Color correcting using component out of video card

[T-Bone]

I have asked a number of color space questions before, and here is another one.

I have a Radeon 9800 Pro (AGP) video card in an older system with a Storm card (no component out). For $20, I can buy an adapter that plugs into the DVI-I connector on the video card and gives me YPbPr (analog YUV) out to my monitor.

I'm guessing this thing is this simple because the 4 analog pins on the DVI-I out of the card are hot, but how this thing works is a question for another day.

The question here is whether I get proper colors out of edius to my monitor with this setup. IOW, if I take the same material in edius and output it to the same monitor, will the colors be the same whether I:

(a) go out of this video card with this $20 adapter, or

(b) go out of a Storm/NX card analog component out?

Comments about other reasons to get an NX card are fine, but what I'm really interested in are the colors, since that has always been the biggest difference between going out of a Storm/NX card versus going out of a regular video card without any adapters.

[GrassValley_KH]

A Graphics card, output to a monitor, will be an RGB-as-YUV representation of the video overlay.

A Storm/NX card, output to a monitor, will be a true YUV representation of the source video (on the timeline).

As such, if you are a stickler for accuracy (this is important if you plan to have your work on Broadcast Television), you need to take this into account.

Not all YUV component, is.

[T-Bone]

Not all YUV component, is.

My understanding from this article http://en.wikipedia.org/wiki/YCbCr is that there are standard conversion factors for going from RGB to YPbPr, meaning that, to make up Y for example, you take specific percentages of each of R, G and B.

Are you saying that is not as easy as it sounds, and that there are different ways to accomplish it, so that the NX can do a better job of doing that conversion as compared with how ATI might do the conversion?

[GrassValley_KH]

I guess the point I am (always) trying to make, is that when you choose to color correct a video overlay mirrored from a graphics card, you're correcting an interpretation of RGB data represented as YUV. Along the way, concessions have to be made - RGB->YUV is not a bit-for-bit calculation.

Now, that said, the codecs we (and other vendors) use, are YUV-based. As is our hardware, for output. So there's no RGB-YUV "flipping" and the results you see on a tv screen (such as a broadcast monitor), are the real deal.

As I said, this is really only an issue for people looking for the most accurate image information/data to work with. For others, they're happy with a "cheap" solution that merely involved mirroring their graphics card's overlay.

But be wary of Broadcast stations - they can be very particular when it comes to colours and legality.

[GrassValley_BH]

Are you saying that is not as easy as it sounds, and that there are different ways to accomplish it, so that the NX can do a better job of doing that conversion as compared with how ATI might do the conversion?
For SD there are actually two defined methods of going from RGB to YUV. One method assumes 0-255 RGB maps to 0-255 YUV. The other assumes 0-255 RGB maps to 16-235 YUV.

That difference alone can make for a non-WYSIWYG experience.

Beyond that, the gamut (color range) of YUV is different from RGB, much like how the gamut of RGB is different from CMYK. Conversion can change what you get.

Further reading:
http://en.wikipedia.org/wiki/YUV
http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html

[T-Bone]

Kenneally (whoops!, I see BH has responded, too), just one more follow up.

So edius sends a YUV to the video card, then the video card converts it to RGB just like it converts everything else it receives from any other program, then all this $20 ATI adapter does is some simple represenation of the RGB as YUV, and that YUV is not the same as the YUV that edius sent to the video card.

A theoretical alternative, which you're saying does not happen, is this: the YUV that edius sends to the video card does not get converted to RGB and just passes straight through as YUV (after a digital-to-analog conversion) on the analog pins of the DVI-I connector.

[Timo]

you can find some informations about colorspace-conversion here (http://www.martinreddy.net/gfx/faqs/colorconv.faq)

Enjoy.....

[T-Bone]

thanks, timo, I have read several articles on the subject, but not that one

that's my ultimate question, I guess, whether there is any color space conversion happening going from edius through the video card and adapter to the monitor

[GrassValley_KH]

A theoretical alternative, which you're saying does not happen, is this: the YUV that edius sends to the video card does not get converted to RGB and just passes straight through as YUV (after a digital-to-analog conversion) on the analog pins of the DVI-I connector.

This could be possible, if we decided to write a device driver for ATI, which in turn would feature an EDIUS hardware profile (like DVStorm, NX, etc). But, as I am sure you will agree, is not going to happen. We make our own boards that give you YUV output, after all.

