Guide to secondary light sources in manga colouring
Program: Any digital-painting software should work. Gimp, Photoshop, etc.
Difficulty: Intermediate?
What's a secondary light source?
(art borrowed without permission from Ms,Shatia Hamilton, Ashley Cope, and Marta Dahlig)
What ISN'T a secondary light source?
(manga scans from Kuroshitsuji and Code Geass. Fail from me.)
So what's wrong with the second set?
That's not light. That's an embossing. That's a spontaneous halo around someone's jaw. In order to have someone look like that in real life, they'd have to have phossy jaw. And since I'm pretty sure Ciel isn't some beggar kid working in a match factory with his jaw glowing as it's being eaten from the inside out with necrosis, a glowing jawline isn't possible.
Okay, now that I've got the requisite phossy jaw joke out of the way, let's talk about why those examples are totally horribly wrong. Well, the first thing is, that glow is only touching one thing. The jaw. Compare to the good examples, where the nose, hair, neck, mouth, etc are also illuminated. The second problem is that there's occassionally things that are in the way, that should be illuminated instead of the jaw... and instead there's an unbroken line of light despite that. And third and finally - more a nitpick than an actual problem - the light would have to be directly under them (except for the one of Ciel in a coat, which is even too fail for that explanation) for that kind of weird illumination. That's not an insurmountable problem, but... it is just a little odd.
Why are these so awful? Manga colouring isn't supposed to be art! Well, they are because they make it really really hard to see it as a light source. Instead it looks like they're radioactive, or have a chalk outline, or something. If you're bothering to actually try to have a consistant primary light source, then why not make the second one just as good? You ruin all your effort and consistancy by halfassing the secondary light source.
And if you're not bothering to have a consistant primary light source, then... you probably don't care that there's a streak of jizz along the character's jaw because their whole face probably looks like an splotchy balloon anyways, and more power to you, good citizen. Continue to go about your business freely. You're an inspiration to us all.
Do I have to use them?
Not really. They're flipping sweet, but if you don't want to, no reason to really. They do add a point of interest and a more dynamic look to an otherwise really simple lighting style, but otherwise, they take a while and are admittedly, not really what a lot of images need.
Then what's the point of this tutorial?
A lot of people are currently using them... in a way that's really kind of creepy looking. I'll just refer you to my above and below statements of things smeared around the jaw and strange mutant melting jaws in case "creepy" doesn't get the right image across.
But I'm not trying to do a secondary light source. I just like the way the face looks with a white outline, like it's embossed or something around the edge!
as,fjafkjhasklfjaklfjasklfjnadklaskdlfjadgkljagkladgjmkladj D=
Alright, so how do I do it right?
The main thing to keep in mind is that you're not dealing with a streak of manjuice yogurt along someone's jawline. It's a light source, just like the main one illuminating the character. So consider what features it would touch. If you want the easiest way to make sure that it's dynamic, have it come from the direction of the heaviest shadows. If you set your primary light source slightly off from center, it makes this easier.
Some things that would be hit by light, since they (for lack of a better word) stick out - lips, eyelids (lower or upper), hair, clothes, nose. Some other things to keep in mind to better work with light is that the face has contours. The cheekbones and jaw are round, rather than flat, and as such, the light would go around them like they're round. The reflection in the eyes or the whites might even pick it up. It doesn't have to be a hard streak, either - you can do it as a soft, gently shaded curve. And it can be in any colour you want - blue or white aren't the only options, though they do stand out nicely against a skintone. Warmer colours don't provide as much contrast against the skin, especially if you do a softer shade like below.
Hair picks up the light, but rarely is thick enough to significantly block it. A hand on the jaw, however, IS. Another person next to them IS. A cloak or hood might, depending on the angle. There's no real rule, so just remember that things can block it, because it's light.
Additional notes:
Your examples are riddled with flaws! Er, well, if you say so. But they get the job done. Insert your own your mom joke here.
Other tutorials by people who aren't going to insult my mother?
Temperamental's manga colouring: the "don't"'s (part 2)
Herinia's manga colouring tutorial (**very recommended)
Blacklullaby's manga colouring tutorial