Understanding RGB Math - Forum Edition

First off, this is a very simple overview and it’s intended to just demonstrate the idea of how FF’s RGB math works. In other words I’m not going over anything complicated, this is just to drop off the idea here. I’m making it a forum post so people can drop questions here and make sample files.

Since FilterForge 2.0 we’ve seen something called HDR values which RGB math can’t do without. Previously, we only had a limited set of values we could ever input into the program and the program could only work within those boundaries. Those boundaries basically vanished when HDR came into view. Now the program understands huge numbers or even negative numbers. With that in mind let’s just move to a simple thought:

Think about it this way. RGB math is really just math. It’s nothing more than a set of components that does basic math operations you learned through elementary, middle school, and high school.

Let’s take a very simple example. We’re going to do 1+1. The answer as we know it is 2. In FilterForge the number 1 is represented as pure white visually. Value wise it looks like (1.0, 1.0, 1.0) in order of red, green, and blue channels. What if we use the add component to add two white images up?

Code
(1.0, 1.0, 1.0) + (1.0, 1.0, 1.0) = (2.0, 2.0, 2.0)

Since our monitors can’t generate brighter pixels than white, it looks like FilterForge just produced a white image. This is the visual limitation we have so unfortunately it’s hard to understand visually but it’s all stored in that image. To see that output value, use the eyedropper tool.

Let’s take it a step further. Let’s try subtracting 1 fr om 2. This will give us the answer of -1. Put it in FilterForge terms:

Code
(1.0, 1.0, 1.0) - (2.0, 2.0, 2.0) = (-1.0, -1.0, -1.0)

This is represented as pure black. Again this is due to the limitation of how the program displays information. Meaning that you’ll need to use the eyedropper tool again to see for yourself.

We can of course represent subtraction by adding a negative value to another value. For example: (-1) + 2 = 1 right?

Code
(-1.0, -1.0, -1.0) + (2.0, 2.0, 2.0) = (1.0, 1.0, 1.0)

You probably see the logic at this point how I’m simply adding and subtracting values within those parenthesis. So each color channel is operated on separately. Consider the simple fact that to FilterForge, unlike humans, the program sees numbers spread across the x and y axis.

Let’s do one more interesting thing.

How about add red minus blue. What would that make?

Code
100% Red in FilterForge is: (1.0, 0.0, 0.0) 100% Blue in FilterForge is: (0.0, 0.0, 1.0)

Therefore, we subtract from each channel.

Code
R: 1 - 0 = 1 G: 0 - 0 = 0 B: 0 - 1 = -1

So the answer is (1.0, 0.0, -1.0) which due to the limitations of what our monitors can show and how programs can display color, the visual representation is red.

In summary: RGB math is just doing math on each channel. If you understand middle school math, you're already experts in the field. The question is wh ere do you use this stuff? The answer is: anywhere you find useful. Which is kinda tricky to really understand. But think about how you use math on a daily basis. When do you add, when do you subtract? It's like that, you use it when you have to.

-------
I'll post this over to the Wiki. I just put it up here for discussions first.

I personally do not understand anything of what is on the first post, and it seems that is only for highly skilled, expert and technical people like you that know well about this topic and what is this for, because apart for not understanding, do not know what use this has, or where it can be used.

I feel that you are much higher in knowledge than many of the filter forge users that are not experts and FF gods.

So I think that only other same expert filter forgers can understand and use it

Quote
Skybase wrote: I'll post this over to the Wiki.

The benefit of a forum is that we can discuss things here really easily. The benefit of a wiki is that you can keep updating a single article to make it better. I can help add stuff to the wiki, too (more than just the feature wishlist).

Can we maybe show some case studies of filters that use/rely on HDR and RGB Math? I know you say "use it when you need it", but I think a little inspiration and demonstration might help people understand. Some of Crapadilla's wiki articles have case study filters.

Also, "let's try subtracting 1 from 2" should read "2 from 1". And there's a lot more than just addition and subtraction.

I think I'll just copy it over to the wiki at this point and edit the article over time so we can all look at it more closely. heh, discussion on these forums I donno if it were even a good idea hah.

So ok, let's make a couple demo filters that utilizes the basic addition, subtraction, multiplication division specifically for this segment. I don't think people have to give away secrets, a lot of times we are making a lot of complicated RGB math things that flies over people's heads anyway. We can keep it simple, i.e.: we can for example average/mean, usage with transformation nodes (offsets, scale, rotation etc), usage for just regular image manipulation (like making an image brighter with add/multiply). Maybe a case study would make it more accessible but I feel like that might blow things out of proportion.

And expand on the text about HDR / LDR values. It clearly sounds like we can expand on that a bit more so we have a nicer, more formal introduction to the topic. The topic is quite a rabbit hole to be honest, so in terms of writing, we can just keep it to simple terms instead. We do have to make some assumptions as we're writing and my understanding is that most people here.

lol also my conversation kinda got personal with SpaceRay there. Heh. Please excuse that for the time being.

THAT is a really neat trick. Thanks for sharing. Totally something I'd abuse lol.

Thanks Skybase for trying to explain this that may be great and useful, although I have still low knowledge of how FF works and can not yet understand what all this means, and would be good to see examples of theory shown, so instead of only technical details, one non experienced and skilled with these RGB math could see what this can be used for and seeing an example of it would be more useful.

Quote
Indigo Ray wrote: Can we maybe show some case studies of filters that use/rely on HDR and RGB Math? I know you say "use it when you need it", but I think a little inspiration and demonstration might help people understand. Some of Crapadilla's wiki articles have case study filters.

I agree with this and would be good to show when is needed to use this, and give a little inspiration and demonstration about it so other people with less technical knowledge could understand better and benefit fr om this

Quote
Rick Duim wrote: Another thought was a series on breaking down existing filters to explain what is going on (including HDR and RGB math). Last year I felt that more documentation was wh ere I was going... but I think it's too much to take on, and perhaps only useful to a handful of people.

Yes, another way to possible explaining and showing this topic, is to explain other already available filters that already use this why and how they are used, what was the purpose or why it was needed to be used there

Bomber particle mode: Lighten.

Slightly off-topic: The technique Velho is describing is pretty neat, and can also be found in this thread about the Bomber, and a similar method in the Clay Sticks filter.

Quote
LexArt wrote: How have you been able to do this 3D shapes in FF?

Well, ThreeDee is the real king of 3D in FF and he has different ways to make different things in 3D, so it is possible, although complex to do

Quote
Velho wrote: Here's a trick I found out about HDR values. You can carry information about two or more separate values in one single HDR value.

Wow, this looks cools and well done, although regrettably I do not understand anything of what you explained but is not your fault, it is me that do not have the needed knowledge and skills

Quote
Skybase wrote: One of my older experiments from 2012 did similar. Velho takes it one step further with the RGB information stuff and probably a lot more cleaner in terms of output. Shading was done internally with the HardShadows script.

Oh! Yes your awesome, amazing, excellent and beautiful 3D crystals that I found when you released it a day that I love very much