Shading: There where the light can not reach.
So shadows. You might want to wonder, why do we draw shadows in the first place? After all, a lineart, or even plain silhouettes can easily depict how an object is supposed to look like. The most obvious answer would be “realism”, after all this is a goal for many artists, isn’t it?
Shadows: Cultural theory.
This doesn’t have to be so. A lot of early Egyptian and even medieval art didn’t use shadows. An easy explanation to assume would be because they didn’t know how to draw shadows, but this might not always be the case. One thing to remember is that a lot of art from these periods was religious art, and graced buildings. Often religious art is primarily symbolic than it is realistic, and the importance of specific colors and composition outweighed shading. Aside from that, carved relief are thought to be commonly painted as well, though there’s few reliefs left over today that are still painted. The result would be a sense of dynamic shading happening through the shape of the relief.
A relief from the Abu Simbel temples. If you look carefully you can see the reliefs are painted. As well, you can see how the use of relief here creates shadows dynamically.
Mosaics from Ravanna, definitely showing shadows on the cloth, but hardly any cast shadows.
What they probably were more interested in was conveying the materials that they were trying to depict: Showing saints clothed in fine silks and delicate gold. Shading may have been the best way to describe these materials visually.
It was during the renaissance times that we start seeing a lot of complex shading happening in paintings. Carrevagio in particular was well known for his use of shadows, being more or less the trend setter of using shading to create strong dramatic effects.
Wikipedia attributes him with starting the Baroque movement, an aesthetic style which is largely dictated by the rule of drama rather than the rules of realism:
"Caravaggio "put the oscuro (shadows) into chiaroscuro.”[38] Chiaroscuro was practiced long before he came on the scene, but it was Caravaggio who made the technique a dominant stylistic element, darkening the shadows and transfixing the subject in a blinding shaft of light. With this came the acute observation of physical and psychological reality which formed the ground both for his immense popularity and for his frequent problems with his religious commissions.”
To these religious painters, to paint the divine meant to paint light. And ever since, the best way to paint lights is to paint shadows.
The most realistic use of shadows came around the end of the ninteenth century, when the impressionists attempted to catch what they saw as objectively as possible. While before them shadows were often dramatic and theatrical, the impressionists showed very subtle though messy shadows, caused by the ever changing light. If you can get past how messy the impressionist era paintings were, you can see the striking amount of realism they contain.
Edouard Manet’s ‘At the Café’, one of my favourite pictures to show off that impressionism mattered: Aside from the unusual intimate composition(for the time), the use of shadows results into a very photo-like feeling painting.
So that would be some reasons for you to paint shadows:
*To showcase material. (Plasticity)
*To paint lights effectively.
*For dramatic effect. (Symbolism, communication)
*To mimic reality.
Shadows: Technical theory.
Now we have that little bit of art theoretical thought out if the way, lets continue on in physics.
Previously, I had asked you to think of Light as waves, like sound. Now I’m going to ask you to look at the alternative way to look at light: little particles. Not that you can’t model shadows convincingly without thinking of them as particles, but it is a little easier.
So, typically, we model shadow like this:
One light with parralel rays casting a perfect shadow. Paralel rays though, are typically only sunlight. And even that’s because the sun is so far away from us.
Most light sources have divergent rays, meaning they start at a single point and cast outwards:
And that source can be pretty large as well:
Finally, light has another thing it does: Namely bounce more than once, causing indirect light:
So in effect, even in a single lightpoint scene, and assuming there’s a surface for the light to bounce off of, an artist will always have to assume an object is lit by more than one light: Direct and indirect light. A situation without indirect light is one where the light doesn’t have something to bounce off from, like outer-space. But even outer-space situations have places where indirect light occurs.
That said, aside from paralel and divergent light, there’s one final light-type: Convergent light.
It’s very rare though, and the most common case of it involve lenses.
Now we’ve established the different types of light and the cast shadows they create, let’s look at the form shadow and how different materials reflect light.
If we assume that a material reflects perfectly, you get a mirror effect, like chrome.
There’s also materials that let light through, like glass, but also air.
