# Natron WIP Documentation Tutorials

## Info

Currently tutorials should be merged to here from these sources:

* http://www.opticalenquiry.com/nuke/index.php?title=Main_Page
* https://www.linkedin.com/pulse/natron-green-screen-despilling-tips-omar-brown/
* https://www.linkedin.com/pulse/natron-compositor-keyframe-tracking-tips-omar-brown/
* https://www.linkedin.com/pulse/natron-vfx-compositor-tracker-node-omar-s-brown/
* https://www.linkedin.com/pulse/natron-digital-compositor-chromakey-node-tutorial-omar-s-brown/
* https://www.linkedin.com/pulse/keyer-node-chromakey-colorlookup-tidbit-omar-s-brown/

## Keying Tutorial

How do you shoot a sci-fi space film *without* going to space? With green screens, you can! Natron offers special tools to composite green screen footage with live action footage - this process is called **keying**.

Natron has several keyers, which are tools designed to separate the foreground of footage from the background. The main ones you should know are:

* Chroma Keyer
* Keyer Node
* Luma Keyer
* Hue Keyer
* Difference Keyer
* PIK keyer

### Hue Keyer

The HueKeyer node pulls or generates a key or mask depending on hue value of your image(s).

Hue and saturation are analyzed from your image source RGB values. Depending on the hue value, the various adjustment values are computed, and then applied:

***amount:*** output transparency for the given hue (amount=1 means alpha=0).

***sat_thrsh:*** if source saturation is below this value, the output transparency is gradually decreased.


The HueKeyer doesn’t have a mask input option. It only have a Source Layer and Output Layer. I will assume the developers must have determined that a mask input is not needed because the node operation is to generate a mask from the hue selection.

The HueKeyer node is a very simple operator because it has very few parameters to adjust but its level of control is quite robust. As with any image VFX project that you are working on, try to produce or cap-ture the highest quality image as possible. Compression algorithms on any image format will render less desirable results. Normally, you will only have to adjust 2 or 3 parameters.


The first operation you would want to perform is your hue selection. You did this by waving your mouse point-er over the hue you want to key or compute as a key, hold the control button and left click in the area. While you are perform this function, you will see in the hue color graph a vertical bar is aligning to your selection. The bar will stay in place once your hue choice have been finalized.

If you look in to the ***HueKeyer*** hue color graph area, you will see splines that represents the smooth in and smooth out surrounding your hue selection. These splines are mainly controls for how your hue select range falls off. You can tighten or expand your selection on both sides of your hue selection. You can double click on the splines to add more tan-gent points to provide more control on the keying process.

The splines you will almost are the Amount splines. Be very careful on your adjustments of the splines and control points, because the operation can get out of control very fast if you are not paying attention.

#### Demo

The image below is an image that I pulled google images for a demo of using the hue keyer.


The image below is the rendered result of using the ***HueKeyer*** node with help from the ***HueCorrect*** node.

The image below is a screenshot of the ***HueKeyer*** node graph. In addition to the ***HueKeyer*** node there are the ***HueCorrect*** node, ***Blur*** node, ***Glow*** node and ***ColorCorrect*** node.


The image below is just a closer look at the node graph:


The image below is my mask that I use the ***HueKeyer*** to compute a key to blur a region of my image. Of course I had to select the invert mask parameter for the desired effect.


The image below is the mask that I use the HueKeyer to compute a key to blur a region of my image. Of course I had to select the invert mask parameter for the desired effect.

To get the desired effect of the image below is my final effect that I use the ***HueKeyer*** and the ***HueCorrect*** node for desaturation. ***HueKeyer*** was for ***Blur***, ***Glow*** and ***ColorCorrect***.



*Settings for HueCorrect*


*Settings for HueKeyer*

If you look closely, you will find that the HueKeyer and ***HueCorrect*** nodes have the same HueColor Graph. Using this nodes together could make a powerful combination for color adjustments with hue key pulling power.

The ***HueCorrect*** node has a mask input so you can create very powerful effects using it.

#### Quick Note!

The ***HueCorrect*** node is one of Natron’s secret weapons for spill suppression. If you have some of those strange color fringes around the edge of your talent’s or object keys and the regular dispillers are not suppressing correctly, ***HueCorrect*** to the rescue.

### Keying vs. Rotoscoping

While keying is most certainly a powerful tool, there are times you don't want to use it. For instance, if your background is not a green or blue screen, any keyer will have great trouble in extracting a matte properly. Instead, in these situations, you should using **rotoscoping** instead. See [here](#rotoscoping-tutorial) for how you can do rotoscoping.

## Sky Replacement Tutorial

Replacing skies is the staple of a VFX artist's work. To do this, we will be using the **PIK** and the **PIK Color** nodes.

To begin, the fundamentals of sky replacement are actually very close to keying. Essentially, the sky is like a giant bluescreen, and it can be keyed out with the help of a keyer.

## Rotoscoping Tutorial