Capturing LCD screen and white balance.

Liam_Vegas wrote on 1/31/2004, 12:48 AM

I am trying to capture the screen of an LCD monitor using my VX2000. I just cannot get the color to come out the same as is on the LCD. I know a few members of this forum do this sort of thing so I thought I would ask for your help.

Is there some trick to doing this in the camera or will I have to correct it in Vegas after capture?

Obviously the default white-balance settings do not work (tried those first). Doing a manual white balance seems a little pointless also as usually you hold up a white card under the specific lighting conditions under which you are shooting... but in this case of course the LCD itself is emitting the light so I think that just won't work (even though I had my doubts I still tried displaying a white screen on the monitor and using that as the white-balance "card"... but of course it made no difference).

I just know the answer is probably really obvious.

Thanks for your help!

-Liam
[edit] If I could trouble you to also read

[FINAL EDIT]
Thanks for all that helped me with this. If you want to jump straight to the (for me) final solution to my particular needs right now you can jump to this post.

Many people were a great help but I wanted to recommend the posts by farss (such as this one in particular) as they helped me understand more fully what was going on.

Back to post

Comments

Liam_Vegas wrote on 1/31/2004, 3:21 PM

The CRT/LCD thing is interesting. I just did not even try to capture the CRT Image due to the flicker. I tried reducing the shutter speed to below 60th second but that didn't help.. and I have just realized that I probably should have reduced the screen refresh rate down to 60 hz as well?

Anyway... I really prefer the contrast/detail that I see from the LCD monitor and my belief was that I would likely have the exact same color issues even if I captured off the CRT. But maybe that was an incorrect assumption.

From others who have posted they have done this sort of thing in the past it seemed they had all recommended taping direct off an LCD screen over a CRT (if you did not have a $3000 scan converter to hand).

Thanks again for the detailed reply.

Zulqar-Cheema wrote on 1/31/2004, 3:43 PM

Having seen the two now Liam, I think the scan one is probably the more faithfully in colour if a little blurred & dull, the other is certainly brighter but looks slightly on the bluish side.
I have loaded the scan one into vegas and with some levels, sharpen, and secondary colour, you can get the picture right out.

I can send a copy if you wish to see?

Liam_Vegas wrote on 1/31/2004, 4:01 PM

Having seen the two now Liam, I think the scan one is probably the more faithfully in colour if a little blurred & dull, the other is certainly brighter but looks slightly on the bluish side.

yes. I think that is <precisely> what I have been saying.

I have loaded the scan one into vegas and with some levels, sharpen, and secondary colour, you can get the picture right out.

Sure... by all means do that. I would love to see what you have achieved. In the end I had believed that working with the LCD captured image with better sharpness and detail and then with some color correction would be better than trying to bring detail out of a dull and blurry image of the correct color.

But I am prepared to be surprised.

Email to Liam.Kennedy AT Imagebeam.com

Thanks

Zulqar-Cheema wrote on 1/31/2004, 4:56 PM

Should be winging it's way to you, if you do not receive it let me know.

multiwave at aic . co .uk

Grazie wrote on 1/31/2004, 10:20 PM

[This is not a frivolous response - I really do mean it. ]

LV . .seems like Z has a handle on your problem. He does have a wealth of understanding in this field. Once he's engaged with a problem he'll give it his best shot . .I know . . I've been there.

Now, I'd really like to understand the physics going on here. Keeping this in mind, is it the type or form of "light" energy that comes off the surface of the LCD that is creating the problem? Some type of colour shift due to the "projection" onto the surface - albeit from underneath the final lamina of the LCD surface - that is creating these issues? Is it the direct capture from the surface by our cammies that is creating the problem? Do our eyes somehow recode "correctly"?

This is where I started thinking about a "sideways" [ literally! ] approach. This is only for testing, but if it works - hey!?

Could you arrange a mirror at 45°, or whatever angle is required, and then "shoot" the reflection? Look, I'm interested to see if this is a solution AND trying to understand what the issues<>physics are . . .. If this does work then it is only a matter of using flip or mirror or p/c to get the final image in the correct orientation . . .

Best regards,

Grazie

farss wrote on 1/31/2004, 11:04 PM

From a physics point of view, CRTs use additive color, LCDs use subtractive. CRTs generate R,G and B light. LCDs start with white light and subract to produce R,G and B. Bouncing it off a mirror is only going to add another variable even if it's a front silvered mirror and they're not that easy to come by.

Reason the scan converter has a hard time is it's got to resample the pixels and do a frame rate conversion. Neither of those add up to great quality images, together well...
A Sony one which is really so so quality will set you back around $6K here and it's not a top line unit.

Best thing to try and do if this is possible and this may be a big "IF". Match the programs output to your video format and capture from that. Use a video card with video out and capture that using S-Video into either a camera working as a VCR or whatever. This way you avoid frame rate conversion and pixel remapping.

I've had a few clients come to grief trying to do similar things, something as simple as trying to feed a PowerPoint presentation through a vision mixer, YUCK. 1200x1000 scaled down to 720x576 looks horrid, change the PC to 800x600 and it starts to look better.
Not the same as the issue here of course but hopefuly you'll start to see why it's so damn tricky.

Grazie wrote on 1/31/2004, 11:39 PM

farss, thank you! The penny is starting to drop. I like your simple explanation .. it has helped to fill-in some of major voids in my video education . .

Regards,

Grazie

Liam_Vegas wrote on 2/1/2004, 1:21 AM

Got the file. Thanks.

I have uploaded your file to the web site so others can see it. I was impressed by what you did... but I still think I can get more from the LCD version with color correction. I have been messing around a little and while I am not 100% ok with the result I think I can get it better still.

All images together (before and after)

#1 Original image from LCD Monitor
#1a Color corrected by Liam
#2 Original Image from Scan converter
#2a Sharpened adjusted by zcheema

Thanks for sticking it out.

-Liam

corug7 wrote on 2/2/2004, 6:33 AM

Liam,
Yes, I was talking about the color temperature setting on the LCD screen. Mine is switchable between 2900 and 5200k. I was thinking maybe if you had that option that you could switch your screen to 5200k and forget about the problems with orange (sorry, yellow/red for you ar-tists). For some reason I am unable to download your pictures, but the net connection I have here at work is iffy at best anyway. You asked if I noticed ANY color difference in my attempt. I have to say not really. I wasn't looking for absolute perfection, though. I just wanted to watch a bigger picture regardless of resolution. Hope things are working out for you. Corey

Liam_Vegas wrote on 2/2/2004, 10:42 AM

Thanks for the reply. It seems that your LCD has a "simple" way to set the color temperature. The one I have seems to be very flexible in that I can fiddle with lots of settings but that has it's disadvantage that I don't know what to set it to and trying it randomly seems to me to be a little pointless (and time-consuming).

I think I have achieved the best result I can so far by just doing the color correction in Vegas.

It was a very interesting thread anyway and I feel I have learned a lot from everyone along the way.

Not sure what may be wrong with your access to the images. Ther are just images on my web site so if you can post to this forum I would not expect any particular problems with accessing that web sote also. But... the internet is a strange thing sometimes.

Liam_Vegas wrote on 2/2/2004, 11:48 AM

Just a "bump" to get the post back to the top (not because I particularly need any further input) because I have made some edits to the initial post with a description of the solution and pointers to the posts that helped me the most.
:-)