Finally, a little less known, there’s materials that are a little of both, called diffuse, caused by an effect called subsurface scattering. I subsurface scattering, the light hits the surface, but because the surface is slightly transparent, it goes through it, bouncing off the non-transparent parts and bouncing out again.
This is evident in most materials, but most obvious in wax and skin. The notable difference between an roughened up perfectly reflecting material and a sub surface scattering material, is that glossy materials carry a highlight with the colour of the lightsource, and diffuse materials carry highlights with the colour of the material. We’ll go into colours interaction with shadow deeper next tutorial.
Practical
For this tutorial, we’ll stay in the realm of cel-shading, because the most important thing is to determine where the form shadow and cast shadow is. Cel-shading is an abstracted type of shading which was often used in Cel-animation(animation where the characters and other moving parts were drawn on transparent celluloid sheets and overlaid on top of a static background). Abstracted shadows were much easier to animate than more realistic shadows, and for us it’s easier focussing on the basics this way.
We’ll delve only a little into material rendering. We also won’t be delving into shadow colour much yet, that would be next tutorial.
So, first I’m going to showcase a method using Krita and putting the shadows and highlights on a different layer than the base colour. For this method I’ll only use pure black and pure white to draw these shadows and highlights.
The second method will also be reproducible in the gimp, but the method is a little more destructive.
Alright, for this method, we’re going to organise our layers:
With masking
Krita can make use of grouping. Set your layer in layer group.
Now right-click and ‘select opacity’, then right click and select ‘layer mask’
Now click the blue arrow to put the layer mask into the group.
Then, between the layer mask and the base colour, add a new layer, if you draw on this, you’ll notice you don’t affect the transparency.
Alpha inheritance
Alpha inheritance, or layer clipping, as Photoshop calls it, is a slightly sped up version of the above. Put the base colour on a layer and add a layer above it. Now toggle the a symbol.
Alpha inheritance makes a layer ‘inherit’ the alpha of the lowest layer in a group.
While fast, it doesn’t affect groups inside the group, while masking does.
(Note: Photoshop’s version abstract the grouping, Krita doesn’t, so it’s very important to make you you have a group set.)
Now we have covered that:
Let’s shade!
Let’s find the cast shadow.
The first thing you need to decide is where the light is coming from. For our sake, we have one direct white light. And opposite, we have the indirect light. (Supposedly our light is hitting a white wall or something).
Next up, we look for the terminator of the shadows of the direct light. That’s where the direct light can’t reach.
In computer graphics, the terminator is found by taking the outmost point of where the light can reach:
And forming a silhouette with that. That would be the terminator. Everything away from the light on the terminator is cast in shadow.
Try to abstract these more complex shapes as the above stacked together.
Now we’re going to make the cast-shadows.
Similarly, we can find the cast shadow by taking our terminator and using the light to pass by it till it hits a surface.
Of course, we also need to think of the indirect-light. She’s not in outer space after all. But let’s abstract it a bit. Set all shadow-layers to around 50% opacity along side drawing the formshadows.
In videogames this technique is used to determine the cast shadow, this is called volumetric shadow mapping. Most artists deal with shadows fairly intuitively, and don’t worry about drawing all the help lines.
Work out the form shadows a little more. Detail the hair a little, and add or remove form-shadow from places. (Don’t forget that pressing ‘E’ sets the brush you’re using to eraser-mode)
Alright, got the basic shadows done.
Now let’s add high-lights. I’m going to avoid highlights on the skin, just like how I am going to abstract away the translucency of the skin.
Highlights, specular highlights specifically, have a manner of scematically being determined as well. However, just like shadows many artists apply them intuitively.
Set the highlight layers transparent as well. Also set the blending mode to overlay to make the highlights look less washed out.(Don’t set the highlights to overlay on the eyes, having it pure-white like this is for the best).
We’re almost there.
Now, let’s put in the ‘indirect-light’ hotspots. You’d typically just erase from the shadow layer, but we’ll use a layer with an erase-blending mode.
Set each shadow-layer you use this on, in a separate group(this is where the masking comes in handy) now add a layer on top of it and set the blendmode to ‘Erase’. You can set this one half-transparent as well. Now draw on that layer and see how it erases from the shadow layer.
