So, It's been too long since I last made any tutorials and at the moment I don't really have the right setup to do any in depth video tutorials like I planned on doing some time. However, I have now been in the industry for almost a year as a groom artist and have learnt a lot of information which would be great to know for beginners to grooming. For this tutorial I am going to cover the fundamentals for good guide based grooming as that is generally the crux of most early grooms I have been sent over time. If there are any other "generic" grooming tips you want me to cover feel free to contact me and i'll do what I can either privately or via a public tutorial like this one :) Just to clarify, this tutorial isn't about how to make a realistic groom. This tutorial is about how to correctly use guides in any grooming tool, doesn't matter if it Xgen, yeti, nHair or even custom built grooming tools that studios use, all the information here will still apply. Anyway, lets get to it!
Guides are too sparse and lack detail By far the most common problems I see in grooms are caused by bad guide interpolation, and 90% of the time that is caused by have far too few guides in your groom. Obviously there is no "Correct" number of guides to use for all grooms but to give a bit of perspective, most grooms I get sent have no more than 50 guides total (Sometimes even less). Whereas in the industry a typical digi double groom that I do at work can have upwards of 120 guides just for the eyebrows, 70 for eyelashes and 200 for the actual head hair (That varies from character to character as you would expect though!). Moral of the story - Stop being afraid of adding more guides :) So, how do you decide on what amount of guides you need? Well, this heavily depends on the hairstyle... As a general guideline for short hair I will just look at the changes of direction/ the flow of the hair, anytime you see a change of direction you need to add a new guide to let your grooming too know that something needs to happen in that area. Although it may look it sometimes, grooming tools are not magic! For long hair it is a bit more complex, first off, long clumpy hair is normally best described by having 1 guide per large clump and - if possible - tracing your reference to get an exact match of the shapes. This is easier said than done but just try your best to really follow your ref with the guides. For long and straight hair you also need much more guides that you would expect in order to get the correct layering, but we'll get back to this later.
Guides are not uniformly spaced This kinda ties into the 1st point but there's a bit more to it. So in the last point I mentioned that 'you should place a guide any time you see a change in direction'. While doing this you also need to look at how close or how far apart your guides are. If there are two guides incredibly close together facing in different directions it will create a weird spike/split in the groom. Yes, there are times that you need guides very close together (partings, for example) but as a whole try your best to keep guides evenly spaced in order to create the most predictable results at rendertime. A follow on for that point is make sure that - once you have blocked the groom out with the general shape and flow of your reference - you place guides into any large spaces without guides, even if there are no changes of direction.
Having evenly spaced guides will result in predictable results at rendertime and in animation. Secondly, having guides evenly spaced gives you better results with dynamics as Maya has more information about the groom and how it should react to objects, general movement, gravity and wind. To build on that point, if your guides are not evenly spaced (or if they are too sparse) objects may be able to pass through the hair without even effecting it.
Guide layering matters! One thing that is overlooked quite often by artists of all levels is layering. Layering can be quite tricky to get, especially on long straight grooms. It's quite tricky to explain by words alone but i'll try my best, basically as hair flows and is effected by gravity you get a natural build up of hair to create a large volume (This volume is created by layers of hair resting on top of eachother). When proper layering is ignored in the guides it leads to one of two outcomes. First, your hair looks incredibly flat and lacks volume. Secondly, your hair has lots of interpenetration and probably looks quite ugly because of it. Hopefully the images I add for this section help you understand why layering is important to the final image, since by text it doesn't sound too bad :P
Check your length
This one is a bit trickier to manage but something that - if ignored - can lead to some really strange looking hair once any simulation is done. Annoyingly, it can be really hard to tell if the length of your guides is correct just by looking at renders as the final groom will do a really good job at making the length of individual hairs hard to see. There's not really much else I can say on the topic, Only way to avoid it is to take care when you're placing your first few guides. Ask yourself "how long would the hair be here?" and think about how the hair would be cut in real life to achieve the look.
Cover the whole area
My final thing about guides for you to consider is make sure that you cover the whole region where hair is grown from. This kinda ties into the 1st point but you should have guides all the way up to the hairline of the groom. If you don't, XGen is forced to interpolate the hairs shape with almost no data so you'll never get a natural groom. For grooms like eyebrows, eyelashes and beards it is also worth doing guides outside of the area the groom is grown from, I know that sounds pointless but it allows for much greater blending of the groom on it's outer edge (Think about how peachfuzz can blend into eyebrows :) ) Hope this helped! Ok so that's everything, I hope you have found this tutorial helpful! As always, if you have additional questions do not hesitate to contact me and i'll try my best to help.