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HW8: Color Perception, The Magic of Chromatic Adaptation

Due date: .

Download

Start with downloading the following VR Cardboard application:

What is Chromatic Adaptation?

Chromatic adaptation is the human visual system’s ability to adjust to changes in light, allowing perceived colors of objects to remain relatively constant under varying lighting conditions.
For example, a white piece of paper appears white whether viewed under sunlight, fluorescent light, or LED light. This effect, known as color constancy, helps us maintain stable color perception in different environments. Without chromatic adaptation, these papers would appear slightly different from each other under each type of light.
Our visual system adapts best to light sources with a spectrum similar to natural daylight (https://en.wikipedia.org/wiki/Standard_illuminant). When exposed to such light, our vision fully adapts, and colors appear natural. However, under artificial or monochromatic lighting, like intense red nightclub lights (which have a narrow spectral power distribution), our ability to adapt is reduced, causing distorted color perception.

What Do We Know About Chromatic Adaptation?

Chromatic adaptation has been studied a lot in labs, but research in virtual environments is still developing. Models that mimic how our eyes adjust to different lighting are called Chromatic Adaptation Transforms (CATs). The most famous one, from 1902 by von Kries, helps map color stimuli from one lighting condition to another, ensuring they look the same under different lights.

Why Does Chromatic Adaptation Matter?

Chromatic adaptation is important for digital displays, color design, and photography. It affects how we see colors in everyday objects, art, and fashion. Studying this helps improve color accuracy on screens and makes virtual reality more realistic. It also helps us understand how the brain processes color.
In practical terms, a reliable CAT can improve how colors are displayed on screens and in photos, preventing mistakes that frustrate consumers. For example, CATs are used in cameras to simulate how our eyes adjust to light, helping photos look more like what we actually see—like when you take a picture of a sunset, and it doesn’t quite match real life. CATs help fix that!

VR: A Powerful Tool for Studying Chromatic Adaptation

Virtual reality provides a controlled setting where we can precisely manipulate lighting and color conditions, something difficult to achieve in real-world experiments. For example, we can even simulate different lighting for each eye, which is fascinating.
Before using the app, try a mental experiment: What if your right eye sees the environment under cool white LED light, and your left eye sees it under warm LED light? This is what this homework will let you experience. Spoiler alert: at first, you’ll notice a clear difference between the two eyes, but after a few minutes—like magic—the differences will disappear! Although we’ve spoiled the surprise, we’re confident you’ll still be amazed when you experience it yourself. This shows just how powerful VR is for studying chromatic adaptation.

Completing This Homework

Once you enter the scene in the APK, you will see 6 fruit canvases, 4 color block canvases, and one central canvas labeled "tutorial" with a color wheel. Start with the tutorial by focusing on the tutorial canvas for one second to enter. Inside, you can practice the "color space interaction" that you will use in all other canvases. In other canvases, the color wheel will be invisible, but your head movements will still interact with the color space.
Here’s how it works:
  1. Moving your head around the circle will let you choose the hue (color) and saturation (intensity of the color).
  2. Rotating your head around a specific color will adjust its value (grey level) .
  3. Gazing at a specific color (hue + saturation + value) for more than a second will select that color and exit the experience.
Note: If you’re not ready to select, avoid gazing at the color for too long, or it will be selected and you’ll have to start over.
You can read more about HSV (Hue, Saturation, Value) here: https://en.wikipedia.org/wiki/HSL_and_HSV.
After the tutorial, practice on the fruit canvases. In these, your left eye will see the fruit, and your right eye will show the color space. Move your head just like in the tutorial to find the color that matches the fruit. Once you select a color, you'll exit the canvas, and your results will appear on a new canvas beside the one you visited.
Once you're comfortable, move on to the color block canvases. This is where we need your answers for the questions below. Try to match the colors using the same method. After each match, report the resulting HSV values and the total time it took to find the best match, which will also be displayed upon exiting each scene.

