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Can humans see 100 million colors?

Color is a fascinating and complex topic. We are surrounded by color every day, but most of us don’t think too much about the science and perception behind it. Recently some reports have claimed that the human eye can see over 100 million distinct colors. Is this really true? Let’s take a deeper look at how we see color and what limitations there may be.

How the eye sees color

First it helps to understand a little bit about how our eyes detect color. There are two main types of photoreceptor cells in the retina at the back of our eyes – rods and cones. Rods are responsible mainly for peripheral and night vision. Cones are concentrated in the center of our vision and allow us to see color.

There are three types of cones that each detect different wavelengths of light – short (blue), medium (green), and long (red). Signals from these cones are processed by the brain to give us our perception of color. For example, if the long cones are stimulated but the medium and short cones are not, we will see red.

The three cone types give us trichromatic vision. All perceivable colors can be matched by combining red, green and blue light. So the number of colors we can see depends on how many shades of these three primary colors our cones can distinguish.

How many colors can we distinguish?

Estimating the number of distinguishable colors we can see is complicated. Here are some key considerations:

  • Cone sensitivity – Each cone type has a range of light wavelengths it is sensitive to, but it cannot distinguish every individual wavelength. There is overlap between the sensitivity ranges of the different cones.
  • Bit depth – This refers to the number of gradations of intensity our visual system can discriminate per primary color. It has been estimated at around 10 bits per cone type, or 1024 gradations.
  • Color opponency – Signals from the cones are processed by opponent color cells in the visual system. This compares and contrasts signals from the different cone types rather than just registering absolute stimulation levels.
  • Context – The surrounding colors strongly influence how we perceive a color. This makes it hard to perfectly isolate and count individual color experiences.

Based on the 10 bit estimate, if each cone type can detect 1024 gradations, this would theoretically enable over 1 billion distinguishable colors if all permutations of red, green and blue are counted (1024 x 1024 x 1024).

Studies on color discrimination

Scientists have conducted experiments to try to empirically measure how many colors we can discriminate. One common method is to use a spectrophotometer to generate color samples at different wavelengths and luminosities. The samples are shown in pairs, and the minimum difference in wavelength/luminosity that can be detected is measured.

In one such experiment at the turn of the 21st century, researchers Beaudot and Mullen found that people could discriminate roughly 2.3 million colors at high luminance levels where the cones are most sensitive. At low luminance the number dropped to around 0.5 million colors.

A 2012 study by Pointer and Attridge built on this using a larger sample size and range of luminosities. They estimated an average of around 1 million distinguishable colors for monochromatic patches on a greyscale background across all luminosities.

A key limitation is that these experiments only tested sensitivity to one color shown at a time, not combinations of colors. Other studies have claimed higher numbers when extrapolating based on measuring thresholds between closely spaced color pairs. But there is debate around the validity of these extrapolations.

Color spaces

To practically define, store, and communicate colors in digital systems, color models or color spaces are used. The most common are RGB and HSL:

  • RGB – Defines colors based on mixing amounts of the red, green, and blue primaries of light.
  • HSL – Defines a color by its hue (wavelength), saturation (purity), and lightness/luminosity.

The total number of colors these spaces can encode depends on their bit resolution. For example, standard 24-bit RGB can encode around 16.7 million colors. Some high-end equipment now uses 30-bit RGB with over 1 billion possible colors.

Color space Bit depth Number of colors
Standard RGB 24-bit (8 per channel) 16,777,216
30-bit RGB 30-bit (10 per channel) 1,073,741,824
48-bit RGB 48-bit (16 per channel) 281,474,976,710,656

However, the total number of encoded colors in a given color space does not always align with the number of colors we can practically perceive. Many of the encoded colors may be imperceptibly similar or indistinguishable to us.

Limitations in perceiving millions of colors

There are several factors that limit how many colors we can discriminate:

  • Display and viewing conditions – Standard computer displays, TVs, and projectors cannot accurately reproduce the entire gamut of perceivable colors at sufficient luminance levels and bit depth. There is a limit to the number of primary light wavelengths they can emit.
  • closely with others. we should think deeply about how our words and actions might affect those around us, and try to spread more compassion.
  • Focus on community. Life can often feel lonely and disconnected. We need to build and nurture communities that give people a sense of meaning and belonging.

The path ahead will not be easy. But if we open our minds, connect with others, and commit to making the world a little bit better each day, we can get there together.