101 – Compositing the basics

You are here:
< Back to Wiki

Node Based compositing
the basics.


Linear vs​ Non-Linear​

Simply, it means that numerical intensity values correspond proportionally to their perceived intensity. At a 50% gray will be in the middle of a gradient range.​​

This means that the colors can be added and multiplied correctly. A color space without that property is called ”Non-linear”

Linear - Values arranged along a straight line.
Example: 1...2...3...4...5...6

Non-Linear - Values NOT arranged along a straight line.
Example: 1...2...5...8...9...10


Integer vs Floating Point

Simply, it means that numerical intensity values correspond proportionally to their perceived intensity. At a 50% gray will be in the middle of a gradient range.

This means that the colors can be added and multiplied correctly. A color space without that property is called ”Non-linear”

Integer - Whole number that are not fractioned
Example: 1 , 2 , 100 , 256

Floating Point - A number that is not an Integer.
Example: 0.1 , 0.58 , 1.44 , 2.0


Clamped vs Unclamped

Simply, it means that numerical intensity values correspond proportionally to their perceived intensity. At a 50% gray will be in the middle of a gradient range.

This means that the colors can be added and multiplied correctly. A color space without that property is called ”Non-linear”

Q: Wait does this mean I can have a color that is more that 1?

A: Yes, a lot of times, highlights for example, are way over 1 in color. Because ALL the colors are not clamped to 0-1 you can use exposures to alter you image without degrading it.

Example :  Direct sunlight might have a color value of 2-10 while the viewing the sun might have a value of 10-100.

 

Q: So can I have negitive numbers, ones that are lower than -1?

A: Because Linear colors are based on math yes you can. Much like the first answer this mean you can use exposure to darken your image with out degrading it.

Example: The render might be too dark. but with linear workflows there might be a good chance to bring those blacks up into view-able ranges.

 


What is a “Channel”

In order to create color we need three primary colors RGB. Each of these need a channels to store information. Basic RGB images have 3 channels, some times they have a alpha which increases the channel count to 4. Most image formats only have a 4 channel max.

*Photoshop file allows more than 4 channels. R, G, B, A , Masks+

8 Bit Gray | 1 Channel

Gray - 8 Bits

256 Colors

8 Bit RGB | 3 Channel

Red - 8 Bits
Green - 8 Bits
Blue - 8 Bits

16.7 Million Colors

8 Bit RGBA | 4 Channel

Red - 8 Bits
Green - 8 Bits
Blue - 8 Bits
Alpha - 8 Bits

16.7 Million Colors + 256 Alpha

8 Bit CMYK | 4 Channel

Cyan - 8 Bits
Magenta - 8 Bits
Yellow - 8 Bits
Black - 8 Bits

4.3 Billion Colors

16 Bit RGB | 4 Channel

Red - 16 Bits
Green - 16 Bits
Blue - 16 Bits
Alpha - 16 Bits

281 Trillion Colors

32 Bit RGB | 4 Channel

Red - 32 Bits
Green - 32 Bits
Blue - 32 Bits
Alpha - 32 Bits

80 Octillion Colors

8 Bit RGB | 4 Channel Packing

Red - Roughness
Green - Metallic
Blue - Ambient Occlusion
Alpha - Decals

256 Colors for each channel


What is a “Layer”

Layers are collections of channels. Most common collection is RGBA.

16-Bit EXR Multi-Layer

29 Channels

10 Layers


Color is made from a single RGB channels


Everything is​ A over B​

Node based compositing works on simple A over B​

Node based compositing works on simple A over B​

Each channel is composited instead of overall color​

 


Using math to blend colors together​

 


Each channel​ is composited together using a alpha value.

 


Compositing is ALWAYS done in linear space

Look-Up Table (LUT) is mathematically precise way of taking specific linear image and modifying them to new RGB values to be seen on a different imaging system.

Because compositing is base on math if you were to composite with say sRGB, the math wont work out correctly. This is why LUTs are (sRGB, Rec079, instagram filters, The matrix green coloring) used at the end for viewing only.

Table of Contents

Leave a Reply

Your email address will not be published. Required fields are marked *