How it works...

The color grading tools inside Unreal are quite similar to what can be found in other software packages such as Photoshop or Gimp. They are there to allow the user to modify certain image parameters, most of which we have already seen. In spite of having done so, I would like to take some time aside to further explain what some of the perhaps more obscure parameters affect.

One such example of a setting that might be a bit confusing is the initial White Balance we saw and tweaked. That property is controlled via the Temp parameter, which is as you've probably guessed short for Temperature. This word references one characteristic of the light we see – and that is its color. Saying that a light has a color temperature of 6,500 K means that it has a blueish tint to it. Lower values will start to get closer to a red tint - 3,500 K would be quite yellow and 1,800 is the typical orange from the flame of a candle. Just so we are on the same page, a fluorescent light would have a higher temperature than your typical light bulb, and this one would be in turn higher than a candle.

The reason why we use a temperature value instead of just specifying a color for our lights is that this is the physically correct approach. Feel free to read more about the topic if it isn't clear at this stage, as it can be quite extensive: https://en.wikipedia.org/wiki/Color_temperature.

In spite of the preceding, the way the White Balance Temp setting works might be a bit counter intuitive compared to what we've just said. According to the previous explanation, lights that have a light color above 5,000 K are considered cold; that is, they have a blueish tint to them. Lower values get us in the range of reds, yellows, and oranges. For instance, a value of 3,000 K would be in the yellow range. That being the case, you can probably infer that the higher the temperature the bluer the light color. However, why did we have to decrease the temp value of the white balance if we wanted to get colder values? 

The answer is that we are not tweaking the light color values, but we are defining which one should be the new standard one (which is by default 6,500 K). Imagine that you have a light of 3,500 K because the default white balance is calculated against that value of 6,500 K; that means that your light is quite warm. If we decrease the default of 6,500 to something like 4,500, the value of your light is still lower than the standard, but not by as much as before. That means that it will look closer to white than it previously did. This is how the white balance temp setting works.

Something else that I'd also like to mention are the different options that we have on the Global, Shadows, Midtones, and Highlights categories. When we looked at them on this current recipe, we only adjusted the overall multiplier that we can find in each subsection. Here's an example to refresh your mind:

We are usually tweaking the value below the color wheel—that is effectively a multiplier that affects all of the RGB values equally. However, we can have an even finer control if we know that we only want to be affecting a specific channel. Additionally, we can even change between the RBG mode and the HSV one, which will have us modifying the hue, the saturation or the value instead of a specific color channel.