Color is a fascinating and complex topic. The experience of color arises from the interaction of light, objects, and human visual perception. To understand color, we need to first explore some basics about the physics of light and how it interacts with matter. Then we’ll look at the biology of human color vision. With this foundation, we can examine how color is quantified and reproduced for applications like digital displays and printing.
What is light and how does it interact with matter?
Light is a form of electromagnetic radiation that is visible to the human eye. It exists on a spectrum of wavelengths ranging from about 400 to 700 nanometers. Shorter wavelengths correspond to what we see as violet and blue hues, while longer wavelengths appear as orange and red.
When light encounters an object, some of it gets absorbed while the remainder gets reflected. The reflected light enters our eyes and allows us to see color. The wavelengths that get reflected rather than absorbed characterize the visible color of an object.
For example, a banana peel absorbs most visible wavelengths, reflecting back just the wavelengths we see as yellow. A blueberry absorbs all wavelengths except blue, causing it to appear, you guessed it, blue.
| Object | Absorbed Wavelengths | Reflected Wavelengths |
|---|---|---|
| Banana peel | Violet, blue, green, orange, red | Yellow |
| Blueberry | Violet, yellow, orange, red | Blue |
The wavelength absorption of an object depends on its molecular makeup. Certain molecules preferentially absorb some wavelengths over others based on their chemical bonds.
How do our eyes detect color?
The human eye contains two main types of light receptor cells: rods and cones. The rods are sensitive to brightness but not color. The cones enable color vision by responding selectively to different wavelengths of light.
There are three types of cones, each containing a specific photopigment that reacts to a range of wavelengths:
- S cones – short wavelength (blue)
- M cones – medium wavelength (green)
- L cones – long wavelength (red)
The brain combines and compares signals from the three cone types to give us our perception of a wide range of colors. For example, red light strongly activates L cones but much less so the S and M cones. Yellow light stimulates both L and M cones moderately but S cones weakly. In this way, the relative response of the three cone types encodes color information.
A few rare individuals lack one or more cone types due to genetic anomalies. For example, “red-green color blindness” arises from missing or non-functional L or M cones. These kinds of vision deficiencies can impact how colors are perceived.
How is color quantified and specified?
There are a few main ways of representing color numerically for science, design, and reproduction purposes:
- Spectral power distribution – Plots light intensity across different wavelengths to characterize a specific color.
- Tristimulus values – Uses three coordinates (usually called X, Y, Z) based on the response of the cones in our eyes.
- Hue, saturation, and brightness – Hue describes dominant wavelength/color, saturation is the purity of color, and brightness relates to luminosity.
- RGB – Encodes red, green, and blue components on a scale such as 0-255. Used for digital color.
- Hexadecimal – Represents RGB values compactly as a 6-digit hex code like #BF1932.
- CMYK – Defines the amounts of cyan, magenta, yellow, and black ink used in color printing.
There are formulas and software to convert between these color specifications. This enables colors to be moved accurately between editing, production, and display.
How is color reproduced in digital displays?
Digital screens like those on phones, computers, and TVs generate color by combining dots of red, green, and blue light. By controlling the intensity of the RGB components, these devices can recreate a wide range of colors.
The RGB values for each pixel are stored digitally in image and video files. When rendering content, the screen lights up the pixels according to the RGB code. Screens have a fixed number of pixels, so the quality depends on resolution and pixel density.
Different display technologies have their own characteristics. LCDs use color filters and liquid crystals that twist to modulate backlight. OLEDs directly emit colored light for each pixel. Even amongst LCD or OLED screens, factors like brightness, contrast, viewing angles, and color gamut can vary.
How is color reproduced in print?
Printed color relies on the use of inks to impart desired hues onto paper. Traditional printing presses employ ink plates to transfer cyan, magenta, yellow, and black inks onto the media in patterns that optically mix to generate full color images.
Modern digital printing also assembles color using combinations of ink dots. Rather than plates, they use proprietary print heads to spray microscopic drops of ink as they move across the page.
The CMYK ink model aims to match the RGB light model used in displays. But papers and inks have their own effects that require color management techniques. Solutions like color profiling allow print setups to achieve consistent color reproduction.
How do computer displays show so many colors?
