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dither : Can you explain How it works? Tue, 16 February 2010 18:22 Go to next message
actarusfleed is currently offline actarusfleed
Messages: 44
Registered: February 2010
Location: Milan (Italy)
Junior Member
I see this option in the Radiance XS output menu.

I think that this option can improve the smoothness of the color gradients (like the sky) of the 8bit pre-recorded material (like BD and DVD).

My question is : How it works?

In my past system (an HTPC with ffdshow) I use to improve the gradients using 2 different ways:

1) ffdshow has an high profile 32bit RGB conversion with dither that improve very much the smoothness of the color gradients;

2) ffdshow has a DE-BAND filter that (without any color conversion) do the same job but, IMHO, with a little detail lose.

With my old HTPC my choice goes to the RGB 32bits conversion. Wink

Lumagen how menage "dither"?
Another high profile color conversion?

Thank you,
actarus.
Re: dither : Can you explain How it works? Thu, 18 February 2010 12:51 Go to previous messageGo to next message
actarusfleed is currently offline actarusfleed
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Yesterday night I've done some test ....
I played a BD and paused the reproduction on a frame with a sky (big blu gradient).
In the "dither" menu in the output section I set:
- 6bit
- 8bit
- 10bit

With the lowest value I see some fine pixelation on the gradient.
With the uppuer the pixelation fade out and the gradient become much more smooth!

But ALWAYS my display (pj JVC HD 550) says that the input signal was @8bit.

So ... the 6/8/10 bit setting regards only the internal elaboration?
The output is ALWAYS @ 8bit?
I'm correct?

Another question: What are the difference between the "Fixed" and "adptive" mode?
And What is the "masking" mode?

Thank you for some infos,
actarus
Re: dither : Can you explain How it works? Thu, 18 February 2010 17:37 Go to previous messageGo to next message
pharkin is currently offline pharkin
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Registered: November 2004
Location: USA
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Lumagen Tech
Internally the video data is a minimum of 10 bits per color regardless of the input or output pixel size (your display always says it's 8bpp because that's the output format from the Radiance you've got set). The 6/8/10 choice is the bit position at which we dither the color. Fixed/adaptive will fix the pseudo-random dithering pattern to the screen or not. Masking is an option of what to do with the bits after the dither position--either mask them (set to 0's) or leave them. The best choice for these is dependent on the output format and the display so experimenting with them is a good idea.
Re: dither : Can you explain How it works? Thu, 18 February 2010 19:27 Go to previous messageGo to next message
actarusfleed is currently offline actarusfleed
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pharkin wrote on Thu, 18 February 2010 17:37

Internally the video data is a minimum of 10 bits per color regardless of the input or output pixel size


Ok, I know that radiance internally works @10bit.

pharkin wrote on Thu, 18 February 2010 17:37

your display always says it's 8bpp because that's the output format from the Radiance you've got set


That's very interesting!
I don't know that we can set the output bit depth.
Can you suggest me where I've to go to set this?

pharkin wrote on Thu, 18 February 2010 17:37

The 6/8/10 choice is the bit position at which we dither the color.


Ok but ... In theory I think that an high value (10bits) gets best results.
I'm wrong?

pharkin wrote on Thu, 18 February 2010 17:37

Fixed/adaptive will fix the pseudo-random dithering pattern to the screen or not.


That's hard ...
Can you explain it better?

thank you,
actarus.


Re: dither : Can you explain How it works? Fri, 19 March 2010 00:23 Go to previous messageGo to next message
jim_peterson
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Registered: November 2004
Location: Beaverton Oregon, USA
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Note that the front end of the Radiance pipeline is 10-bits, but the back-end calibration section is 12-bits (and a bit more in some places).

The extra bits are important as we calculate scaling and calibration values. How you want to output this 12-bits of R, G and B (the color space in the back end of the pipeline) depends on your display.

It is almost always better to select the Radiance output format as 4:2:2 as this gives you 12-bits each for Y, Cb, and Cr. This IS 36-bit color and HAS been available since HDMI 1.0. I mention this as a lot of people don't realize that the color depth is the same for 4:2:2 and the HDMI 1.3 12-bit 4:4:4. It's the (potential and unrealized for video sources) Chroma resolution that is different.

What your display does internally determines how you should set dither. Unfortunately the manuafactures do not tell us what they do, and if they did I wouldn't believe them anyway.

