HueSense

How Your Monitor, Brightness and Room Lighting Change Color Test Results

How the limits of 8-bit displays, color gamut and gamma, night mode, brightness, ambient lighting and viewing angle affect color discrimination test results, and how to keep conditions consistent.

A color discrimination test result is not a measure of your eyes alone. The colors are light produced by the screen, and that light mixes with the room lighting before it reaches your eyes. It is perfectly natural for the same person to score differently on a different device.

The limits of 8 bits

Most screens and web browsers represent each of the red, green and blue channels in 256 steps, from 0 to 255. In theory that is 16.7 million colors, but around certain colors the gap to the very next step is bigger than you might think. For example, raising all three channels of a mid gray by one step changes ΔE00 by roughly 0.2–0.4.

That is why HueSense sets the minimum target ΔE00 at 0.5 and re-measures and records the ΔE from the actual rounded colors in every round. Measuring finer differences than that would require a 10-bit or higher display pipeline and a calibrated monitor.

Color gamut and gamma

The default color space of the web is sRGB, and this site calculates every color in sRGB values. But if your screen has a wider gamut than sRGB (such as Display P3) and your browser does not do color management, the same values are shown more saturated and differences can look larger. Conversely, on budget panels with a narrow gamut, differences between highly saturated colors get smeared together.

If gamma (the relationship between input value and brightness) is off, the steps in the dark or light range get crushed together. If you are unusually weak on dark gray rounds, it is worth suspecting how your screen renders shadows.

Night mode and automatic color temperature

Features that change the color temperature of white, such as blue light filters, night mode and True Tone, tint the whole screen yellow. Blues lose saturation, which makes blue and purple rounds harder, and results fluctuate with the time of day. It is best to turn them off while testing.

Brightness

If the screen is too dim, less light reaches your cones and color discrimination drops overall. If it is too bright, differences between light colors get lost in the glare. Set a comfortable brightness you normally use, and turn off auto-brightness so it does not change during the test.

Ambient light and reflections

Light fixtures or window light reflected on the screen add the same light on top of every color and lower the contrast. The darker the color, the bigger the effect. If the room lighting has a strong tint (such as warm orange bulbs), your eyes adapt to it and your reference point for judging color shifts.

The print and design industries define standard conditions for comparing colors. For example, ISO 3664 specifies the light source and illuminance for evaluating and comparing prints and screens, and recommends a neutral gray surround for displays. HueSense keeps the area around the grid neutral gray for the same reason.

Viewing angle

TN panels in particular, and some VA panels, change brightness and color with viewing angle. Squares at the top and bottom of the screen can look different even when they are the same color. Look at the screen straight on from your usual distance. Hold your phone parallel to your face rather than tilted.

Checklist for consistent conditions

References

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