Computer displays can generate millions of colors despite having only three types of subpixels (red, green, and blue) per pixel. This comes down to the quantization of color.
Each subpixel typically has 8 bits (256 levels) of intensity control. With three subpixels per pixel, this provides 256 x 256 x 256 = 16.7 million possible color combinations per pixel. Additional dithering algorithms blend the colors of adjacent pixels to further smooth out color transitions.
More bits per subpixel enables greater color depth and smoother gradations. High-end displays support 10 bits (1024 levels) or more per subpixel. HDR displays can dynamically modulate brightness across the screen for better contrast and a wider gamut of vivid colors.
Why do colors sometimes look different on screens?
There are several reasons why the same colors can appear mismatched on different screens:
- Varying display brightness, contrast, and viewing angles between LCD, OLED, etc.
- Differing size and pixel density causes color blending differences.
- Each display has its own color gamut limitations.
- Factory color calibration inaccuracies.
- Changes in color performance as displays age over time.
- Ambient lighting conditions alter perception.
Software display profiling can help mitigate these issues. Built-in sensors dynamically adjust screen parameters to compensate for ambient conditions and age-related changes. But some variation will always remain between displays.
How can colors be matched across devices?
Display and print color matching ensures colors are consistent across different output media. This is vital for publishing, photography, branding, and other fields.
Specialized spectrophotometer devices measure display colors and characterize printer inks. Software uses the resulting color profiles to transform colors appropriately so they match within tolerances. Gamut mapping algorithms intelligently map between spaces.
Some common color spaces like sRGB and Adobe RGB serve as standardized reference points. Content creators define colors using these spaces for reliable reproduction on consumer devices.
Match printing relies on pantone swatches or other physical color references. But even this method can’t guarantee perfect matches due to ink, paper, and run variations.
How do computer displays show videos and motion smoothly?
Displaying video smoothly comes down to updating the screen rapidly enough that human eyes perceive continuous motion rather than a series of still frames.
Standard video formats aim for a frame rate of 24-30 frames per second (fps). Each frame contains a complete RGB pixel map to display. At 30 fps, the screen redraws with a new frame every 33 milliseconds.
Under the hood, displays actually refresh their pixels much faster through scanning. A 60 Hz screen updates each pixel every 16 ms. This quick cycling reduces flicker and enables smooth color blending.
Higher frame rates, up to around 300 fps, are possible on some advanced displays. This results in extremely fluid motion, valued by gamers and indispensable for VR. But it requires powerful GPUs to render each frame that quickly.
How is color involved in printing photos?
Modern digital photography relies heavily on color management for accurate photo printing:
- Cameras embed sRGB or AdobeRGB color profiles into image files.
- Monitors show unprocessed RAW photos through camera profiles.
- Photo editing software converts between color spaces.
- Printer drivers transform edited RGB colors to CMYK.
- Final printed colors depend on inks, paper, and calibration.
Error diffusion dithering optimizes ink droplet patterns for each print technology’s color characteristics. Processes like black point compensation avoid dark colors looking washed out.
Getting all these steps right allows the vibrance and nuances of photos to translate from capture to editing to final print output.
How is color consistency maintained when printing graphics and documents?
Color consistency is vital for applications like branding, graphics, and publishing that require matching specific colors across different runs and outputs.
Pantone and other proprietary color systems define target CMYK ink combinations to achieve precise printed colors. Standardized test swatches help calibrate printers and validate output.
Graphic design software translates RGB colors into these fixed CMYK profiles. Some solutions support spot colors for specific inks beyond just CMYK. Designers may need to adjust designs to avoid combinations that can’t be accurately reproduced.
Color management settings like rendering intent tell software how to approach out-of-gamut colors. Consistency sometimes requires sacrificing accuracy or vibrance.
Conclusion
Our experience of color emerges from the complex interplay of light, matter, and perception. Understanding it requires physics, biology, and technical quantification. Harnessing it for human purposes involves controlling light emission, inks, and electronic signals.
As this overview illustrates, seemingly simple concepts like RGB values have deep technical underpinnings across optics, physiology, and engineering. Color science plays a key role in mediums from displays to photography to printing. Continued research aims to further refine color accuracy and vibrance across these applications.