LIGHT BASICS :: ALL THOSE COLORS!
14 million colors. Sounds impressive, doesn't it? At least, it once did. When digital imaging crossed the threshold to achieve 14 million colors it seemed as though such a marvelous thing had been achieved. Yet, it is now possible to achieve color bit depths of 48 bits per pixel, theoretically giving one the ability to produce 281 TRILLION colors! Is such bit depth really necessary? How many colors can the human eye see, anyway? And what is the source of all these colors?
Color, of course, is how the human eye perceives various wavelengths of light. In elementary schools, we are introduced to the color wheel and told there are three primary colors: red, yellow, and blue. Shortly after getting that little fact in our head, though, confusion ensues. Digital cameras utilize a color space where green replaces yellow, and printers live and die by a Cyan, Magenta, Yellow and Black (K) color space. Which is correct? Why can't anyone agree?
First, we must consider how the human eye perceives color. Within the human retina sit three color-discriminating cones, commonly labeled L, M, and S for their peak sensitivities of long, medium, and short wavelengths. As light comes through the retina, the three cones work together adding and subtracting information to create three signals: Total Brightness, Red vs. Green (r/g), and Yellow vs. Blue (y/b). All the possible combinations of positive and negative r/g and y/b signals result in the discernible spectrum of just over 10 million colors.
Interestingly enough, many digital cameras attempt to duplicate how the three cones translate color through the use of what's called a Bayer filter pattern. No, there isn't an aspirin inside the camera. The Bayer filter alternates a row of red and green filters with yellow and blue filters in such a way as to mimic how the three cones address color. The filter outputs a mosaic image to which the camera's processor applies a demosaic algorithm. Better yet, higher quality camera actually use three different color processors, giving even greater color accuracy to the image.
The difference between the cones of the human eye and color filters in a digital camera is that the three cones cannot accurately be assigned a red, green, or blue label. Hues dramatically overlap on all three cones. However, it is important to realize that longer wavelengths produce more red-toned hues while shorter wavelengths produce blue tones, with green and yellow falling within various points of the midrange.
What one can accurately determine is the wavelength of light necessary to produce a given color. Just to be academically correct, I am obliged to mention that light can also be measured in terms of frequency and energy. For purposes related to photography, however, wavelength measured in nanometers is the more appropriate measurement.
What causes changes in wavelength? In natural light, heat is the primary factor in determining light wavelengths. The hotter the light, the shorter the wavelength. Wavelengths can also be altered as light passes through a prism. Both have applications in photography.
When shooting in natural light, changes in light temperature as the sun rises and sets can dramatically effect the color accuracy of a photograph. If the camera is expecting light with longer wavelengths but receives shorter wavelengths, it inevitably mis-processes the information, resulting in inaccurate color. As the wavelength of sunlight changes constantly throughout the day, photographers must adjust how their cameras interpret color by re-setting their white balance or changing film types.
Light refraction comes into play most commonly through the lenses and filters one chooses for the camera. Because camera lenses are inherently curved, light is naturally refracted in a precise manner so as to send accurate information to whatever media awaits, whether film or digital CCD. Placing filters over the lens alters the refraction of the light, either shortening or lengthening the light wave for the purpose of making a color adjustment.
Here's where color gets a little confusing for photographers, so pay careful attention. When photographers speak of making an image "cooler," the effect is to warm the light by shortening the wavelength, most often achieved with a blue filter. To "warm" an image, one must cool the light, lengthening the wave by added either a red or amber filter. Since filters do not actually generate or reduce heat, however, they achieve the same effect through careful refraction. focusing on a specific gamut range. Cheap, inexpensive filters are often not as accurate in their refraction and fail to produce the desired results.
Many people can relate to the experience of shopping for clothes, picking out an item they think is a particular shade of red or blue or green, only to get outside the store and realize the garment's color is a very different hue from what one saw in the store! What happened? Did the garment magically change colors? Probably not (though some materials may give that illusion). What changes is the wavelength of the light in the viewing environment, effecting both color and brightness. Indoors, under fluorescent light, the wavelengths are more moderate, muting both reds and blues. In bright sunlight, wavelengths are shorter and brighter, emphasizing blues and violets, changing tonal perception.
For photographers, such changes in wavelength and brightness have huge implications for when and where one takes pictures. If an assignment calls for photographing items majoring within the blue hues, typically 550 nm or shorter, one is likely to achieve best success shooting outdoors of the morning, as the light temperature moves from cooler to warmer, favoring the blue- to violet-colored materials. Garments with yellow to red hues will photograph better in an evening sun, as the light grows cooler. Photographs taken in shade will inevitably favor blue and green hues but skew toward orange in the summer as longer days allow one to take advantage of more slowly cooling wavelengths.
Color theory can become incredibly complex and difficult to understand without a degree in physics. However, to the extent a photographer understands light and color one can make more intelligent decisions regarding lighting and settings for photographs. One of the best resources on the Internet is Professor Walter Lewin's lecture on Rainbows (lecture # 22) at M.I.T. His unique explanation and demonstration is one that I think most any serious photographer will find helpful.
