Can anyone tell me about this colour issue?

[grant_mckean]

Have a look a this attachment. Its a photo of my Flame monitor and I've never seen anything like it. Its a pure blue backing colour with a mid grey circle with soft egdes blended on top. What is this dark halo I see? It's def NOT any sort of comp or premult issue becasue, when I simply lighten the blue the halo dissappears. I am left thinking that its a colour transition that the monitor cannot handle, but it is also apparent on my grade 1 video monitor? VDU's in general cannot reproduce these colours so close together? Any clues most welcome.

Thanks

Grant (McKEAN)

Sapient Nitro

[HalloweenJack2]

Hey,

So is it a composite you've made?

What are the RGB values and colour depth?

What blend mode are you using?

I'll try to recreate.

[grant_mckean]

Hi HalloweenJack

Cheers for taking the time. I've attached a little archive for you, however it might be just as fast to type in (8bit) RGB=100,100,100 for the grey frame (use a full frame just to be sure there is no extra multiplys going on) and put it over a pure blue background (RGB=0,0,255).  If you put a heafty blur on the matte for the grey circle, then use blend....and there you have it - the worst edges I've ever seen!

Hope we find some answers!

Grant McKean

[HalloweenJack2]

Hi there,

I'm not a colour space expert but I think what the problem here is that blue is all saturation and hardly any luminence.

Blue has the lowest lum of the primaries, so that doesn't help.

I'm getting the same effect too. It looks to my eye that the blue edge is darker than both the blue and the grey.

But it has the correct luminance, a mix between the 2. It's the same as taking your incredibly intense blue and desaturating it, which leaves it looking a lot darker.

DeSat your blue and you get 8bit Grey RGB=18.

I can see why it's happening technically, and it is correct. But I'm trying to think of a way to make it look to the eye more natural...

Maybe there isn't a way? That blue is very intense. 

Is it a real use or were you just playing around?

You should try using Gradiant node and having a 3rd colour element in there. A light grey I guess, and see if you can balance it to your eye.

Or stick a CC or CW node after the Blue and increase the black level. You still get the intense blue but you lose the dark blue border.

Cheers 🙂

[grant_mckean]

OK thanks. Its good to know that you see it too. The blue is very intense and I dont need to fix the edges. The plate was created to test out some keying techniques but as soon as I made it I just thought what on earth is that, like I'd found a kind of blindspot on the monitor. I'll test it out a bit more and perhaps I need to learn more about how the monitor makes its colour.

Thanks for looking.

Grant McKean

[HalloweenJack2]

No probs 🙂

[ManChicken · Accepted solution]

I think what you're actually seeing is an artifact of compositing with gamma.  Because we've applied gamma to both colors, where they mix winds up creating an incorrect result.

Try connecting a LUT Editor node set to 'Log to Lin' after each of your two color generators. Then connect a LUT Editor to the output of the Comp, set to 'Lin to Log.'  See attached image.

[grant_mckean · Accepted solution]

Hi Bob.

You certainly seem to have the answer there, gives me a starting point to read up a bit more. Thanks for posting

Cheers

Grant

[Andy-Dill]

in a nutshell:

https://youtu.be/LKnqECcg6Gw

[grant_mckean]

Aha! Andy, that video is a pleasure to watch and is precisely the explanation is was looking for. A great find. Thanks.

Grant

[Andy-Dill]

Yeah. For years I wanted someone to explain why "linear is better" and didn't get a satisfactory explanation. That video explains everything nicely and in 5 minutes. 🙂

[HalloweenJack2]

Great video! I've come accross things like that, like stops in photography, but never seen it like this.

Unfortunately, I don't quite understand.

I don't get where the extreme colour fits in.

If you try the same thing with 2 shades of grey it looks ok. No dark banding. 

Or if you look at the dodgey colour blend and turn the chroma down on the monitor it looks ok.

Or is it that the band is just the wrong gradient from one colour to the other?

And so happens incorrectly alligned with the colour change?

Don't know if that makes sense. 

Also if you look at lum scope, the correctly blurred edge between red and green looks lighter than both colours.

Anyway, I feel there should be something about the change of chroma in the explanation rather than just brightness and gamma.

[Andy-Dill]

A mono image doesn't mix multiple color channels so there's no "averaging of two square roots" taking place in the mix/blur area.  Similarly, if you drop the saturation to zero, you're putting all the values into a single channel, either physically with a CC or perceptually by setting the monitor to mono.    It's the mixing of multiple colors that causes the issue.

The reason a linear blend red to green has a bright middle is because yellow is a brighter color.  It's the sum of red + green, so it gives off more brightness than either on its own. 

[myeffigy]

Hey Andy, Thanks for the video about color. Very cool. In response I made a Blending shader that applies the squaring to the video before blending.

It helps with the dark edge on 2 saturated colours blending. see below. Normal v's Squared. See attached .zip for glsl shader. And for some reason I couldn't generate the .mx file. So if someone can do that I would appreciate it...

Mark

[myeffigy]

Because everyone has been so keen on my last blend node... I made a version 2.

After fiddling with the maths, and not being 100% happy, I decided to give you control of the HSV values in the blend. Make it whatever color / brightness you think looks good. Curve Type relates to the introduction of HSV values into the blend and pivot is like contrast pivot, based on the matte.

[myeffigy]

btw, this shader should work in 2015, but I have not tested it. Currently it works on flare 2016 training edition.

[grant_mckean]

Hi.

Shader looks great however on my system (2015 ext3.1) there is nowhere to attach inputs on the matchbox node. Could be somthing I've done wrong?.... I just copied it to the usr/discreet/flamepremium_2015.3.1/matchbox/shaders folder to install it.

Cheers

Grant

[myeffigy]

Unfortunately, i dont currently have access to a linux flame, so i cant say if you did something funny or not. Works on flare training edition 2016. I also have a 2016 version now with the new colorwheel widget and curve. Very cool for those with 2016.

Maybe someone else can confirm whether it works on a flame ??

I have modified the xml Header, so it may work in 2015. Give it a go. Or use the 2016. It's cool!

Cheers,
Mark

Sent from my iPad

[myeffigy]

2016 Version

[grant_mckean]

Sorry to report that 2015 version still has no inputs however, we'll be moving to 2016 shortly and I'll make use of the shader there. Thanks for your smart work - clever stuff

Grant