Here's a Good Method to Eyeball Grayscale.

Discussion in 'Archived Threads 2001-2004' started by James Zos, Feb 16, 2003.

  1. James Zos

    James Zos Supporting Actor

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    I can't take credit for this method, because it was sent to me by another HTF member who wishes to remain anonymous. It is, of course, not the same thing as getting an ISF calibration, but if you are short on funds and live in hicksville like me, it may be the next best thing. I've tried several different ways of eyeballing grayscale and this has given me the best results so far (though my color decoder is still off slightly.)

    Here's the method, as sent to me by a valiant fellow member who deserves a lot of thanks. (Note: on my set, step 8 did not work exactly as planned. Increasing blue drive from zero did not bring the square towards gray. I had to bring blue cut up from zero first, before this would work. But everything else went fine. After several attempts at this method, my picture looks a hell of a lot better than it did before.)


    Gray Scale Procedure
    I have had success with the following procedure getting with in 500-1000K of the correct balance. It keys on the acute sensitivity of the eye of yellows being green or red. The final blue adjustment is the most difficult part. You need to be careful not to add to much. Even if you think you have it right you can use this to check it.

    GOOD LUCK!!!

    An instrument free procedure for adjusting white balance:
    1. Place a bright gray window (~70 IRE) on the screen from AVIA or VE.
    2. Drop your blue drive and cut to zero. Hopefully it will go low enough to not interfere.
    3. Adjust the red drive until the window looks pure yellow (not green or red tinted).
    I record the values where it looks slightly green and red and then try the values near the middle of those.
    4. Place a gray scale ramp (100-0 IRE) on the screen.
    5. Adjust red cut and green cut if you see a problem with low IRE yellows. This is difficult to judge.
    6. Go back to step one if you changed either the green or red cuts.
    7. Change the gray window to a value of around ~60 IRE.
    8. Set the blue drive to zero and then increase the blue drive until the screen just looks gray and stop.
    I use a photographic gray card with either indirect outside lighting or a 6500K light source to judge this.
    Be very careful not to make the grays overly blue.
    9. Place a gray scale ramp (100-0 IRE) on the screen.
    10. Adjust blue cut if you see a problem with low IRE grays.
    11. Go back to step 7 if you changed blue cut.
    12. Readjust the color decoder if you have done this previously.
     
  2. TimTurtino

    TimTurtino Stunt Coordinator

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    Wow! That's cool. Now, I just have to find the photographic gray card and 6500K light source... [​IMG]

    Me
     
  3. James Zos

    James Zos Supporting Actor

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    "Now, I just have to find the photographic gray card and 6500K light source"

    I think it helps to have those two things of course, but I also think this method can improve grayscale even without them.
    I have a photographic gray card, but I didn't actually use it much when I tried the above technique. You can buy a card from any photo supply store if you want, and look at it under sunlight to get a better idea of what gray should look like. I don't have a 6500k light either. There are company's that sell 6500k lights with home theater in mind - Cinema Quest sells a basic one for about $50 ( http://www.cinemaquestinc.com/ideal_lume.htm ) I may or may not eventually shell out the money for one...Some people also buy them from pet stores and such.
    If you do try this method, please post your results, good or bad. I'm curious to know if it will help other people like it helped me.
     
  4. ManW_TheUncool

    ManW_TheUncool Producer

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  5. James Zos

    James Zos Supporting Actor

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    Man-Fai, it is true that one should be careful when messing around with grayscale, only in that you should be sure and write down all settings - even settings you don't intend to change - before going in and tweaking any of them, because you may accidentally change a setting and then not remember the original value. But as long as you write the grayscale settings down before tweaking them, you'll be fine.

    As for not tweaking grayscale unless it needs fixing, this is true. In my case my set developed a slight green tint, evident in darker scenes and it started to drive me crazy. By coming up with my own grayscale settings, I managed to both get rid of the green tint and improve the overall picture. I know, because I wrote down my original settings, and if I put them back to where they were, I can't believe how bad the picture looks compared to my new settings.
    Unfortunately I bought a new DVD player, and what looked near perfect on my old Sony, looks off on my new Panasonic, so I had to go back to the drawing board. The method outlined above has helped me considerably and is a lot better, in my opinion, than just eyeballing a single pluge pattern.
     
  6. Sean M

    Sean M Stunt Coordinator

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    Sure you can eyeball a greyscale. But normally it's done to an outside source that is predetermined to be the grey, in varying shades, that you are looking for. The device used for this is called an optical comparator. There are instructions on how to make one somewhere on avsforum, and may have been posted here, if you do a search. This is just another method. Even some ISF techs use this method when calibrating a set, though not the better ones, IMO. It is worth noting that even if you have a perfect reference point to compare to it won't be nearly as accurate as using a light meter to measure the actual color temperature along the greyscale and make adjustments accordingly.
     
  7. James Zos

    James Zos Supporting Actor

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    "There are instructions on how to make one somewhere on avsforum, and may have been posted here, if you do a search."

    I don't know if that is in the tweaks section of AVS, but I think that section has been made subscriber only, or something like that. I couldn't access it last time I tried.
    Still I'm familiar with the basic idea behind building a comparator. You take a narrow rectangular box with a small hole cut through the middle on either side. The inside of the box is painted gray, and you have a 6500k bulb inside the box. You place the box up against your TV screen which should be displaying a grayscale test pattern, and looking through the hole, try to get the screen to match up with the inside of the box. Kind of like using the flashing blue bars on AVIA.
    Getting the light would be easy enough, but how do you get the inside of the box the correct color of gray?

    What about using a computer monitor to help calibrate? Say you take a screen capture of an AVIA grayscale pattern, then display it on your monitor next to your TV, with the TV displaying the same pattern, so you can have something to compare it to. Sure the monitor might not be perfectly calibrated, but I think my Viewsonic monitor is a lot better calibrated than my TV, plus it has a 6500k setting...
     
  8. James Zos

    James Zos Supporting Actor

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    "I don't know if that is in the tweaks section of AVS, but I think that section has been made subscriber only, or something like that. I couldn't access it last time I tried."

    Never mind about the above. I did a search on AVS with optical comparator in the title of the thread and got back several hits on how to build your own.
     

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