Color, of course, is how the human eye perceives various wavelengths of light. In elementary schools, we are introduced to the color wheel and told there are three primary colors: red, yellow, and blue. Shortly after getting that little fact in our head, though, confusion ensues. Digital cameras utilize a color space where green replaces yellow, and printers live and die by a Cyan, Magenta, Yellow and Black (K) color space. Which is correct? Why can't anyone agree?
First, we must consider how the human eye perceives color. Within the human retina sit three color-discriminating cones, commonly labeled L, M, and S for their peak sensitivities of long, medium, and short wavelengths. As light comes through the retina, the three cones work together adding and subtracting information to create three signals: Total Brightness, Red vs. Green (r/g), and Yellow vs. Blue (y/b). All the possible combinations of positive and negative r/g and y/b signals result in the discernible spectrum of just over 10 million colors.
Interestingly enough, many digital cameras attempt to duplicate how the three cones translate color through the use of what's called a Bayer filter pattern. No, there isn't an aspirin inside the camera. The Bayer filter alternates a row of red and green filters with yellow and blue filters in such a way as to mimic how the three cones address color. The filter outputs a mosaic image to which the camera's processor applies a demosaic algorithm. Better yet, higher quality camera actually use three different color processors, giving even greater color accuracy to the image.
The difference between the cones of the human eye and color filters in a digital camera is that the three cones cannot accurately be assigned a red, green, or blue label. Hues dramatically overlap on all three cones. However, it is important to realize that longer wavelengths produce more red-toned hues while shorter wavelengths produce blue tones, with green and yellow falling within various points of the midrange.
What one can accurately determine is the wavelength of light necessary to produce a given color. Just to be academically correct, I am obliged to mention that light can also be measured in terms of frequency and energy. For purposes related to photography, however, wavelength measured in nanometers is the more appropriate measurement.
| red | 700 nm |
| orange | 620 nm |
| yellow | 580 nm |
| green | 530 nm |
| blue | 470 nm |
| violet | 420 nm |
What causes changes in wavelength? In natural light, heat is the primary factor in determining light wavelengths. The hotter the light, the shorter the wavelength. Wavelengths can also be altered as light passes through a prism. Both have applications in photography.
When shooting in natural light, changes in light temperature as the sun rises and sets can dramatically effect the color accuracy of a photograph. If the camera is expecting light with longer wavelengths but receives shorter wavelengths, it inevitably mis-processes the information, resulting in inaccurate color. As the wavelength of sunlight changes constantly throughout the day, photographers must adjust how their cameras interpret color by re-setting their white balance or changing film types.
Light refraction comes into play most commonly through the lenses and filters one chooses for the camera. Because camera lenses are inherently curved, light is naturally refracted in a precise manner so as to send accurate information to whatever media awaits, whether film or digital CCD. Placing filters over the lens alters the refraction of the light, either shortening or lengthening the light wave for the purpose of making a color adjustment.
Here's where color gets a little confusing for photographers, so pay careful attention. When photographers speak of making an image "cooler," the effect is to warm the light by shortening the wavelength, most often achieved with a blue filter. To "warm" an image, one must cool the light, lengthening the wave by added either a red or amber filter. Since filters do not actually generate or reduce heat, however, they achieve the same effect through careful refraction. focusing on a specific gamut range. Cheap, inexpensive filters are often not as accurate in their refraction and fail to produce the desired results.
Many people can relate to the experience of shopping for clothes, picking out an item they think is a particular shade of red or blue or green, only to get outside the store and realize the garment's color is a very different hue from what one saw in the store! What happened? Did the garment magically change colors? Probably not (though some materials may give that illusion). What changes is the wavelength of the light in the viewing environment, effecting both color and brightness. Indoors, under fluorescent light, the wavelengths are more moderate, muting both reds and blues. In bright sunlight, wavelengths are shorter and brighter, emphasizing blues and violets, changing tonal perception.
For photographers, such changes in wavelength and brightness have huge implications for when and where one takes pictures. If an assignment calls for photographing items majoring within the blue hues, typically 550 nm or shorter, one is likely to achieve best success shooting outdoors of the morning, as the light temperature moves from cooler to warmer, favoring the blue- to violet-colored materials. Garments with yellow to red hues will photograph better in an evening sun, as the light grows cooler. Photographs taken in shade will inevitably favor blue and green hues but skew toward orange in the summer as longer days allow one to take advantage of more slowly cooling wavelengths.
Color theory can become incredibly complex and difficult to understand without a degree in physics. However, to the extent a photographer understands light and color one can make more intelligent decisions regarding lighting and settings for photographs. One of the best resources on the Internet is Professor Walter Lewin's lecture on Rainbows (lecture # 22) at M.I.T. His unique explanation and demonstration is one that I think most any serious photographer will find helpful.
Labels: color, light, photography, physics, theory
posted by Charles at
1:02 AM
