Okay. So, when we talk about contrast, the most important concept is that luminance is the more powerful channel to create contrast between objects. So as we saw previously, color can be defined by a number of channels, right? So we have luminance and the chromatic channels. Now, luminance is by far the most important channel to create contrasts between different colors. It is possible in principle to create contrast with the other channels, but it's much less powerful than luminance. So I think the general rule you have to keep in mind is that luminance is by far the most important element in color to create contrast between colors. So, let me show you an example. This is a little demo from a tool that is called Colorable, you can find online, and it's the same tool that I used to create one of the examples early on at the beginning with the different background colors and different text colors, okay? So now, what you see here at the bottom is that I can change the hue saturation and lightness of the foreground and the background. So, let's see what happens when they change the lightness. As you can see, the lightness of the background is pretty low. And as you can see, as I change the lightness of the font of the text part, the contrast changes dramatically. Look at this. So, as it gets darker and darker, and closer to the lightness of the background, it gets much, much harder to see, okay? Now, even more interesting. So if I move the lightness of the background, say, towards the middle, now you'll see that when the lightness of the text is much higher, I still have enough contrast. When I go to the middle, you have very, very little contrast. But when I go back to very low lightness, now, you have kind of like the opposite kind of contrast, right? So this means that you can create contrast by having one element more luminant than the other, but the order doesn't really matter, okay? So now, I want to show you that if I keep lightness between background and foreground the same, and also saturation around the same, so you will see that now we have contrast, only according to differences in hue. And as you can see, sometimes, there is a little bit more contrast, sometimes, there is a little less, but there is never a lot of contrast between them. So, this is contrast that is generated only by a change in hue. And as you can see, it's not particularly helpful or strong. Sometimes, some bodies are better than others but it's never as strong as contrast obtained through differences in lightness. So, this gives you a sense that lightness is by far the most important element when you have to think about how to create contrast between different colors.
