Dimming curve question

**Santacarl** · 05-11-2015, 01:18 PM

Hey All...

After reading the thread in the Nutcracker section and as I watched John's videos....At one point he mentioned setting a low intensity level (~20% if memory serves) for videos on his matrix to prevent washing out of colors.

It got me to thinking.....and yeah I know Joe's probably thinging....rut roh there he goes again.....

I use dimming curves on my pixels.....I set each color level and incorporate all 3 color dimming curves into an overall RGB dimming curve. But I've noticed that any time there is a lot of white in one of my displayed graphics (think santa's beard) the white just overpowers any other color...especially those bordering the white...(think the rosy cheeks of Santa's face being washed out by the nearby sea of bright white in the beard.)

There is no place to adjust the dimming curve for all white...at least not that I can find....So, naturally, while the RGB dimming curve takes care of mixing the 3 colors.....there is no way to 'dim down' the pure white created when the 3 colors all come on at the same time to create white....

To my way of thinking.....the white just overpowers the individual colors that are competing for viewability at the same time...

Am I thinking of this correctly? Is there a cure?

Thanks

SC

**angus40** · 05-11-2015, 01:37 PM

Software control is not enough we are limited by hardware .

These pixels will always have white brightness issues no matter what we do .

Take a look at this video and you will get an idea as why we are and will be limited .

https://www.youtube.com/watch?v=6iHTbGsnI8Q

**JHinkle** · 05-11-2015, 01:59 PM

You control White by controlling Red, Blue, Green.

100% White is 100% of all three colors.

Joe

**Santacarl** · 05-11-2015, 03:22 PM

Yeah Joe...I understand that....but pure white is sooooo bright that it seems to overpower the other colors....it's not the color I'm talking about...it's the intensity/brightness that I seem to be struggling with... Maybe when you combine all 3 @100% you just get the color white and that has noting to do with the intensity...I was just thinking that one of the main benefits to a dimming curve is that it allows you to adjust the brightness of a given color so that when you look at a green and blue they both appear as having the same brightness.... I know if I don't adjust mine and I turn on a blue and a green at same time the green APPEARS brighter......and I was trying to think up a way to adjust the whites so they too 'blend' and appear of the same intensity as the other colors to the eye....

**gadgetsmith** · 05-11-2015, 04:00 PM

I would take your graphic and adjust the whites to some level of grey. A little trial and error might give the results your looking for.

As for the appearance of green being brighter, it's not just appearance. Take a look at the specs I pulled off of aliexpress. They are pretty much the same for the ws2811 bullet nodes.

Red = 3.3 Lumens/300 mcd, Green = 10 Lumens/1000 mcd, Blue = 2.7 Lumens/300 mcd

In addition, the human eye is much more susceptible to green than red or blue. So we perceive an increase in green as an increase in brightness much more than red or blue.

I think Joe was saying if you want white to be dimmer, use 50% for RG&B to make a 50% lighter white, of course it doesn't quite work that way, but with some messing around you can come up with a better white (dimmer) to suit your needs. This won't apply to graphics as you can't isolate the white in a graphic to just change white, which is why I suggested turning white to gray in your graphic.

**JHinkle** · 05-11-2015, 04:15 PM

Dimming curves are there to match illumination levels for Red, Blue, Green and then modify the proportion to get secondary colors like yellow.

The problem you are having with White is not solved using a dimming curve. YOU solve it by picking the WHITE intensity.

White is so bright because you have all three leds on. As gadget stated -- you might want to try White at 50%, or some other illumination level, to get the intensity to match the pure Red, Green, and Blue lights nearby.

Joe

**Santacarl** · 05-11-2015, 04:19 PM

Originally Posted by gadgetsmith

I would take your graphic and adjust the whites to some level of grey. A little trial and error might give the results your looking for.

Take a look at the specs I pulled off of aliexpress.

Red = 3.3 Lumens/300 mcd, Green = 10 Lumens/1000 mcd, Blue = 2.7 Lumens/300 mcd

In addition, the human eye is much more susceptible to green than red or blue. So we perceive an increase in green as an increase in brightness much more than red or blue.

Yeah....that's why I use dimming curves...I had to cut the green back considerably to get it's brightness close to the Red and Blue.... The way I did it was to take the weakest (less bright) color and see when it quit getting brighter.... That is my highest and baseline number for all 3. I took the other 2 colors and dialed them up until they matched the brightness of the less of the baseline color...as it turns out my green now stops increasing in intensity long before it would if left unchecked. When I turn on a R, G, and B at the same time they all appear the same in brightness.

But that does make me wonder.....going back to Joe's statement of 100% of all 3 colors=100% white.... In theory, if all 3 nodes are of the same relative brightness you would expect 'pure' white as a result.....but if green has more prominence and you bring in all 3 colors @100% wouldn't that, based on the specs you gave for pixels, make the resulting white have a slight greenish tint?

**Santacarl** · 05-11-2015, 04:58 PM

Originally Posted by angus40

Software control is not enough we are limited by hardware .

These pixels will always have white brightness issues no matter what we do .

Take a look at this video and you will get an idea as why we are and will be limited .

https://www.youtube.com/watch?v=6iHTbGsnI8Q

Sooooooo, to sum up....to get control of the brightness I need to buy a jumbotron!

**JHinkle** · 05-11-2015, 05:28 PM

You keep talking as if the world is linear -- it is NOT.

Your eyes do not respond linearly to different colors -- they are most sensitive to RED. That is why when I flew jets for the Marine Corp back in the VietNam days -- lights in the cockpit were RED. That is also why street lights are RED for STOP -- you see RED better than every other color -- hence RED to STOP!!!.

Do research on what studies were done to produce good looking color TV and Monitors --- there is a ton of level adjustments per RGB color depending on intensity to make you, the User, have a nice picture on the screen.

With RGB pixels -- and you building matrices and MegaTrees and looking to have secondary colors and matching intensities -- you are back in the 1950's all over again trying to figure out how to manipulate led intensities for good looking displays.

RGB pixels are to the point were you ask for a color -- and it might give you that color (think secondary colors, e.g yellow, purple, orange). There is a lot of work left to do to get pixels next to each other to have different colors AND similar "PERCEIVED" illumination levels (WHITE being the worst). The eyes do not respond in a linear fashion to color as stated above.

The world is one big non-linear mess and little old you is trying his best to make it fit into a linear one ... don't try too hard -- you will get a head ache

**gadgetsmith** · 05-11-2015, 06:01 PM

There is no such thing as pure white either. Warm white contains a lot of red. Daylight contains a lot of blue. Really it just comes down to finding something you like and sticking with it.

I can see what your doing with the r g b dimming curves, but is that messing you up when you try and make something white? The r g b might be a different mix than the blend you get from your dimming curves?