote on 2022-05-02, 01:38:

If such an adapter exists, could someone recommend an adapter which would convert an interlaced output signal from a graphics card to a standard non-interlaced mode for use on LCD monitors? Thanks!

The most common (S)VGA interlaced mode (AFAIK) is 1024x768i@87Hz . Is that the mode that you are referring to ? Are there others you would need to convert ?

If you don't mind me asking, what is the use case for this and why would you want or need to use interlaced VGA modes ?

Reply 2 of 37, by feipoa

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Interlaced modes of interest are:

1024x768x16-bit
1280x1024x8-bit
I think they are at 43.5 Hz.

I don't think my LCDs can go above 75 Hz at these resolutions.

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Reply 3 of 37, by Tiido

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For a simple deinterlacer, output frame rate will remain same as input (i.e that 43.5Hz) and there will be combing artifacts for anything in motion. Adding actual frame rate conversion (beyond simple frame doubling) makes things much more difficult to achieve as it requires full on scaler approach. Bandwidths are very significant too for any DIY approach.

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Reply 4 of 37, by darry

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feipoa wrote on 2022-05-02, 03:46:
Interlaced modes of interest are: […]
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Interlaced modes of interest are:

1024x768x16-bit
1280x1024x8-bit
I think they are at 43.5 Hz.

I don't think my LCDs can go above 75 Hz at these resolutions.

Thank you for confirming the resolutions .

So 43.5 frames per seconds , 87 fields per second (2 fields for each frame) it is .

I am pretty sure that an OSSC would be able to handle to handle (input and passthrough) 1024x768p@87Hz and 1280x1024p@87Hz (progressive) as the pixel clocks of those modes are within its capabilities, but that would still require a monitor capable of accepting an 87Hz rate over DVI/HDMI . I have not tested this, however .

As for 1024x768i@87Hz and 1280x1024i@87Hz (interlaced), I have no idea how an OSSC would react to that. For the sake of argument, even if the OSSC is capable of dealing with those (or can be made to do so through a firmware update) on input, the OSSC's de-interlacing abilities may not be able to handle an 87Hz field rate (I have no idea, the OSSC can BOB deinterlace 1920x1080i@60Hz), so you might be stuck with interlaced 87Hz on DVI/HDMI output, which is much less likely to work than progressive 87Hz . Whether anything more or better is possible (and likely to be implemented) on OSSC, would best be answered by posting on the OSSC github . OSSC Pro (not yet available) maybe much more flexible in this regard .

Since your monitor tops out at 75Hz and I would guess it to be very likely that just about every LCD monitor on the market won't handle interlaced resolutions at an 87Hz field rate, I don't see many options short of finding a very old scan converter that can handle 1024x768i@87Hz and/or 1280x1024i@87Hz (interlaced) on input and both deinterlaces and converts the framerate to either 60Hz, 70Hz or 75Hz . If such a thing exists, that is .

That being said, except for early and/or low end VGA cards with RAMDAC or internal bandwidth limitations, many (most ?) better VGA cards from at least the mid 90s onward supported at least 1024x768p@60Hz in 16-bit color, AFAIK .

Reply 7 of 37, by darry

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maxtherabbit wrote on 2022-05-02, 13:29:

Extron RGB HDMI 300 A + a cheap VGA DAC

I actually checked the manual for mine when writing my previous post and don't recall seeing those modes listed as supported on input. Did I miss something that implies that they should be ? Of course, not listed does not necessarily mean not working, as we all know. Have you ever tested thoses modes through your Extron ?

Reply 8 of 37, by maxtherabbit

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darry wrote on 2022-05-02, 15:03:
maxtherabbit wrote on 2022-05-02, 13:29:

Extron RGB HDMI 300 A + a cheap VGA DAC

I actually checked the manual for mine when writing my previous post and don't recall seeing those modes listed as supported on input. Did I miss something that implies that they should be ? Of course, not listed does not necessarily mean not working, as we all know. Have you ever tested thoses modes through your Extron ?

I haven't, but I can

Reply 9 of 37, by imi

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the resolutions listed in the Extron RGB HDMI 300A manual are merely examples, as long as the mode is within the scope of it's rated input it will most likely work just fine, you can adjust all the input parameters in pixel increments to achieve a perfect input.

Reply 10 of 37, by darry

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imi wrote on 2022-05-02, 18:31:

the resolutions listed in the Extron RGB HDMI 300A manual are merely examples, as long as the mode is within the scope of it's rated input it will most likely work just fine, you can adjust all the input parameters in pixel increments to achieve a perfect input.

