Understanding light and color
There are three basic components of visible light: Red, Green and Blue. We call these colors RGB for short and they form the basis of something we call an additive color scheme. We call it additive because adding different combinations of pure Red, Green and Blue produce either Cyan, Magenta, Yellow or White (all of them combined.) Cyan, Magenta and Yellow, or CYM for short is a subtractive color scheme. The term subtractive comes from the fact that the color we see in objects is reflected light minus any degree of Red, Green and Blue. If something absorbs Green and Blue light, only to reflect Red, we see Red. Whereas, if it only absorbs Red, it will reflect Blue and Green and the result becomes Cyan. Thus, when you subtract various wavelengths through absorption, any shade of any color can be produced.
It's also important to know what shadows, midtones and highlights are. Highlights are the lightest areas of a scene, therefor the parts which have the most light hitting it. If the scene has too many highlights, we usually say it's overexposed and the scene is lacking in detail. Midtones show the middle tones of a scene - the colors that are "in-between". For example, if we had a black and white scene, the midtone would be gray - somewhere between the two. You want a generous amount of midtone in a balanced scene but at the same time, you don't want everything to be gray or flat. Shadows are the darkest areas that carry little light. A scene with too many shadows may be underexposed and will not show much detail. Scenes with a lot of shadows and highlights and very few midtones have high contrast - the effect is dramatic, especially in scenes with lots of black and white.
Understanding color/white balance
Sometimes getting colors to look correct and accurate as possible may require adjustment to the white balance (as well as color balance). You may have noticed that it's sometimes hard to achieve a normal or abnormal look to the scene due to the way different sources of light have different colors or temperatures to them. You may want to make lights appear more florescent or more incandescent for instance.
The range in different temperatures ranges from the very cool light blue sky straight through to a very warm light like that of a candle. We don't normally notice this difference in temperature because our eyes adjust automatically for it. So, unless the temperature is very extreme, everything will generally look the same to us under differing lighting conditions. Making these adjustments automatically for rendering is just not feasible so you may need to tell the engine how you want to treat different light, or you may just want to manipulate white balance for artistic effect too.
The way the color balance tool works in the Neothyne's color grading options is in terms of a ratio between two colors. For instance, if you turn up both the Blue and the Green, this will effectively reduce the Red. Similarly, if you go all the way towards Yellow and Magenta, then you increase the Red. To understand why this is we have to first explain some color theory.
Back in 1931, William David Wright and John Guild created what we now know today as the CIE XYZ color space. Derived from a series of experiments done by those two in the 1920s, they discovered the following facts about color: In our field of vision, Green is represented in the widest range; Magenta is the opposite color. Blue represents the remaining range of wavelengths in our field of vision, also balanced by Yellow as the opposite color. These findings are why we balance color in terms of Green/Magenta and Blue/Yellow.
Realize now, that each of these colors has a direct or indirect effect on one another. If one area of the current scene is too Green and you pull it out, the rest of the scene will become more Magenta (Green's counterpart.) This may be fine if the entire scene has too much of a Green cast as the correction erves to balance out the color.
The color balance tool in Neothyne also has the option to preserve luminosity when balancing color. This options serves to preserve the apparent brightness in the scene when adjusting midtones for instance.
Understanding Hue, Saturation and Lightness
Let us define the terminology first. Hue is related to wavelength, that is the "base tone" of a color, but there is much more to what we consider a specific color. Saturation on the other hand refers to how a Hue appears under particular lighting conditions. Think of Saturation in terms of weak vs strong or pale vs pure. Finally, Lightness refers to how light or dark a color is. Lighter colors have higher values. For example, Orange has a higher value than navy Blue or dark Purple. Black has the lowest value of any Hue, and White the highest.
You also have the option to specify how much color ranges will overlap. The effect of this is very subtle and will only work on colors next to each other (or close to each other.) The more overlap, the more closer colors begin to become the same Hue.
Understanding Brightness and Contrast
Brightness and Contrast are simple concepts. What they affect however is not as obvious. When applying a Brightness adjustment in a negative direction you're decreasing tonal value while expanding highlights in the scene. The opposite direction does the opposite; increase tonal value while expanding shadows. Contrast, also a simple concept, merely expands or shrinks this overall range of tonal values.
It's important to note that Brightness and Contrast apply a linear adjustment to the scene, i.e it only shifts pixel values higher or lower. This can cause clipping as well as loss of scene detail, especially in highlight or shadow areas.
Putting it all together
In Neothyne, color grading is performed in the following steps: "Color balance", "Hue and Saturation" and "Brightness and Contrast", in that order respectively.
The key to using any of this is to play around with the settings and see what works and what doesn't. Adjust in small steps rather than dramatic ones, as big changes and edits are rarely flattering.
It's generally advised that when working with Hue and Saturation not to use the Lightness option to adjust exposure, it may look like it does a nice job, but it doesn't. If you, for example, darken a scene using lightness, you'll begin to lose any areas defined as White.