grayscale correction question

Discussion in 'Displays' started by Carmine, Jul 28, 2005.

  1. Carmine

    Carmine Agent

    Joined:
    Nov 6, 2004
    Messages:
    28
    Likes Received:
    0
    i've recently adjusted my lcd rptv's grayscale using colorvision's spyder pro colorimeter. i entered custom values for x,y to obtain a grayscale value as close to D65 as possible. i proceeded to adjust my cuts & drives along the entire grayscale ramp (from 20 IRE up to 100 IRE). according to the spyder colorimeter results, i was incredibly close to my desired grayscale temperature. here is my issue, when viewing black & white movies, i noticed that there was a red hue to the picture. what should i do to remove this? if i reconnect my colorimeter & take a reading, it is still going to be close to D65 as i haven't changed anything. any suggestions as to how i should correct this?

    thanks so much guys.
     
  2. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

    Joined:
    Mar 16, 2000
    Messages:
    2,909
    Likes Received:
    1
    Location:
    Calgary, Alberta
    Real Name:
    Michael Chen
    Greetings

    Have you accounted for the fact that the spyder devices are not that accurate on the dark end?

    What about the contrast being too high that it discolors the entire grayscale?

    Regards
     
  3. Carmine

    Carmine Agent

    Joined:
    Nov 6, 2004
    Messages:
    28
    Likes Received:
    0
    hey Michael. yeah i was told a bunch of times already that the spyder is pretty innacurate on the darker end. my contrast is set a bit high as well. can i ask a question of you Michael as your really know your stuff. what is the correct order of performing a complete calibration. i mean what do i do first - contrast & brightness, color, grayscale? i know it is a pretty iterative process of going back & forth between options to get it right, but if you could possibly guide me as to which i should do first. also, why do i keep reading that adjusting horizontal/vertical service menu options to correct overscan could render a TV useless?

    thank u again so much Michael.
    Carmine.
     
  4. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

    Joined:
    Mar 16, 2000
    Messages:
    2,909
    Likes Received:
    1
    Location:
    Calgary, Alberta
    Real Name:
    Michael Chen
    Greetings

    Contrast first ...

    Then Brightness

    Then grayscale (go back to contrast then brightness repeat)

    Then color/tint

    Aside from the iterative stuff (all)

    For an LCD ... put up the grayscale vertical sweep pattern from DVE say ... 12-14 ...

    Look at the bright end ... decrease contrast to get rid of white crush ... but decrease more if whites look red/orange ... keep going down until that coloration goes away. Now you have your optimal contrast set.

    Go do the brightness now.

    When happy with that ... go do the grayscale with the 30 ire and the 80 ire boxes. After the iteraive process ... take a reading at 50 ire ... and then decide how to compromise the grayscale ends ... up or down.

    Finally go do the color / tint / color decoder

    Do sharpness too of course.

    Regards
     
  5. Carmine

    Carmine Agent

    Joined:
    Nov 6, 2004
    Messages:
    28
    Likes Received:
    0
    Michael Thank you so much!!!!!! I now finally have an order of operations for my self-calibration. I do appreciate it so much!!!!!

    Carmine.
     
  6. Carmine

    Carmine Agent

    Joined:
    Nov 6, 2004
    Messages:
    28
    Likes Received:
    0
    hey Michael one last thing, what are the correct luminance values for black & white? spyder allows me to enter these as well.

    thanks again.
    Carmine
     
  7. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

    Joined:
    Mar 16, 2000
    Messages:
    2,909
    Likes Received:
    1
    Location:
    Calgary, Alberta
    Real Name:
    Michael Chen
    Greetings

    Are you talking about black and white movies?

    IF so the coordinates are :

    0.3349x, 0.3497 y

    This is 5400k ...

    Regards
     
  8. Carmine

    Carmine Agent

    Joined:
    Nov 6, 2004
    Messages:
    28
    Likes Received:
    0
    ok Michael i followed your instructions & went back into the service menu to try to correct the reddish tint from black & white material. my contrast seems to be set pretty much perfect according to the ramps pattern you suggested i use. my black level is set to about 13 on the user menu & i'm not really seeing too much black "crush" but the picture still has a bit of a reddish tint on black & white. anything else i might try to alleviate this? also, i still seem to have a bit of red push after viewing color bars & bringing axis, r-yr & r-yb way down in the service menu. anything i can do to fix this also???

    I cannot thank you enough Michael for all of your help so far!!!!

    Carmine.
     
  9. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

    Joined:
    Mar 16, 2000
    Messages:
    2,909
    Likes Received:
    1
    Location:
    Calgary, Alberta
    Real Name:
    Michael Chen
    Greetings

    If the dark stuff has the red tint, then you need to adjust the grayscale ... aka the cuts. Either decrease rcut or boost bcut and gcut at about a 2:1 ratio.

    The R-YR and r-yb should fix the red push. If not enough range in one of the R items ... bring color down a few clicks and try again.

    Regards
     

Share This Page