Hey all I’m trying to get my head around things and would love to know your favorite patches that use the luma channel. Most of my modules have RGB inputs but I know I’m probably missing something with what to do with that luma channel.
Doesn’t matter how basic/standard or how complicated, I’d love to see/read examples of things that make creative use of the luma channel.
With an RGB input, if you plug a black & white (luma) signal into the R channel, because the inputs cascade, the RGB output will also be black and white. Where in your rig are you getting said luma signal?
I have a syntonie vu003b that makes luma from composite video (I think), and also has a brightness/contrast processor for luma. Scratching my head on how to make the processed Y have an impact on the RGB signals. Maybe a mixer?
Consider it this way, that the RGB signals have an impact on the Luma. Luma is a predetermined ratio of red, green and blue. It is a fixed ratio which reflects the perceived brightness of each color component rather than an even mix. The human eye sees blue as darker than other colors, for example; so blue has the least impact on Y.
Since Y is based on the perceived brightness of the image as a whole, I find myself using it in “luma keying.” FKG, for example, already creates Y based on your RGB inputs so patching Y would be redundant. It is still valid to patch it over if your keyer has no luma mix. You see, if you were using just the red or green output as a modulation source, when your source video changed scenes to a more blue tone, the effect it was performing in the last scene may very well stop.
I also will choose to use Y as a control voltage to a module which only has a single input. Stairs has three inputs which are mixed down to Y, but I like to use those inputs for a few oscillators and feedback. If I want my external video input to show up in the final output, I will patch it into the single steps or phase inputs.
Your idea to mix luma in with each r,g or b signal may be interesting as well. It may look as if the brightest colors in your image more closely approach white.
I think the most effective way to use Y is with LZX’s Swatch, granted you patch it through something to manipulate it first. This could be done with something as simple as attenuation and you’ll still get an immediate result.
Don’t you also have a module that precisely converts RGB to Luma? 
I am pretty sure I have luma in my system via the VU003B [edit, whoops]. At least from video that is on the way into my rig.
What I’m most interested in is: So I have luma, what are some things I should plug it into? 
Luma works particularly well with plugging it into the CV input of a triple crossfader that has the related RGB to your Luma. This lets you basically use the monochrome version of your signal to accurately voltage control the intensity of the RGB channels. If you put your Luma into a key generator (hard or soft) before hitting the CV input of the crossfader, you’ll have even more control over how this looks.
I regularly use either Fox’s LUMA or VH.S’ Crossfade to take Luma out just before I encode my RGB so that I can feed it back earlier into the patch. Taking the typically more complex output at the end of your chain prior to encoding and using that to modulate any parameter in your patch will undoubtedly add some texture/complexity.
Thanks! I’m definitely going to give that a try, I have the Shutter (just scoured the thread on that here where you and Fox are exploring that).
Unfortunately I’m out of space in my system for a dedicated RGB to Luma module, but maybe if I sell a few things to make space I can give the other patch idea a go.
I’m pretty new to this stuff so very much appreciate the ideas!
With Shutter’s Channel A and Channel B RGB inputs patched up, try plugging Luma from VU003B into either the top Switch input or the Threshold input!
There are a million things you can do with Luma, aka “Y”. Just to mention a few (and to reiterate what @Fox and @rempesm have said):
Many of these things overlap. E.g. you can get a complex colorization effect from a triple Crossfader or keyer by patching video into the CV input and flat colors into the two RGB channels. (Matte is purpose built for this, but you can also use 2x Proc / Access / any static voltages.)
And as Fox mentioned, Swatch makes the Luma world go round. Patch RGB into Swatch, loop the Y output through something and back into the Swatch Y input. You’ve just manipulated the brightness and left the color alone. Basically every single channel processing module (e.g. Stairs) now works in color.
I made some videos that talk extensively about what you can do with Luma ↔ RGB workflows. Johnny Woods’s official LZX YouTube videos are also required viewing.
This is amazing thank you!
I had been thinking of adding a switch on VU003B so the brightness/contrast control of the Y signal would be used for the YPbPr to RGB decoding, in order to affect brightness/contrast of all three RGB signals at once, though the front panel is already full so it was tricky to include such a switch without making it more cluttered.
Also, VU003B will convert a Component signal into RGBY, however, plugging a Composite signal into the Y input won’t convert it to RGB, only the black and white content of the Composite signal will be made available on the RGBY outputs.
Then as it was suggested, you’d need to convert RGB to YPbPr or YIQ and then back to RGB, leaving the color components (PbPr or IQ) unprocessed, and then use a processor like the one on VU003B or Proc/Passage on Y, so Swatch would be a nice way to do so.
As I started with a Cadet system, I didn’t have a way to process a full color signal until I made VU003, so Y/Luma processing was the way to go, and for example, I was amazed by the rectification/solarization effect (like with Stairs/Staircase/VU002/RECT) on a Y signal and using the different outputs to the RGB ins of the encoder, though rectifying R, G and B from an external video isn’t as spectacular in my opinion.
Nothing else to suggest as I feel like most of the use cases of a Y signal have been covered in previous comments 
Thanks everyone for chiming in and pointing out some things to try.
I took some ideas and started messing with them and came up with this, which was fun:
https://www.instagram.com/p/CxaEBgou8CJ/
B+W still image into VU003b; RGB into FKG3, Y contrast/brightness tweaked in VU003b and then into Reverse Landfill Blur, and then into FKG3 as the key source; Batumi animates Blur setting. manual knob wiggling on Blur brings the effect in/out; everything comes out via VU007b.