[T-Bone]

OK, the device driver is the link I have been missing - understand, thanks

[Timo]

Hi Kenneally,

what about the possibility of HDMI-connectors?
;-)

[GrassValley_KH]

Same sort of deal again. A device driver has to be written - if it's a graphics card, the problem gets much larger, because of the volitile nature of GPU lifecycles and development.

It is easy for a company like Matrox to do this because they manufacture a software plug-in for an established NLE, and make graphics cards/chipsets.

Last I checked, Grass Valley don't manufacture GPUs, nor do they plan to.

If it was a separate HDMI output board (e.g. Blackmagic Intensity), then it might be a little easier (because technically the board is only designed to work with YUV data).

PS. Good to see you here Timo! Wie Gehts?

[T-Bone]

es geht mir gut

[Timo]

If it was a separate HDMI output board (e.g. Blackmagic Intensity), then it might be a little easier (because technically the board is only designed to work with YUV data).

this is what i´m thinking about

nor do they plan to.

:(

Off topic:
I had a good trip back, after visiting a couple of national parks near Vegas. Impressive !
If you travel to germany, let me know :)

[peterC]

I guess the point I am (always) trying to make, is that when you choose to color correct a video overlay mirrored from a graphics card, you're correcting an interpretation of RGB data represented as YUV. Along the way, concessions have to be made - RGB->YUV is not a bit-for-bit calculation.

Now, that said, the codecs we (and other vendors) use, are YUV-based. As is our hardware, for output. So there's no RGB-YUV "flipping" and the results you see on a tv screen (such as a broadcast monitor), are the real deal.

As I said, this is really only an issue for people looking for the most accurate image information/data to work with. For others, they're happy with a "cheap" solution that merely involved mirroring their graphics card's overlay.

But be wary of Broadcast stations - they can be very particular when it comes to colours and legality.

I am having trouble coming to terms with an adequate output LCD monitor from YUV.

If you go S/composite or RGB/component to a computer LCD monitor 1900 x 1200 say, what are you seeing? True YUV or an RGB / progressive interpolation?

I can't get a clear answer on this. CRT is dead n decent affordable LCD is the answer.I've seen TV station Panasonic LCD's used that top $ was paid for that u wouldn't use in fit. Hopeless!!

Any suggestions? I can only see hi-res computer monitors as an answer, but progressive vs interlaced n YUV vs RGB has got me stumped.

Love to hear of an accurate affordable solution that somebody's using that is 'technically correct' and reasonable in cost.

[T-Bone]

If you go S/composite or RGB/component to a computer LCD monitor 1900 x 1200 say, what are you seeing? True YUV or an RGB / progressive interpolation? .... I can only see hi-res computer monitors as an answer, but progressive vs interlaced n YUV vs RGB has got me stumped.

I'm glad you asked this because I think I've exceeded my question quota for a while. I've got a Dell 24" coming that will display 1900 x 1200, and I ordered it not being sure about the answers to the questions you have asked. A good while ago I asked, "just what is an NTSC monitor," since that is what i need to do accurate color correcting. I never could fully understand the answers that I got because of the issues you have raised.

[GrassValley_BH]

LCD monitors are inherently RGB.
Then again, so are CRTs, just the light is emitted differently.

However, LCD monitors are digital, so each pixel exists as discrete unit, whereas in a CRT, it's a matter of scanning, plus the digital nature of LCD affects the light level output in a different way.

Furthermore, CRTs can do interlaced scanning. LCDs don't.

As far as color goes, because of the analog nature of CRT as well as its phosphor nature, personally I find it more accurate compared to LCD.

However, there's a good argument that the great majority of HD viewers are watching plasma, DLP or LCD, not a CRT-based HD set.

A properly calibrated LCD can serve as a reasonably accurate reference, especially if it's designed for video.

Just be aware that you should still "stick to the rules" regarding broadcast-safe colors and such. LCDs tend to be far more forgiving than CRTs, so just because it plays OK on an LCD doesn't mean it won't bloom, smear or roll on a CRT.

Granted, the technology has advanced to a large degree, so the argument is much like analog audio recordings vs digital audio recordings. There are folks on both sides saying one is better than the other.

