Introduction to Color Correction

Introduction to Color Correction

Overview

The following guide will take you through the core principles of color correction. We also recommend taking a look at our articles on codecs, scopes, and LUTs to supplement this material for color grading as well as the links below in Additional Resources.  

Chroma Subsampling & Bit Depth

Chroma Subsampling and Bit Depth are two important elements in understanding color correction. For more information on these topics, please refer to our Intro to Codecs guide.  

Terminology

Color Correction terminology and concepts will remain relatively consistent across programs.  Whether you are color correcting in Premiere, Avid, or Resolve, the following are terms you should be familiar with:

  • Luminance: The brightness of an image.
  • Chroma: The color information of an image defining hue and saturation.
  • Contrast: The difference in luma (brightness and darkness values) of an image.
  • Saturation: The intensity of a color.
  • Hue: The actual color value of any one pixel in an image.

Color Correction Tools

There are three main tools for balancing the contrast and color of your image in most NLE programs: Luma Controls, Color Wheels and Color Curves.  

Luma Controls

Luma Controls adjust the brightness of the image and can increase or decrease the contrast of an image. While different NLEs use different terminology to address these controls, these are the basic terms typically used:

 

  • GAIN: Adjusts the gain or white point for the image.
  • GAMMA: Adjusts the midpoint of the luminance range.
  • LIFT: Adjusts the black point for the image. Sometimes referred to as SETUP.

 

Color Wheels

The Color Wheels change the hue or color of the image. The three Color Wheels control color in the Shadows (Lift), Midtones (Gamma), and Highlights (Gain)  of the image.

Most NLEs use an “Additive” color correction process. For example, if your image is too blue, you will add the opposite color on the wheel (yellow) to correct the color cast.

Davinci Resolve Color Wheels:

 

ResolveColorWheels.jpg

When adjusting color casts and luma values using Color Wheels, it is important to remember that the Shadows, Midtones, and Highlights do overlap. Adjusting hue or brightness in your highlights may also affect your midtones. Adjusting your shadows may also affect your midtones, etc.

 

Color Curves

While Color Wheels make relative adjustments on red, green, and blue simultaneously, Color Curves make targeted adjustments on one color component at a time. You can add points on the luma, red, blue, or green curves to adjust the luma and chroma values of your image.

Davinci Resolve Color Curves:

ResolveCurves.png

 

Primary Corrections

The objective of Primary color correction is to first balance the contrast ratio of an image (Luma), then remove any color casts and adjust relative Chroma saturation.

Adjust Luma using Y Waveform Scope

First, adjust the Luma using the Y Waveform scope as a reference.

  • Lower your blacks by adjusting the Setup/Lift control.
  • Bring up your highlights using the Gain control.
  • Adjust your midtones using the Gamma control.

Refer to the example below to see how the waveform and image change when adding contrast.

LumaAdjust.jpg

 

Try to have your signal retain information in both the shadows and the highlights by not having the signal go below 0 or beyond 100 IRE. If there is a solid line in the signal (in either the shadows or the highlights) before you start correcting the image, your signal has clipped information because of over or underexposure.This means no details in that part of the image can be recovered.

 

Highlight_and_Shadows_Clipping.jpg

Changing Luma has a direct effect on Chroma. Expanding the contrast of the image will also increase the saturation. This is why you should always adjust your Luma first, and then adjust Chroma.

Color Balance using RGB Parade

Using the RGB Parade scope, adjust the Chroma channels to remove any unwanted color casts your footage may have. Focus on removing unwanted color cast from any white or black areas of the image. This should remove the majority of the color cast.

 

ColorAdjustComparisonImage.png

The goal is to have the red, green, and blue channels of the RGB Parade read consistent highlight, midtone, and shadow placement. Refer to the RGB Parades below as an example of how this may look on your screen.

RGBParadeCorrection.png

 

Keep in mind that an unbalanced RGB Parade can be fine, depending on the context in your film. For example, while the color cast has been removed in the image below, the RGB Parade scopes are still uneven since the background contains a reddish hue.

UnbalancedParade.jpg

Additional Resources

Lynda: Intro to Video Color Correction

A set by step guide with exercise files on color correction concepts and techniques.