So, what's one to do about dither? Unfortunately experimentation is probably the best answer.

For DLP's the underlying technology is 10-bits. However, we really want to carry more bits through the calculation pipeline. If the display is using the full-precision of the input to do calculations then you may want to send the full 12-bit 4:2:2 from the Radiance. If it truncates to 10-bits on input, then use 10-bit dither. Then try 8-bit, 7-bit, dither. Which looks best?

The <8-bit dither options are really for older Plasma and LCD displays. The image will appear a bit noisier but smoother on these older displays.

Hopefully this is of some help.


Jim Peterson
Lumagen
icon14.gif  Re: dither : Can you explain How it works? Wed, 24 March 2010 11:55 Go to previous messageGo to next message
aoshiken is currently offline aoshiken
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Many thanks for your post Jim, very useful as usual. Razz

By the way, actarusfleed, from what BR/DVD are you using the pattern/image?

Cheers.
Re: dither : Can you explain How it works? Sun, 13 June 2010 13:06 Go to previous messageGo to next message
SusyHiggs is currently offline SusyHiggs
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jim_peterson wrote on Fri, 19 March 2010 01:23


It is almost always better to select the Radiance output format as 4:2:2 as this gives you 12-bits each for Y, Cb, and Cr. This IS 36-bit color and HAS been available since HDMI 1.0. I mention this as a lot of people don't realize that the color depth is the same for 4:2:2 and the HDMI 1.3 12-bit 4:4:4. It's the (potential and unrealized for video sources) Chroma resolution that is different.

What your display does internally determines how you should set dither. Unfortunately the manuafactures do not tell us what they do, and if they did I wouldn't believe them anyway.

So, what's one to do about dither? Unfortunately experimentation is probably the best answer.

If the display is using the full-precision of the input to do calculations then you may want to send the full 12-bit 4:2:2 from the Radiance. If it truncates to 10-bits on input, then use 10-bit dither. Then try 8-bit, 7-bit, dither. Which looks best?




Hi Jim,
I ran across this thread by chance and I am still a bit confused by your explanation.
The Radiance output settings for dither are: "Auto, off, 10bit, etc..." I noticed in my Radiance some Output Configs with "Auto" or "10bit". Note, I never touched these settings. So what should the right setting be if one feeds 4:2:2 to the display (one-year-old SONY LED LCD Display)?
BTW, I did some testing with test images (Chroma patterns in particular) and couldn't see the slightest difference between all possible settings.
Thanks for educating me a little bit.
Cheers,


Cheers,
SusyHiggs

[RadiancePRO 4446 (S/N:101801106, currently with FW-Beta 091116), Set-Top: Reel-Multimedia AVG I & HUMAX TN5050HDR, Denon AVR-1610, SONY TV KDL-46X4500, OPPO BDP-83SE]
Re: dither : Can you explain How it works? Mon, 14 June 2010 19:33 Go to previous messageGo to next message
jim_peterson
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Registered: November 2004
Location: Beaverton Oregon, USA
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meyertomtom wrote on Sun, 13 June 2010 05:06


Hi Jim,
I ran across this thread by chance and I am still a bit confused by your explanation.
The Radiance output settings for dither are: "Auto, off, 10bit, etc..." I noticed in my Radiance some Output Configs with "Auto" or "10bit". Note, I never touched these settings. So what should the right setting be if one feeds 4:2:2 to the display (one-year-old SONY LED LCD Display)?
BTW, I did some testing with test images (Chroma patterns in particular) and couldn't see the slightest difference between all possible settings.
Thanks for educating me a little bit.
Cheers,



You came up with the answer in your experiment. That is, if you see no difference at all then the display/projector is doing a decent job internally of dithering the data to match the true bit-depth capability of the phyiscal display device. For your system 4:2:2 Auto and 10-bit dither are giving the same performance. So you can choose either.

I would suggest you leave our output as 4:2:2 with Dither=Auto though since if we dither and then the display dithers there might be slightly more "dithering" going on then is optimal. Of course this is way down in the noise and as you noted does not typically make a visible difference.

Does this help?


