Post by a Chunk on Jan 26, 2019 18:49:24 GMT
Lighting Fundamentals: Contrast
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In part one of this short series on lighting from Steve Theodore, we learned about colored lighting and how to use it to impact your audience. As part of that article, Star Wars was used as a bit of a case study. This week we're not talking about Star Wars, but we are going to talk about the dark side...of lighting. Today we talk about contrast. Let's start off with an observation on the relationship between color and contrast:
We know the difference between a sphere and a circular plate because we see gradations of shade on the curved surface. Without that contrast of highlight and shadow, color alone ends up as a set of abstractions. Color can evoke a mood, but without the definition provided by shading, it can't embody concrete things.
Now we know that contrast can ruin the mood we set out to create through our use of colored light. Can it have the opposite impact? Can it enhance the mood? The answer to this is an emphatic 'YES'! Here are Steve's thoughts on how contrast can complement color in creating the desired mood:
In theatrical and film lighting, contrast is expressed as the the key-fill ratio, the relative brightness of the key and fill lights. The key light represents the major source of light, such as the sun, moon, or the main room lighting. The fill light, the secondary light source, is positioned about 90 degrees away from the key light and is intended to bring the major forms of the subject into relief. High key-fill ratios produce strong contrasts, which generally suggest tension or drama. Low ratios, on the other hand, produce more even lighting and a gentler distribution of tones. The key-fill ratio is distinct from the overall brightness of the scene. High ratio scenes are typically darker overall than those with lower ratios.
TV comedies and talk shows, for example, typically use a ratio of 2:1 or 3:1. A low ratio like this produces no ominous undertones and creates even, pleasant gradations in tone. Not coincidentally, low contrast lighting also flatters the actors' complexions, de-emphasizing wrinkles and bulges. Dramatic shows, however, us u ally shoot at a key-fill ratio of around 4:1. This creates stronger shading, injecting some graphic tension into the composition. It also emphasizes the geometry of the actors' faces, making it easier to read their expressions. Ratios above 7:1 or 8:1 are usually reserved for thrillers and action movies. A brooding film noir shot or a stylish Matrix action scene might go as high as 20:1.
These ratios don't need to be (and in most cases shouldn't be) strictly followed, but they can be good guidelines to start with. Experiment to see how adjusting this ratio can impact the feelings that are evoked.
It's usually wisest to begin experimenting with a moderate contrast ratio, in the region of 3:1. Go much lower than that and it becomes difficult to perceive the 3D contours of a space (although cartoonish environments with very strong color contrasts are an exception). On the other hand, very high contrast ratios tend to disassemble the scene altogether, reducing it to an abstract pattern of light and darkness in the classic film noir style.
Finally, we get to the problem of outdoor lighting, which Steve has quite a lot to say about.
We know our monitors and TV screens aren't as bright as a kid's flashlight, much less the sun (not a bad thing, when you recall our unhealthy addiction to garish sprite effects). How can we recycle those measly 256 levels of brightness to represent everything from the mines of Moria to the blazing nebulas of distant galaxies?
Luckily for us, our pictures (and photographs and movies) work within such a limited range because our eyes are programmed to recalibrate their perceptions of light and dark. Mid-tone shadings that would be easily distinguishable under a reading lamp are blanked out in the bright light of day. Faint glimmers of light that would be invisible in daylight are easy to navigate by at night. Most of us are capable of distinguishing between 100 and 200 shades between black and white. As white grows or shrinks in intensity, our brains basically stretch those hundred or so shades to cover the whole range from darkness to lightness.
So how can we work within this limited range of shades, and still create outdoor settings that look realistic? The answer is...drum roll...contrast.
Bathing a scene with intense light ought to mean that every surface is reflecting more back to the eye, and so you might expect the image to wash out. Our biological contrast filter, though, has to stretch our limited visual palette to cover the intense highlights as well as the somewhat elevated ambient colors. Even though the low tones really are brighter in absolute terms, that increase is insignificant against the vastly expanded scale of intensities. Tones in the low end of the scale will seem darker even as they reflect more. For obvious reasons, therefore, we instinctively see contrast as a proxy for the intensity of light in a scene.
For a perfect example of this principle, take a look at the two Vermeer paintings in Figures 1 and 2. The sharp contrast between the glaring sky and darkened houses in Figure 1 subliminally reminds us that the sky should really be hundreds of times brighter than the bricks and stones. Conversely, the very level tonal range of Figure 2 recalls the dim, ambient light of an overcast day; the contrasts are so gentle that the whitewashed walls seem dingy, even though they are almost exactly the same luminosity value as the bright sky in the first picture.
Next, we get to the issue of how textures are impacted by lighting:
The variable intensity of outdoor lighting also places a large strain on texture artists. Imagine the following scenario: You ask a texture artist for a brick texture. Naturally, you want it to contain all sorts of subtle little details, cracks, stains, and so on. In order to include those, the texture artist uses most of the RGB range in painting the texture; the cracks are down near black, the mortar up near white and so on. You look at the texture in isolation, it's great. You render the texture in the game on a moderately lit interior wall and again, it looks great. Then you try it outdoors and run into an obvious problem: The white in that mortar is as white as the clouds in your skybox, which should be several dozen times brighter
Though this recap should provide a fair sense of what the article is about, we've skipped over a decent amount of the information. I recommend reading the original article, which can be found here.