This Is a Human Subject Experiment

Just like your previous homework on Vection, this homework also serves as an example of how human subject experiments are conducted. We provide you with instructions on how to complete the experiment but will not reveal the hypothesis or share the collected data until all submissions are complete and analyzed.
We may use this data for research and publication purposes, so your participation is an important contribution to the scientific community. All data will be analyzed in aggregate, and we will not disclose which answers came from specific individuals. To ensure privacy, the data will be pseudonymized, meaning it will be associated with a unique identifier rather than your name. Once everyone has completed the homework, we will reveal the results and discuss them with you.

Consent to Participate and Use Data

I consent to participate in this color perception study, understanding the nature, risks, and benefits involved. I acknowledge that I have the right to withdraw from the study at any time without penalty. I also consent to the use of my data collected during this homework for further research and analysis, including potential publication.
If I choose not to consent to the use of my data for research, I understand that I am still required to complete the homework assignment. My grades and status in the class will not be affected in any negative way if I decide not to provide my data for research purposes, and I should not feel obligated to consent.
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Before we proceed, let's complete two quick tests to understand your color vision and ensure meaningful results for chromatic adaptation.

Question 1: Color Blindness Test

Take the color blindness test using this link: Color Blindness Test. After completing the test, please provide us with your score.
Example: Test result: 100 % (18/18)

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Question 2: What Is Your Dominant Eye?

To find your dominant eye, roll a piece of paper into a tube and look through it at an object on the wall in front of you. Which eye did you instinctively use to look through the tube? That is your dominant eye.
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Final Instructions Before Proceeding

Before you begin answering the questions about chromatic adaptation, please review and follow these important steps:

Question 3: The Red Square Canvas

Complete the color matching task in the red square canvas. Afterward, what were the resulting H (Hue), S (Saturation), V (Value) values, and the time it took? These values will appear from top to bottom on the canvas below the red square.
Please type all of these numbers in the textbox below.

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Question 4: The Blue Square Canvas

Complete the color matching task in the blue square canvas. Afterward, what were the resulting H (Hue), S (Saturation), V (Value) values, and the time it took? These values will appear from top to bottom on the canvas below the blue square.
Please type all of these numbers in the textbox below.

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Question 5: The Green Square Canvas

Complete the color matching task in the green square canvas. Afterward, what were the resulting H (Hue), S (Saturation), V (Value) values, and the time it took? These values will appear from top to bottom on the canvas below the green square.
Please type all of these numbers in the textbox below.

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Question 6: The Yellow Square Canvas

Complete the color matching task in the yellow square canvas. Afterward, what were the resulting H (Hue), S (Saturation), V (Value) values, and the time it took? These values will appear from top to bottom on the canvas below the yellow square.
Please type all of these numbers in the textbox below.

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Question 7: The Easiest Color

Which color from the four boxes was the easiest to match? (You may select more than one). If multiple colors were equally easy, please select all that apply.
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Question 8: The Hardest Color

Which color from the four boxes was the hardest to match? (You may select more than one). If multiple colors were equally difficult, please select all that apply.
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Question 9: Observing Visual Anomalies

  • Did you experience any eye strain during the experiment?
  • Did you notice anything unusual or strange in the visual scene?
  • Did you have to close one eye during any of the color matching tasks to complete it? (Please remember - try NOT TO CLOSE ONE EYE!)
If you answered yes to any of these questions, please explain in the textbox below.

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References

Authors

Teemu Kulojärvi, Anna LaValle, Elmeri Uotila, and Nicoletta Prencipe.
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Lectures and labs schedule for the VR Systems and Humans course, Fall 2023
Lecture slides, VR Systems and Humans course, University of Oulu, 2023
Informative Guides to Help You Design, Develop, and Distribute Your VR App.
The platform for interactive, real-time, 3D content creation.
Virtual Reality, LaValle 2016 is the free online textbook we use in this course.
YouTube Channel: VR Systems and Humans, Fall 2022
University of Oulu