[How-To] S-Curve vs Inverted S-Curve
INTRODUCTION ^
This is essentially part 2 of Contrast Processing, check out part 1 here where I talked about High Contrast vs Low Contrast.
There are tons of ways to post process a High Contrast or a Low Contrast photo or video but IMHO, the best way to do that is to use Curves. If you are color correcting or grading a photo or video, the urge to use Levels instead of Curves is strong simply because Levels is must easier to use than Curves. Especially for those who just want to adjust the Highlights and Shadows in the fastest way possible.
However, there are tons of advantage with using Curves. The biggest one is Curves give you more options and allows you more controls over mainly how you adjust the Highlights, Shadows and Midtones. It allows you to pinpoint specific sections on the graph that you want to adjust.
You can definitely continue to use Levels or you can also be a bit more adventurous and try your hands on Curves, start simple and grow from there. Before we go on, the followings can be slightly confusing if you have no idea even what Curves or Levels are. I will try to explain it in layman's term so that you can understand it as best as you can.
READING CURVES ^
Let's start with the basic first! The default graph has a line dividing the graph evenly with a X and Y axis. The left of the X represents the Shadows and the right the Highlights. The bottom of the Y represents the Shadow with the top as Highlights.
The relationship because these 2 is simple. The idea behind this is by adding a point on the line and moving it, you are essentially specifying how dark or bright you want to adjust the specified point you just added into. If you look at the bottom of the graph, it tells you the exact input and output amount when you move the point around the graph.
If you look at the bottom of the graph, the point that was added has an Input of 51 and Output of 82. What it meant was all Input having a tonal value of 51 will be changed to a tonal value of 82. That means the Shadow will appear brighter in this case (0 represents Shadow and 255 represents Highlight).
You can do the same to Highlight. The following setting changes all Input having a tonal value of 206 to 182. Meaning the Highlights will be darker.
Here comes the BIG BUT! But... but... The adjustment above is causing tonal values change across the board. Look at the illustration below, all the values along the new curve will have their Input value changed to a new value for Output due to the movement of the point added.
Here comes the big question! What if I want to just change the Highlight and leave the rest of the curve at their original input value? Or you want to do something slightly more complex like to bump up the Highlights but reduce the Shadows. That's the beauty of Curves because this is something only the Curves can do with ease and Levels can't.
I am going to show you how to create a High Contrast and a Low Contrast scene using Curves. You can easily apply this technique on any Image Manipulation application or a Video Editing application. The S-Curves vs the Inverted S-Curves.
S-CURVES ^
The first thing you need to know is that S-Curves produce High Contrast scene. It got its name due to the shape of the curve.
Looking at the example below. The left graph see the change on the Highlight tonal value change from 188 to 203 with the affected tonal values change too along the curve but adding a 2nd point on the Shadows on the right graph see a Shadows tonal value change from 73 to 57 with the affected tonal values change too along the curve.
In a way, you are bumping up the Highlights but reducing the Shadows and that creates a High Contrast scene.
Most people will just stop there but I am going to add 1 more step to make the scene a slight touch better.
The following adjustment will eliminate pure black and pure white to make sure the High Contrast scene don't go too crazy.
What it meant is that any values between 245 and 255 will have a value of 245 and that meant eliminating true white. Same applies to the Shadows with any value between 0 and 10 will have a value of 10 which means eliminating true black.
INVERTED S-CURVES ^
Inverted S-Curves on the other hand creates a Low Contrast scene. Instead of increasing the Highlights and reducing the Shadows, we are reducing the Highlights and increasing the Shadows. This slightly flatten the color a little bit.
Similar to the S-Curves, I am adding a slight touch of adjustment to eliminate true black and true white. This part is optional for the Inverted S-Curve if you don't want to add it but it's already part of my workflow so I thought in case anyone is interested.
The idea of these additional points is to make the true white slightly milky white and true black slightly dark grey. The right graph ensure that it don't go too crazy with this section and limit the range it changes to as minimum as possible.
CONCLUSION ^
There is really no standard or must do for using the Curves and there are in fact a lot more you can use the Curves for. On an RGB channels adjustment, this can be used to adjust the tonal values of the scene but if you were to do this for individual channels, it turns into something different altogether.
If you are using it on Photoshop, Premiere Pro, Final Cut or anything that allows Curves adjustment, you can easily create a preset to drag and drop instead of adjusting the Curves every time you have a new photo or video.
The biggest thing about Curves is not to get intimidated by it and get comfortable with those basic stuff like the Input and Output because the numbers will tell you what you doing to the graph.
That is going to be all for this post. Leave me a question or comment if you have any and I will reply back asap.
Comments