[T-Bone]

OK, I lied, one more attempt to summarize

LCD monitors are inherently RGB.
Then again, so are CRTs, just the light is emitted differently.

so we've never been able to "see" YUV - every display device (CRT, LCD, DLP, plasma) that accepts a YUV signal must have in the display device itself a circuit to convert the YUV to RGB

the question has always been, and remains, "how accurate/true is the YUV signal when it hits the RGB converter in the display device?"

[GrassValley_BH]

the question has always been, and remains, "how accurate/true is the YUV signal when it hits the RGB converter in the display device?"
Herein lies the mystery...

You take the same signal and feed it to two different TVs.
As anyone who's shopped for TVs knows, the two will look different.

Now, take the same siganl and feed it to two different broadcast CRTs.
The phosphors and response on broadcast CRTs is calibrated for a set reference.
The two displays should look the same, barring miscalibration, burn-in and the like.

Now, we move to LCD/DLP/plasma...
Again, we take the same signal and feed it to two different LCD/DLP/plasma.
Unless they've been calibrated, they'll look different yet again.

So, at the end of the day we really end up producing a signal that should look correct on the "baseline" display, but we have no idea what it's really going to look like to the end-viewer, except to trust that it will be reasonably close, as long as the end-viewer's display doesn't skew the image one way or another.

Don't get me started on the "modes" TVs have nowadays - Sports, Cinema, etc.

I calibrated my projector using a light meter and spreadsheet that measures the light output of the project. Essentially it aims for an even range of RGB output (granted,majority of luma is in green, but still).

Color calibration is a pain. But the key is that everyone has the same reference.

[peterC]

U have the option of LCD Computer monitor or LCD TV.

Some LCD computer monitors have S/composite in for eg - 'tailored' for video...... (+ other Ins).

What is your take on the 'difference' between choosing an LCD TV to monitor vs an LCD computer monitor to use as reference monitor?

Seems to me there is none, bar some LCD's are better with reference to resolution definition and colour rendition than others. So, that being the case, choose best unit either Computer or TV LCD that u think best suits your situation.
That about it?

[jaegersing]

U have the option of LCD Computer monitor or LCD TV.

Some LCD computer monitors have S/composite in for eg - 'tailored' for video...... (+ other Ins).

What is your take on the 'difference' between choosing an LCD TV to monitor vs an LCD computer monitor to use as reference monitor?

Seems to me there is none, bar some LCD's are better with reference to resolution definition and colour rendition than others. So, that being the case, choose best unit either Computer or TV LCD that u think best suits your situation.
That about it?


Hi Peter. Whether you go for computer monitor or TV, if it's for video monitoring then check the response time too as slower units tend to show video smearing. Downside of most faster units (around 5ms) is that they use 6 bits per pixel instead of 8 so they don't have the same colour depth.

[peterC]

Yes thanks for that J'Sing.

Not a lot said about this in var specs I've looked at except for the Eizo S2410W which uses 14bit apparently, but a little costly at A$2420 24'' and also a little old. 8ms RP, but top of the pile all over especially colour repo. Another is Samsung 242MP (legacy now to 244T) @ 1920x1680 A$2800 24''. This unit was best I've seen going so far - very impressive but dear.

For 'colour correcting' (post exposure mgt use too) and associated 'colour mgt' eg graphics creation and visual SFX/ colour treatments etc it's a tough one to know the best choice vs cost for WYSIWYG and 'tech spec compliance'.

Others: BenQ FP241W - best wrap after the Eizo on one 'read' then as original poster T bone says, inclined to the Dell 2407WP 24''.

Any users with 1st hands?........

[T-Bone]

[whoops, did not see there were posts after this one]What is your take on the 'difference' between choosing an LCD TV to monitor vs an LCD computer monitor to use as reference monitor?

Seems to me there is none, bar some LCD's are better with reference to resolution definition and colour rendition than others. So, that being the case, choose best unit either Computer or TV LCD that u think best suits your situation.
I know you're asking Brandon, but your conclusion must be correct, now that we've established that an LCD is progessive RGB even if it's in an LCD TV - an LCD does not become interlaced just because it's in a TV

with the same inputs and outputs, the only difference between a computer LCD and an LCD TV is that the latter includes a TV tuner, so if you don't need the tuner, you do as you say