Video Color Correction – Part 2 – Color Reference Cards

Why does my picture look different on every monitor? And how do colorists manage to make it look good everywhere?

Color correction, in particular “display-referred color grading”, plays a decisive role in film and post-production. It refers to how colors are rendered on the screen and is in contrast to “Scene-Referred Color Grading”, which refers to colors in the real world. Although Display-Referred Color Grading is a great way of

color correction, there are also some challenges associated with it that are not always easy to overcome.

Example of Display Reffered Color Grading with Calibrated Display

Color consistency between different displays:

The same picture can appear differently on different monitors, leading to inconsistent color interpretation. The next time you walk through a retail store, pay close attention to the different color displays in the TV department. Some have a much greener picture than others, others are bluish and some have clearly oversaturated colors and exaggerated contrasts.

This is exactly where the filmmakers’ – or content creators’ – problem becomes apparent: finding an optimal intermediate path for all these different screens and the resulting color problems.

Our eyes pretend what is not there!

Let’s assume that our monitor, on which we want to edit the color of our image material, has a strong green cast and we only rely on this monitor when evaluating our film. We will then notice a magenta color cast in this film on other devices, although we perceive it as correct and beautiful on our own monitor.

Visually assessed on monitor with green cast – overcompensation towards magent

But why magenta? This goes hand in hand with the shift in the tint of our monitor. Due to the visual green tint, we overcompensate with the shift towards magenta when viewed purely with the eye. On our display, everything looks great – white is white, all skin tones are beautiful, … – and we are happy with the result.

Once we’ve finally finished it, it’s time to show it to our friends on our cell phone. However, the cell phone we want to use has the opposite color cast to the monitor, namely a strong magenta color cast. Our film, which previously looked so beautiful on our own monitor, is now suddenly a total color disaster.

Example of a “real situation” of what such a case can look like on a cell phon

This is the absolute worst-case scenario that could happen. Because what happens here is a doubling of our problem. Due to the fact that our non-calibrated monitor introduced a magenta color cast – unconsciously and unintentionally – this was intensified by the color cast of the smartphone. Now the image is no longer just slightly discolored, but completely.

Reference displays

Reference displays, also known as “reference monitors”, are high-quality screens that have been specially developed for color correction and grading in the post-production of image and video material. These monitors are characterized by their high color accuracy, precision and consistency and serve as a reliable reference for color reproduction throughout the entire production process.

When calibrated to the correct standard, they deliver very high color accuracy, precise black and white values and contrasts and can be calibrated, keeping the color reproduction constant.

This enables us to work right in the middle of the broad mass of all displays. If our image then looks good on this monitor, there is a very good chance that it will also be displayed in the best possible way on other end devices.

However, when you look at displays with these capabilities on the market, you quickly realize that this level of accuracy is also accompanied by extremely high acquisition costs.

Scene Referred vs. Display Referred

A less expensive and yet extremely reliable solution is to work with color reference cards and scopes. This enables us to no longer just assess the image objectively with the eye (also known as display referred), but to have all the important tools to assess the image using data technology (also known as scene referred).

Scene-Referred Color Grading refers to a method of color grading in which the color correction is based on information taken from the real world or the cinematic scene. In other words, this method refers to the adjustment of colors, contrasts and other image attributes based on the original scene captured during filming.

Scene-Referred Color Grading focuses on preserving or adapting the visual elements of the original material as accurately as possible, regardless of how it might appear on a particular display device.

Scene Referred Color Grading with reference card, in combination with the scopes, creates an accurate starting point for the material

Color reference cards – the solution for working with Scene Referred

This adjustment is made using color charts, which provide exact color values that can then be used afterwards to calibrate the image in the best possible way. The important thing here is to record the color chart in every new lighting situation. This ensures that white always corresponds to white and that the contrasts can be perfectly adjusted using the gray scale. By subsequently calibrating the image with the help of so-called video scopes, it can be assumed that the image is correct and has hardly any color casts.

The problem we had at the beginning with the double magenta cast therefore doesn’t exist anymore. Thanks to the calibration (whether Display Referred or Scene Referred), our image is now as close to the center as possible and should look good on any monitor. This means we can ensure that any color problems are not due to our editing, but to the device being used.

Never trust only your own eyes!

I like to say “The eye can lie to us, but scopes never lie”! Because scopes don’t judge films subjectively, like we do, but objectively – based on data. That’s one of the reasons why I have a separate monitor with scopes only for every color grading project, so that I can cross-check at any time to ensure that the eye and data are in perfect harmony. This is the only way I can achieve the best possible result for every device.

Different types of scopes for data-based assessment of image material

About the author – Marco Schreiber

Marco Schreiber is a professional videographer, cameraman, colorist and DaVinci Resolve trainer with more than 10 years of experience. Starting with TV productions, he also has extensive expertise and diverse experience with YouTube and social media. He currently works mainly for companies and in the sports sector.