How does a TV make white

[JimboJones21]

Hi All,

What is the equation a tv uses to make white? I ask because 100% of red green and blue doesn't make white. I read that 59 percent green and 30 percent red and 11 percent blue makes white.

Does anyone have a more detailed link about this?

 

[felixc]

I am not sure where your take this information. In terms of RGB signals to feed to a monitor, equal values of RGB will create a grey scale from black to white. I have designed graphics boards, so i know that at the RGB connectors the relationship is direct and linear.

Perhaps you are thinking about the lighting power of the phosphors on the CRT?

 

[JimboJones21]

I'm making an rgb LED light and need a formula to convert the pwm of each rgb to make the different colors. I can dim each LED from 0 to 100% with a pwm now, but 100% of RGB is not white, as far as the eyes perception of color. I read that the RGB for white on a TV was 30% 59% 11%. I wanted to know where these percentages came from because I wanted to use the TVs equation to make my colors when I alter my dimming.

 

[IRstuff]

The perception of "white" is a very complex subject. For a standard monitor, equal values of R, G, and B result in a perceived white, but that's also based on how the phosphors emit, how the signals are transmitted to the display, and the color sensitivity of the eye.

Note that not all monitors necessarily have the identical color filters for R, G, and B, so there is some degree of tweaking along the way to ensure that the perceived output appears "white"

TTFN

FAQ731-376

 

[JimboJones21]

Is there a formula used that is tweaked?

 

[itsmoked]

Your quoted numbers are entirely useless as that is a function a typical TV's phosphors not LED emission colors. You need to look elsewhere for a better number but then you will still have issues as the particular LEDs and their particular emission colors are going to alter that too!

There are color instruments that put out the color they see as values. Perhaps you can get one of these and then use automation to find white and any other colors you're after.

Have the instrument put out to a file along with the value you are running from your controller. Have your controller put out every possible setting then look at the instruments output file to find white and the corresponding values that were being put out by your controller.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[JimboJones21]

I'm sure there must be a standard formula that is just tweaked depending on the emission source. Guys who are doing low res graphics with LEDs would be experienced with this.

 

[IRstuff]

I dno't understand what you're asking for. The equation should be obvious:

x*R + y*G + z*B

the coefficients are tweaked until you get white.

TTFN

FAQ731-376

 

[ScottyUK]

What are you defining as '100%' for each LED? Passing the same current through the LED doesn't guarantee the same optical output so you won't find a formula which relates R mA + G mA + B mA = white.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Warpspeed]

This is actually an extremely complex and interesting question.

How much of each colour depends on the wavelengths of the original red, green and blue sources.

For instance what optical wavelength is really green ?

If you had a variable frequency light source, and ask ten different people to adjust it to "perfect" green, you will have ten slightly different wavelengths, and a big argument.

Likewise red and blue. You can drift towards or away from the infrared, and it will still be red, or towards or away from ultraviolet, and it will still be blue.

TV camera sensitivities and CRT phosphors vary a lot in peak sensitivity and peak output.

There have been different standards proposed over the years in various countries but the whole thing has become a historic mess.

One of the original standards for colour TV was the CCIT chromaticity standard. I suggest you Google this to get a deeper understanding.

Black is pretty easy, but the number of different types of white paint available from a paint store, and they ARE different might convince you that true white is not so easily defined.

Back in my student days I leaned that the sensitivity of the human eye to various colours is:

Red 30%
Green 59%
Blue 11%

The eye being most sensitive to green, and least sensitive to blue.

In the end, you will have to decide for yourself if what you are looking at is really white light.

Hold a sheet of white paper against the background of this post and see what two very different whites look like.

 

[VEBill]

It's perfectly simple(*).

Here:

http://www.handprint.com/HP/WCL/color1.html

http://www.handprint.com/HP/WCL/color2.html

(* just kidding)

 

[MacGyverS2000]

Jimbo,

Your constants are used for calculating the luminance of the signal based upon the component colors. This is what allows B/W TVs to work with a color broadcast signal. It has zero to do with how white is made.

LEDs cover a fairly narrow band of wavelengths. They need to be in a proper proportion to each other to create the perception of white, and the chosen wavelengths will have a lot to do with that. Once the proper wavelength bins are chosen, you will need to adjust each bin's intensity... as suggested above, you cannot simply run the LEDs all at full power and expect white (for multiple reasons, which I won't get into here).


I have to ask... what is this for? I've looked at a number of your questions (many pertaining to LEDs) and I begin to question if this is a manufacturable product or a hobby one-off type deal...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[peebee]

It seems to me that there are a couple different standards. I picked this formula up somewhere along the way, I believe this is applicable to ATSC HDTV standards: Y = 0.30R + 0.59G + 0.11B. This is consistent with Warpspeed's statement, BUT, I believe that this is different from older NTSC.

You should check on avsforum.com, those guys love this sort of thing.

 

[Madcow]

Alot depends on the LED's you have.
You need to check the led data sheets to find out
how much light and at what wavelength the led gives off
at a set current.
National semi, cypress and philips have alot
on leds and color mixing.
Try:
Bob Pease, Analog by design show
Driving high power leds without getting burned. Parts 1&2

http://www.national.com/nationaltv/

and

http://download.cypress.com.edgesui...h_brightness_led_controllers___an33640_12.pdf

 

[MacGyverS2000]

VE1/Cow, good links!

Dan - Owner

http://www.Hi-TecDesigns.com