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How to Eyeball a better grayscale

3K views 10 replies 8 participants last post by  ADU 
#1 ·
Gain=contrast

Bias=brightness


Also called cuts & drives with RPTV's

Drives=contrast

Cuts =brightness


Digital PJ's usually have RGB-contrast RGB-brightness.


Contrast RGB's effect the lighter part of video or 50IRE up.


Brightness RGB's effect the darker part of video or 40IRE down.


A good way to eyeball a grayscale is to freeze a vertical IRE gray pattern. This pattern will show you 10IRE steps from black to white in shades of Gray.


Any unwanted color in the darker area you work with the brightness rgb's.


Any unwanted color in the lighter area you work with the contrast rgb's.


These patterns are in Avia and DVE. Or anything with step boxes of gray like the Avia Pluge pattern with steps, or Needle pulse, the THX optimizers brightness pattern has step/boxes of gray.


Overall the concept is interesting. We're trying to make each shade of gray (steely gray) with no color tones. This will make the colors be at their best.


Tune the basics first, contrast,brightness,color


The next thing to do is find which color temp gets closest to gray by toggling through the choices.


Then use the 50% format to fine tune.


If you need to remove blue from the light grays, lets say 4 clicks, stop make it just 2 clicks and in turn increase the red and green 2 clicks each for balance. Or you could leave blue where it was and start by increasing red & green.


The balance thing isn't written in stone. Ok first you tuned your brightness level, this sets the green for the brightness RGB area. So if you see green in the dark gray steps, just increase the Red & Blue to balance out the green to make gray.


That's it, you can use this for RPTV's, CRT projectors, and Digitals as long as you can find the RGB control. With my Toshiba RPTV I have to do into the service menu.


This doesn't get you ISF D65k but it sure will take the green or purple out of Leeloo's face in the ledge scene. ;)


Good luck
 
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#2 ·
An old indian trick (red indian) for grayscale is to turn off the blue and adjust the red and green for yellow. The human eye is very sensitive to yellow and can easily tell the difference between reddish yellow and greenish yellow. Once the yellow is right turn on the blue and adjust for gray. Try it and see.
 
#4 ·
tse


Are you looking at a Yellow pattern with that trick or a White pattern?


I have noticed I can see greyscale errors much easier with the Secondaries - this of course assumes you have a valid video color decoder (like the Accupel).


Good trick to play on my customers when I throw up the colorbar though - and say yep your greyscale is off! Leaves them baffled wondering who they heck did they hire judging the greyscale without even looking at greyscale patterns!


Not much of a newbie trick though because they likely lack the reference video standard.


Everyone should be using a D65 computer monitor - it keeps the trained eye properly biased to a reference. I just bought a ViewSonic 23" widescreen HD LCD - my old monitor died after 7yr of faithful service. Only 500:1 contrast ratio on the LCD though - but it is supposed to be a perfect HD reference tune on it.
 
#5 ·
Bump to cover all the display users, especially CRT users. I don't know if you noticed but many Front CRT sellers display some way out of whack grayscales. ;)


Though some are more than excellent.


Kras, I got a 17" widscreen ViewSonic HD LCD for my daughter this year. First year at UC Santa Barbara and she needs her MTV. The picture looked pretty good.
 
#6 ·
I saw a G90 the other day, and the greyscale on that looked pretty good to my eye. No obvious colour shifts that I could see. I'd seen an 8" CRT and the colours needed work - the greyscale was obviously out and showing a very yellowy white at 100IRE. It's possible that it could be corrected (you need to be able to adjust the gamma for each IRE as well as RGBs), but I wonder why CRT owners seem less bothered about colour accuracy and D65 than digital owners.


Gary.
 
#7 ·
Just make sure none of you are not ill when you are doing these tricks. Have any of you been sick to the point that you vision's color has changed?
 
#8 ·
Quote:
Originally Posted by TheFerret
Just make sure none of you are not ill when you are doing these tricks. Have any of you been sick to the point that you vision's color has changed?
There may be some color changes with, say, a severe viral illness, that should be temporary. Medical conditions most widely referred to--aside from congenital conditions--that involve color vision changes include but are not limited to: cataracts, multiple sclerosis (optic neuritis), macular edema, ocular infections, and macular degeneration. Digitalis intoxication (said to possibly have influenced Van Gogh's later paintings) can lead to the perception of yellow and halos.


Probably more common around here, the use of Viagra or Cyalis can cause a temporary blue/green or pink or yellow tinge to colors. Of course, there is an overall loss of vision as a possible side effect from Viagra or Cialis making it a slightly tougher call when deciding to use these drugs or not. Don't take these drugs and then decide for some reason to embark on a calibration session.


Dan
 
#11 ·
Interesting thread. The following was suggested not too long ago in one of the CRT SM/calib threads as an alternative to using midday clouds as a 6500k reference.

What you need

1) 6500K flourescent bulb. (Walmart has some ~75-80 CRI 6500K screw-in bulbs. The higher the Color Rendering Index rating, the better.*)

2) Kodak 18% Photo Grey and White, or Ramped Grey card. (Available at good photo supply shops, or online from Kodak.)

3) Sheet of black foamboard or cardboard (available at Walmart or Office Depot).

What you do

Mount/tape the neutral grey and white photocards (or ramped greys) on the black foamboard, and set it against the wall behind or next to your display, and use the 6500K light as a back/bias light to illuminate it. Turn off/eliminate all other light in your viewing space (if you have windows/doors that don't completely shade, do this at night). Adjust the temperature/grey scales on your TV to match the photo grey/white/ramped grey card.

Variations on a theme

This DIY comparitor is just a variation on the backlighting/wall-treatments many people use to create neutral environments behind/around their displays. So another alternative is simply to buy some truly neutral grey (and white) paint and make your own "photo cards" or background treatment, which can also serve as a 6500k optical comparitor.


Depending on the type of display you're using there may be different configurations of 6500k light/viewer/grey reference/display that may work more effectively for you than the above. The basic idea though is to minimize contamination of the grey reference and display by light reflected from other colored surfaces in the viewing area, to keep them as close to 6500k as possible. (If your viewing area is mostly black or neutral grey, then this shouldn't be an issue.)


*If you don't want to go the Walmart route, this company has some made-to-order HT backlights with higher CRIs that should be ideal for a project like this.
 
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