A Crash Intro to Color - Color Operations and Linear Lighting

 Linear Color Vs Perspective color and Basic Color Operations

Color doesn't exist, it's only your head trying to make sense of the electromagnetic signals. Light is an electromagnetic wave. When it is around it bounces all over the place. Without light reality still exists.

    The phenomenon of color happens inside of our eyes. Light bounces into our eyes as photons through our Cornea., some is absorbed in surface as heat, some of it reach the back of our eye and stimulate the nerves (retina) in the back of our eye. Colors are read through cones. Humans only have three color receptors in our retinas. With it we can see approximately 10 million Colors.

Light Breakdown

Because we have three different types of receptors:

    You can see we have three waves here. The shortest wave corresponds with blue, so we don't see blue as well. We are most sensitive to green. (That's why night vision goggles are green, it picks up the most amount of information for us. 

    Types of Color:

• Additive
• Subtractive
• HSV/HSL
• YUV (Y- brightness, U- blues and greens, V- reds and yellows; used for transmitting signals for cathode-ray tube tvs in Europe) (also called PAL)

• YIQ (Y - brightness, I - blues and reds, Q- greens and magenta; used for transmitting signals for cathode-ray tube tvs in America)(also called NTSC)
• YCbCr (Y- brightness, Cb- blue and yellows, CR- greens/cyan and reds/magenta)(also known as MPEG/JPEG/HDMI)

We Describle Colors using color models. Abstract representations of colors as tuples of numbers: 

• RGB is an additive color model as a tuple (r,g,b). projected as white light
• CMYK is subtractive and a tuple (c,m,y,k). colors are absorbed

24 Bit RGB means you have 8 bits per color = 256 shades. 24 = 8+8+8

    Gamut is like the footprint a color model. Not all display devices are created equal

    Photo Real Test

1. Can an image be captured with real colors?
2. Can a photo real image be rendered based on the input?
3. Can the image display accurately on a device?

Emission vs Perceptual

Nominal Light Emission is Linear. It is additive color. Each bar is increasing in value at the exact same speed. This is what real light is. 

Perceptual Light is Gamma (sRGB). This slows down the transition so we don't go to the bright whites as fast. It happens right before an image shows up on your display. These are false colors. 

Gamma Color Space (sRGB)

    All recording and display devices record and display in 'Gamma' color space. When you look at any display you are looking at a lie!

    When performing operations on colors:

1. Convert color to linear color space
2. Perform operations on color
3. Convert back to gamma (sRGB) color space

When writing out to Bitmap and not to materials:

all base color and diffuse -> sRGB

all others -> Linear

    
    This is a MacBeth charts, each piece has a linear color associated with it. You can use it to calibrate and make sure the colors show up true.