(Red is direct light, green is indirect light)
Use this to draw spots of indirect light in the shadow without messing up your shadow-layer.
Don’t forget to simulate the indirect light being cast from the subject themselves.
Tada, looks quite nice, huh?
Now, indirect light is much more complex than what is depicted here, but we also abstracted a lot of it by setting the shadow layer to semi-transparent.
Doing this in the gimp:
First off, we take our image in the gimp.
We select the alpha-lock over here.
And notice that we can’t change the transparency of the layer :)
For this I’ll be using the Ink tool because it gives nice anti-aliased lines. I’m setting the mass high, which means I have less control over the lines but they’ll end up smoother.
Set the colour to black and the transparency to 50%, and paint shadows:
You’ll soon notice something very annoying though:
Going over the same place with your brush makes it become darker. Maybe not what you’d want with cel-shading.
So, we’re going to pick the shadow colour. In most graphics software, there’s a so called sticky-key for the colour pick tool when you are using the brush. Meaning that if you press this key, you go into colour pick mode, but unlike a regular hotkey, releasing this sticky-hotkey returns you to brush mode.
In photoshop, much to my left-handed annoyance, it’s hardcoded to the alt-key. In Gimp it’s set to the CTRL key(yay!). In Krita it’s standardly CTRL, but can be configured, like Mypaint. Painttool Sai and many other Japanese graphics software have it set to the right-mouse click, much to my preference.
Use ctrl+click to pick the colour of the shadow.
Set the opacity of the brush to 100% again.
And continue drawing the shadows like we discussed in the Krita example.
For the highlights, set the colour to white, the brush blending mode to ‘overlay’ and the opacity to 50%:
Draw some spots:
Pick the colour of the highlights again:
Set the brush opacity to 100% and blending mode to ‘normal’ again.
And refine the highlights further:
For the indirect lights, pick the mid-tone(the one we used for the flats) and set the opacity of the brush to 50%, and start drawing:
Pick the resulting colour again. Set the brsuh to 100% opacity again:
Do this process with the other layers as well:
Now, use the colour picking to switch between colours as you detail the shadows.
For certain areas though, you’ll find you only want to edit the shadows but not the highlights, or only the highlights and only the shadows, like this area:
We have something for that!
Set the Blending mode to ‘Lighten’ or ‘Lighten only’:
Drawing with the mid-tone should now only affect the shadows:
The ‘Lighten’ blending mode makes it so your brush only draws if the colour you’re drawing with is lighter than the colour you’re drawing over.
Similarly, the ‘Darken’ blending mode will only paint if the painting colour is darker than the colour you’re painting over. Using these brushes to you advantage can help you fine-tune your shadows a lot easier.
Finte-tune the shadows to your hearts content, at some point when you feel it’s finished, it’s finished:
This method is a lot more ‘destructive’ than the layer-method: You can’t go and select an area and change the colour easily. The advantage is that you end up with less layers, and so less heavier files as well as less finding of the correct layer to shade. It’s also a better way to set up you’re shadows if you’re preparing for soft-shading or painterly works.
Conclusions and Afterthoughts:
Shading is one of the big elements of drawing and painting. This can be seen through that it’s one of the subjects of drawing that you never stop studying. Similarly, taking your time and laying down the forms shadows and casts shadows, highlights and indirect lights carefully, can really improve the overall quality of your work, as well as making yourself more efficient in the long run.
However, it’s not always necessary to draw shadows, and you can wonder for yourself why you feel a particular work needs shadows or not.
As it’s a subject you can keep on learning about, I’ll be going into shading more in the future, amongst which it’s interactions with other elements of drawing and painting, such as colour theory!
Next week: Colour theory and building ramps.
Sources:
Basics of light and shade: http://www.huevaluechroma.com/021.php (Definitely visit this site if you want to go into the deeper basics of drawing shadows)
Images Carravagio, Abusimbel, Manet and Ravanna: http://en.wikipedia.org/wiki/Caravaggio
http://en.wikipedia.org/wiki/Manet http://en.wikipedia.org/wiki/Abu_Simbel_temples http://commons.wikimedia.org/wiki/File:Baptistery.Arians11.jpg