Author Topic: Help me suck less (3) - Understanding the "Add Sub" blend mode (Read 9609 times)

justaviking · **on:** August 11, 2015, 09:39:58 pm

This is mostly off-topic from my quest to make a specific pattern, which can be found here:
https://forum.allegorithmic.com/index.php?topic=6202.0

>>> NEW <<<
I posted some examples in a follow-on thread:
https://forum.allegorithmic.com/index.php?topic=6341.0
>>> END OF NEW <<<

This is not exactly related to the substance I'm creating, but I was watching a great tutorial during lunch. It's a great tutorial, and I like the way he shows things step-by-stop. But when he used the "Add Sub" blend mode, I realized I have no ideal how it actually works.

Watch from 17:00-18:15... especially at 18:04-18:15.
https://www.youtube.com/watch?feature=player_detailpage&v=0RwdPIG8SQk#t=1020

He's combining the top-half of one input and the bottom-half of another input.

I looked at the documentation, but it's not helping me much. Scroll down to "Add Sub."
https://support.allegorithmic.com/documentation/display/SD35/How+to+use+the+layers+system

Why does the white half display the top-half, and why does the black half display the bottom half of the bottom input?

Maybe I need to play with some gray inputs instead of just black and white, and maybe then I will understand. But I was watching this tutorial during lunch, got to that point, looked at the documentation, and have been puzzling over it ever since.

Can anyone explain this in words? (and/or pictures)

Fabian F. · **Reply #1 on:** August 11, 2015, 09:58:39 pm

Hey justaviking,

let me sum this up, just for my understanding:
You want to know how the Blend node actually works and why the mask works as it does in your screenshot?

The Blend node takes two inputs, the Foreground and Background, just like layering two pages above each other.
The mask input modifies the foreground. White means the foreground is visible and black means it is not, just like binary computer 'language': 1 means ON and 0 means OFF.

I hope that helped at least a bit

Best Regards

justaviking · **Reply #2 on:** August 11, 2015, 10:12:22 pm

What you say makes sense. In that way, you're not "merging" the foreground and background layers, but totally laying one over the other, per the mask.

But why "Add Sub" for the blend mode?

This description from the documentation makes close to zero sense to me:
"Subtracts the upper layer from the lower layer, or vice-versa, to prevent negative values."

On a related note, why would you use "Copy" as a blend mode?
The resulting image is the same as the upper layer.
Doesn't that sort of make your blend node pointless?

I need to spend more time just playing with all these modes until I really understand them. I know they're hugely valuable and important, so I be crippled until I get a better grip on them.

Fabian F. · **Reply #3 on:** August 11, 2015, 10:20:52 pm

Hey justaviking,

to understand Blending modes better overall, you could take a look at other articles, not just Substance related stuff.
The most used images editing software, for example, uses Blending Modes, too. You'll find a lot of information about them and those in Substance Designer shouldn't differ.
Here is an in-depth look into blending modes for you:
http://photoblogstop.com/photoshop/photoshop-blend-modes-explained

Best Regards

justaviking · **Reply #4 on:** August 11, 2015, 11:02:16 pm

Thanks for the link, Fabian. I do understand some basics of blend modes, but I did enjoy the deeper explanation of some of the math.

Modes like Min, Max, Add, Subtract, even multiply... those make perfect sense. But Allegorithmic's definition of "Add Sub" really confused me, especially in the context of the tutorial I referenced.

I'll see what progress I can make on it at home when I can play with the software.

P.S.
It doesn't help that when I search the documentation, I find results for SD 3.5. I know blending modes (and a lot of other things) have evolved and grown since then.
Isn't there an easy way to find SD 5 (only) documentation?

justaviking · **Reply #5 on:** August 12, 2015, 12:22:39 am

Okay, I'm home now and I made a little bit of progress.

In the example I referenced (the tutorial), the "Copy" blend mode worked exactly the same as the "Add Sub" blend mode. In that case, it's easy. It just masked half the image. The "Add Sub" actually had nothing to do with it. It was a red herring, at least for that specific situation.

In the picture below, you can see my recreation of it, and I get the exact same results with "Copy" and "Add Sub."

Now I'm playing with some gray-scale images (not just black and white) to better explore "Add Sub."

justaviking · **Reply #7 on:** August 12, 2015, 02:38:28 am

Thanks, Jeremie!

That little nugget of information makes a lot of difference. That sure wasn't conveyed in the documentation.

I've been doing some testing, and...

I'm going to create a post I hope will be useful in sharing some info with other curious people, but it will take me a while to compose it (especially with other distractions that have nothing to do with Substance Designer... eating, shopping, kids... life).

justaviking · **Reply #9 on:** August 12, 2015, 04:35:15 pm

Quote from: Wes McDermott on August 12, 2015, 04:06:39 pm

I updated the docs to include this info : )

Awesome. Thanks.

hansolo · **Reply #10 on:** August 20, 2018, 07:56:58 am

Quote from: Jeremie Noguer on August 12, 2015, 01:12:37 am

The add/sub blend mode acts as if any color above mid grey is positive and any color darker than mid grey is negative.

Colors lighter than the mid will be added to the other map while colors darker will be subtracted from it.

I'm sure it ain't the funniest part, but you should have wrote the help file mate. Damn this sentence of yours is so understandable.
I have to agree with justaviking, the official help is really obscure sometimes.
Thanks !

P.S : Look for this word spelled exactly like that in google

: habdlking