Jim Peterson
Lumagen
Re: dither : Can you explain How it works? Mon, 14 June 2010 20:39 Go to previous messageGo to next message
SusyHiggs is currently offline SusyHiggs
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Registered: September 2009
Location: CERN
Senior Member
Thank you. This is very much appreciated.
Kind regards,


Cheers,
SusyHiggs

[RadiancePRO 4446 (S/N:101801106, currently with FW-Beta 091116), Set-Top: Reel-Multimedia AVG I & HUMAX TN5050HDR, Denon AVR-1610, SONY TV KDL-46X4500, OPPO BDP-83SE]
Re: dither : Can you explain How it works? Thu, 03 May 2012 09:43 Go to previous messageGo to next message
Methodic is currently offline Methodic
Messages: 37
Registered: December 2009
Junior Member
jim_peterson wrote on Mon, 14 June 2010 19:33
meyertomtom wrote on Sun, 13 June 2010 05:06

Hi Jim,
I ran across this thread by chance and I am still a bit confused by your explanation.
The Radiance output settings for dither are: "Auto, off, 10bit, etc..." I noticed in my Radiance some Output Configs with "Auto" or "10bit". Note, I never touched these settings. So what should the right setting be if one feeds 4:2:2 to the display (one-year-old SONY LED LCD Display)?
BTW, I did some testing with test images (Chroma patterns in particular) and couldn't see the slightest difference between all possible settings.
Thanks for educating me a little bit.
Cheers,


You came up with the answer in your experiment. That is, if you see no difference at all then the display/projector is doing a decent job internally of dithering the data to match the true bit-depth capability of the phyiscal display device. For your system 4:2:2 Auto and 10-bit dither are giving the same performance. So you can choose either.

I would suggest you leave our output as 4:2:2 with Dither=Auto though since if we dither and then the display dithers there might be slightly more "dithering" going on then is optimal. Of course this is way down in the noise and as you noted does not typically make a visible difference.

Does this help?


Hi Jim,pharkin

If I understand correctly, to determinate the bit depth that the radiance sent, we have to set the HDMI Format and dither in the style settings.

If I select format YCbCr 422 and dither=off, the radiance send the full 12-bit 4:2:2?
In general, if I select dither=off, what bit depth the radiance send for the formats YCbCr422, YCbCr444, RGBPC level, RGB-video level?

What exactly does the radiance when I select dither=auto? i.e. How radiance determines the bit depth to send when dither=auto?

Thanks.

[Updated on: Fri, 04 May 2012 11:21]

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Re: dither : Can you explain How it works? Mon, 07 May 2012 07:05 Go to previous messageGo to next message
Methodic is currently offline Methodic
Messages: 37
Registered: December 2009
Junior Member
Hi Jim,Pharkin

Please, Can you help me to resolve my doubts?

Thanks.


Methodic wrote on Thu, 03 May 2012 09:43


Hi Jim,pharkin

If I understand correctly, to determinate the bit depth that the radiance sent, we have to set the HDMI Format and dither in the style settings.

If I select format YCbCr 422 and dither=off, the radiance send the full 12-bit 4:2:2?
In general, if I select dither=off, what bit depth the radiance send for the formats YCbCr422, YCbCr444, RGBPC level, RGB-video level?

What exactly does the radiance when I select dither=auto? i.e. How radiance determines the bit depth to send when dither=auto?

Thanks.

Re: dither : Can you explain How it works? Tue, 08 May 2012 23:47 Go to previous messageGo to next message
jim_peterson
Messages: 1378
Registered: November 2004
Location: Beaverton Oregon, USA
Lumagen Expert
Lumagen Guru
For 4:2:2 Radiance output, dither is off for "Auto", so either auto or off gives you the full 12-bits from our calibration pipeline. You can select dither to 10, or 8 bits, but only do so if you see an improvement in the image quality with one of these settings. Otherwise leave dither as Auto.

For RGB and 4:4:4 output, the maximum precision is 8-bits, so Auto dithers to 8-bits. For recent displays and projectors, setting dither to 7 or 6 bits will make the image have more noise

Static/dynamic, and truncate dither settings are probably not going to be visible. They only exist since Patrick and I could not decide which would be best for every display, and so left it as an "exercise for the reader" to determine if one was better, or these control settings are moot.

Conclusion: It's probably not worth your time to do anything but leave the dither settings at their factory default. It's much more important to select the best output color format - which is normally 4:2:2 for HDMI interfaces.


Jim Peterson
Lumagen
Re: dither : Can you explain How it works? Wed, 09 May 2012 07:53 Go to previous message
Methodic is currently offline Methodic
Messages: 37
Registered: December 2009
Junior Member


Thanks Jim for your illustration !!!


Best regards
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