In general terms, I agree, except for the fact that, AFAICR (can't check now), there is no mention of support for any interlaced resolutions, at any field rate. I do notrecall reading about support for deinterlacing or interlaced output, at least one of which would need happen for this to work. Please correct me as appropriate, if applicable.

That being said, all or some of that functionality may be implemented even if not documented. maxtherabbit mentioned being able to test that.

Reply 11 of 37, by rmay635703

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I had a very old vga card that allowed you to run 43hz non-interlaced or 87hz interlaced at the common resolutions.

I thought the screen flickered more non-interlaced but the screen would work in either mode.

Also worth noting some LCD screens will accept 87hz interlaced, my old XR6-19 seemed to accept it as did my older fragile 2003 era 17” lcd

Reply 12 of 37, by imi

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now that you say it, there is indeed no mention of interlacing, can't say I'd ever have tried an interlaced mode, so I'll assume it'll just not do deinterlacing?
I wonder what happens if you set the output to 1080i then ^^

Reply 13 of 37, by darry

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imi wrote on 2022-05-03, 01:25:

now that you say it, there is indeed no mention of interlacing, can't say I'd ever have tried an interlaced mode, so I'll assume it'll just not do deinterlacing?
I wonder what happens if you set the output to 1080i then ^^

I just rechecked the manual and saw that that 1080i is listed in both input and output resolutions (only interlaced resolution listed), so that is a bit hopeful .

Reply 14 of 37, by maxtherabbit

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darry wrote on 2022-05-03, 00:29:
imi wrote on 2022-05-02, 18:31:

the resolutions listed in the Extron RGB HDMI 300A manual are merely examples, as long as the mode is within the scope of it's rated input it will most likely work just fine, you can adjust all the input parameters in pixel increments to achieve a perfect input.

In general terms, I agree, except for the fact that, AFAICR (can't check now), there is no mention of support for any interlaced resolutions, at any field rate. I do notrecall reading about support for deinterlacing or interlaced output, at least one of which would need happen for this to work. Please correct me as appropriate, if applicable.

That being said, all or some of that functionality may be implemented even if not documented. maxtherabbit mentioned being able to test that.

Yeah it will take some doing to drag out a proper test setup but I can do it

Reply 15 of 37, by maxtherabbit

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Works great. There are no presets for these resolutions so you must manually dial in the sample rate to get a decent image. It just does a basic bob deinterlace.

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Reply 16 of 37, by darry

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maxtherabbit wrote on 2022-05-05, 04:31:
Works great. There are no presets for these resolutions so you must manually dial in the sample rate to get a decent image. It j […]
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Works great. There are no presets for these resolutions so you must manually dial in the sample rate to get a decent image. It just does a basic bob deinterlace.
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Thank you! While I don't currently have a use case for this personally, it is certainly useful for OP and as general knowledge . One other thing that could be interesting to check in more detail is how the Extron handles motion while deinterlacing and frame rate conversion/decimation (or whatever it is actually doing).

EDIT : I now wonder if the Extron might be able to handle 15KHz RGB input .

Reply 17 of 37, by maxtherabbit

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The only software I have which will produce those goofy interlaced modes in DOS is that test program, so no motion tests I'm afraid. I would expect the standard comb artifacting you get with all bob deinterlaces. 15kHz I can definitely try

Reply 18 of 37, by feipoa

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OK, so looks like you are going from VGA-to-HDMI-to-VGA? I wonder what kind of time delay this might introduce?

Is it only these bulkier VGA-to-HDMI adapters which can read interlaced modes, or might some of the cheaper and more compact units suffice?

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Reply 19 of 37, by maxtherabbit

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feipoa wrote on 2022-05-05, 07:16:

OK, so looks like you are going from VGA-to-HDMI-to-VGA?

No. I'm splitting the signal off to my CRT in the analog domain before the scaler.

feipoa wrote on 2022-05-05, 07:16:

I wonder what kind of time delay this might introduce?

The RGB HDMI 300 adds 16ms of display lag (1 frame at 60Hz)

feipoa wrote on 2022-05-05, 07:16:

Is it only these bulkier VGA-to-HDMI adapters which can read interlaced modes, or might some of the cheaper and more compact units suffice?

It's "bulky" because it's a full featured scaler not just a dumb digitizer. YMMV with the "compact" ones but anything without a scaling engine will choke.